Hung Windows Price China – Thermal Break

1. System Overview — Gravity Is Aligned With the Direction of Travel

Every other common window format arranges itself so that gravity and motion are not in the same line. In a horizontal slider the sash moves sideways and gravity acts downward into the rollers, so the track carries the weight and the operating force is friction alone. In a side-hung casement the hinge axis is vertical, so the sash weight acts along that axis and produces essentially no moment about it; gravity shows up as hinge shear and as sag at the free edge. In a top-hung awning the hinge axis is horizontal, so gravity produces a moment that grows with the opening angle, and the hardware carries a permanent tension. In a double-hung window gravity acts along the very direction the sash travels. That single fact reorganises the whole product. The sash weight is not a load to be carried by a bearing surface, it is a load to be cancelled; the component that cancels it is a spring, and a spring is not a support — it stores energy, it relaxes, it fatigues, and when it stops delivering force there is nothing left between the sash and free fall. So a double-hung window is a machine for holding a mass in mid-air against its own weight, using a device whose output varies with position while the load it is opposing does not vary at all, with friction as the only element that absorbs the residual mismatch. Every engineering consequence in this article follows from that sentence: why the balance is a safety component rather than a comfort component; why two balances on one sash must be matched and what racking does when they are not; why the sash weight the balance was set for at the factory is not the sash weight the building will carry in fifteen years; why the seals are doing a structural job as the source of friction as well as an air-sealing job; why the tilt release is a deliberately releasable connection under a suspended mass and the tilt position is a different load case; why the meeting rail is simultaneously the only compression seal line, the longest leak path in the middle of the glass, a thermal bridge and the place where the lock pulls two moving bodies together; and why the escape arithmetic of a double-hung is unforgiving — roughly half the glazed height gives the net clear opening, and the sash has to stay up while somebody climbs through it.

Richocean manufactures thermally broken aluminium single-hung and double-hung windows in Foshan, Guangdong — 6063-T6 frames and sashes with PA66GF25 polyamide breaks, matched balance pairs set to the actual sash weight and travel, stainless springs and shoes for wet jamb pockets, jamb liners with controlled clearance and replaceable weatherstrip, tilt-in sashes with positively retained pivots, meeting-rail locks that draw the rails together rather than merely latch them, laminated and heat-soaked toughened insulating units with warm-edge spacers, SS316 hardware for marine exposure — for villas, apartments, hotels, schools and heritage-sensitive elevations across Europe, North America, the Middle East and Southeast Asia, each system documented with its sash weight and the balance setting it requires, the matched-pair tolerance, the residual imbalance band and the friction that absorbs it, the tilt hardware rating, the net clear opening calculation against the egress requirement of the jurisdiction, Uw with its component breakdown, fRsi at the meeting rail and sill, air, water and wind classes with test bases, acoustic rating with the build-up behind it, hardware duty cycle and salt spray verification.

2. The Balance as a Safety Component — What a Falling Sash Actually Does

Because gravity is aligned with travel, the balance is the only thing standing between the sash and the ground, and that makes it a safety component in the same sense that a lift brake or a stair handrail fixing is one — not an item whose degradation merely makes the product less pleasant. It is worth being concrete about what a falling sash does, because the consequences are what justify the specification. A lower sash released at height accelerates until it hits the sill or the sash stop, and the impact is a mass arriving at speed over a very short distance, so the peak force is far larger than the sash weight. The corner joints, which are mechanical connections with limited resistance to a sudden load, are the first casualties: they open, they deform, or the sash racks permanently out of square, after which the window no longer seals and cannot be adjusted back. The glass is the second casualty, since an insulating unit supported on a distorted boundary sees edge stress it was not designed for, and a laminated or toughened pane can survive the impact while the seal fails and the unit fogs later. The sill and the jamb liner take the load next, and a cracked or deformed liner is not a repair — it usually means the frame is compromised. And if anything is in the path, a hand, a finger, a child’s head at sill height, the injury is real. This is why a balance is specified against the sash weight it will actually carry, with margin, and why it is specified as a matched pair, and why its degradation is treated as a defect requiring action rather than as stiffness requiring lubrication.

The failure chemistry of a balance is worth separating from its rating, because a correctly rated balance can still fail early through mechanisms that have nothing to do with load. The spring is the first: a spring operating in a jamb pocket is in an environment where driven rain enters past the sash, condensation runs down the liner, and at a coastal site salt is carried in with the air. A carbon-steel spring in a permanently damp pocket corrodes, and corrosion reduces the section that carries the load, so the spring’s force falls and its fatigue life falls faster than its force does — the classic sequence is a spring that still looks intact but has lost both its output and its remaining life. Stainless springs, or springs inside a sealed tube, cost more and are the reason a coastal project should not accept the inland default. The cord or ribbon in a block-and-tackle arrangement is the second: a polymer cord in a pocket that alternates wet and dry, hot and cold, and that sees ultraviolet whenever the sash is open, loses strength and stretches, and stretch changes the force-displacement relationship even before rupture. The shoe and pivot pin are the third: they are sliding contacts in a dirty channel, so they wear, and wear increases clearance, which increases rattle in wind and reduces the precision with which the sash is located — and a sash that is loosely located does not compress its seals evenly. The lubricant is the fourth: whatever lubrication the shoe and the channel had migrates, washes out or loads with dust, so friction rises, which is felt as stiffness and is often misdiagnosed as a balance problem when the balance is fine and the friction is not.

Then there is the second-order safety consequence that is almost never written into a window schedule, and it is the reason this section matters to the egress discussion later. A lower sash that will not stay up is not merely inconvenient during an emergency; it is an obstruction in the escape opening. The net clear opening of a double-hung is produced by raising the lower sash, and the opening only exists while the sash stays where it was put. If the balance is degraded, the sash creeps down under its own weight — slowly at first, over minutes, then faster as the friction that was masking the imbalance wears away — and it can close the escape route behind the person climbing through, or fall on them while they are in the opening. So balance condition is an item on a fire-safety inspection, not only on a maintenance one, and in a building with bedrooms served by double-hung windows the periodic check that the sash holds position at full raise is as much a life-safety check as the check that the window opens at all. Where a project has this exposure, the specification should require a positive sash stop or a friction brake independent of the balance spring, so that a failed spring produces a sash that is hard to move rather than a sash that falls — because those two outcomes are separated by a small component and a design decision made years before anyone needed it.

3. Two Balances, One Sash — Matching, Mismatch and the Weight That Changes

A sash is held at two edges, so it has two balances, and the pair has to be matched. This sounds obvious and is routinely violated, because the two balances on a sash are usually the same part number and the assumption follows that they behave identically. They do not. Each balance is a spring with its own set, its own corrosion history and its own wear at the shoe, and the two sides of a window are not in the same environment: one side may face the prevailing wind and the driving rain, the other may be sheltered by an adjacent wall or a balcony, so the two springs age at different rates. Over years the pair diverges, and the divergence produces a load case that the sash was not designed for. If one balance delivers more force than the other, the sash is pulled up harder at one edge than at the other, so it experiences a moment in its own plane — it racks. A racked sash is no longer rectangular in the opening, so one corner of the meeting rail and one corner of the sill line lose their seal compression while the opposite corners are over-compressed, and the binding side develops friction that makes the whole sash hard to move. The visible symptoms are the ones people report: the window is stiff, it leaks at one corner in wind, it rattles, and it will not stay level when raised. The cause is a mismatch measured in a few newtons of difference between two springs, and the fix is a matched pair, not a stronger one.

The mismatch case gets worse when only one balance is replaced, which is the most common maintenance error on a hung window. A new spring paired with a ten-year-old spring is a deliberately mismatched pair: the new one delivers its rated force and the old one delivers whatever it has left, so the sash racks immediately and the new balance carries more than its share, which accelerates its own decline. The correct maintenance is to replace balances in pairs on the same sash, and on a double-hung, ideally on both sashes, since the upper sash’s balances have been in service the same length of time and the two sashes share the meeting rail — so a mismatch between the upper and lower sash also unloads the meeting rail seal at one end. This is a maintenance-regime item that belongs in the handover documentation rather than in a conversation with a technician on site, because the technician who is called to fix a stiff window will replace what looks broken, and what looks broken is usually one side.

The other half of the balance problem is that the sash weight the balance was set for is not a permanent property of the window. Balances are set at manufacture against a stated sash weight and a stated travel, and both are properties of the assembly as built. The weight changes whenever the glass changes, and the glass changes more often than people expect over a building’s life: a failed insulating unit is replaced, and the replacement may be a different build-up; an acoustic upgrade adds a laminated pane; a security upgrade adds laminated glass or a film; an integral blind or a between-glass screen adds mass; a thermal upgrade moves from double to triple glazing. Each of these adds kilograms to a sash that is being held in mid-air by a spring set for a lighter one, and the result is a sash that will not stay raised — the classic post-renovation complaint, usually blamed on the window rather than on the glass substitution that nobody told the hardware supplier about. The same argument runs in the opposite direction and is more dangerous: a sash that becomes lighter than its balance setting rises on its own, and a self-rising sash can slam into the head of the frame with enough force to damage the sash, the liner and the glass, and to injure anyone whose hand is on the rail. So a glazing change on a hung window is a hardware change, and the balance setting has to be recalculated and reset, or the balances replaced for the new weight. The discipline is identical to the one a sliding window needs when its glass changes and the roller rating has to be re-checked — with the difference that on a hung window the consequence of getting it wrong is a falling or a flying sash rather than a stiff one.

Travel is the third variable and the one that is most often overlooked, because it is not a force. A balance has a working stroke, and the sash travel has to sit inside it. If the sash can be raised further than the balance’s stroke allows, the balance reaches its stop or goes slack at the top of the travel, and the sash is then unsupported exactly where it is most exposed — at full raise, which is also the escape position. If the travel is shorter than the stroke, the balance never reaches the part of its curve it was selected for and the operating force is wrong throughout. Travel also has to be coordinated with the sash stop: the stop defines how far the sash can go, and it has to be set so the sash cannot be raised past the point where the shoe disengages from the balance or where the pivot leaves its channel, since a sash that comes out of its hardware at the top of the travel is a sash that falls into the room. So the balance, the stop and the liner geometry are one design, and specifying the balance alone leaves the other two to whoever is assembling the window. Finally, the anchorage of the balance into the frame deserves a sentence, because it carries the whole sash weight as a sustained tension: the balance is fixed into the jamb liner or the frame section, that fixing is permanently loaded, and on a thermally broken frame it must bite into aluminium and never into the polyamide break — the same rule that governs an awning window’s head fixings, and for the same reason, since a polymer under permanent tension creeps and a creeping anchor releases the sash slowly and without warning.

4. Friction Is the Second Half of Position Holding — and the Seal Is Its Source

No spring delivers a perfectly constant force, and the sash weight it opposes is perfectly constant, so the two never cancel exactly at every position. The residual — the difference between balance output and sash weight at any point in the travel — has to go somewhere, and in a hung window it goes into friction. That makes friction a functional element rather than a nuisance, and it is the mechanism by which a sash stays where it was left: the balance carries most of the weight and the friction carries the error. The design consequence is that there is a band, and the window has to sit inside it. If friction is too low relative to the residual imbalance, the sash drifts — it creeps down under a balance that is slightly weak, or creeps up under one that is slightly strong, and the drift is progressive and gets reported as “the window will not stay up”. If friction is too high, the sash is stiff, the operating force rises above what a user finds acceptable, and — importantly — the force required to raise it approaches the point where people stop opening the window at all, which turns a ventilation asset into a fixed pane with extra cost. So the specification is not “smooth operation” but a stated operating-force band at a stated point in the travel, with the residual imbalance and the friction that absorbs it both identified, because a window that meets the force band for the wrong reason — a weak balance masked by high friction — will fail as the friction falls with wear.

Where the friction comes from is the part that matters for durability, because it is not primarily the shoe sliding in its channel. The dominant contribution on a well-made hung window is the compression of the weatherstrip between the sash and the jamb liner, and between the two sashes at the meeting rail. That has two consequences that run in opposite directions over the product’s life. First, anything that changes the seal’s dimensions changes the operating force: a seal that swells with absorbed moisture, or that softens and expands in heat, increases compression and therefore friction, so the same window is stiffer in a humid summer than in a dry winter and stiffer on a hot west elevation than on a shaded north one. Second, anything that changes the seal’s resilience changes both friction and air performance at once, and usually in the same direction — a seal that has taken a compression set is thinner, so it compresses less, so friction falls and air leakage rises together. That is why a hung window whose sash has suddenly become easy to move is not a window that has been fixed; it is a window that has lost its seal, and the easy movement is the symptom of the leak rather than the cure for the stiffness. Compression set and stress relaxation are the governing material properties here, exactly as they are on a casement gasket, and the same rules apply: specify the seal material against the exposure, specify the compression it works at, and treat the seal as a consumable with a replacement interval and a replacement method that does not require removing the glass or taking the sash out of the frame.

The clearance in the jamb liner is the second friction source and the second wear source, and it governs a symptom that has no equivalent on other formats: rattle. The sash rides in a channel, and the channel has to be wide enough for the sash to move freely when the seals are swollen and the liner is dirty, and narrow enough that the sash is located precisely. As the liner and the sash edges wear, the clearance grows, and a sash with excess clearance moves in the wind — it taps against the liner, it buzzes at the meeting rail, and it produces the noise that occupants report long before they report any loss of performance. Rattle is not cosmetic. It is a fatigue input into the sash corner joints and the glass edge, it is evidence that the seals are no longer being held at their designed compression, and it is an acoustic path, since a sash that can move in its channel can also transmit structure-borne sound into the frame. The clearance is therefore a specified tolerance with a wear limit, and the liner is a serviceable part rather than an integral one — which is a design decision made at the extrusion stage and one that determines whether a ten-year-old window is repaired by replacing a liner and a set of seals, or replaced entirely.

Two further items complete the friction picture and both are commonly missed. Lubrication in a hung window’s sliding interfaces is not a maintenance activity the way it is in a hinge: the shoe and the channel are in a dirty, wet environment, and any lubricant applied on site attracts and holds the dust that the environment supplies, so an over-lubricated liner becomes an abrasive paste that wears faster than a dry one. The correct answer is a liner and shoe material pairing chosen for dry running, with lubrication only where the balance manufacturer specifies it and only with the specified product. And the balance’s own internal friction is a variable rather than a constant: a corroded spring, a frayed cord over a worn pulley, or a shoe binding in a distorted channel all add friction that is not designed friction, and they add it unevenly between the two sides of the sash — which is how a balance problem presents as a mismatch problem and produces the racking described in the previous section. The diagnostic that separates the two is simple and belongs in the maintenance regime: raise the sash, release it, and observe. A sash that stays is balanced and has adequate friction. A sash that drifts down has a weak balance or too little friction. A sash that drifts up has a strong balance — and is a hazard. A sash that moves unevenly, with one edge leading, has a mismatched pair and is racking. A sash that is stiff throughout has excess friction, usually from swollen or over-compressed seals, or from a binding shoe. Four observations, five diagnoses, and no tools.

5. The Tilt Release — A Releasable Connection Under a Suspended Mass

The tilt-in function is what makes a double-hung window cleanable from inside, and it is one of the format’s genuine advantages over an outward-opening casement or awning: both faces of both sashes can be brought into the room, so a window on the tenth floor can be cleaned by the occupant rather than by a cradle. The mechanism is straightforward in principle — the sash is lowered to a set position, a latch or release disengages the pivot from the balance shoe, and the sash rotates inward about its bottom edge — and it is the most safety-critical detail in the product, because it is a deliberately releasable connection in a system whose entire purpose is to hold a suspended mass. The design requirements follow from that, and they are specific. The release must not be operable at an arbitrary height: if a sash can be tilted while it is raised, the mass it carries is at the top of its travel and the distance it can fall before the pivot takes the load is at its maximum, so the release has to require the sash to be lowered first, and that requirement has to be built into the geometry rather than into the instruction sheet. In the tilted position the sash weight is carried by the pivot pins and the tilt hardware, not by the balance, so the tilt hardware has its own load case and its own rating, and it is a different one from the sliding case — a static load at an angle, with the sash’s centre of mass well inside the room and a moment about the pivot that the hardware has to resist without rotating further. Positive retention in the tilted position is not optional: a sash that can pivot out of its hardware while tilted is a sash that can fall into the room, and the retention has to survive a user leaning on the glass to clean the top corner, which is exactly what people do.

Returning the sash is the other half of the load case and is where most field damage occurs. The sash has to be rotated back until the pivots re-engage the shoes, and re-engagement is a blind operation from the user’s point of view — they cannot see the pivot and the shoe meeting inside the liner. If the sash is released before engagement is complete, it drops under gravity onto whatever is partly engaged, which damages the pivot, the shoe, the liner and sometimes the sash rail. If it is forced back without engagement, the pivot is driven into the liner at the wrong point and the channel is scored or split. So the geometry has to make correct re-engagement the easy path and incorrect re-engagement difficult: a lead-in that guides the pivot into the shoe, a positive feel or sound at engagement, and a stop that prevents the sash from being pushed home before the hardware is seated. This is a design property of the liner and the shoe, not a training matter, and it is worth specifying because it determines whether the tilt function survives twenty years of use or becomes a source of progressive damage that eventually jams the sash.

Then there is what the tilt function costs elsewhere in the design, because a releasable pivot is a discontinuity in the sash’s structural perimeter. The pivot point is where the balance force enters the sash, so it is a loaded connection in the sash rail, and a rail that has been designed to allow release has less material and a different section than one designed as a continuous member. Under wind load the sash transfers load to the frame through the pivot and through the seals, and a pivot that is engineered for release rather than for load transfer will deflect more, which moves the sash in its plane and unloads the seals — the same racking argument as a mismatched balance pair, arriving by a different route. So the pivot has to be rated for the wind load case as well as for the sash weight case, and the rating has to include the repeated engagement and disengagement cycles that the tilt function imposes, since every tilt is a load reversal at a connection that is not permanently made. Where the project is on an exposed elevation or the sash is large, the honest engineering is to check the tilt hardware against the wind class rather than only against the sash weight, and to accept that a large sash may need a tilt arrangement with more than the minimum two pivots, or may be better specified as a sash that is removed for cleaning rather than tilted — an arrangement that is less elegant, requires more space inside, and does not put a releasable connection under a suspended mass at head height.

The security and child-safety consequences of a releasable connection close this section. A tilt release that can be operated from inside can also, on some designs, be reached or defeated from outside if the sash is open, so the release mechanism’s position and its resistance to tampering belong in the security assessment rather than being treated as a cleaning feature. Where the window is in a room used by children, the tilt function is a hazard in its own right: a sash tilted inward into a room is a heavy glass panel projecting at head height, held by a pivot, and a child who pulls on it is applying a load the retention was not necessarily designed for. The answers are a tilt limiter that restricts the angle, a retention that requires a deliberate two-stage action, and a tilt position that is stable rather than balanced on the edge of release. And where the building has a fall risk — a window above a balcony or in a room on an upper floor — the tilt function must not become the route by which a sash can be removed and the opening left unguarded, so the release has to require a tool or a deliberate sequence rather than a single hand movement. None of this is difficult to specify; all of it is routinely left to the catalogue default, which is chosen for ease of manufacture rather than for the building it goes into.

6. The Junctions — Meeting Rail, Sill Trough and Head Pocket

A double-hung window has three crowded junctions and each of them is asked to do several conflicting jobs in a small space. The meeting rail is the first and the most important, because it is the only place in the assembly where a compression seal exists between two bodies that both move. Everywhere else the sash seals against the frame, which is fixed; at the meeting rail the lower sash seals against the upper sash, and the lock is what pulls them together. That makes the lock a compression device before it is a retention device, and it is the reason a hung window with good weatherstrip and a poor lock leaks: if the lock does not draw the two rails together with enough force and enough travel, the seal between them is never compressed to its working range, and the air path along the middle of the glass stays open however good the material is. The lock’s throw, its cam action, its engagement with the keeper and the stiffness of the two rails it is pulling all determine the compression achieved, and a rail that deflects under the lock’s force simply bows instead of compressing the seal — so rail stiffness is a sealing property, not only a structural one. On a wide sash one central lock is not enough: the rails can bow away from each other between the lock and the jambs, opening the seal at both ends, which is why wide hung windows need additional locking points toward the jambs, and why the number of locks is set by the rail’s unsupported span rather than by the security class.

The meeting rail is also the longest leak path in the middle of the glass, a thermal bridge across the view, and a visual obstruction, and the three problems are the same problem. Air and water that get past the perimeter seals have a direct route along the meeting rail gap, which runs the full width of the window at the height where the interior surface is coldest in winter and where the exterior surface collects the most water in a storm. Thermally, the rail is two sash sections, their seals, a metal lock and often a metal reinforcement all packed into a narrow gap in the middle of the glazing, so it is a concentrated bridge with a correspondingly low interior surface temperature — which is why condensation on a hung window appears at the meeting rail before it appears anywhere else, and why the meeting rail’s fRsi deserves its own line in the thermal assessment rather than being averaged into the frame value. Visually, the rail puts a horizontal bar across the middle of the view, and its thickness is the sum of two sash depths plus the seal plus the lock — so a slim-line hung window is an exercise in making all four thinner at once, and each of those thinnings costs stiffness, seal compression range or lock throw. The honest trade is usually to accept a deeper rail and get the stiffness, the compression and the throw, rather than to thin the rail and compensate with a better seal material that has no room to work in.

The sill is the second junction and it is a trough, for the same reason a sliding window’s sill is one: the lower sash runs inside it, so it cannot be a shedding lip and has to be a container. Water arrives from three directions — driven rain forced under the lower sash by positive pressure on the windward face, condensation running off the interior glass and the meeting rail, and on a wide window the whole width of the opening — and it has to leave through weeps whose total area is a small fraction of the trough’s cross-section. The trough’s capacity has to be assessed against the combined inflow at the design exposure, the floor has to fall toward the weeps, the weeps have to be baffled so wind cannot drive spray back through and insects cannot enter, and the baffle has to be cleanable, since a blocked weep on a hung window turns a drained sill into a reservoir directly beneath the lower sash, where it wets the sill seals, feeds mould and algae, corrodes the balance shoe at the bottom of its channel and, in cold climates, freezes and lifts the sash off its hardware. The balance shoe and the bottom of the jamb pocket sit in this wettest part of the assembly, which is the mechanical reason a stainless spring and a stainless or polymer shoe are specified for coastal and high-rainfall sites rather than accepted as an upgrade. And because the sill is a trough crossed by a moving sash, it can never achieve the watertightness class of a casement on the EN 12208 basis — a specification that demands one has specified the wrong format rather than a better window.

The head is the third junction and it is crowded with hardware rather than with water. In a double-hung the head has to accommodate the upper sash in its raised position, the balances for both sashes where they are housed in the jamb but anchored or accessed at the head, the head weatherstrip, and the sash stop or check that limits travel. The anchorage of the balance into the frame is a permanently loaded tension connection, so it has to bite into aluminium of adequate thickness and never into the polyamide break — a polymer anchor under sustained tension creeps, and a creeping anchor releases a sash slowly, silently and after handover, which is the same failure that governs an awning window’s head fixings. Where the upper sash is fixed, as in a single-hung window, the head is much simpler: one sash, one set of balances, one seal line instead of two, and no meeting-rail movement between the upper sash and the frame — which is why a single-hung is cheaper, tighter and more durable, and why the choice between single and double hung is a real engineering decision rather than a preference. The double-hung’s answers to the single-hung’s limitations are the tilt-in cleaning of the outer face of the upper sash and the ability to ventilate from the top as well as the bottom, and where neither is needed the single-hung is the better product. Where the upper sash does have to open, the head’s hardware count, its anchorage and its seal interruptions all have to be detailed, and the detail is what separates a double-hung that still performs in year twenty from one that has become a fixed window with a rattling sash.

7. Egress Arithmetic — Half the Height, and the Sash Has to Stay Up

Codes require habitable rooms, bedrooms above all, to have an emergency escape and rescue opening with a minimum net clear opening area, a minimum opening height and width, a maximum sill height above the floor, and operability from inside without keys, tools or special knowledge. A double-hung window can comply, which is more than an awning can say, but it complies on arithmetic that is much less generous than the window’s size suggests — and the arithmetic is what causes late-stage surprises on projects that specify hung windows for their appearance or their ventilation and check the escape requirement afterwards. The net clear opening of a double-hung is the width multiplied by the vertical distance from the sill to the lowest point of the upper sash when the lower sash is fully raised. That distance is not the lower sash’s height and it is nowhere near the total glazed height, for two reasons. First, the lower sash when raised occupies the upper part of the frame, so its bottom rail — the meeting rail — defines the top of the opening, and the opening is only as tall as the travel allows. Second, the sash itself has depth: the rail that forms the top of the opening is a physical member projecting into it, and the clear height is measured to its underside, not to the glass behind it. So a window whose glazed area looks ample delivers an escape opening that is a fraction of it, and the fraction gets worse as the sash travel is limited by the balance stroke, the sash stop and the liner geometry. The practical result is that a double-hung has to be substantially larger than a casement to deliver the same compliant net clear opening, and that difference is a cost, a facade proportion and a structural consequence, not a footnote.

Three further requirements interact with the format in ways that are easy to miss. The lock has to be operable from inside by one hand without a key or a tool, so a meeting-rail lock that needs two hands, or that is stiff enough to require force beyond what a frightened person will apply, is a compliance problem as well as a usability one — and the same lock is the device that compresses the meeting rail seal, so a lock made easy to operate may under-compress the seal unless the cam action is designed to give both. Where the window has a tilt function, the escape route uses the raised position and not the tilted one, which means the tilt hardware is irrelevant to egress but the balance is not: the opening only exists while the sash stays up, so a degraded balance is an egress defect and not merely a maintenance one, as discussed in section 2. And where a fall risk requires an opening limiter on the lower sash — a common requirement on upper floors and in rooms used by children — the limiter caps the travel and therefore caps the net clear opening, which puts the limiter and the escape requirement in direct conflict. That conflict cannot be resolved by a better product; it is resolved by the schedule, either by using a limiter that is releasable by an adult without a tool and proving that the released travel delivers the compliant opening, or by providing the escape opening elsewhere in the room.

Ventilating from the upper sash is the format’s other distinctive capability and it has its own arithmetic. Raising the upper sash alone puts the opening high in the wall, out of the reach of a child and out of the reach of an intruder from outside, and it works with stratification, since warm air leaving high is replaced by cooler air entering low. It is a genuinely good night-ventilation strategy for a bedroom, and it is safer than opening the lower sash. But it is not an escape configuration, and it is worth being explicit that a room ventilating through its upper sash has no compliant escape opening at that moment — so where upper-sash ventilation is used at night in a bedroom, the lower sash has to remain operable to the full travel, unlocked or openable without a key, and the balance has to hold it there. Security grilles and shutters interact with all of this: a grille over a hung window has to be releasable from inside without a key, and its release has to be reachable, which on a tall window means reachable at the height where a person can operate it while standing on the floor. And a security film or a laminated pane added for intrusion resistance does not help the escape case at all — it makes the glass harder to break through, which is the point, but codes generally do not permit escape through glass, so the opening has to work regardless.

The sizing conclusion is worth stating plainly because it is the one that saves a project money rather than costing it. If the room needs a compliant escape opening, the hung window has to be sized from the net clear opening requirement backwards: establish the required area, height and width, add the travel the sash needs to achieve them, and only then look at the glazed area the facade wants. Where that produces a window larger than the design intends, the alternatives are a different format for the escape opening — a casement or a tilt-and-turn in its turned position delivers nearly the whole glazed area as net clear opening — with hung windows used elsewhere on the elevation for their appearance and their ventilation. That is a pairing decision, exactly as it is for awning windows, and it belongs on the window schedule at design stage. What does not work is specifying hung windows throughout, discovering at permit stage that the bedrooms are non-compliant, and then trying to recover by enlarging openings in a structure that has already been designed around them.

8. Performance Envelope — What a Hung Window Is Rated Against

9. Five Formats Compared by How Gravity Relates to Travel

10. Technical FAQ

11. China Market Positioning — Why Foshan, Why Richocean

Hung windows concentrate a supply chain whose hardest items are not components but reconciliations, and all of them come from the fact that gravity is aligned with travel. A spring has to cancel a constant weight with a variable output, and the residual has to be absorbed by a friction band that is itself produced by the seals, so the air performance and the position holding are the same problem. Two balances on one sash have to stay matched for twenty years while sitting in two different micro-climates on the same window. The jamb has to house two sash channels, two balance systems, the weatherstrip and the tilt hardware inside a section depth that also has to accommodate a thermal break. The tilt function has to be a deliberately releasable connection in a system whose whole purpose is to hold a suspended mass. And the meeting rail has to be a compression seal between two moving bodies, a thermal bridge, the longest leak path in the middle of the glass and a visual obstruction, all inside the depth of two sash rails. Foshan in Guangdong runs the chain that keeps those reconciliations consistent — aluminium extrusion to tight section tolerances in 6063-T6 with multi-chamber thermally broken jambs sized for two sash channels and the balance hardware behind them, PA66GF25 polyamide break rolling with the balance anchorage designed into aluminium and never into the break, matched balance pairs set to the actual sash weight and travel with a stated tolerance, stainless springs and shoes for the wettest part of the assembly, jamb liners with controlled clearance and replaceable weatherstrip so the wear part is the liner and not the frame, tilt hardware rated for the static angled load case and for the wind case rather than only for the sash weight, meeting-rail locks with the throw and cam action to reach seal compression on a wide rail, anodising and PVDF coating with salt-spray-verified performance, SS316 hardware for marine exposure, insulating units with warm-edge spacers and laminated or heat-soaked toughened plies, and the engineering discipline that keeps a sash weight, a balance setting, a matched-pair tolerance, a friction band, a tilt rating, a net clear opening calculation and an fRsi assessment in the same calculation rather than on seven separate schedules.

Richocean manufactures thermally broken aluminium single-hung and double-hung windows in Foshan for villas, apartments, hotels, schools and heritage-sensitive elevations across Europe, North America, the Middle East and Southeast Asia, delivering single-hung, double-hung, tilt-in, non-tilt, heritage-proportion and large-format configurations — including projects where the vertical proportion of a hung window is required by the elevation but the performance of a fixed or casement unit is required by the brief, resolved by pairing formats on the schedule rather than by asking one product to do both — with the documentation a suspended-load assembly demands: sash weight as built and the balance setting it requires, matched-pair tolerance and the replacement-in-pairs rule, residual imbalance band and the friction that absorbs it, operating force band at a stated point in travel, balance stroke against sash travel and the sash stop setting, balance anchorage specification and the prohibition on anchoring into the polyamide break, spring and shoe material with salt spray verification, jamb liner clearance tolerance and wear limit, tilt hardware rating for both the static angled case and the wind case with its engagement cycles, meeting rail lock throw and rail stiffness, Uw with its component breakdown and the jamb treated as the crowded section it is, fRsi at the meeting rail and the sill computed separately from the frame average, air, water and wind classes with test bases, acoustic rating with the build-up behind it and an explicit statement of the meeting rail’s contribution, glass specification on the ASTM E1300 basis with the safety requirements for a falling-sash hazard, the net clear opening calculation against the egress requirement of the jurisdiction with the sizing shown, positive sash stop or friction brake independent of the balance spring, hardware duty cycle and corrosion verification at the project exposure.

12. Example Applications

Illustrative configuration; not a quoted project. A North American market residential project specifying thermally broken aluminium double-hung windows in bedrooms and living spaces, where the elevation requires the vertical proportion and the brief requires compliant escape openings: sash weight calculated as built from the actual insulating unit build-up including the laminated pane specified for a falling-sash hazard, with the balance pair set for that weight and that travel rather than for a nominal band, since the sash weight is the input that everything else in the format depends on and a later glazing substitution silently de-tunes it; matched pairs supplied and recorded, with the replacement-in-pairs rule written into the maintenance documentation on both sashes, because the two sides of a window sit in different micro-climates and diverge over years, and a diverged pair racks the sash in its own plane, loads one corner of the meeting rail and the sill line, unloads the other, and produces a stiff window that leaks at one corner in wind; operating force specified as a band at a stated point in travel with the residual imbalance and the friction that absorbs it both identified, on the reasoning that a window meeting the force band because a weak balance is masked by high friction will fail as the friction wears; weatherstrip specified by compression set and stress relaxation behaviour at the project’s temperature and humidity range rather than by hardness alone, and specified as a consumable with a replacement method that does not require removing the glass or taking the sash out of the frame; jamb liner with a stated clearance tolerance and wear limit, supplied as a serviceable part so a ten-year-old window is repaired by replacing a liner and a set of seals rather than replaced entirely; tilt hardware rated for the static angled load case and for the wind class, with positive retention in the tilted position that survives a user leaning on the glass, a release that requires the sash to be lowered first by geometry rather than by instruction, and a lead-in that makes correct re-engagement the easy path; meeting rail locks sized for the rail’s unsupported span with additional locking points toward the jambs on wide sashes, so the rails cannot bow away from each other and open the seal at both ends; a positive sash stop independent of the balance spring, so a failed balance produces a stiff sash rather than a falling one — which matters twice here, since the escape opening only exists while the sash stays up and a creeping sash can close the route behind the person climbing through; net clear opening calculated from the sill to the underside of the raised sash’s meeting rail for every bedroom and checked against the jurisdiction’s minimum area, height, width and sill height, with the window sized from that requirement backwards rather than from the glazed area forwards; stainless springs and shoes with salt spray verification where the exposure requires it, since the balance sits in the wettest part of the assembly; sill detailed as a trough with falls toward baffled, cleanable weeps and with the balance shoe and pocket bottom protected from standing water; and fRsi computed at the meeting rail and the sill separately from the frame average, using the interior humidity the bedrooms actually produce. The controlling decisions are the balance setting against the as-built sash weight, the matched pair, and the net clear opening calculation — the first because it decides whether the sash stays where it is put, the second because a diverged pair produces four symptoms that all look like different problems, and the third because it decides how large the window has to be and therefore what the facade, the structure and the budget look like.

Illustrative configuration; not a quoted project. A heritage-sensitive hotel elevation in a European city where the original openings were timber vertical sliders and the brief requires the same proportions with a thermally broken aluminium product, acoustic performance against a busy street and inside cleaning at six storeys: single-hung units specified wherever the upper light never needs to open, on the engineering reasoning that a single-hung has one moving sash instead of two, one set of balances instead of two, one seal line at the head instead of a moving one, and no meeting-rail movement between the upper sash and the frame — so it is cheaper, tighter and more durable, and the double-hung’s answers to its limitations, namely tilt-in cleaning of the upper sash’s outer face and top-and-bottom ventilation, are not needed where a fixed upper light serves the elevation; double-hung units reserved for the rooms where night ventilation through the upper sash is the strategy, with the upper-sash opening positioned high and out of a child’s reach and out of an intruder’s reach from outside, and with the lower sash still required to deliver the compliant net clear opening, since upper-sash ventilation is not an escape configuration; slim meeting rails pursued only where the rail stiffness, the seal compression range and the lock throw can all still be delivered, on the reasoning that thinning the rail costs one of the three and that a deeper rail with adequate stiffness, compression and throw is the honest trade rather than a thin rail with a better seal material that has no room to work in; acoustic glass derived from the measured source spectrum at the facade with asymmetric pane thicknesses so the two panes’ coincidence effects do not reinforce each other, a cavity width chosen with the mass-air-mass resonance moved out of the band that matters, and a laminated pane with an acoustic interlayer where the spectrum is traffic dominated — with the explicit statement that the meeting rail is the dominant weak line in the assembly and that no glass build-up recovers a leak path along the middle of the glass; the tilt function retained on the upper floors because a window on the sixth storey cannot be cleaned from a cradle every quarter, with the tilt hardware rated for the wind case as well as the sash weight and with retention that survives leaning; a fall-risk assessment resolving the conflict between an opening limiter and the escape requirement, using a limiter releasable by an adult without a tool and proving that the released travel delivers the compliant opening, or providing escape elsewhere in the room; balances set for the as-built weight including the laminated acoustic build-up, supplied as matched pairs with the replacement-in-pairs rule documented, and anchored into aluminium with the anchorage prohibited from the polyamide break; positive sash stops independent of the balance spring throughout, since a hotel sash that creeps down is a guest-safety and a liability issue rather than a maintenance ticket; stainless springs and shoes with salt spray verification for the urban exposure; and sash retention and tilt-release tamper resistance included in the security assessment rather than treated as cleaning features. The controlling decisions are the single-hung versus double-hung split, the meeting rail proportion, and the resolution of the limiter against egress — the first because it buys performance and durability for free wherever the upper light does not need to open, the second because the rail is simultaneously the seal, the leak path, the thermal bridge and the sightline and thinning it costs one of the four, and the third because it cannot be resolved by a better product, only by the schedule.

13. Price Drivers — What Actually Moves the Cost

On hung windows the cost follows the suspended load rather than the square metre of glass, and it is concentrated in the jamb and the meeting rail. The balance specification leads: a pair matched to a stated tolerance and set against the as-built sash weight and travel costs more than a catalogue balance selected from a nominal weight band, and the difference is whether the sash stays where it is put for twenty years or drifts in year five. The spring and shoe material follows, since the balance sits in the wettest part of the assembly — a stainless spring and a stainless or engineered-polymer shoe cost more than the inland default and are what a coastal or high-rainfall project actually needs, because corrosion reduces the section that carries the load, so a spring’s fatigue life falls faster than its force does and it can look intact while it has lost both. The anchorage is a small line with a large consequence: a fixing specified by material and thread engagement into aluminium, with the polyamide break excluded, costs nothing and prevents the failure that releases a sash slowly, silently and after handover. The positive sash stop or friction brake independent of the balance spring is another small component that separates two very different outcomes — a failed balance producing a stiff sash rather than a falling one — and it is the cheapest life-safety item in the product.

Jamb section depth and liner quality then price the crowding: two sash channels, two balance systems, weatherstrip and tilt hardware inside a section that also has to carry a thermal break, with a liner specified as a serviceable part with a stated clearance tolerance and wear limit so that the wear part is the liner rather than the frame. Tilt hardware prices the rating — for the static angled load case and for the wind class, with engagement and disengagement cycles counted as load reversals at a releasable connection — plus the retention geometry, the release that requires the sash to be lowered first, and the lead-in that makes correct re-engagement the easy path. The meeting rail prices the reconciliation between thinness and function: rail stiffness, seal compression range and lock throw are three properties competing for the same depth, and the number of locking points on a wide sash is set by the rail’s unsupported span rather than by the security class. Weatherstrip prices the material against compression set and stress relaxation at the project’s actual temperature and humidity range, plus a replacement method that does not require removing the glass. Glazing prices the build-up rather than the pane count — laminated plies where a falling sash is a hazard, heat-soak testing on the EN 14179 basis where toughened glass is used, asymmetric thicknesses and cavity widths chosen against a measured source spectrum where acoustics matter, coatings checked against the solar and thermal stress case on the ASTM E1300 basis, warm-edge spacers, and the edge seal and desiccant quality that decide whether an expensive unit fogs in year five or year twenty-five. And because sash weight is dominated by glass while the balance is set for a weight, every acoustic, safety or thermal upgrade has to be re-checked against the balance setting, so the cost of the upgrade includes the hardware it forces — the single most common source of an unbudgeted variation on a hung-window project.

Single-hung versus double-hung is a real price decision rather than a preference, and it runs in the obvious direction: a single-hung has one moving sash, one balance pair, one seal line at the head and no moving meeting rail, so it is cheaper to make, tighter in service and more durable, and it is the better product wherever the upper light never needs to open. The double-hung’s premium buys tilt-in cleaning of the upper sash’s outer face — which is worth a great deal above the third storey, where a cradle or a mast has a cost of its own — and top-and-bottom ventilation with the upper opening out of reach. Sizing from the net clear opening requirement backwards is another cost driver that is invisible until late: a hung window has to be substantially larger than a casement to deliver the same compliant escape opening, because only the lower portion of the glazed area is usable and the raised sash’s rail forms the top of the opening, so the difference is structural, facade and budget, and discovering it at permit stage is the most expensive way to find it. Where the requirement cannot be met, pairing formats on the schedule — a casement or a tilt-and-turn in its turned position for the escape opening, hung windows elsewhere on the elevation — costs less than enlarging openings in a structure already designed around them. Security class prices the meeting rail lock and its keepers, sash retention, tilt-release tamper resistance and glazing retention on the EN 1627 or PAS 24 basis, and it is a property of the whole window rather than of the lock. Acoustic performance prices the glass and the rail, and it is worth stating that the rail is the dominant weak line, so an acoustic upgrade that ignores it buys less than it appears to. Corrosion class and certification close the list: SS316 throughout with salt spray verification, galvanic isolation between dissimilar metals, and type testing with the air, water and wind classes, the thermal and acoustic assessments and the hardware duty cycle stated, which is what allows a specification to be checked at handover instead of argued about afterwards. Indicative ranges only, not offers; final pricing depends on balance specification and matched-pair tolerance, spring and shoe material, anchorage detail, positive stop, jamb section depth and liner serviceability, tilt hardware rating and retention geometry, meeting rail depth and number of locking points, weatherstrip material and replacement method, sash sizes and glass build-up, single versus double hung, the net clear opening requirement and the sizing it forces, security class, acoustic spectrum, corrosion class, certification scope and the access details required for cleaning and maintenance. Richocean prices hung windows against the suspended load and the two crowded junctions, quoting the as-built sash weight, the balance setting and the matched-pair tolerance together with the net clear opening calculation and the classes, because a hung window selected on Uw and appearance alone transfers its cost into drifting sashes, corner leaks, rattling in wind and a bedroom that does not comply for the life of the building.

14. Installation, Commissioning, Maintenance and the Richocean Philosophy

Installation starts with the frame, because the balance works against a jamb that has to be plumb, straight and square for the sash to run true. A jamb out of plumb in the plane of the window makes the sash bind on one side, which adds friction that was not designed, masks or exaggerates the balance setting, and wears the liner unevenly; a jamb out of plumb across its depth makes the sash tilt in its channel and unloads one edge of the meeting rail seal. Both are installation defects that present later as hardware problems, which is why they are checked and recorded rather than assumed. Fixings are installed to the specified type, spacing and substrate, with the frame free to accommodate thermal movement along its length rather than restrained, since a restrained frame distorts and distorts the liner with it, changing the clearance the sash runs in. The balance anchorage is verified into aluminium and never into the polyamide break, and the thread engagement is checked, because this is a permanently loaded tension connection and a creeping anchor releases a sash slowly and without warning. Sill falls toward the weeps are proved before the sashes go in, weeps and baffles are cleared and verified, and the perimeter junction is built as a sequence — weathertight and drained outside, flexible and thermally broken in the middle, sealed inside, never a single rigid fill. Sashes are then installed with the pivots fully and equally engaged in their shoes on both sides, the sash stop set so the travel sits inside the balance’s working stroke and so the pivot cannot leave its channel at the top of the travel, and the liner clearance checked against the specified tolerance.

Commissioning is the physical protocol the design promised, and on a hung window it has items that do not exist on other formats. Sash weight is confirmed as built against the installed glass build-up, because a glass substitution during construction silently changes the demand on every balance and is the most common cause of a sash that will not stay raised. The balance setting and the matched-pair tolerance are verified on both sashes, and the pair is confirmed as supplied rather than assembled from mismatched stock. Operating force is measured at a stated point in the travel and recorded, since it is the baseline every future complaint about stiffness or drift will be compared against, and a window that meets the force band for the wrong reason will fail as the friction wears. Position holding is proved by raising each sash to full travel and to intermediate positions, releasing it, and observing — the sash must stay where it was left, must not drift down, must not drift up, and must move evenly with neither edge leading, since an uneven sash is a mismatched pair that is racking. The positive sash stop or friction brake independent of the balance spring is verified, because it is the component that converts a failed balance from a falling sash into a stiff one. The tilt function is exercised through its full cycle on both sashes: release requires the sash to be lowered first, retention in the tilted position holds under a load applied as a person would apply it, and re-engagement returns positively with the lead-in doing its work — and the cycle is repeated, since every tilt is a load reversal at a releasable connection. The meeting rail lock is checked for throw and for the compression it actually achieves, with the seal contact verified along the whole rail and at both ends, since on a wide sash the rails can bow away from each other between the lock and the jambs. Head and sill drainage is proved with a water test, with discharge observed at the weeps and no water at the balance pocket or the interior sill. Air and water field testing is carried out on the sample the specification requires. Net clear opening is measured for every room on the escape schedule, from the sill to the underside of the raised sash’s meeting rail, and compared against the jurisdiction’s requirement, with the lock’s one-hand operability confirmed. Security lock, keeper, sash retention and tilt-release tamper resistance are verified. Glass is inspected for edge seal integrity and for the laminated or heat-soaked specification where a falling-sash hazard was identified. fRsi-relevant details at the meeting rail and sill are confirmed against the assessment. And the documentation is assembled with the class ratings and their test bases, the as-built sash weight and balance setting, the matched-pair tolerance and replacement rule, the operating force and position-holding records, the tilt hardware rating, the net clear opening schedule, the thermal and acoustic assessments, the hardware duty cycle and the maintenance access method. Richocean delivers each of these as a record rather than as an intention, because a hung window’s performance decays through spring relaxation, seal compression set and liner wear rather than failing visibly, and only the record shows what it started at.

Maintenance is what keeps a suspended mass suspended. Position holding is the first item and it is checked rather than assumed: each sash is raised to full travel and released, and observed for drift down, drift up, uneven movement with one edge leading, and stiffness throughout — four observations that separate a weak balance, a strong balance, a mismatched pair and excess friction without tools, and that belong on a periodic inspection in any building whose bedrooms are served by hung windows, since a creeping sash is an egress defect and not only a comfort one. Balances are replaced in matched pairs on the same sash, and on a double-hung ideally on both sashes, because the two sides sit in different micro-climates and diverge over years, and because a new spring paired with an old one is a deliberately mismatched pair that racks the sash immediately and overloads the new balance. Springs and shoes are inspected for corrosion at the bottom of the jamb pocket, where driven rain and condensation collect, and any spring showing corrosion is replaced rather than lubricated, since corrosion reduces the load-carrying section and the fatigue life falls faster than the force. Cords and ribbons are inspected for fraying and stretch, since stretch changes the force-displacement relationship before rupture does. Anchorage fixings are torque-checked, with any showing movement investigated rather than retightened, because a creeping anchor in a polymer is not cured by torque. Lubrication is applied only where the balance manufacturer specifies it and only with the specified product, on the reasoning that the shoe and channel are in a dirty wet environment and an over-lubricated liner becomes an abrasive paste that wears faster than a dry one. Weatherstrip is inspected for compression set, swelling, hardening and the dust line that is the visible evidence of an air path, and is replaced at the stated interval by the method that does not require removing the glass — remembering that a sash that has become easier to move has usually lost its seal, and that the same loss reduces the friction that was masking any residual imbalance in the balances. Jamb liner clearance is checked against the wear limit and the liner replaced as the serviceable part it was specified to be, since excess clearance produces rattle, which is a fatigue input into the corner joints and the glass edge, evidence that the seals are no longer held at their designed compression, and a structure-borne acoustic path. Tilt hardware is exercised and its retention checked, pivots and shoes inspected for wear and for correct engagement on both sides, and any sash that drops on re-engagement investigated rather than re-tilted. Meeting rail locks are checked for throw and for the compression they achieve, keepers for shift, and rails for bowing between the lock and the jambs. Sill weeps and baffles are cleared seasonally with the discharge observed, and the balance pocket inspected for standing water, since a blocked weep makes a reservoir that wets the sill seals, feeds mould and corrodes the balance shoe. Insulating units are inspected for fogging, which means the edge seal has failed and the thermal performance is permanently degraded. Condensation or water marks at the meeting rail are recorded rather than wiped away, because persistent wetting there indicates an fRsi problem at the rail rather than a cleaning problem. And where the window serves a bedroom on an upper floor, the net clear opening is re-measured periodically and the sash confirmed to hold at full raise, since the escape route only exists while the sash stays up.

Richocean works hung windows as suspended-load assemblies whose numbers travel together: the as-built sash weight from the actual glass build-up and the balance setting it requires, with the balance stroke confirmed to contain the sash travel and the sash stop set so the pivot cannot leave its channel; matched pairs with a stated tolerance and the replacement-in-pairs rule documented; the residual imbalance band identified and the friction that absorbs it specified as a stated operating-force band at a stated point in travel, with the weatherstrip chosen by compression set and stress relaxation at the project’s actual temperature and humidity range; the jamb liner specified with a clearance tolerance and a wear limit as a serviceable part; the balance anchorage specified by material and thread engagement into aluminium with the polyamide break excluded; spring and shoe material verified by salt spray for the wettest part of the assembly; tilt hardware rated for the static angled case and for the wind class with its engagement cycles counted as load reversals, and retention specified to survive a user leaning on the glass; the meeting rail lock sized for the rail’s unsupported span with additional locking points toward the jambs on wide sashes; fRsi computed at the meeting rail and the sill separately from the frame average; the net clear opening calculated from the sill to the underside of the raised sash’s meeting rail against the jurisdiction’s requirement, with the sizing shown and the limiter conflict resolved on the schedule; and a positive sash stop independent of the balance spring so that a failed balance produces a stiff sash rather than a falling one. OEM and ODM service covers single-hung, double-hung, tilt-in, non-tilt, heritage-proportion and large-format configurations for villas, apartments, hotels, schools and heritage-sensitive elevations, delivered with the documentation a suspended-load assembly demands: class ratings with test bases, the sash weight and balance setting, the matched-pair tolerance, the operating force and position-holding records, the tilt rating, the net clear opening schedule, the thermal and acoustic assessments and salt spray verification.

The founding philosophy fits the format exactly: a double-hung window is not a vertical sliding window, it is a machine for holding a mass in mid-air against its own weight, using a device whose output varies with position while the load it opposes does not vary at all, with friction from the seals as the only element that absorbs the residual — so its failure is a falling sash rather than a stiff one, and its escape opening exists only while that sash stays up. So every reconciliation is named, every rating is quoted on the basis it was derived from rather than the basis that looks reassuring on paper, the failure mode is stated as a falling mass rather than left implicit, the consumables are identified — seals, liner, balances, shoes — rather than assumed permanent, the net clear opening is calculated rather than inferred from the glazed area, and position holding is measured so that decay has a number attached to it. That is what a hung window document set is for, and it is why Richocean quotes the as-built sash weight, the balance setting, the matched-pair tolerance and the net clear opening alongside the classes rather than separately. For a project quotation, a balance review against the as-built sash weight and travel, a matched-pair and racking diagnosis for sashes that move unevenly or leak at one corner, a tilt hardware review against the wind class, a meeting rail and lock review for wide sashes, a net clear opening and egress schedule, a single-hung versus double-hung split that buys performance wherever the upper light does not need to open, a seal and friction review for windows that have become easy to move, or a corrosion specification for the actual exposure, send the elevations, the opening sizes, the sill heights, the glass build-up, the exposure and the egress requirement of the jurisdiction: the system will be calculated, rated, tested, documented and delivered as one suspended-load assembly.