Windows · Hardware

Sash weight and hinge load

It is not the weight that tears a hinge out of the frame — it is the width. A sash hangs from its hinge side, so its own weight acting at half its width tries to rotate it out of the opening. The top hinge resists that by being pulled straight out of the frame, with a force of F = W · b / (2 · h), where b is the sash width and h the distance between hinges. Two sashes of identical weight can put wildly different loads on the same fitting.

The sash

Sash width (mm)

Sash height (mm)

Profile face width (mm)

Visible width of the sash profile. Sets how much of the sash is glass.

What it is made of

Total glass thickness (mm)

Add up the panes only, not the cavities: a 4-16-4 unit is 8 mm of glass, a 6-16-33.1 is about 12. The weight calculator works out the whole unit if you need it.

Sash profile

Typical linear weights to orient you. Your supplier's figure for the exact section is always better — reinforcement alone can double it.

The hardware

Distance between hinges (mm)

Top hinge to bottom hinge, measured vertically. The bigger this is, the gentler the pull-out. It is usually the sash height less about 250–300 mm.

Rated capacity of the hardware (kg)

From the hardware catalogue. Many sets also cap the sash width independently of weight — check both.

—

Sash weight

— kg

Pull-out on the top hinge

— kg

Glass

— kg

Profile

— kg

How this is worked out

glass = (b − 2p) · (h − 2p) · t_glass · 2500 kg/m³ profile = 2 · (b + h) · linear weight W = glass + profile vertical load, mostly on the bottom hinge: ≈ W pull-out on the top hinge: F = W · b / (2 · h_hinge)

The second line is the one that matters. The sash's centre of gravity sits about half its width from the hinge, so the weight acts on a lever arm of b/2 and tries to rotate the sash out of the opening about the bottom hinge. The top hinge stops that by resisting a straight pull out of the frame — and it is those fixings, in a hollow profile or a soft masonry reveal, that let go first.

Which is why the arithmetic behaves in a way that surprises people: a wide, short sash is harder on the hardware than a tall, narrow one of the same weight. Wider means a longer lever; taller means the hinges are further apart and resist it better. Make a sash 20 % wider and 20 % shorter and you have kept the weight roughly the same while making the pull-out around 50 % worse.

Worked example you can check by hand

900 × 1400 mm sash, 70 mm PVC profile at 2.2 kg/m, 4-16-4 unit (8 mm of glass), hinges 1100 mm apart.

glass light = (900 − 140) · (1400 − 140) = 760 × 1260 = 0.9576 m² glass = 0.9576 · 0.008 · 2500 = 19.15 kg profile = 2 · (0.9 + 1.4) · 2.2 = 10.12 kg W = 29.27 kg F = 29.27 · 0.900 / (2 · 1.100) = 11.97 kg (117 N)

Now make the same window a 1400 wide by 900 tall sash — same area, same glass, near enough the same weight — with hinges 600 mm apart, and the pull-out goes to about 34 kg. Three times the load on the same screws, for a window that weighs the same.

What this page does not do

Side-hung and tilt & turn only. Sliding, lift-and-slide, pivot and bottom-hung sashes distribute their weight completely differently.
Static weight only. No wind on an open sash, no slamming, no someone leaning on it, no repeated-cycle fatigue — and hardware is usually rated on cycles, not just on a static hang.
It does not know your hardware. Rated capacities here are typical bands. Real sets also limit sash width, sash height and the width-to-height ratio independently of weight, and those limits are in the catalogue, not in any formula.
It does not check the fixing. The pull-out force is only half the question; the other half is what it is screwed into. The same hinge in reinforced PVC and in unreinforced PVC are different products.
Typical linear weights are typical. Steel reinforcement, thicker walls and the exact section can move the profile weight by a factor of two.

Read this. A pre-dimensioning aid for people who already specify windows. It is not a hardware selection, and it does not replace the fitting manufacturer's tables, which are the only thing that decides whether a set is suitable. If a sash falls, no formula defends you — the catalogue does.