What wind load means when your flat is on the 14th floor
Wind pressure roughly quadruples between the ground and the top of a tower. Here is what the numbers on a spec sheet are actually telling you.
If you are buying windows for a flat on an upper floor, one number on the specification matters more than it does at ground level: wind load.
The number
Winkraft uPVC doors and windows withstand a wind pressure of over 3000 Pascal, equivalent to a wind speed of about 245 km/hr.
For scale: a severe cyclone makes landfall in India at roughly 120–180 km/hr. So the figure has real headroom, which is the point of quoting it.
Why height changes everything
Wind speed increases with height above ground, and pressure rises with the square of speed. The practical consequence is that the same window, on the same building, is under several times more pressure on the fourteenth floor than on the second.
This is why a window that has been fine in a bungalow for a decade is not automatically fine in a tower. It is also why the failures you hear about in high-rise buildings tend to be windows that were specified for a low-rise and installed high up.
What actually fails
Rarely the glass. Usually one of:
- The seal, which lets water in under pressure long before anything breaks
- The locking points — a single-point lock on a large sash concentrates all the load on one place
- The fixing into the structure, which is an installation matter rather than a product one
That is why the range uses multi-point locking, and why hardware is fastened into steel reinforcement inside the profile as standard rather than into the uPVC itself. The load has to reach the building through something that can carry it.
What to ask for
If you are specifying for anything above about six floors:
1. Ask for the wind load figure in Pascals, not a reassurance.
2. Ask whether the locking is multi-point on every opening sash.
3. Ask what the hardware is fastened into.
4. Ask about the installation standard. Winkraft installs to BS8213-4, the British standard for the installation of windows and doorsets — the number to ask about, because a well-made window fitted badly is a badly performing window.
The systems
For high-rise work the usual specification is Casement Windows or Tilt N Turn Windows, both of which take multi-point locking and are available with concealed heavy-duty hinges for continuous weather seals.
Sliding Windows are common in Indian towers for the practical reason that a sash cannot blow open into the room, though the achievable glazing thickness is lower — 4 mm to 22 mm rather than up to 36 mm.
If your project is a tower, send the elevation and the floor levels with it. Wind load is one of the few window questions where the right answer changes as you go up the building, and we would rather size it properly than quote a single specification for every floor.