Window opening types

Frequently asked questions

Why does a casement seal better than a hung window?

Because of how the closing action meets the seal. A casement swings shut against a continuous gasket and is then pulled tight by its locking points, so the seal is compressed all the way round — the harder the wind pushes, the tighter a correctly hung outward-opening casement closes. A vertically sliding window cannot do that: the sashes have to slide past each other and past the frame, so the contact is a sliding fit with brushes or a compression seal only where the meeting rails come together. That gap is the reason an old sliding sash window is draughty and the reason its modern equivalents work hard on the meeting rail. The trade-offs run the other way in other respects — a hung window projects into nothing when open, which matters on a footpath or a balcony, and it ventilates at top and bottom at once, which drives a useful stack effect a casement cannot.

What is an egress window, and does Britain have the same rule?

It is a window sized and positioned so a person can escape through it and a firefighter can get in, and both markets require something like it while defining it differently. American residential code sets explicit minimums for a bedroom or basement: a clear opening area, a minimum clear height and width, and a maximum sill height above the floor — four numbers, all of which must be met by the CLEAR opening with the window fully open, not by the frame's nominal size. British guidance sets an unobstructed openable area and a minimum dimension with a sill height range instead, and applies it to upper-storey habitable rooms and to inner rooms rather than to bedrooms as a class. The trap either way is the same: replacing a window like for like in overall size can fail the requirement, because a modern frame's sections and its opening mechanism eat into the clear opening that the old one had.

Why does the word sash cause so much confusion?

Because it names a component in one market and a product in the other, and both usages are correct where they live. In North America a SASH is the glazed frame that moves — or does not — inside the outer frame, so a casement has a sash, a double-hung has two, and a manufacturer's parts list talks about sash replacement for any window type. In Britain SASH WINDOW is a specific thing: the traditional vertically sliding window with weights in a boxed frame, cords over pulleys, and a pair of sashes that counterbalance. So a British reader meeting the phrase *casement sash* reads a contradiction, and an American reader meeting *sash window* reads a redundancy. The practical fix in a cross-market specification is to name the OPERATION rather than the product — side-hung, top-hung, vertically sliding — because those phrases mean the same thing everywhere and no market has claimed them for something else.