Sash window

Louw believed that the sash window was developed in England, but concluded that it was impossible to determine the exact inventor.

These windows are commonly found in older buildings in warmer climates, as they promote airflow and are easy to clean.

A significant advantage of double-hung windows is that they provide efficient cooling of interiors during warm weather.

Opening both the top and bottom of a sash window by equal amounts allows warm air at the top of the room to escape, thus drawing relatively cool air from outside into the room through the bottom opening.

[citation needed] Traditional problems with solid wooden sash windows include rot, swelling or distortion of the woodwork[6] or rattling in the wind (due to shrinkage of the wood).

Over time the plasticizer chemicals used to make vinyl sashes flexible evaporate leaving the material brittle and prone to breaking.

Vinyl is also weaker than wood and aluminum sashes and requires extra support in large window openings.

Vinyl is limited mainly to residential usage and low rise commercial due to its flammability and the toxic fumes it produces when burned.

In the future fire rated versions of UPVC windows may be used in high rise construction, but currently flammability and toxic fumes are a significant obstacle.