25 Mar 2009

Why sash windows work

Alan Burgess of Masterframe has taken the trouble to prove what many of us had long suspected. That sash windows work as superb ventilators. The trick is to open them a little at both the top and the bottom and this sets up a circulation of air that will clear the room of stale air, bad smells or excess heat in summer. Alan, together with his technical director Ray Rabbett, have run a series of simulations on software used by the ventilation trade which shows just how effective the traditional sash design is compared to other common window formats, such as top hung casements or tilt and turn. The results of their work will be published shortly.

For Burgess, it’s of more than academic interest. He is, and always has been, passionate about sash windows, and his company makes nothing else. He’s long felt that the powers-that-be have been conspiring against the sash design and pushing us all gently towards a more modern, European style, using energy efficiency arguments to jolly us along. Burgess feels that his contemporary re-working of the traditional sash designs are the equal of casements and tilt and turns in this respect, but now he has some proof that they are actually superior in terms of ventilation. And in a critical passage in Part F, the ventilation regulations, there is a reference that says that, when replacing windows, rapid ventilation should not be made worse. Up until now, no one has challenged the assumption that this simply means that the openings should be of similar size. But it transpires that a single opening casement is far less effective at rapid ventilation than a combination of top and bottom openings.

In common with many people, Burgess has long decried the ripping out of Victorian sashes and their replacement by top hung casements. Up till now, the objections have only ever been aesthetic. If this research is taken on board — and Part F is up for consultation very shortly — then it means that in future existing sashes will either have to be repaired or replaced on a like-for-like basis.


  1. I remember being taught that feature of sash windows many many years ago in architecture school. We do tend to forget though..

    It would be a god outcome to seem them return to the mainstream .

    But.. in our modern world where we will increasingly rely on mechanical or stack-based ventilation systems, will he window layout be irrelevant to ventilation-effectiveness?

  2. I am in the US, Portland Oregon, fixing and weatherizing double hung windows. I am not getting much support around here for fixing old windows, the new replacemnet window mafia is very strong. I was wondering what the latest technology and techniques for weatherizing old double hung windows are. I have a method, but always looking for better ways.

  3. AnonymousJune 25, 2009

    I'm trying to repair several wood double hung windows and finding that I need heavier weights. Not having much luck finding those.

  4. Thanks very much informative and specific information. Sash windows can be repaired effectively also. A simple google search for sash window repairs will help you out