# Making sash windows - rail and stile dimensions



## rich1911 (8 Feb 2019)

I'm working out the profile of sash stiles and rails when using double glazing and wanted to do a quick sanity check.

Looking at U-value requirements (unless the planning dept say otherwise), I will need a 22mm thick unit. Centre of plane U value 1.2 which is a 4-14-4 with argon and softcoat.

Allowing 2mm either side for window tape.

Aiming for a stile/rail width of 45mm to keep the overal proportions similar to the original. Is that possible? It only leaves 9.5mm either side for beading.


For the rebate, if I want to have a 3mm? air gap all round and make sure the edge seals are hidden, the rebate needs to be about 15mm deep? So the glazing bead would 15x9.5mm.

My existing widows have a 9mm parting bead and 22mm staff bead and outer lining. Total depth of the frame is 143mm. The reveal is 43mm.

So should I try and keep the sash rails/stiles at 45mm or widen the frame, growing it inwards say 20mm and going to 55mm rails and stiles to allow a glazing bead of 15x14.5mm. Modern wood sashes apear to be 57mm and the frame is 160mm deep.

For seals and clearance, should I allow 2mm + 2mm between the stiles and parting/staff beads?

Please rip this to shreds if I am barking up the wrong tree!


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## Bradshaw Joinery (8 Feb 2019)

Are you making a complete new window or repairing an old one with new sashes? If the latter, use 4-6-4 glass with low-e and Argon (most cost effective) and use a 32mm rebate, 14mm bead. U values dont matter if your repairing. Even if your replacing, new windows should, by the letter of the book, have whole window u value calculations not just glass u values and also CE marking, although im sure your Inspector wouldn't know this...


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## Trevanion (8 Feb 2019)

rich1911":1kcu8279 said:


> Allowing 2mm either side for window tape.



I absolutely hate glazing tape, horrible product and I don't know why people bother with it. You get a much better and neater seal with low modulus neutral cure silicone. Tape grows to look filthy in a couple of years.



rich1911":1kcu8279 said:


> Aiming for a stile/rail width of 45mm to keep the overal proportions similar to the original. Is that possible? It only leaves 9.5mm either side for beading.



Ideally, you want your beads to be as close to square as possible, I would say 9.5mm isn't quite enough to hold the glass firmly.



rich1911":1kcu8279 said:


> My existing widows have a 9mm parting bead and 22mm staff bead and outer lining. Total depth of the frame is 143mm. The reveal is 43mm.
> 
> So should I try and keep the sash rails/stiles at 45mm or widen the frame, growing it inwards say 20mm and going to 55mm rails and stiles to allow a glazing bead of 15x14.5mm. Modern wood sashes apear to be 57mm and the frame is 160mm deep.
> !



My 24mm double glazed sash boxes tend to be 158mm thick, which allows for 2 X 55mm sashes, 6mm wooden parting bead, 1mm per sash clearance between the sash and parting bead/staff bead and 20mm inner and outer casings.

I will be starting a boxed sash job in the very near future and I did promise to do a thread on sash making while I was doing it.


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## Fitzroy (8 Feb 2019)

Yes please, a box sash WIP would be awesome. Have 10 to renovate or replace at some-point and all the questions above have been circulating my brain for a few years. 

F.


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## rich1911 (8 Feb 2019)

Bradshaw Joinery":ti61ny7d said:


> Are you making a complete new window or repairing an old one with new sashes? If the latter, use 4-6-4 glass with low-e and Argon (most cost effective) and use a 32mm rebate, 14mm bead. U values dont matter if your repairing. Even if your replacing, new windows should, by the letter of the book, have whole window u value calculations not just glass u values and also CE marking, although im sure your Inspector wouldn't know this...



Hi Bradshaw Joinery,

Difficult to say if I am repairing. As the cills and outer linings are rotten, I had intended to replace.

I don't want any scarf joints. So only the head and inner lining will be salvageable. All the sashes will be replaced.

I'd like to use thin units but I keep reading horror stories about them. I don't understand why a thinner unit would be more likley to fail?

Yes, I ready that 1.6 is the whole window which is pretty difficult to measure I would think! Centre of pane at 1.2 seems to be a rule of thumb...


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## rich1911 (8 Feb 2019)

Trevanion":3k3bfydg said:


> rich1911":3k3bfydg said:
> 
> 
> > Allowing 2mm either side for window tape.
> ...



Thanks for the input Trevanion. 

So many ways a means to glaze a window! Theres the whole wet/dry thing too....

I guess the important thing is to make sure that whatever you use is compatible with the DGU seals. I have no idea if butyl tape is better than epdm seal or if silicone mastic is better than those. 

I, for one, would be interested to see your thread of a sash build. The more pics the better!

Cheers!


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## thomashenry (10 Feb 2019)

If you are re-using any part of the originals then you are repairing, I think... can’t imagine that BC give that much of a toss TBH.


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## thomashenry (10 Feb 2019)

thomashenry":j2fe5855 said:


> If you are re-using any part of the originals then you are repairing, I think... can’t imagine that BC give that much of a toss TBH.



Also, I think this means you should be able to have single glazed units rather than be forced into double glazing.


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