Sash Window Draught Proofing and Double Glazing

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Fitzroy

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I’m thinking about windows in my house, about the last thing to sort after moving in 10yrs back.

I’ve had a few companies come look and quote for slim glazed units and draught seals. However they all use the brush things which I think a rubbish. Additionally the thermal performance of slim glazed is not great.

So I’m toying with a few things. Firstly using Aquamac AQ21 for the seals and secondly making the replacement sashes and installing vacuum glazing.

I’ve made a prototype sash for one of the kitchen windows, for which 5yrs ago I bought some slim glazed units, rush of blood moment.

Having made the prototype I’m left with some questions. Wonder if there are any answers or thoughts/advice/criticism out there.

1. How to bed the unit. Can I just fill the frame with neutral cure silicone and push the unit in?

2. There is only a 1mm gap round the unit. Most sites show a 2mm gap at the base with packers. Is this required?

3. The bead (see image) is it just planted and pinned to the frame or is the silicone under it also?

4. The original window is pegged in each tenon, are they just pegged or draw bored? Do they also need glue?

5. I made the meeting rail with a slot that the glass slides in to, copying the original. Does this work with DGUs?

6. The DGU rebate interferes with the top tenon to the meeting rail. If I went for a thicker DGU I can’t workout how it doesn’t end up impacting the tenon to much. What depth DGUs should I be able to fit in a 50mm deep sash?

7. Does the draught seal design look sensible.

Thanks

Fitz
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Doug71

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It's all looking good to me 🤞

1,2 & 3. I don't do much with the slim/heritage type units, they had a bad reputation for failing but must be better now as loads of people seem to use them.

I have used the Hodgson Heritage putty for fitting them with and without beads, these are their recommended methods but others also work.



4. I don't peg sashes, the glues is so good these days that is all you need.

5. I use a bead rather than a groove for DG units, looks the same once done.

6. You need to be able to get a fastener on the back of the top sash, think the narrow ones are about 15mm so this kind of limits the unit thickness.

7. The draught seal looks good, that is how I do them on the stiles. You might need to take the one on the middle rail a bit deeper as it's about 5mm when compressed and that looks like it might be a bit tight.
 

eezageeza

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1. How to bed the unit. Can I just fill the frame with neutral cure silicone and push the unit in?

Yes, I bed mine fully, back, sides, front, so the DG unit is fully enclosed by silicon.

2. There is only a 1mm gap round the unit. Most sites show a 2mm gap at the base with packers. Is this required?

I think the gap is to allow a degree of movement; 1mm might be a bit tight, but if thats what you've got, go for it!

3. The bead (see image) is it just planted and pinned to the frame or is the silicone under it also?

I put silicon under the bead before pinning.

4. The original window is pegged in each tenon, are they just pegged or draw bored? Do they also need glue?

I'd use PU glue to make sure all the gaps are as full as possible, to minimise the chance of water ingress.

5. I made the meeting rail with a slot that the glass slides in to, copying the original. Does this work with DGUs?

Don't know! All my frames are beaded all round.

6. The DGU rebate interferes with the top tenon to the meeting rail. If I went for a thicker DGU I can’t workout how it doesn’t end up impacting the tenon to much. What depth DGUs should I be able to fit in a 50mm deep sash?

Don't know.

7. Does the draught seal design look sensible.

Yes!
 

Fitzroy

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@Doug71 @eezageeza Thanks so much for taking the time to respond, super to get some confirmation that I'm on the right track and for the heritage putty links, I've been around the web a few times on this and bumped into that stuff but then forgot it's name.
 

mr rusty

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Couple of points.

If you are going to make new sashes for the original box frame to take DG, you do have to consider the additional weight. Many single glazed sash windows had 3mm glass. Change that to 2 x 4mm and you have loads of extra weight.

If you use ordinary red or whitewood then you do have a risk of the timber expanding a fair bit when its wet/dry so take this in to account.

If you are going to the trouble of remaking sashes, why not remake the box as well and make the whole lot deeper for 18mm or 24mm DGU? - you may in any case need larger weight pockets for additional weights. I added 50x50mm lead on top of original cast irons, and still had enough clearance height.

The windows I made were internally beaded, dry glazed with epdm tape and dry glazing clips. There's a complete thread on my project here https://community.screwfix.com/threads/talk-box-sash-windows.183451/
 

Ollie78

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A quick note on the hybrid polymer sealants which is what the heritage putty is.
Dryseal is the original one but very expensive I think they had a patent for many years which ran out, they changed their formula after that.
Hodgesons is good but again a bit expensive, the one I use often is from chemfix and is called Timbaglaze which is cheaper and very similar. We did a test with Stixall from toolstation and it worked exactly the same it even smells like the original dryseal used to, I know of one company that uses it exclusively.

Doug has answered everything I think but I would personally not use a bead for the glazing, for the heritage listed stuff I normally just bed and face with the polymer sealant so it looks just like putty, the bead will rot first causing problems.
The trick is getting a good tool for smoothing it ,the Palu smoothing tool is best.

Your joinery looks fine but I do not recommend a stepped meeting rail I have seen so many split over the years, it only takes a small misalignment to make them horrible in operation and one less than carefully person slamming the lower sash can pop it clean off.
The splayed meeting rail is best, it allows for seasonal movement can cope with some misalignment and is more robust over time.

Don't seal the stiles of the sash just the parting and staff beads and the meeting rail.

Ollie
 
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Fitzroy

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Thanks @mr rusty and @Ollie78 for your input.

Agree regards sash weights although for this exact sash, a lower one in one of the windows in what was a working area of the house, it has no assistance mechanism. No weight pockets or pully cutouts in the box. The top one does but not the bottom.

Regards making new boxes, most of the property has panelling around the windows so changing the boxes would involve messing with this, which is one of the things I’m trying to avoid.

Thanks regards the splayed meeting rail rather than stepped. Do you mean a wedge shape with opposing angles?

I’ll go review your screw fix thread. Looks like some good discussion there.

Fitz
 

baldkev

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Depending on your existing sash profile, you might be able to fit stepped dgu's. This is where one pane of glass is essentially smaller, creating a rebated effect, so the smaller one fits within the sash internally.
 

Ollie78

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Thanks @mr rusty and @Ollie78 for your input.

Agree regards sash weights although for this exact sash, a lower one in one of the windows in what was a working area of the house, it has no assistance mechanism. No weight pockets or pully cutouts in the box. The top one does but not the bottom.

Regards making new boxes, most of the property has panelling around the windows so changing the boxes would involve messing with this, which is one of the things I’m trying to avoid.

Thanks regards the splayed meeting rail rather than stepped. Do you mean a wedge shape with opposing angles?


Fitz

As long as it is an actual box you can easily cut a pocket and a pulley hole in the lining.

If the boxes and cills are in decent condition or sensibly repairable I agree that a restoration of them is less collateral damage than having to re-do all the interior stuff, especially if its panels and shutters. Its a balance between the level of work and the level of disturbance. If you are already planning to do plastering or major work inside then a nice new box is more attractive.

Yes, opposed wedge shaped fillets. I do mine 9 degrees like cills. I actually stick mine on afterwards as fillets because of the issue with having a spindle or tennoner knife set up for each different sized job is silly expensive and with modern limiter tooling its too much of a long thin single protrusion so they would have to be a brazed cutter.
I machine an 8mm rebate in the meeting rail of the lower sash for the pile or Schleigel suff to sit in.

Ollie
 

mr rusty

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I made my sashes with rebates around the parting bead so the sash faces run barely 5-6mm apart, and then used a double row of pile (one on each sash) to close the gap at the meeting rails. Perhaps novel, but it's been and still is perfect.
 

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