Sash construction - Double glazing

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rich3911
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Sash construction - Double glazing

Postby rich3911 » Thu Feb 07, 2019 9:57 am

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.

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

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!

(Hope it ok to make this another thread?)

sash profile.jpg

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Re: Sash construction - Double glazing

Postby JonR » Thu Feb 07, 2019 11:37 am

Pretty sure a 16mm softcoat argon/kryton gas filled unit will get you well within regs Google a U value sealed unit chart, yes to 15mm rebate and a 3mm gap all round the unit. You said you got 40mm thick sashes I would thicken them to 44mm if your going to totally renew the window. Not keen on external beading ok for a modern sash but if you want it to look more original you could I guess butyl putty the units in or how I did mine internally bead with a putty bead moulded in the frame.

Anything back from building control/conservation, I think if they have anything to say then that will help you decide the finer details.

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Re: Sash construction - Double glazing

Postby rich3911 » Thu Feb 07, 2019 1:33 pm

JonR wrote:Pretty sure a 16mm softcoat argon/kryton gas filled unit will get you well within regs Google a U value sealed unit chart, yes to 15mm rebate and a 3mm gap all round the unit. You said you got 40mm thick sashes I would thicken them to 44mm if your going to totally renew the window. Not keen on external beading ok for a modern sash but if you want it to look more original you could I guess butyl putty the units in or how I did mine internally bead with a putty bead moulded in the frame.

Anything back from building control/conservation, I think if they have anything to say then that will help you decide the finer details.


Hi Jon,

I wasn't sure about external beading either! Our Orangery windows are done like this.

I believe for replacement windows I need a U value of 1.6 for the whole window, about 1.2 for the centre of the pane.

A 4-12-4 with Argon and Pilkington soft coat is 1.3 so I think I'd need 4-14-4.

A 4-8-4 gives a U of 1.7

Maybe I have that wrong, but I was using www.glasstops.co.uk

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Re: Sash construction - Double glazing

Postby rich3911 » Thu Feb 07, 2019 2:02 pm

Looking at a modern sash windows, they apprear to use 57mm rails and stiles. The frames are about 160mm deep. So if I went to those dimensions, I'd loose 20mm of reveal. Not too bad.

Got this from planning today:
"planning permission would not be required to replace a complete sash with another wooden framed sash with a double glazed unit because the new windows are of a similar appearance - i.e. sash units that look the same except the glass is double rather than single glazing. Unless it’s a listed building, then listed building consent is required."

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Re: Sash construction - Double glazing

Postby jfc » Thu Feb 07, 2019 6:16 pm

Planning permission wont be needed but you will still need a building notice .
An old thread here that may help ... http://woodworkuk.co.uk/forum/viewtopic.php?f=9&t=1911&hilit=making+a+sash+window

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Re: Sash construction - Double glazing

Postby JonR » Fri Feb 08, 2019 6:33 pm

As you plan on making a huge saving making the windows yourself why not get a costing on heritage units it will help to keep your window in character and narrower rebates will help keep the meeting rails slimmer, i read that thicker units have double reflections and bulges from pressure and ruin the look of sashes, somebody here may be able to elaborate abit on that.

I had a look at Ravensbyglass they seem to be a manufacturer of heritage units and not a middle man, there based in Dundee,

"This is our thickest heritage unit, with an overall thickness of 16mm and a 7mm sightline.

Minimum size is 150mm x 150mm Maximum size is 750mm x 1200mm

Centre pane U value for unit incorporating 4mm Super Low 'E'- 8mm superspacer argon filled cavity- 4mm Clear Float= U Value of 1.6 W/m2K

Centre pane U value for unit incorporating 4mm Super Low 'E'- 8mm superspacer krypton filled cavity- 4mm Clear Float= U Value of 1.1 W/m2K

http://ravensbyglass.co.uk/domestic/heritage-units/

Being in a conservation area you should get some slack on overall spec and i think BC would be more than pleased with heritage units.

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Re: Sash construction - Double glazing

Postby rich3911 » Fri Feb 08, 2019 6:52 pm

JonR wrote:As you plan on making a huge saving making the windows yourself why not get a costing on heritage units it will help to keep your window in character and narrower rebates will help keep the meeting rails slimmer, i read that thicker units have double reflections and bulges from pressure and ruin the look of sashes, somebody here may be able to elaborate abit on that.

I had a look at Ravensbyglass they seem to be a manufacturer of heritage units and not a middle man, there based in Dundee,

"This is our thickest heritage unit, with an overall thickness of 16mm and a 7mm sightline.

Minimum size is 150mm x 150mm Maximum size is 750mm x 1200mm

Centre pane U value for unit incorporating 4mm Super Low 'E'- 8mm superspacer argon filled cavity- 4mm Clear Float= U Value of 1.6 W/m2K

Centre pane U value for unit incorporating 4mm Super Low 'E'- 8mm superspacer krypton filled cavity- 4mm Clear Float= U Value of 1.1 W/m2K

http://ravensbyglass.co.uk/domestic/heritage-units/

Being in a conservation area you should get some slack on overall spec and i think BC would be more than pleased with heritage units.


Hi Jon,

I heard some horror stories about Slimlite DGU's.

The units you linked are certainly in the right ballpark U value wise. I assume it's the Krypton that makes all the difference...

I will look into them and get a quote.

Cheers.

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Re: Sash construction - Double glazing

Postby Meccarroll » Sat Feb 09, 2019 2:09 pm

The glass specification will obviously have an effect upon your section sizes Rich.

I think you really need 57mm deep sections for standard double glazed units unless anything has changed.

Take the pulley system (groove) into consideration and look at any furniture you might need to see if it will work with your section size. You will need draft strip as well and that will be set in a groove so try to take all the grooving into account too.

If you use your current suggested sections, will you be able to fit a centre fastener on the meeting rails?

I'm not 100% sure but I think you may have to reach a compromise between looking original and being practical when upgrading to double glazing.

Regardless of the Orangery, I'd probably go with Levellers design (Venetian Style). Just my opinion (right or wrong) but I think the windows would look far more elegant venetian style than as now fit. The box sections currently look to have been squared off which could be made to look more ornate by adding a mould (I think Leveller may have already mentioned adding a moulding to the outer box sections).

Again I am not 100% sure but I think one problem with going too slimline on larger sizes of glass is the glass bowing and touching in the middle. I don't think they last as long either but I could be wrong.

Check Mumford and Woods web pages they offer some insight into glazing for historical buildings.

Mark

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Re: Sash construction - Double glazing

Postby rich3911 » Sat Feb 09, 2019 5:11 pm

I might photoshop them in and see what it looks like with venetian sytle windows...

20190209_165516 (Medium).jpg


These are the windows that all need doing... eventually.



20190209_165529 (Medium).jpg



20190209_165609 (Medium).jpg




You can see there are 4x triples and we have two bays:


20190209_165553 (Medium).jpg



(No idea wahts going on with the orientation, they are the right way up here and when you click on them....)

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Re: Sash construction - Double glazing

Postby Leveller2911 » Sat Feb 09, 2019 5:27 pm

I think venetians would look great but I would make the glass in the top sash the same height as the bottom sash glass (same as the double on the first floor?) but thats just my opinion and as Mark said they would look more elegant.. Currently they look very uniformed and maybe a tad bland... There is nothing wrong with having different styled sash windows on one house. When I've worked on some properties in London I made bay windows,doubles,swept heads and venetians all on one property..

Re glazing, with standard units I use 4-12-4 softcoat Low E argon fill giving a U value of 1.1 or 1.2 (iirc) oh and a superspacer. My usual traditional Ovolo I use is 12mm wide by 7mm high so I tend to make the sashes 12mm (ovolo) 2mm security glazing tape, 20mm unit, 2mm tape and 15mm bead so around 52mm overall thickness of sash. Sometimes go to 54mm thick and make the unit thicker if needed.. Slimlite type units are ok but they don't last as long as standard ones due to less vulcanised rubber around the perimeter.

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Re: Sash construction - Double glazing

Postby rich3911 » Sat Feb 09, 2019 5:41 pm

Hmmm not sure that works as the window is very wide in proportion to the height. Might look better on a taller or narrower opening?

20190209_165516 venetian.jpg

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Re: Sash construction - Double glazing

Postby rich3911 » Sat Feb 09, 2019 5:49 pm

and with the middle sash boxes back in...

20190209_165516 venetian2.jpg


I could certainly add some detailing to the outer linings to make them less plain...

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Re: Sash construction - Double glazing

Postby Leveller2911 » Sat Feb 09, 2019 5:55 pm

rich3911 wrote:Hmmm not sure that works as the window is very wide in proportion to the height. Might look better on a taller or narrower opening?

20190209_165516 venetian.jpg


If you bring the meeting rails down so the glass height is the same in the top and bottom sashes I think it would look much better than a triple. Mould a nice staff/bead moulding to the outside linings, nice shaped sash horns and it would look great. Remember that just because an existing window was made to a certain design it doesn't mean they got it right back then. Throughout history people have made windows where many are just right and others were complete rubbish and look pants. Don't think that our ancestors got everything right because they didn't. You aren't doing the house a dis service by changing/tweeking the design. :) The reason Edwardian windows didn't have glazing bars is because tastes changed ,Georgian windows had loads of glazing bars and very slim sections, Edwardians deleted the bars and in general made the sections heavier.

Far more aesthetically pleasing than the triple one. If you go ahead with a triple I would still run the cords over the outside sashes and thin down the centre boxes as they look really heavy..

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Re: Sash construction - Double glazing

Postby rich3911 » Sun Feb 10, 2019 3:32 pm

Like this:

20190209_165516 venetian3.jpg


and as now:

20190209_165516 (Medium).jpg

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Re: Sash construction - Double glazing

Postby Leveller2911 » Sun Feb 10, 2019 5:07 pm

rich3911 wrote:Like this:

20190209_165516 venetian3.jpg

and as now:

20190209_165516 (Medium).jpg


Yes, you could make the centre sashes a touch wider but up to you but they would look in keeping with the double boxframe above the ground floor window.

Personally its a venetian all the way for me but as I said its just my opinion. Its only marginally a bit more work as the sashes are different widths compared to the existing window but easy enough to run the cords over the top of the pullys and run them in a groove in the top sashes . Thing to remember is the pullys need to be cut down and fitted high as possible so the cords run tight to the head lining. I just use a grinder and cut the top flange off and they slip in the pully recess in the lining and just up into the head lining. Once you get your head round the idea its quite easy..

Re: sash thickness , When I make them I run a groove up the stiles of the sashes (router cutter from wealden tools with 3 bearings to give a different depth of groove ) back and front of the stiles and both sides of the sash to take the Mighton pile/bubble carrier (draught strip carrier) and allow about 3mm or so for draught strip and that way the draught strips are hardly visible to the eye because they are hidden behind the staff,part beads. On the top and bottom I fit aquamac 21 draight strip and the meeting rails I run a groove and fit pile/bubble carrier but this time with pile. Only pile I use because I'm not a fan as then gum up with paint and dust over the years and then don't do the job..

I really don't like those plastic part beads with the flipper seals as they look awful and you can't paint the black. I'm sure others have different ideas but thats what I do and not have any issues .

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Re: Sash construction - Double glazing

Postby rich3911 » Sun Feb 10, 2019 7:07 pm

Leveller2911 wrote:
rich3911 wrote:Like this:

20190209_165516 venetian3.jpg

and as now:

20190209_165516 (Medium).jpg


Yes, you could make the centre sashes a touch wider but up to you but they would look in keeping with the double boxframe above the ground floor window.

Personally its a venetian all the way for me but as I said its just my opinion. Its only marginally a bit more work as the sashes are different widths compared to the existing window but easy enough to run the cords over the top of the pullys and run them in a groove in the top sashes . Thing to remember is the pullys need to be cut down and fitted high as possible so the cords run tight to the head lining. I just use a grinder and cut the top flange off and they slip in the pully recess in the lining and just up into the head lining. Once you get your head round the idea its quite easy..

Re: sash thickness , When I make them I run a groove up the stiles of the sashes (router cutter from wealden tools with 3 bearings to give a different depth of groove ) back and front of the stiles and both sides of the sash to take the Mighton pile/bubble carrier (draught strip carrier) and allow about 3mm or so for draught strip and that way the draught strips are hardly visible to the eye because they are hidden behind the staff,part beads. On the top and bottom I fit aquamac 21 draight strip and the meeting rails I run a groove and fit pile/bubble carrier but this time with pile. Only pile I use because I'm not a fan as then gum up with paint and dust over the years and then don't do the job..

I really don't like those plastic part beads with the flipper seals as they look awful and you can't paint the black. I'm sure others have different ideas but thats what I do and not have any issues .


Thanks for the info on seal arrangments. With the meeting rails, they traditionally meet on a diagonally slanted face (sure theres a proper term for that!), but I have seen modern sashes with rectangular rails with a projecting seal. The seals meet but the rails dont. Can that work?

One more thing about the pics above. I kept the mullions either side of the middle sash wide so that they can be sash boxes for the weights. Running the cords over the head to the outer sides means a thinner mullion, but I wasn't sure that looked right?

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Re: Sash construction - Double glazing

Postby thatsnotafestool » Mon Feb 11, 2019 7:33 am

rich3911 wrote:....
One more thing about the pics above. I kept the mullions either side of the middle sash wide so that they can be sash boxes for the weights. Running the cords over the head to the outer sides means a thinner mullion, but I wasn't sure that looked right?


I think a thinner mullion is better as it would match those in the Orangerie.
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