Retrofit double glazing onto old single glazed sash windows

[Deleted member 174758]

In some cases the weights are individual lead blocks, maybe an inch thick, strung together, which are easier to add or remove.

They used to tell you that they'd all be lead in college, but most of the ones I've worked on are cast iron and were presumably made by a local iron foundry (very commion in former industrial areas). The problem with cast iron is that it isn't as dense as lead, so the weights are noticeably bigger than lead ones and adding extra weights on top isn't always possible. With those the solution is often to replace them - Mighton sell steel and lead weighhts made to order, but you do need to weigh each sash, complete with glazing to find out the weight needed. (It's also worth the OP knowing tht Mighton are one of the two big firms selling sash repair parts, the other being Reddiseals who also do weights)

I'm with Opps on the DIY approach - it should be within the capabilities of a competent DIYer. The one thing I will add to what he says is that messing with old sash cord isn't worth the effort, so if you are doing the refurb replace the cord with a good quality waxed cotton type. It'll last decades and saves having to strip the window down again in the future if an old cord breaks.

 

[mrrusty]

so if you are doing the refurb replace the cord with a good quality waxed cotton type

and if you do this, make sure you allow a little more for stretch than you think you need. I made sash windows to replace the old ones, re-using old cast iron weights and adding lead on top, which worked well but was dimensionally fairly tight. Initially perfect, 3 years later I could do with shortening some of the cords by 10-20mm as on a couple of windows out of the 8 I made, the weights are now just bottoming out, meaning I have to push the top sashes up the last 5mm or so when fully closing. As yet can't be bothered to dismantle everything to get at the cord cleats.....

I found I was approximately doubling the weight going from single glazed 3mm glass to 4-16-4 DGU. I used internal beading and reddiseals dry glazing system (dimensions and design details blatantly copied from one of the big makers who post their CAD drawings online.....)

 

[opps]

replace the cord with a good quality waxed cotton type

My mate who restores sash windows uses the pre-stretched nylon cords. I think he uses then because if they are less likely to show the dust when feeding them into the sash box.

I agree that as a low cost item it makes sense to replace them. Oh, and he uses Reddiseals as well. Through him I can get Timbabuild epoxy resin filler for £25 inc vat, my local decorators' merchant charges £35. From memory, Reddiseals would charge me about £30.

 

[Deleted member 174758]

I've always been a bit leery of the nylon cords having had some in the past which stretched, and stretched, and stretched, but they were from a bit of an iffy supplier (one of my local builders merchants who tend to be a bit of a cheap jack operation so they really are a supplier of last resort these days)

 

[JohnD]

se if you can find a straight-laid core rope (not twisted or braided, which will "stretch" by compressing the fibres, not by stretching them)

I'm not sure I've got the name right.

Or a polyester cord which does not stretch as much as nylon.

Either will be stronger than cotton.

 

[JohnD]

..

 

[Deleted member 174758]

Either will be stronger than cotton.

You make it sound as though it will snap in an instant, but it actually does reasonably well. I've had it specified by the Conservation Officer a few times (this being an old cotton area it was a local product at one time). The wax not only helps prevent rot but helps lubricate things a wee bit. Last stuff I used was white with red fleck - never seen black cotton, but then I've never looked for it. We use chain on really heavy windows if possible

 

[JohnD]

..

 

[groovybug]

Thank you everyone, sorry I haven't been on for a few days. I can imagine how it's done now. The toughest bit I guess is routing the frame accurately to allow the double glaze glass to sit snugly. And then make sure it's completely draught proof. There are some movement between the windows and the outer sash box that cant be fixed with just beading. Do you recommend adding a trim of hard wood to the window so it sits tight within the sash box?

And last question is, where do you recommend to custom-order the double glaze glass from?

 

[JohnD]

Have you definitely ruled out secondary glazing?

 

[groovybug]

Have you definitely ruled out secondary glazing?

I did consider it. I know it works great however it just doesn't look great. I just came across this magnetic type that is kind of removable during the summer months, that might work better than the permanent aluminium box type. What do you think?

 

[JohnD]

I prefer the slim Aluminium profiles, but painted white to blend in with the frames and reveals, and in vertical sashes of the same dimensions as the original

If the room has net curtains you will not see them.

I don't agree with removable glazing, you will soon get fed up with removing and refitting it.

It is much better for draughts and noise, and saves a lot of work altering the glazing rebates and changing the weights.

My neighbour's listed building has them and the original timber windows remain original. They do seem to need quite a lot of painting and periodic maintenance, they still have puttied glass and cotton cords. I suppose sooner or later they will need new replica sashes.

 

[mrrusty]

IMO it is not really possible to successfully alter single glazed sashes for DGU. The timber sections are just not big enough. It is possible to fit very slim DGU but their performance isn't great. I think the choices are new windows, secondary glazing or shutters.

 

[groovybug]

IMO it is not really possible to successfully alter single glazed sashes for DGU. The timber sections are just not big enough. It is possible to fit very slim DGU but their performance isn't great. I think the choices are new windows, secondary glazing or shutters.

My windows are about 5cm/2 inch thick, and I think I can fit 18-20mm double glaze glass in. I'm not sure how much it will improve the thermal and acoustic performance to make it worth doing though.

 

[mrrusty]

they are a bit thicker than many then, so I agree 18mm is possible and potentially worthwhile. If you also fit brush seals it will make a lot of difference. It's still an awful lot of mucking about though.