Double glazing in listed buildings

[tobydog]

I recently received this in an email from the Listed Property Owners Club. Some of you might find it interesting.

https://www.lpoc.co.uk/wp-content/uploads/2017/11/Double-Glazing-in-Listed-Buildings.pdf

 

[MikeG]

Thanks for posting that. It's a useful summary.

Over the years I have seen things change slowly in this field. Twenty years ago most local authorities resisted allowing double glazing even in new extensions to Listed Buildings. I don't think I've run into that issue at all in the last 5 years or so, so long as the timber window profiles remain slim and flush (ie not "storm" casements). There are some pretty good sash windows available now with double glazing, and there are certainly plenty of good side hung casements which if well detailed are an asset in an extension to a LB.

On the horizon, I hear, are vacuum units. These hold out the prospect of being more thermally efficient with less depth than current sealed units. Maybe if/when these come along this eminently sensible advise you link to will see more inappropriate 60s & 70's windows replaced with something rather more in keeping with the building, but also to something approaching modern levels of thermal performance.

 

[88v8]

I'll have to put my specs on to read that, but the availability of 3/8" units with machine drawn or hand drawn glass, faced with putty, has certainly made a difference. Yes, in some lights there is still a double reflection, but at least there is no excuse now for fitting float glass.

Still awaiting though, an authentic looking solution for leads.

With our small windows, can't say I'm bothered about any heat saving but not having to vac the water off the glass every morning would be nice.

Ivor

 

[MatthewC]

I wish this advice had been available seven years ago when I did my house.

Twenty years ago most local authorities resisted allowing double glazing even in new extensions to Listed Buildings. I don't think I've run into that issue at all in the last 5 years or so,

Yes, that fits. I wanted to get rid of a 1950s Crittal door with windows either side, and replace with a double sash window, made specially. The CO refused to countenance the very idea of double glazing in this new window (and was actually quite unhelpful in other ways...), although I now wish I had ignored this and done it anyway. At least I was allowed to put DG in part of the ground up rebuild of the brick extension.

 

[88v8]

Being poorly, have had time to read that interesting article.

Thirtyumm.. seven years ago I had new box sashes made, with rebates to accommodate 1" sealed units. The sashes were hardwood, once glazed they were verrrry heavy, so much so that I hung them on chains and had to cast my own lead weights.
Four windows, sixteen panes.
I bedded and fronted them with Arbo 1081. It gave a very messy finish, well that might have been me, and couldn't be overpainted, but thirty years later none of those units had blown, even though they were south and west facing and thus subject to thermal stress. In marked contrast to the dg units that were bead-fronted and professionally installed in the 1991 conservatory, after twenty years they were more blown than not, from the tiddlers in the doors to the whoppers in the roof.
So I can understand the concern over slimline units bedded and putty faced. Their apparently short life and the difficulty of extracting them is not a good combination. To what extent this is due to inherent failings of the units and to what extent failings of installation - not observing the correct expansion gap, not sealing the edges, using the wrong materials, one must suspect that this probably has more than a little to do with it given the building industry's customary sloppiness and inattention to detail.

I never liked the look of my dg sashes. The reflection is just.... wrong. Somehow... concave.
But that house is sold.

In manufacture, I have five casement windows rebated for 10mm units, the outer sheet will be machine drawn glass. They will be bedded and faced in the right sort of putty. Hopefully the glass will be wavy. With the exception of three panes, all the old glass has been lost from our cottage so I hope that the appearance will be better.
Those are the easy windows.

Two iron insets in stone muilions, one has old glass. I made secondary glazing for one, but it seals imperfectly and mists, albeit to a slight degree, so I have not done the same with the other even though they are upstairs and there is no visual detriment given their (in)visibility. That pair is westerly.

The detriment of secondary dg is visual, internally of course to a greater or lesser degree, but also externally, that double reflection although only in some lights.

Elsewhere we have leads. 1970s float glass in Critalls. The worst of all worlds, they steam up, are a pain to dry, the frames are beginning to rust, they have no visual life as the glass is all float. I hate float glass. But they are key to the appearance of the frontage. No way could they be replaced with plain casements. I made secondary dg for a set upstairs, it sits beside me as I write, steamed up, for yes, it leaks, and the air in the house being damp, inexorably it steams up.
The frontage is north. Secondary dg to the north will fail as there is no sun to create a thermal pump to expel the accrued moisture.

In contrast, the secondary dg I made tor four windows to the south works perfectly and never steams at all even at the start of winter when the house is at its dampest. Presumably the sun is sufficient to push the leakage out through the external vent holes.

The heat loss I don't care about, not in the slightest faintest degree. But the condensation is a pain. I see no solution for the northerly leads. I am slightly tempted to hoof them out and have them remade with proper wonky glass and get the frames sand-blasted and paint them in two-pack, that would improve the visuals no end, but the misting, the morning waterfall, for that I see no solution. Mock leads in sealed units are horrible, the reflection is just wrong wrong wrong.

At least I have the Karcher. King Enery would have killed for a Karcher.

Ivor

 

[tobydog]

Sorry but I'm on a roll here. I was looking for something else but came across this article which again might be of interest.

https://content.historicengland.org.uk/images-books/publications/traditional-windows-care-repair-upgrading/heag039-traditional-windows-revfeb17.pdf/

At least I have the Karcher. King Enery would have killed for a Karcher.

Ivor

Very sad to admit but at this time of year my Karcher is my friend and my favourite gadget. Thankfully I don't have those pesky leaded windows and the smaller blade option with the Karcher fits very nicely in the panes.