Which sash windows?

[andrew gayton]

curtilage... i see.... well, i think that you can argue the case quite clearly. also check out e.h guidance 'framing options' and the 'period house' bookISBN 000-7192754

 

[Nimster]

Thanks very much everyone.

I'll no doubt be back with more questions later!

Nimster

 

[thiambal]

I have no intention of putting in single glazed windows! We may not be staying in this house for long, so it needs to be re-sellable.

I am sorry to disagree with you - but double glazing will look different and when put into a sash window is likely to be deeper than original sashes and as Victorian sash windows often lack a deep window cill - the window will end up sticking into your room by as much as an inch which looks rubbish.

If the house is listed, then I suspect the CO will want single glazed.

I would give my right arm (well perhaps not) to be able to legally install single glazed sashes in my house - I am legally obliged to use double glazed. The nonsense is that two streets away is a street of identical houses in a conservation area where they are breaking the law if they do not use single glazed.

 

[Matey Plumber]

My Mother's house in s/w Co Durham had 2/2 like the pic above, even in the bay.
Her house was turn of the century-ish.

My 1891 house has 6/1 at the front and 1/1 at the back.
The 6/1 at the front are app 40%/60% in proportion.
The 1/1 at the back are 50%/50%.

But mine was a posher terrace than my Mother's.

 

[Nimster]

Thiambal

Sorry to disagree with you, but in our previous house we had some new timber double glazed (sliding) sashes, and some original single glazed. The new ones were so good (the panes are only 5mm or so apart) that people presumed we had just cleaned up the originals. They didn't stick into the room at all - they sat within boxes/frames that were exactly the same size as the original ones - and had the original architrave round them. We had very narrow window cills, but the windows didn't intrude into the room at all.

Maybe suppliers vary, but the guy who did ours was obviously good.

Wait a mo and I'll put up a (distant) picture.

Here we go:
http://www.photobox.co.uk/album/album_photo.html?c_photo=89764731
This is our house with replacement sashes in the main bedroom window and sitting room. The small bedroom window is original, as are next door's windows. What do you think? I know it's only an external view, but the inside was excellent.

Nimster

 

[thiambal]

Nimster,

I am sure Biff will correct and errors but if you have to install double glazed windows (which you pretty much do now unless you are listed or in a conservation area) then they have to meet a certain U-value which a 5mm gap would not provide. I think the required gap is somewhere around 16mm (Biff?) which makes the sashes nearly an inch deeper than your 5mm ones.

Essentially, your existing ones would not meet building regs and replacements meeting the required u-value would like as not stick out into the room a bit. You windows do look nice though I admit - although a still mourn the loss of the cylinder glass in so many of my windows. (only 2 panes left)

There are some new regs which allow you to use lower u-value windows as long as you compensate for the energy loss elsewhere but it is all a bit complicated.

Sam

 

[Nimster]

I see, thanks for clarifying that. If this is the case, we can hopefully install lower u-value windows rather than full double glazed, as we're listed. I would prefer something higher than single glazed, but if the only other option is full double glazing, then we'll be putting in single glazed sashes. I'm not having monstrosities in the house - defeats the object of removing the UPVC!
Thanks again
Nim

 

[biffvernon]

Nobody has called the double glazed windows I've made, monstrosities. But they're probably just polite.

Yes, you do need an air gap of about 16mm in the sealed unit if you want a U value below 2 (remember it's the lower the U-value the better). I don't see that this makes them stick into the room though. The overall depth of my vertically sliding sash windows is about 160 mm. That's about the same as an old single glazed one and much less than the thickness of most walls.

A more important issue is the width of the glazing bars if you go for a 'Georgian' type design. Double glazed units need a glazing bar about 32mm wide rather than the 20mm or less that is found on many old single glazed windows. But with a 2 over 2 window I would argue that the advantages outweigh that particular design prejudice in many situations.

And then there's the modern spiral balances instead of traditional boxes with weights. Spiral balances have the advantage that the profile at the window edge can be slimmer and yet stronger, allowing more light in to the room and no worries about a sash cord breaking.

 

[thiambal]

That is interesting Biff. When we looked at having a rotten window replaced and it looked like we may have to have double glazed we were advised that it would end up sticking into the room, I have also seen examples of this.

Given that the original windows had one pane of 2mm glass and the double glazed have two panes of 4mm(?) plus 16mm gap that is an extra depth of 20mm to accomodate for each sash. How to you get an extra 40mm+ into the windows with either making them thicker or changing the look of them significantly.

I am not questioning that you do it, I would just love to know how so that I can get it done the same way when I have to replace.

Cheers

Sam

 

[biffvernon]

Two sashes of 60mm thick, 10mm parting bead, 15mm bead inside and out, makes 160mm altogether.

Old sashes, with lambs tongue glazing bars, have quite a bit of wood on the inside of the glass. This is probably where most of the difference is made up. Try measuring the thicknes of the actual wood in the sash, Thiambal, never mind the glass.

It's tight in a single skin wall but no problem in a 9inch, or greater, wall.

 

[thiambal]

All seemed reasonable to me Biff, so I went away and measureed my existing windows.

They are only 130mm. So I am not sure how they could be replaced with double glazed without sticking out into the room an inch or so.

 

[biffvernon]

So you need to find another 30 mm. Is it a single skin wall - just a four and a half inch brick plus plaster? In which case you'll be losing more heat through the wall and should consider dry-lining with insulation, making the whole wall twice as thick and giving plenty of room for the window. If the wall is a more sensible thickness then there should be plenty of room for a 160 mm window by setting the outside edge further out. Or is it some other construction, wattle and daub or something?

 

[thiambal]

No, decent thickness walls in a victorian terrace.

I never really thought about taking up the extra space externally rather than internally. I guess this would affect the external look of the windows though. Still perhaps better than them sticking into the room.

 

[Nemesis]

Actually - think carefully, leaving less of a gap externally can detract from a building - looks mean, and also less weather protection.

Unless the windows are huge do you really need DG?

 

[thiambal]

ally - think carefully, leaving less of a gap externally can detract from a building - looks mean, and also less weather protection.

Unless the windows are huge do you really need DG?

I am inclined to agree with you Nemisis. I think is will detract from the look of the house.

This really just started as a theoretical discussion - I have single glazed sashes most of which are in excellent condition and will probably see me out. One was really knackered and had to be replaced. As we are not listed or in a conservation area building regs obliged the use of double glazed replacement (despite the fact that in the conservation area two streets away in identical houses I would have been breaking the law by using double glazed).

It is a crazy, crazy world.

 

[Nemesis]

Sad I know! I doubt the DG will see you out ...

The whole question of what can be saved and therefore is simply repair really isn't clear is it?

 

[biffvernon]

leaving less of a gap externally can detract from a building - looks mean

A glance through the pictures on my snapshot page at Biff's Window Pics shows that the majority of these windows are set quite forward. I hadn't thought about this at the time photographing, the pictures taken to show interesting windows in interesting houses. Generally, 19th century windows are set back a brick's width and older windows are set forward, but there is great variation so that is a very rough rule.

 

[Nemesis]

If you look at modern pastiches too often what is all wrong is the fact that the windows are set very far forward, it is a detail many builders ignore.

 

[Gervase]

Very true - a job I was doing recently involved installing some wooden windows from Magnet into an old cottage. The windows weren't bad, in fact - simple double glazed casements that, given the budget, were ideal.
Except, that is, for the sill. Almost every off-the-peg window these days has a projecting sill because they're invariably installed virtually flush with the external face of the wall.
With these particular windows I had to saw and plane the built-in wooden sills completely off to allow the windows to sit back four inches in the hole on some heavy slate sills with a nice plastered reveal.
Fiddly, but worth doing to avoid the pastiche look.

 

[thiambal]

I have to admit that our windows are set further back than the majoirty in Biff's windows. However, the window particularly in question had suffered particularly from the prevailing weather so I would have been reluctant to set in any further forward.

As the stone cill slopes away I guess would would need and thicker wood cill on the window to take up the additional space if you did set the windows further into the opening.

The whole question of what can be saved and therefore is simply repair really isn't clear is it?

We were advised by our building control office that at least 20% of the original window (not including weights, glass and other furntiture) needed to remain for it to be repair rather than replacement. Whether that is 20%, weight, surface area etc is unclear.

Our compromise was to have new sashes made and installed (repair as less than 80%) followed a new box frame a modest time later (also a repair as less than 80%). Probably not in the spirit of the law but......