Sash window renovation - low-e and double glazed??

[Simon]

Greeting all

Does anybody out there have any experience of having double glazing added to origional sash and case frames. I live in a listed building in a conservation area and already know that we don't have many choices. If we want double glazing or any sort of additional heat conservation other than draft proofing we would have get the origional sash windows double glazed.

There is company based here in Edinburgh i think that can do this for us although i'm skeptical about the claims on their website. They propose that with low-emissivity glass they can reduce heat loss as per below.

Slimlite Super Low Emmissivity

Construction 4mm Low E / 3.2mm Cavity, Gas / 3 or 4mm float = U Value 1.5 Construction 4mm Low E / 4.8mm Cavity, Gas / 3 or 4mm float = U Value 1.2 Construction 4mm Low E / 6.4mm Cavity, Gas / 3 or 4mm float = U Value 1.0

My concern is that everything i read suggests that the cavity between the glass will be so small using a traditional sash frame that the double glazing can't make enough difference to my heating bills to warrant getting it installed.

Can low-e glass really be that good?

If so why are conventional double glazed units made with such large cavities?

I hope someone's got the answers.

Cheers in advance if you do.

[Stuart Noble]

A neighbour of mine has just had Everest 2ndary glazing done. Quite impressive and, strangely (given their reputation), not that expensive.

Stepped DG panels in sliding sashes look pretty naff from the inside and it means replacing/increasing the sash weights, which the channels they run in may not be designed to cope with. The thickness of the sashes pretty much determines the maximum gap you can have.

I doubt if anything other than draught proofing will be cost effective but the Everest stuff seems to cut noise quite significantly.

[Martin Bonner]

We've just had our 1900's sash windows replaced. (No, not short lived plastic, proper wooden ones). The changes were:

1. The frames stuck out further into the room - this didn't bother us at all.
2. The glazing bars are much thicker - this did bother us, but we've got used to it (it helps that there are only two panes in each sash. Georgian windows with eight panes would look dreadful).

You could try asking your conservation officer what they feel about such changes.

Alternatively, there is a company called Ventrolla

that will renovate existing sash windows and draught-proof them. They claim that this will achieve most of the benefits of double-glazing without destroying the appearance - my suspicion is that they are right. They are quite expensive (not much cheaper than having the windows completely replaced, but no problems with listed building consent).

[Tony Bryer]

Those U-values look suspiciously good though it may just be that they are centre-pane figures (i.e. effect of spacers and frame ignored)

[meow2222]

then forget it. Even if the CO allowed it, replacing all the old glass would lose historic fabric and not help property value any.

there is another option, that is to use secondary glazing that can be removed with nothing left behind. But any form of secondary glazing would produce rot if you dont also use a tray of desiccant.

1. glass sheet with friction edging that presses into place in the outer frame
2. desiccant that is replaced/ heated dry from time to time.

The key is that its 100% removable, its not fitted, so no issues with LBC.

Really thats true of all dg, regardless of cavity size. Retrofit is rarely worthwhile on financial grounds. Its only in new construction and essential replacements that dg makes sense.

A much more knowledgeable place for period property qs imho is

[normanwisdom]

If you work out the cost benefit you will almost certainlly find that DG etc is not worth the effort (but don't use their figures!) - esp so as you won't be getting the draught proofing which comes with new windows In any case DG and trad windows are just about incompatible due to thickness, weight, appearance etc. I'd restore the windows as they are and then apply other heat saving measures - either to the windows (thick curtains, 2ary glazing, draught proofing etc), or to another part of the house. Almost every other way of reducing heating bills is more cost effective and cheaper than DG.

cheers Jacob

[chris French]

I agree that secondary glazing would be the way to go. We have secondary glazing fitted here to most of the windows - predating us, I would imagine at least 20 years old. Though ours is the type win separate internal frames with sliding sashes. I don't think I've seen what you describe with the friction fitted glass.

There is no desiccant though, but it doesn't seem to have caused any problems here so far.

>

[Simon]

Cheers for the advice everybody.

We have quite basic secondary glazing already, it's the annoying type that opens into the room...consequently we never opent he windows in that room and are thinking about getting rid of it entirely. I also don't like the appearance of it at all. It does work though....especially with regards to noise reduction.

I still haven't made up my mind but i'm veering toward just the full refurb and keeping the original single panes. Although i may change my mind because i'm like that. The cost implication of getting the DG isn't that great since we're getting the windows done anyway. It works out about 50% more expensive if we go DG. But then again, that 50% could get me a wood burning stove or the like (carbon neutral too by the way). I've got some concern however regarding these HIPS (Home Information Packs) or PIPS in Scotland soon to be introduced. I hear we'll need to sell our houses with a survey which includes a energy efficiency assessment. Not that DG would make my house energy efficient....it's closer to a wind tunnel than a home at the moment, what with doors, floor boards, skylights and fireplaces all adding to the gale.

I'll let you all know if i do eventually go with these DG sash units and let you know if the hype is for real.

[meow2222]

You pay a high premium for a listed building, ripping the character out and replacing it does not seem sensible to me. If you want efficiency you're in the wrong house. The typical LB buyer will be paying a substantial premium and wont be interested in the fact that such a building will achieve a z energy rating - something dg wont change anyway.

Given what you've said I think you could do with checking that forum.

NT