Refurb - replace existing double glazed windows?

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David_Dublin

Registered User
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Hi All.

We're planning a refurb on a 1920's semi-d house. It will include improving insulation, and a small extension. The house already has double glazed windows. We'll obviously need new windows for the extension, and perhaps replacement windows for some of the back windows to tie in with the new ones, for aesthetic reasons. That still leaves about 5 existing windows and I don't know if they are "good" or not, i.e. I don't want to end up with great insulation everywhere, and then 5 windows "letting all the heat out". The windows do not seem draughty, but I don't know what their UValue is etc, so how do I go about making an informed decision on replacing them or not?

Any advice appreciated.
 
Hi David,

Do you know how old the current windows are? Between the window panes, there should be a date/company stamp/marking on them which would indicate the date of those windows.

Some companies do thermal imaging (haven't used any myself) - which would/could give you a rating for those windows.

Also, you will be just replacing the internal glass itself (assuming frames are ok to re-use), but there might be "leakage" between the frames & walls also from day they were put in. So even replacing the glass itself may not make significant savings in relation to heat loss.

A big thing also is ventilation - you need to let the stale air out, fresh air in - so make sure the house is ventilated, place has to breath.

Would you think of getting BER person in to guide you in relation to this? Have you engaged an architect in relation to the re-furb itself?
 
How cold do the internal glass and frames feel on days like today?

External insulation can make a huge improve to the existing portion of the house, and it's best move the windows out to sit within this rather than leave you with cold bridges around them where they are. If you're doing this, new windows might make sense.
 
Thanks for the replies.

I'll check the windows later to try to ascertain their age/maker, and to see how cold they feel.

I have a QS doing an initial costing on some drawings we have, but have not formally engaged an architect, will do as soon as we have ascertained what sort of scope we should be consdiering.

Would a BER at this stage be worthwhile? Could it provide mre informed input than an architect?

I'd consider replacing the whole window, or re-fitting existing window, or fitting new double or triple glass, I suppose the thing I'd want to be sure of is that it is based on informed decisions.

The option of external insulation is not open to us throughout, possibly to the rear snd new extension only, its a part red brick.

Re ventilation, I've never fully understood how this works without just letting all the heat out, but I'm sure it must. Anyway, the architect should be able to ensure the right decisions are made in this respect.

Thanks again.

David
 
David_Dublin said:
Re ventilation, I've never fully understood how this works without just letting all the heat out, but I'm sure it must.
Click to expand...

Living and breathing in a house releases massive amounts of moisture into the air everyday. Failure to eliminate this effectively will result in mould growth and other serious problems. There is also a need to replace the oxygen consumed as well as eliminate carbon monoxide. The simplest way of doing this is through open vents, and they're easy and cheap to retrofit in existing buildings. Historically it wasn't that big a problem here as the building methods employed here meant there were plenty of air leakage points and drafts throughout the standard house. However, and that standard of building materials and methods improves, this becomes a much more serious, and potentially life-threatening issue.

A better solution is MHRV where a heat exchanger is used to heat the incoming air. That requires ducting throughout the house along with the heat exchanger and fans and investment that all entails.
 
Thanks for the info Leo. Am I right in thinking that MHRV is most appropriate to Passive House approach, and would not be prudent investment in a 1920's building where we are just going for a "reasonable" level of insulation/air tightness.
 
Sorry, just one more question. We have 6 chimneys in the house. 4 will never be used, one we intend to replace with a stove, the other we'd like to keep, and we'd use it only occasionally.

What's the best way to deal with draughts when the remaining occasionally in use one? And for the others that will never be in use again? Any ideas/recommendations welcome.
 
New builds (not trying to achieve Passive House) may have MHRV installed - fresh clean air while removing "bad" air. It can be retrofitted, but cost factor involved.
Does the house already have vents within the walls, especially within the rooms that has a fireplace, or the gas/oil burner area? You could/should get trickle vents as part of the new windows.

As Leo mentioned, lot of moisture from showers / kitchen / people / drying clothes inside - will lead to mould growth - the house needs to breath so to speak.
 
Thanks Jazz01.

Our refurb includes complete re-wire and internal insulation. I wonder should I get the QS to cost up MHRV in the house, just so I know what I am dealing with. Obviously, the occasional use chimney would need to be able to be closed when not in use.
 
No harm getting it priced. A 1920s building is likely very leaky, but the work you're getting done should greatly improve this.

It'll cost a little to run the fans, but you'll also be saving on heating costs by reducing the heat loss through regular ventilation.
 
David_Dublin said:
Obviously, the occasional use chimney would need to be able to be closed when not in use.
Click to expand...

Just re that chimney - if you can, get a (multi-fuel) stove put in. They are the knees of the bees. Range of types out there & worth the investment (they need a well ventilated room though )
 
Jazz01 said:
Just re that chimney - if you can, get a (multi-fuel) stove put in. They are the knees of the bees. Range of types out there & worth the investment (they need a well ventilated room though )
Click to expand...

Could consider a room sealed one with external air supply.
 
The fireplaces are really nice though, mahogany with tiled inserts, original from 1920's, would be a shame not to keep one. I don't think the stove is a runner in the fireplace we intend to keep to be honest.
 

There are no vents in the sitting room where the fireplace is, or the bedrooms actually. But there are suspended floors letting in plenty of fresh air! There is a vent in the kitchen where the boiler is. It's open plan and beside the dining room, where more air gushes in thru the floor boards.

The intention, budget allowing, is to put in underfloor at ground level, i.e. to fill the cavity where the wind whistles in from. We hope that this, along with internal insulation and attic insulation, will greatly improve the snugness of the house.

It's only now with the input above that I have begun to think about MHRV, and have started to read up on it. It is actually quite a compelling option, particularly considering our necessity to insulate internally.

Thanks again for the input.
 
I had a look at the frames on the windows, and there is some printed text on it that reads:

DFX BS 7413 1991 03:31 4/42/01 M/C 31 F

Does this help with ascertaining what spec the windows are, and what decision I should be looking at:

replace the windows completely
replace the glass
leave alone apart from reviewing the seals/surrounds

Thanks,

David
 
Hi David,

Re "BS 7413:1991" part of the above could be details for the specification for white PVC-U extruded hollow profiles with heat welded corner joints for plastics windows (isn't google great )

So that text seems to be in relation to the frames themselves. Was there any text on the inside, between the two panes of glass?

I guess the decision whether to replace the windows (etc) comes down to your budget & recommendation from any window installers you get in to quote you...
 

Thanks for the response. I didn't see anything in between the glass at all, in any of the panes that I looked at. I'll have another look. I have seen posts about a thermal imaging survey related to the quality of windows. I might have a look at that or BER, rather either of them than a salesman trying to sell me windows trying to offer advice on whether my windows need to be replaced!
 
David_Dublin said:
I have seen posts about a thermal imaging survey related to the quality of windows. I might have a look at that or BER, rather either of them than a salesman trying to sell me windows trying to offer advice on whether my windows need to be replaced!
Click to expand...

Just be aware that someone doing a BER calculation will just estimate the UValues for the windows, unless specifically asked to measure them. I doubt many assessors would have the equipment required to measure them accurately. Similar for thermal imaging as well, that will just give you an idea or the heat loss relative to the walls, roof.
 
Thanks for the reply Leo.

That's a bit depressing, so there really isn't any way to make an informed decision based on objective/absolute information on whether to look at upgrading your windows, either partially or wholly.
 
I don't see the need for replacing perfectly good back windows. Who is going to be looking at them.
I consider a BER a waste of time, it's just common sense. Tier exist should be advising you on the best insulation etc.
 
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