Double Glazing in Sash & Case Windows – glass not fitted correctly?

[Yuyamel]

Hi all, We’ve just had double glazing fitted into our sash and case timber frames and I’m unsure if the job’s been done properly. The black spacer bar is very visible from inside (up to +1 cm into the glass in some parts) and the inside of the frame is unevenly cut form the inside, as if they lost control of the tools they used. We also saw they didn’t take out the frame to work on worktop but actually just free standing at the windows- which I assume results in less control when creating a gap for the new unit. The company now suggests covering the spacer bar with timber beads or wood filler, but both would be obvious from the outside. Is this normal for retrofitting double glazing into these windows, or does it sound like the glass wasn’t measured/fitted correctly? And is there a proper fix, or would we be looking at replacing the whole window for a decent finish? Appreciate any advice!

 

[ronniecabers]

Were these new sashes? Were they double glazed before?
If the answer to both of those is no , then it's unlikely you will get a better fit. Reason being is that the rebate for single glazing is much less than the rebate for double glazing, hence you are seeing the side of the spacer bar. The fitting company should have made you aware of this when they first measured them though

 

[endecotp]

What sort of units have they used? Are they proper slim units for wooden sashes, or are they just regular ones?

What does it look like on the outside?

Did they replace the counterweights?

If you wander around the neighbourhood, do other windows look similar or have they been done better?

 

[Yuyamel]

Were these new sashes? Were they double glazed before?
If the answer to both of those is no , then it's unlikely you will get a better fit. Reason being is that the rebate for single glazing is much less than the rebate for double glazing, hence you are seeing the side of the spacer bar. The fitting company should have made you aware of this when they first measured them though

Thanks for the reply! These are the original sashes and not double glazed before. It’s less about just seeing the spacer bar, more that it looks really uneven — in some spots a big chunk of it is showing, almost like the pane is just sitting on top of the frame rather than fitted into it. The company never mentioned this would be an issue when quoting, only after we raised concerns.

 

[ronniecabers]

Seems like poor advice and poor fitting to me.
There are ' Heritage 'units on the market which allow for smaller distances between the edge of the glass and inside face of the spacer bar , normally about 8mm instead of 10-12mm, but if using thin 12mm thick sealed units ( 4mm spacer bar ) , the bar is flexible and doesn't always sit perfectly straight.
Biggest issue with modern sealed units is that majority are made in big plants and it is very common to see the secondary sealant or even the main sealant 'leach ' around the spacer bar , so that at points it can be visible between the glass and spacer bar.

 

[mrrusty]

It's a bodge. You cant just replace single glazing with double in a sash window because the weights needs changing significantly. DGU are more than twice the weight - and often the single glazing was only 3mm in old windows. You could easily need 4kg extra each side - quite a big chunk of lead even if you just add to the weights already there.

The only satisfactory way this can be done is to remake the sashes to fit in the existing frame to take slim DGU, and only then if the weight pockets are big enough for the bigger weights or you are converting to spring balances. Another problem is DGU are designed for dry glazing, and don't work well in sashes designed for traditional putty glazing.

And, the router they have used has slipped and chewed the sash anyway.

TBH, IMHO there is so much buggeration to convert, plus you can only use slim DGU in original sized sashes that you are better off taking the whole window out and replacing with a new window designed for DGU from the beginning.

If you look at timber DGU sash windows from pro manufacturers they are often internally beaded, with the DGU sealed to the frame with glazing tape and/or seals. - like this

 

[Yuyamel]

From the outside you don’t see the spacer bars because they added timber beading, though it’s not very neat. The company now suggests fixing it by covering the spacer bars with either wood filler or more timber beading. Work has paused after they broke a pane, and we don’t feel they’re experts. I saw a friend’s place where double glazing was fitted into original sashes and it looks perfect, so I know it can be done well. We’ve paid a deposit to them. I tried to get other companies to provide me a professional opinion but they don’t want to comment or take over another company’s work. Does their proposed fix make sense, will this at least give decent insulation or should we cut our losses and go for new sashes/windows?

 

[ronniecabers]

Oh absolutely agree its a botch, I would never have recommended putting dgus in there in the first place. At a push you could.have used ' stepped ' units but would.look awful unless you beaded the inside but that would make the glass area smaller

 

[Yuyamel]

Seems like poor advice and poor fitting to me.
There are ' Heritage 'units on the market which allow for smaller distances between the edge of the glass and inside face of the spacer bar , normally about 8mm instead of 10-12mm, but if using thin 12mm thick sealed units ( 4mm spacer bar ) , the bar is flexible and doesn't always sit perfectly straight.
Biggest issue with modern sealed units is that majority are made in big plants and it is very common to see the secondary sealant or even the main sealant 'leach ' around the spacer bar , so that at points it can be visible between the glass and spacer bar.

 

[Yuyamel]

Seems like poor advice and poor fitting to me.
There are ' Heritage 'units on the market which allow for smaller distances between the edge of the glass and inside face of the spacer bar , normally about 8mm instead of 10-12mm, but if using thin 12mm thick sealed units ( 4mm spacer bar ) , the bar is flexible and doesn't always sit perfectly straight.
Biggest issue with modern sealed units is that majority are made in big plants and it is very common to see the secondary sealant or even the main sealant 'leach ' around the spacer bar , so that at points it can be visible between the glass and spacer bar.

Yeah, without much expertise I feel the same especially since I asked for advice and requested a professional finish. Attached a pic of the glass here.

 

[ronniecabers]

From the outside you don’t see the spacer bars because they added timber beading, though it’s not very neat. The company now suggests fixing it by covering the spacer bars with either wood filler or more timber beading. Work has paused after they broke a pane, and we don’t feel they’re experts. I saw a friend’s place where double glazing was fitted into original sashes and it looks perfect, so I know it can be done well. We’ve paid a deposit to them. I tried to get other companies to provide me a professional opinion but they don’t want to comment or take over another company’s work. Does their proposed fix make sense, will this at least give decent insulation or should we cut our losses and go for new sashes/windows?

They say they have used ecopane, basically low e glass, the amount of themal insulation you will gain from.a unit that thick , in old sliding sash windows is negligible to be honest. Low e glasses work optimally at 12mm cavity and above

 

[mrrusty]

pic #3 - what a mess. As you have found the rebates are just not big enough for DGU and they have chewed them with the router trying to make them fit. Trying to machine that in-situ is ridiculous. Dare we ask what they are charging you per window to convert?

 

[endecotp]

I saw a friend’s place where double glazing was fitted into original sashes and it looks perfect, so I know it can be done well.

Yes, it can be done well, even on windows with smaller panes and astragals.

I’ve never heard of it being done in situ, and your 14mm units are thicker than normal.

I fear you’ve chosen the wrong company.

 

[Yuyamel]

pic #3 - what a mess. As you have found the rebates are just not big enough for DGU and they have chewed them with the router trying to make them fit. Trying to machine that in-situ is ridiculous. Dare we ask what they are charging you per window to convert?

Thanks, we thought the same. We got another quote and this one was about 1k cheaper which we didn’t think would make such a difference in quality… clearly we were very wrong-Rookie mistake

 

[mrrusty]

£1K cheaper - ouch.