Sash Windows : from 2 pane to single pane ???

[rideforever]

Hi, I'm considering ordering some slimline 14mm double glazing units and routing some sash windows to fit them in, however each sash has two panes, so routing out the middle bar ... well I think it might break ... not sure of the construction.
Is there a good way to do that ?
So can I just throw it away and use a single pane? is it structural and will the sash be weakened by its removal?
It's Victorian.
Cheers

 

[big-all]

you can buy stepped double glazing for this exact purpose or you used to be able too
you will need to alter the weighs or spring mechanism to accommodate the extra weight

 

[endecotp]

The middle bar is an Astragal.

I have heard of them being routered to fit DG units, but have not seen it done personally.

I don’t think the sash will fall apart if you remove it, but again no personal experience.

Are you in a conservation area, and/or is this a listed building?

 

[opps]

Have you checked to see how much weight will be added by the double glazing?

You may have problems sourcing new counterweights.

 

[rideforever]

Thanks, thats useful. its a bathroom widow so not so big.
Actually whilst doing some repairs I have found that the original counterweights were very under weight (although still worked) ... and replaced them with new ones that exactly matched the sashes.
Which actually involved adding some weight to it, therefore I think it will hold a bit more for the double glazing just fine.
I dont have a router at the mom, but I think I could also rout the astragal if I used extra bits of wood alongside the astralgal to align the router, then it should be okay.
The only thing I need to find out is the premium for "low iron" glass.
Which used to be called .... glass.
Before all the normal glass turned green in the 80s.

 

[opps]

I guess you reduce the depth of the astragal, go for a single DG unit in each of the sashes and then make a fake profile for the outside and glue it on.

It might also be advisable to make arris type rails as glazing beads to hold the panels in place. Linseed putty is a no-no because the units cannot expand and contract.

 

[mrrusty]

You may be surprised how much weight you have to add. Many old sash windows had 3mm single glazing. If you go to 4mm DG @10kg/sqm each pane you will find you need 3kg+ each side to maintain balance. The problem is, with the small weight pockets, you may not have enough height. Also, if using corded weights, allow more than you think you'll need for cord stretch.

Why the concern over modern glass? you'll never notice it...

 

[opps]

You may be surprised how much weight you have to add. Many old sash windows had 3mm single glazing. If you go to 4mm DG @10kg/sqm each pane you will find you need 3kg+ each side to maintain balance. The problem is, with the small weight pockets, you may not have enough height. Also, if using corded weights, allow more than you think you'll need for cord stretch.

Why the concern over modern glass? you'll never notice it...

I once worked in a house where someone had fitted DGs. The added weight was so much that the top sash was screwed shut. Presumably to facilitate wider weights in the sash box cavity.

 

[rideforever]

You may be surprised how much weight you have to add. Many old sash windows had 3mm single glazing. If you go to 4mm DG @10kg/sqm each pane you will find you need 3kg+ each side to maintain balance. The problem is, with the small weight pockets, you may not have enough height. Also, if using corded weights, allow more than you think you'll need for cord stretch.

Why the concern over modern glass? you'll never notice it...

In the property there are 11 sash windows all with about the same height.
The ones I would replace (at the back) would be about 60% the width of the biggest one which sits in the middle of the living room bay.
Additionally I could use square weights so I guess its okay, but might add cost.
I was quoted £200 for replacement 4 6 4 slimline units per window plus delivery.
Low iron as well.
So it looks okay really. Router about £100.
But thanks I shall bear it in mind. 4mm is 10kg/m2 but 1mm on the other side.
But as I said the original weights are underweighted for some reason and the windows work.
Therefore I could just get make weights for the additional and see if it works.

 

[mrrusty]

4mm is 10kg/m2 but 1mm on the other side

exactly. If it's about 800x600 it's ~0.5sqm. = +5kg for one pane and + 1.25kg for the increase from 3mm to 4mm = 6.25kg or a bit over 3kg a side....

If it's smaller a bit less of course..