insulating windows

[robbob]

I have lovely Georgian sash windows and am trying to work out how best to improve thermal performance without losing the look and feel of the windows.  Double glazed panels seems tricky and expensive. I was wondering whether an acceptable compromise would be to fix a polycarbonate sheet on the inside of the bottom half of the sash and on the outside of the top half? any thoughts on this? many thanks

[clockmanFR]

Sometimes with original beautiful windows there is little choice.
The thing with mounting secondary glazing internally is the new sub frame.

Basically you will require a flat and square frame around your window that your glazing panel can seal against. You can use poly sheet or 2 sets of double glazing panels with a foam seal attached. These of course will also require a mounting frame. Although with some double glazing panels i deburr the glass and use them as they are.

I just use plastic clips with just 4 screws to keep the panels and mounting frame pushed against the new internal wood frame.

 It sounds simple but in practice the original old frame is not square or level, so each sub frame ends up being bespoke, but when finished, filled (decorators caulk), primed, undercoated and top coat. The Finished window is the same from the outside and not to ugly on the inside and the benefits during the winter are excellent. 

[robbob]

thanks Clockman, i was intending just to screw the panel to the frame with small screws as the frame is relatively straight but your way sounds much more professional!

[Ivan]

clockman - Got any pictures? Would be very helpful if you could post some.

[clockmanFR]

As requested here are some pics. But its summer so only 2 in situ.

One is in the small downstairs office, as you can see we take are security seriously. Actually the bars and steel shutters were put in just after the WW2.

The other is bedroom 3 and 4 shower, toilet room. Both these windows are made of oak and were installed about 1870's. There difficult shapes to replace and not loose the long tall effect.

The office and shower room are both restored rooms, that means there is now 50mm Polyst- plasterboard dabbed (adhesive) to the interior of the exterior facing 4 brick thick walls. The mouldings etc are restored originals.

Frames are 25mm x 30mm section with addition cross bar for rigidity, with small steel corner braces these both our polycarbonate that are attached to the frame that goes against the new subframe that is permanently in position joined to the original window frame. 

[clockmanFR]

This one is the office.

[robbob]

yes thats definitely more professional than i had in mind - i was just going to fix the sheet to the window itself (ie the bit that moves). i was worried in case it added extra weight but the carpenter i spoke to about it said that he didnt think it would make much difference.

[dhaslam]

If the windows are Georgian there should be shutters on all windows.  Shutters can be used at night when curtains are closed anyway.   There shouldn't be a lot of heat loss through glass during daylight hours.

[Barrie]

Saw this on Grand Designs, not cheap but retains existing appearance.

http://www.slimliteglass.co.uk/

[djh]

Bunch of comments about the failure rate of those units on the GBF

[KLD]

clockmanFR

Did you put a seal between the secondary glazing and the frame? Is there any problem with condensation in that space between the two "windows"?

Klaus

[desperate]

One of my customers has windows very similar to those Clockman shows, he had a chippy remove both the internal and external staff beads, then he planted a 50*25 PAR batten on the box, in effect making it thicker, then he had 2 new sashes made up with a deep enough rebate to get a 22mm DG unit in. Plant back on both staff beads and set aside the original sashes and you then have a much better spec window that looks pretty much original and all the original components to restore it to standard if you need to. It all looked very professional to me, but it probably didn't come cheap. I know that our local timber merchant stock glazing bead, meeting rails and bottom rails in ovolo and double ogee, so a bit of creative routery and hammery and bobs related.

Desp

[clockmanFR]

KLD, Yes there is a rubber seal, (6mm gap closing, sticky back laminated type) on the back of the new glazed panel, and this is then pressed against the old window new sub frame with the plastic clips shown in my pics.

If the seal is really good, and the exterior original windows are reasonably sealed, then you get an air cushion of about 50 to 60mm.

The window in the bathroom/shower room has never yet had any condensation on it, and her indoors likes her showers.

Basically i have created a very large air gap double glazing window.

And yes if you do the sealing properly then Mr and Mrs spider can not get in either.