Replace double glazing unit - stupid idea?

[Marineboy]

The upper floor of my house has two rooms with 3-sided dormer windows.

Ever since we moved here I have been unable to clean the triangular side windows, other than a couple of years back when I removed the whole glazing units on both sides. This is not a feasible option to keep on doing on a regular basis. The front windows are fine, I am able to clean them via the opening lights.

So it occurred to me to replace the glazing with something else. I know I will lose some light but that is not a big deal. The larger room faces south so is always bright anyway, the smaller room is just for storage so no matter. The glazing units are 4-20-4, so total thickness of 28mm. I had the idea of sandwiching some insulation material between two sheets of 9mm ply. I found this:

https://www.prowarm.com/products/insulation-boards

which is 10mm, so would give the same thickness as the DG units and I could just fix the sandwiches in place using the existing glazing beads.
I would finish the outward facing ply with a decent exterior paint.

Thing is - is this just a daft idea? How would the U value of the new sandwich structure compare to the DG unit? The windows in the larger room have an area of 0.5 square metres each.

 

[Doug71]

You can buy the insulated panels like in the bottom of pvc doors in 28mm thick quite easily, would just cut to size and be a straight swap. Just google pvc door panel.

 

[Marineboy]

Thanks, it never occurred to me to look at an already made composite. Any idea re the comparative U values?

 

[DrPhill]

Maybe a stupid idea, but...... why not apply a thin opaque white layer to the inside of the triangular bits. Could look just like the plastic pannel, will not lower the insulationn, and could be completely reversible.....

 

[Marineboy]

No, not stupid, it’s worth considering, but I’m still interested in how or whether I can improve the insulation of that panel.

 

[Rorschach]

Insulation would be significantly improved, despite all the hype about heat retention of DG, windows will only ever be one step up from a hole in the wall.

 

[Marineboy]

Yes that’s my gut feeling, wonder what the numerical comparison in terms of heat loss would be.

 

[deema]

Why not just make openers that are hinged in the centre so that you can clean both sides. Same principle as round sash’s.

 

[Jasper42]

Could replace with self cleaning glass, but no experience of using this but just a thought

 

[Woody2Shoes]

Why bother to replace them (apart from anything else, my modifying the existing window, you could get involved in building regs/safety concerns)? Why not cover the DG units on the inside with some thin sheet material e.g. 9mm ply stuck on with hot glue or something you could remove in future (eg silicone gunk round the edge).

Once covered, the outside may get dirty but you'd never notice/care. Timber is a pretty decent thermal insulator and can easily be painted/decorated.

Cheers, W2S

 

[flying haggis]

cover the triangular bits with the same stuff that car windows are tinted with, then it could be peeled off if not required

 

[Marineboy]

Thanks for the suggestions, I don’t have the skill/inclination to make centre hinge windows and not sure how that would work with plastic frames, but the idea of simply covering the inside with a sheet of thin ply has legs.

 

[flying haggis]

As Doug said above replace the s/u with panels, you can get reinforced panels with an mdf middle.

example
https://www.trulypvc.com/conservatory-p ... door-panel

non reinforced

https://www.trulypvc.com/conservatory-p ... oor-panels

 

[Marineboy]

Thanks, but Ive already had a look at those and they are not big enough. Their max width is 750mm but I need 810

 

[flying haggis]

https://www.pvccladding.com/products/do ... 1500mm---/

 

[Marineboy]

Top man, many thanks.