Insulating wood cladding

midonogh

I have a 1969 bungalow. I have filled the cavities with walltite foam. Under each window there is a single skin of brick work and then external wood cladding. Obviously the heat loss is bad through this. I removed some of the cladding and there is about 20mm of expanded polystyrene board sealed by some felt. I expect that it has been in there for 20 years. If I were to remove this and replace with some kingspan panels would I find an appreciable difference. Are there any other solutions I could consider.
Thanks

Andrew_Doran

midonogh wrote: »

I have a 1969 bungalow. I have filled the cavities with walltite foam. Under each window there is a single skin of brick work and then external wood cladding. Obviously the heat loss is bad through this. I removed some of the cladding and there is about 20mm of expanded polystyrene board sealed by some felt. I expect that it has been in there for 20 years. If I were to remove this and replace with some kingspan panels would I find an appreciable difference. Are there any other solutions I could consider.
Thanks

What surrounds these under-window areas out of interest -- is it cavity walls with brick/render?

How much can you move the cladding out, i.e. how much room do you have for additional insulation? Going from polystyrene to PIR/PU of an equivalent thickness will make some small difference but if you can increase the thickness any and do it all at low cost I think it's probably worthwhile.

Whatever you do I'd suggest an airtight seal between the insulation board and the blockwork will be very important for keeping the heat in. You could use builder's expanding foam applied in a bead around the perimeter of the board and in a criss cross pattern as an adhesive & air barrier in this context. Insulation is useless if cold air can get behind it, you get a chimney effect where cold air is constantly drawn upwards.

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You can calculate a very rough U value to get an idea of how much your heat loss would be reduced by using this and doing a comparison between polystyrene & PIR board:

http://www.vesma.com/tutorial/uvalue01/uvalue01.htm

"E P S" would be your polystyrene board and "Polyurethane" a PIR board like Kingspan.

For example, a U value of 0.5 would represent half the heat loss of a U value of 1.0.

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I will be doing something similar with a 1970s cross-wall house which has aluminium cladding boards, bitumen felt membrane but no insulation.

The system I have chosen is rigid mineral wool slabs friction fitted between battens and adhered to wall with adhesive, breather membrane on top and original cladding re-applied. Fake polystyrene over-sills (google) to be used to extend existing window sills.

midonogh

The under window area is single skin brick, polystyrene sheet, tar sheet, cladding. The rest of the house, and the areas adjacent to the cladding is cavity wall block and then external brick work. The cavities have recently been pumped with walltite foam.
Your idea is interesting. I have quite a few 70mm sheets of kingspan left over and if I extended the window sill could deepen the void and fil it with these. I would need new window sills but I will investigate with my brother in law who is carpenter.
Many thanks for your advice

midonogh

My sills are mahogany. I wonder can I get the over sills in mahogany effect