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Andrew[_22_] Andrew[_22_] is offline
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Default solid wall insulation - 1st floor

On 31/05/2021 17:38, RJH wrote:

Im thinking of insulating some external solid walls using 2 layers of 25mm
celotex set overlapped between wall fixed 25mm battens, with plasterboard
over to fix it all in place.

Is it necessary to extend the celotex beneath the floor? Id assume it is
at the ceiling, but Im thinking the floor wont be as much of a cold
bridging opportunity.

Any links/guidance appreciated.

I did, but I used 30mm quinntherm which is more consistant,
and also you can cut down 89mm CLS timber nicely into
three battens of 30mm. Slap first layer onto wall, fix
30mm battens horizontally at top bottom and whereever
using frame anchors right through batten and 1st layer.
Infill with more 30mm celotex and then plasterboard.

On the ground floor I dug out all the screed and went
down to the slab and also did the floor with 3x2
battens infilled with 70mm quinntherm. Upstairs I
pulled up the chipboard flooring (unglued tongues
luckily) and insulated down to the ceiling below
(joists running side to side with a 2 inch gap at the
front wall).

IN my case the ground floor had a normal 65mm cavity
but the upper floor (facing north) was horrid hollow
9 inch blocks with the perps unmortared (!) and plastic
shiplap cladding and no building paper. These blocks started
above the ground floor window lintels and a course of horizontal
bricks bridged the cavity approximately where the
coving was. Appalling heat loss. Now I can keep the
lounge warm with just a 1 bar electric fire apart from
when we have severe northerly winds and blocking highs over

Around the window reveals I made my own foil-backed
plasterboard with turkey foil and spray adhesive, ripped
off the galvanised mesh welded into the underside of the
lintel and glued the PB into place with foaming PU adhesive.
Ditto the sides of the reveal after removing existing plaster
while the wall kept its original plaster.

Also had to extend the BT incoming cable with a bit of
nifty soldering :-)