solid wall insulation - 1st floor

[RJH]

I?m 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? I?d assume it is at the ceiling, but I?m thinking the floor won?t be as much of a cold bridging opportunity.

Any links/guidance appreciated.

[Andrew]

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 Russia.

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 :-)

[RJH]

Many thanks - thorough job by the sounds of it, and plenty to go on. I had thought of mini battens in the reveals - I?ll rethink with the glue idea.

[RJH]

Quick question - what distance did you use for batten spacing? The online guides* seem to suggest 400mm. This?d be fine for a stud partition but I don?t see the need on a solid wall. I?d have thought using 1.2m spaced vertical would be sufficient, easiest (noted you used horizontal) and reduce cold bridging.

[Andrew]

I only used horizontal battens, about 400mm apart, plus a frame aroundthe perimeter of the windows to support the 90 degree joint in the plasterboard. The bottom batten was a spare 125mm x ?? cut down to 30mm depth. Because the infill of the 2nd layer inside the battens was flush with the batten surface, it provides extra impact resistance, but I diy-skimmed it anyway, which wasn't the best result.

[RJH]

Grand, thanks.