BartW Posted November 26, 2022 Share Posted November 26, 2022 Hi, we are nearly ready to install internal PIR in our timber frame walls. The trouble is that out screed to ceiling joist height is 35mm higher than full sheet of PIR. Would it be best to: a) lift boards 20mm off the ground and foam up with expandable foam later? There would be tiles and adhesive later so I guess it would be ok? Then remaining 15mm on top, do the same thing because there will be a plasterboard applied? b) fully plant it on the floor tight to screed and foam up the top? c) install a row of pir boards horizontally, and do 650mm pir cuts from a vertical board, and generate a lot of cutting and waste? what would a self-build-hubber do? thanks! bart Link to comment Share on other sites More sharing options...
Moonshine Posted November 26, 2022 Share Posted November 26, 2022 (edited) Aren't there noggins in that would stop a full board length being installed? I would install a full board then a 35mm slither off cut, expand foam any gaps, then alu tape over joints Edit: it was my assumption that your insulation is going in the cavity, however it sound like it may be on the inside of the timber. Edited November 26, 2022 by Moonshine Link to comment Share on other sites More sharing options...
Bonner Posted November 26, 2022 Share Posted November 26, 2022 d) Buy a sheet of 30mm PIR and cut into strips. Put that on the screed with full sheets on top. Fill 5mm gap with foam. 1 Link to comment Share on other sites More sharing options...
BartW Posted November 26, 2022 Author Share Posted November 26, 2022 Thanks guys, both good suggestions. I will probably end up cutting 35mm slivers to top in order to keep alu faces back and front rather than top and bottom thanks! oh, and would it be good to have horizontal battens top and bottom of the wall to give the plasterboard better bedding or would it be counterproductive? Link to comment Share on other sites More sharing options...
nod Posted November 26, 2022 Share Posted November 26, 2022 Foaming up is your best option You can always cut it off with a saw and foil tape it Cutting 30 mil rips would be difficult to keep the foil on Link to comment Share on other sites More sharing options...
BartW Posted November 26, 2022 Author Share Posted November 26, 2022 1 hour ago, nod said: Foaming up is your best option You can always cut it off with a saw and foil tape it Cutting 30 mil rips would be difficult to keep the foil on Not with a skillsaw? Link to comment Share on other sites More sharing options...
Thorfun Posted November 26, 2022 Share Posted November 26, 2022 2 hours ago, Bonner said: d) Buy a sheet of 30mm PIR and cut into strips. Put that on the screed with full sheets on top. Fill 5mm gap with foam. I like this idea Link to comment Share on other sites More sharing options...
nod Posted November 26, 2022 Share Posted November 26, 2022 20 minutes ago, BartW said: Not with a skillsaw? 😂 Link to comment Share on other sites More sharing options...
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