insulation

[bluebaron]

I find cutting solid insulation (celotex) tricky to get straight. if I want 100mm it there any downside to buying two lots of 50mm and sandwiching them together? (apart from cutting twice).

Price seems about the same.

 

[Mr Chibs]

No, no down side, generally 50mm sheets seem flatter whenever I’ve bought them, and the 100mm seem to have more of a curve to them.

 

[^woody^]

Potential interstitial condensation from non-flat sheets

Just cut one sheet slowly with a jack saw. Wear a mask.

 

[cdbe]

You can get very long jigsaw blades that do a good job on a fairly slow speed. I've also seen special blades for a multitool but I think the reviews were a bit mixed.