PIR insulation wastage allowance?

[Watshot]

Hello chaps,

Doing a 'between and over' warm pitched roof with Celotex. Just wondering how much you guys with more buying experience would allow for wastage?

Over layer is not too bad, few roof windows to chop around, but existing 60's rafters would have been 16" centres in old money, and vary a little bit, so a 1200 x 2400 sheet won't divide up perfectly inbetween.

Would you normally add 10%, or more? Don't want to over do it for obvious cost reasons, so grateful for any advice.

Cheers all.

 

[noseall]

Whatever strip you have left off the sheet can be turned the other way and cut to fit, if you know what i mean.

It is important however to try and fit the stuff a snug as possible.

Foil tape is also useful (very sticky though) as is a foam gun or a mastic gun.

So, wastage should be minimal. Also allow for the thickness of each joist when measuring entire area.

 

[Watshot]

Understood

As always, thanks noseall.