Unsupported PIR Insulation

[frank999]

We are installing Celotex GA4100 between flat roof rafters.

We cut it to make the fit snug so the PIR stayed wedged between the rafters. A few days later though, after fitting the PIR has fallen out, like its contracted.

I see there are special clips:
http://www.toolstation.com/shop/Con...elotex Plastic Rafter Clip/d210/sd2738/p44294

I'm not going to use them, but wonder if its OK for the insulation to float loose (as it will not doubt) when we put the plaster board up, ie just the weight of the PIR to keep it in place.

 

[tony1851]

It wouldn't be the PIR that contracted, more likely the rafters each side have shrunk a little as they dry out.
Just let the plasterboard hold them.

 

[noseall]

It is more likely that the diaphragming effect from the recent winds have pushed it out.

Use foam or foil tape or both to secure it.

 

[frank999]

The Flat roof joists have been in about 6 months so plenty of time for those to shrink, maybe the wind popped them out as suggested.

To secure them, is there anything that set instantly, so I push them back in and expect them to be held in place, expanding foam takes a little while to harden.

 

[noseall]

We make wedges out of foam board off cuts to hold our pieces in place where friction fitting has not been successful.

 

[frank999]

Ahh yes, we have plenty of those lying around on the floor.