Multifoil Insulation: the choice for loft conversions


A modern approach

The days when insulation was just an afterthought to a loft conversion and “we’ll put 100mm of Mineral wool between the rafters” are long gone. The required U values for rafter-level insulation are that you now need to achieve U = 0.18 W/m2K if at all possible. This usually rules out Rockwool because you’d need rafters that were over 220mm deep to accommodate the amount you’d need.TLX Silver multifoil

And even using rigid foam board (PIR) requires 165mm between the rafters (assuming they were at 400mm centres and you had a breather membrane above).

It's all about the air gaps too

But because multifoil insulation makes use of heat reflected across air gaps that you create next to it by using battens of the right size, it needs only a minimum of 125mm rafters and 85mm of PIR board. Less PIR, and the air gaps come free!

Installation is simple 

Fit the PIR 30mm up from the bottom of the rafters, staple TLX Silver to the underside then secure with 38mm x 38mm battens set crosswise at 600mm centres, then plasterboard. Simple.

multifoil insulation used in a loft conversion


Read our case studies related to this blog post

Further reading on this subject can be found HERE

tlx insulation technical helpline