DIY Doctor UK DIY Forums

Hi All, I have done plenty of research but I need so advice on do and do not's as I have read lots about air gaps and condensation etc.

I have about 36sqm to cover
The roof is traditional tiles and felf which I can see from below inside the loft.
The rafters below the roof are small about 75mm from edge to felt.

My plan was to use Celotex or Kingspan say around 50mm leaving a 25mm air gap with the material pushed just flush to the edge of the rafter as a guide. These would be held in place with cross battons to stop the dropping.

I am now wondering if a 25mm air gap is a little to small, I have just watched a youtube demo showing a quilted tough bubble foil which is stapled to the outer of the rafter, thus leaving the full 75mm air gap, any seems are then sealed with a foil based tape at the end.

Any tips would be helpful please.

My house is 2 bed end of terrace.

Many thanks

if you want to use a thinner insulation but retain maximum heat efficiency then use triso super 10, its 30mm thick and you can staple it to the rafters giving you maximum airflow

Thank you very much I have looked that stuff up and plenty of options.

I have one more question you may or may not know the answer to. A local builder is about to finish a large project and he is going to be left with 40sqm of 100mm celotex. He has offered this to me at a price not to be sniffed at.

I am not in the position time wise or space wise to increase the depth of my rafters to allow the min 50mm air gap, but I was wondering if there any reason regulation or practically why I can not attach the Celotex to the underside of the rafters insted of between the rafters? thus leaving me with an air gap above min regs.

I was going to do this using long thin screws and large penny washer to grip the boards.

yes you could do that or cut a section out 50mm x 50mm, jam it in between the rafters 50mm and it sits 50mm on top, if you get my drift