Insulation under or over rafters?

Building regs in my area require 170mm xtratherm/celotex/kingspan etc etc. So with 75mm between the rafters you will need 100mm more. They either want cross battened and then your 100mm or pack the current rafters out another 100mm and use 175mm solid boards. Remember you need an airflow between your insulation and roof. Hope this helps, if not contact your local building insector and ask them for suggestions, they may want it done a certain way!!!

Hello, I would suggest you look at a multi foil insulation. There are several on the market but beware some are not approved yet. You should be looking for BBA certificate approval or LABC approved products. Web Dynamics have a product called TLX for roofing. This product need to installed correctly though. Joints are taped with reasonable overlaps. This product is well used in the construction industry but some local authorities are still refusing to allow the use of the product. TLX is used in conjunction with friction fitted Celotex or Kingspan but you need to check the thickness required for each product. I hope this is of help. Regards Andy