600mm rafter insulation - 110mm depth

helvetica

Hi all, rof insulation enquiry: my rafters are only 110mm deep, so with a 50mm ventilation gap I only have room for 60mm of insulation space. Is it worth my while extending the rafter depth so I can fit, say 125mm of rafterloc then add 50mm thermal liner or sarking board? The house is 30 years old and while relatively modern, there are many other things I would have to do to get an A rating, so how much do I have to do to get a B or C rating? will 50/60mm of sheepswool or rockwool insulation and some plasterboard do the job?

go raibh mhaith agat

ardara1

helvetica wrote: »

Hi all, rof insulation enquiry: my rafters are only 110mm deep, so with a 50mm ventilation gap I only have room for 60mm of insulation space. Is it worth my while extending the rafter depth so I can fit, say 125mm of rafterloc then add 50mm thermal liner or sarking board? The house is 30 years old and while relatively modern, there are many other things I would have to do to get an A rating, so how much do I have to do to get a B or C rating? will 50/60mm of sheepswool or rockwool insulation and some plasterboard do the job?

go raibh mhaith agat

By extending the rafter depth - you are just extending the thermal bridge material - better to add additional insulation to the underside in a continuous run - seal edges then plasterboard.

The sheep wool/rockwool at 50mm will eventually slump - and won't get a decent U-value in any case - ask all insulation manufacturers for U-value calculation and prices.

How to get to a 'B' - where are you starting from? - GET YOURSELF A GOOD BER ASSESSOR

Slig

If you arent using the attic aspace then a better method would be to insulate between the floor joists and then perpendicular above them