Insulation to achieve 0.13 rating help or suggestion greatly appreciated

[Sniffer1977]

Hi all
I’m in the process of pitching up my flat roof into a vaulted ceiling in my bungalow.
i foolishly thought insulation could be 100 mm between rafters and 50 underneath . Building control have advised 100mm underneath which would cause problems re roof height near outside walls .

can anyone suggest a way to try achieve the the U value as I don’t understand these calculators or get them to work with different products . Has anyone used the foil/quilt stuff ?
thanks in advance

 

[cdbe]

They will probably allow you to reduce the thickness/chamfer the edges in areas where it's impractical to achieve the full depth required.

 

[Mr Chibs]

My mates council are requesting 100mm in-between and 50/60mm underneath + plasterboard there are different figures for 600 or 450 centres!

Are they suggesting 100mm underneath only?

 

[freddiemercurystwin]

What size are the rafters, is there a roof membrane under the tiles/slates, is it breathable membrane or traditional felt?

 

[Sniffer1977]

My mates council are requesting 100mm in-between and 50/60mm underneath + plasterboard there are different figures for 600 or 450 centres!

Are they suggesting 100mm underneath only?

They are asking for 100 in between and 100 underneath to achieve a 0.13 value.
the centres are 400 , tiles are Marley edgemere with breathable membrane .

we Are converting the flat roof to a pitched one as it pretty much no insulation in and was very low in height .

any ideas what type of insulation to use that works out cheapest to achieve the 0.13 (they did say they may stretch to 0.14)

cheers

 

[Sniffer1977]

What size are the rafters, is there a roof membrane under the tiles/slates, is it breathable membrane or traditional felt?

Hiya
the rafters are to be 150x 50 with 400mm centres.
it’s Marley edgemer tiles that are going down with a breathable membrane .


we Are converting the flat roof to a pitched one as it pretty much no insulation in and was very low in height .

any ideas what type of insulation to use that works out cheapest to achieve the 0.13 (they did say they may stretch to 0.14)

thanks for any help as my head is mashed with extra cost and confusion to be honest

 

[baker332]

I think you could get a SAP calculation done, to achieve the therm value at 0.13 with 100mm between rafters and 40mm underneath.

SAP calcs take into account the whole house thermal value they're around £250.00

Good luck.