flat roof

[electrified]

That span only needs 4 x 2 anyway.

warm roof would be 95mm + 11mm OSB + 120mm insulation + 18mm OSB then add on firrings if joists are set plumb

is that too much roof thickness, 245mm

need it about 130mm

 

[Notch7]

Your description of the roof gives me the impression you might struggle to ventilate both ends of the joist voids in a cold roof

 

[electrified]

That span only needs 4 x 2 anyway.

warm roof would be 95mm + 11mm OSB + 120mm insulation + 18mm OSB then add on firrings if joists are set plumb

is that too much roof thickness, 245mm

need it about 130mm

 

[Notch7]

need it about 130mm

Sadly there is no way to achieve building regs elemental values with 130mm

you might need to redesign.

 

[electrified]

Sadly there is no way to achieve building regs elemental values with 130mm

you might need to redesign.

yes I think i might have to. what is the minimum insulation thickness of cold roof and minimum air gap?

 

[Notch7]

yes I think i might have to. what is the minimum insulation thickness of cold roof and minimum air gap?

50mm gap

needs ventilation at both ends

150mm insulation in between (check with online calculator like kingspan

 

[mikeey84]

Check this thread: https://www.diynot.com/diy/threads/inverted-warm-roof.590522/

You might be able to get close to what you want

 

[electrified]

Check this thread: https://www.diynot.com/diy/threads/inverted-warm-roof.590522/

You might be able to get close to what you want

you would use 6x2 joists here correct? but the thing is if i had to i’d rather do a warm roof and ensure it works compared to the hybrid which we don’t know, unless you have used it and had no problems?

 

[mikeey84]

I'm no expert I'm afraid! Plenty on here though.

You will need to make some sort of change to your design, as your BCO will make you to ensure it is compliant, unless as above you can prove energy saving elsewhere...

 

[electrified]

I'm no expert I'm afraid! Plenty on here though.

You will need to make some sort of change to your design, as your BCO will make you to ensure it is compliant, unless as above you can prove energy saving elsewhere...

thank you and @Notch7 for you help, i am very thankful.