Warm roof questions

[markblue777]

Hi All,

I was wondering what thickness of insulation would be needed for a warm roof (to go on an extension). Looking about I cannot seem to find the nominal thickness that would be required as I'm trying to draw up some plans. Am I correct in assuming you have ply, vapour barrier, insulation, ply and then felt covering

Cheers
Mark

 

[Bigbud78]

https://www.uvalue-calculator.co.uk/

 

[markblue777]

thanks fella. this seems very handy

 

[Bigbud78]

thanks fella. this seems very handy

No problem, its easier for you to run through it than ask you the questions

 

[Wuffles]

150mm on our GRP roof. Building control will tell you.

 

[RobinBHM]

Generally 120mm or 125mm over (not between) will give you 0.18, which is current regs

note: Firrings need to be under the insulation not above (needing long screws to fix the top osb deck down)

 

[markblue777]

Hi Robin, Thanks.

I have a little render of what the house looks like and how the extension roof will fit in

The red beams are the joists I obviously want the front pitch to match what is there and for it to continue across.

The 200mm block on top of the joists are showing the ply, vapour barrier, insulation, ply and felt. I need to tie the flat roof into the pitched tile roof at the front, I will be getting a roofer to do this so just need to know if from a building prospective is this all doable so the flat transitions to the slope (the thickness may vary but I want the top of the finished roof to flow with what is there so a nice leak free transition can be done) the flat roof will also be having 2 sky lights on it so does this have any effect of insulation other than a cutout for it.

(just click ignore if it asks you to register and you should be able to view the image)
https://www.dropbox.com/s/l5yb5u2s9lwc5 ... 8.png?dl=0

Cheers
Mark

EDIT: noticed the image was not working

 

[Dan j]

125 above the rafters should bring you up to regulations.
Technically the skylights will affect the insulation but its very unlikely the building inspector will take issue with this. If there is an issue you can always offer to make up the difference with insulation between the rafters.
Extensions or conversions are usually given a bit more leeway with this kind of thing.

A good roofer should be able to do what you want without any leaks.
Will you be tiling the slope part of the extension or will this be felt/fiberglass as well?

 

[markblue777]

The sloped part at each end will be tiled. Good to know it is disabled. I know the rear slope is quite shallow at about 17.5 degrees so will need to look for tiles that can support it or i may just have to have it taken up to be a flat roof

 

[kostello]

Hi All,

I was wondering what thickness of insulation would be needed for a warm roof (to go on an extension). Looking about I cannot seem to find the nominal thickness that would be required as I'm trying to draw up some plans. Am I correct in assuming you have ply, vapour barrier, insulation, ply and then felt covering

Cheers
Mark

Celotex website has a calculator and will send you the calcs to give building control

 

[Workshop Bob]

When I built mine last year, the building inspector was happy with 50mm above and 75mm between to keep the overall height down but the area wasn't very large as it was quite a small extension to serve as a new entrance and hallway. I also didn't need a vapour barrier as taping the joints on a celotex board was sufficient. Just my experience but if I was you I would speak to building control, ours were really great and very helpful.

 

[HOJ]

Had one fitted yesterday to an extension I am building, used a fully adhered system from Sika Sarnafill, they provided all the calcs, including wind uplift, laid on 18mm ply, they apply a VCL, with a 120mm Kingspan insulation and Graphite grey membrane on top, and aluminium extrusions around perimeter for side up-stands and the gutter over hang.