Retrofitting membrane and insulation into old roof

[speakermonkey]

Hi All,

Apologies if this is roof construction 101. I recently bought an old house and the garage has zero roof insulation. The roof consists of the timber frames, battens, nails & tiles. I would like to add a membrane and insulation without dismantling or redoing any of the existing roof. I have made a drawing of what I plan to do:

Roof

• speakermonkey
• 10 Nov 2020

What I am unsure on is the membrane (sarking?):

• What type do I need? (low/high vapour resistance)?
• Is it in the right place?
• Is there any issue with having the rafters on the "wrong" side of the membrane?
• Do I need to leave an air gap between the insulation and the membrane?

All comments welcome.

Thanks

 

[datarebal]

You will not be able to finish the underlay properly at gutter level.
If its just to make things a bit warmer easily you could - https://www.superfoil.co.uk/pitched-roof-under-rafter-insulation-applications/

 

[^woody^]

Doesn't it have a ceiling to insulate?

In any case what's the point in insulating a garage? How special is the car?

 

[speakermonkey]

You will not be able to finish the underlay properly at gutter level.
If its just to make things a bit warmer easily you could - https://www.superfoil.co.uk/pitched-roof-under-rafter-insulation-applications/

that seems pretty decent, thanks

 

[speakermonkey]

Doesn't it have a ceiling to insulate?

In any case what's the point in insulating a garage? How special is the car?

No, and it will be a workshop. Perhaps I should have said all useful comments welcome.

 

[^woody^]

No, and it will be a workshop. Perhaps I should have said all useful comments welcome.

Perhaps you should post all useful information, FFS.