Pitched roof ventilation

[pilsbury]

On my kitchen extension, I have a combination of flat warm roof over the majority (center) with a small monopitched roof around the edge - plain tiles with breathable membrane. I'm intending to use rockwool insulation in this part, 270mm deep.

The monopitched roof is an open rafter design matching the rest of the house. I was thinking of blocking up between the rafters on the outer skin and carrying the 100mm wall insulation up and over into the roof space before laying 170mm over the top. This however will block air movement into the small roofspace from the eaves. How much of an issue is this with breathable membrane? Another option is to put vents in the rear cladding of the monopitch?

Thoughts appreciated

 

[Ian H]

What about those air vents that go ontop of the facia, would those let air into the roof space?

Or a second set ofeaves trays under the rafters to stop the insulation blocking the air through the rafter?

 

[pilsbury]

What about those air vents that go ontop of the facia, would those let air into the roof space?

Or a second set ofeaves trays under the rafters to stop the insulation blocking the air through the rafter?

There will be no facia - or soffits - just exposed rafters. As for your suggestion about a second set of eaves trays, how would that work? I've seen some rafter spacer tray thingys when googling

 

[Ian H]

Some thin sheet to keep the insulation off the membrane like this:

I thought about it on mine but then the rafters were plenty thick enough for the full fill & loft insilation not to touch the felt.

 

[Ian H]

I've seen some rafter spacer tray thingys when googling

Bastards stole my idea!!!

 

[pilsbury]

I see you are an artist - I've filled my walls with insulation as opposed to smoke..... The issue I have with my rafters is as they are so short (1.8m) they are just 2x4 leaving little gap once the birds mouth is taken out. I shall however mull over your suggestion and how I can implement (bodge) it.

edit: Thats the exact pic I saw

 

[Ian H]

Sorry, that's a picture of how I ventilated my chimney stack into my loft space.

But I agree, it's a good drawing