Insulating the overhang of warm roof - what am I missing?

[c0wb0y]

Hey folks,

I’m self building a double skin (brick + cavity + block) detached workshop (6m x 5m) with a flat roof that’ll overhang by 300mm on all 4 sides.

1. I've researched the build-up of a warm deck ‘sandwich’ but can’t figure out how to prevent cold air entering at the soffits (and fascia)? I wasn't intending on insulating between rafters or boarding the ceiling so what am I missing?

2. I've asked the bricky to finish the outer brickwork 1 course higher than the inner blockwork to accommodate the wallplate. Is this standard practice or is there a better way because something tells me I'm doing it all wrong.

3. The arrangement below means I'll have a 370mm tall fascia and that horrible 'storefront' look. Any suggestions on how I can reduce the height? I've read posts on notching the joists but surely that'd weaken the structure?

 

[c0wb0y]

Hey folks,

I’m self building a double skin (brick + cavity + block) detached workshop (6m x 5m) with a flat roof that’ll overhang by 300mm on all 4 sides.

1. I've researched the build-up of a warm deck ‘sandwich’ but can’t figure out how to prevent cold air entering at the soffits (and fascia)? I wasn't intending on insulating between rafters or boarding the ceiling so what am I missing?

2. I've asked the bricky to finish the outer brickwork 1 course higher than the inner blockwork to accommodate the wallplate. Is this standard practice or is there a better way because something tells me I'm doing it all wrong.

3. The arrangement below means I'll have a 370mm tall fascia and that horrible 'storefront' look. Any suggestions on how I can reduce the height? I've read posts on notching the joists but surely that'd weaken the structure?

 

[George_engineer]

...

You need to continue the wall and insulation up to meet the roof. This can be timber inside and brick outside, or all in timber if you are having an external soffit.

 

[freddiemercurystwin]

Your insulation will be going up to the underside of the deck presumably? Anyway something like this would be OK, if you don't mind a sloping soffit, you'll still retain your insulation bubble albeit with a minor bridging through the joists. Or just cut the insulation short on top if you're not out there enough for a sloping soffit.

 

[Londoner2]

I had similar to yours but overhang was shorter, it was stuffed with regular insulation, about 0.5.m worth.

 

[b123b]

how do you make that area air tight? do you paint VCL on the inside of that area? Or not bother?

 

[Londoner2]

how do you make that area air tight? do you paint VCL on the inside of that area? Or not bother?

Stuffing with insulation would prevent airflow and make it airtight.