Insulation depth into eaves

[thomp1983]

Hi all,

Finally insulating my extension roof and have a quick question about how far to run the insulation into the eaves,

Option one is the board stops level with the wall plate,

Option 2 I run the board past the wall plate into the eave behind the fascia board

I'm fairly sure option 1 is the right way but wanted to check before I fit it all in tightly and find I'm wrong

Thanks
Chris

 

[Bonni]

Totally confused. Unless you heat the loft space, never put kingspan between the rafters, the condensation is gonna be bad.

The cavity at the wall plate should be closed off with loft insulation, but keep the rafters clear.

 

[thomp1983]

The house is a dormer bungalow so the roof forms the ceiling of the bedroom and bathroom so the roof requires insulating

 

[catlad]

The wall insulation needs to meet the roof insulation.

 

[thomp1983]

There is no wall insulation to meet, the wall plate in question is over my double garage doors so the roof runs straight down into the soffit/fascia above the garage doors

 

[catlad]

Picture from the outside might help people understand better!

 

[thomp1983]

Ok here are some more pictures that should hopefully make things easier to understand.

This is my extension I'm currently insulating the roof of.

That's the wall plate above the garage doors, as you can see I've went with my first option of just running the insulation to meet the wall plate, tomorrow i intend to run a bead of expanding foam along the inside of the wall plate where the foam meets meaning the only gap around the insulation exposed is the 30mm air gap at the top

That shows an eaves opening without any insulation currently fitted

That's the insulation where it ends under the dormer window

Vertical pieces of insulation under the dormer capping off the eave insualtion

This is one of the dormer cheeks, do I put 100mm insulation board straight against the osb cheek or do I need to use 75mm insulation and leave an air gap between the osb and insulation board?

Thanks
Chris

 

[noseall]

do I put 100mm insulation board straight against the osb cheek or do I need to use 75mm insulation and leave an air gap between the osb and insulation board?

Thanks
Chris

Fit your insulation tight against the dormer cheek sheathing ply. Foil tape all joints. Add another layer of foil sandwich insulation across the studs and foil tape all joints again. Fix duplex plasterboards.

 

[thomp1983]

How thick an insulation board would you use across the studs before fitting the duplex plasterboard?

 

[noseall]

How thick an insulation board would you use across the studs before fitting the duplex plasterboard?

As thick as you dare and it depends on the first layer. Fixing starts to become a bore once you are past 50mm.

100mm /50mm is a popular duet.

 

[thomp1983]

Between the studs for the dormers is 100mm celotex there made from 4x2's so 50mm over the studs it is.

 

[noseall]

Between the studs for the dormers is 100mm celotex there made from 4x2's so 50mm over the studs it is.

Just be aware that modern 100mm x 50mm studs finish at a whisker under 95mm and this will be revealed when you try and fit 100mm Celotex etc.

 

[thomp1983]

I'd noticed with the couple I'd put in but it shouldn't be an issue, I'll just fit the plasterboard with some packers to level it up, they'll only be smallish bits anyway as opposed to full sheets

 

[noseall]

I'd noticed with the couple I'd put in but it shouldn't be an issue, I'll just fit the plasterboard with some packers to level it up, they'll only be smallish bits anyway as opposed to full sheets

You should have a secondary layer of insulation dealing with any discrepancy.