Flat rooflight

[SBMS]

Anyone got any recommendations for a cost effective flat, fixed roof light for our flat roof that achieves 1.0 u value or lower? We need two and they are each 2800mm x1300mm. 

[JohnMo]

Roof maker, do a Passivhaus approved one, it's got a U value of 1.0. don't pay for there upstands they are naff.  Sit them on Compafoam CF200 upstands to get thermal bridge free install. 

[SBMS]

3 hours ago, JohnMo said:

Roof maker, do a Passivhaus approved one, it's got a U value of 1.0. don't pay for there upstands they are naff.  Sit them on Compafoam CF200 upstands to get thermal bridge free install. 

Ah damn, now you’ve got me thinking of insulated up stands - never even realised this was a thing… 

[JohnMo]

17 minutes ago, SBMS said:

insulated up stands

I gulped at the cost of Compafoam, but took joiner all of about 15 min to do two roof lights upstands. So overall good value.

[SBMS]

58 minutes ago, JohnMo said:

I gulped at the cost of Compafoam, but took joiner all of about 15 min to do two roof lights upstands. So overall good value.

Is the whole of the upstand made out of it? Have you got any pictures or details?

 

cheers

[JohnMo]

Yes the whole upstand is made from pieces of Compafoam, it looks like polystyrene, is light, but like a stone for hardness. I used 75mm x 100mm, screwed through directly in to the roof structural timber, with a mastic in-between to seal. The roof light is then screwed directly to the Compafoam with mastic to seal.

 

Sorry never got any photos.

 

 

[SBMS]

10 minutes ago, JohnMo said:

Yes the whole upstand is made from pieces of Compafoam, it looks like polystyrene, is light, but like a stone for hardness. I used 75mm x 100mm, screwed through directly in to the roof structural timber, with a mastic in-between to seal. The roof light is then screwed directly to the Compafoam with mastic to seal.

 

Sorry never got any photos.

 

 

Thanks @JohnMo got a video of it online. This looks like a great idea for our upstand. One problem is that we are doing warm

roof construction so putting 165mm insulation on top. Compafoam looks like it’s max height is 150mm and I think regs state

the upstanding needs to be 150 above the finish roof level. Would you do 150mm compafoam then a 165mm timber frame on top or two  layers of compafoam to build a 315mm upstand?

Edited August 31, 2024 by SBMS

[JohnMo]

I would build a wooden frame from the roof structure and around the aperture, to a height just below the top of insulation, so the roof insulation has something to butt up to also, use this framing to secure the Compafoam too. Then build up in two layers of Compafoam to get the correct height you need. Glue and screw the layers together to form the upstand

[SBMS]

Do you mean build a frame that’s 100mm away from the aperture around the aperture. And then on the ‘outside’ of this frame the PIR butts up to it and the inside the compacfoam?

struggling to visualise what you mean

[JohnMo]

24 minutes ago, SBMS said:

Do you mean build a frame that’s 100mm away from the aperture around the aperture. And then on the ‘outside’ of this frame the PIR butts up to it and the inside the compacfoam?

struggling to visualise what you mean

Does this make more sense?

[SBMS]

Would there not be thermal bridging that we are trying to avoid where the timber frame connects to the roof deck? 
 

is the roof light aperture to the left in your section diagram?

[SBMS]

1 hour ago, JohnMo said:

Does this make more sense?

Also - is the compacfoam effectively infilling the frame around the top of the aperture?

[JohnMo]

2 hours ago, SBMS said:

Would there not be thermal bridging that we are trying to avoid where the timber frame connects to the roof deck? 

Making the wooden frame and having it shorter in height than insulation gets rid of any possible bridges. So if you have 200mm of insulation above the roof make the timber upstand about 170mm, the Compafoam then is 150mm plus 30mm, plus any boards on to of the insulation and your roof finish, so about 200mm high Compafoam.

 

2 hours ago, SBMS said:

is the roof light aperture to the left in your section diagram?

Yes

[SBMS]

15 minutes ago, JohnMo said:

Making the wooden frame and having it shorter in height than insulation gets rid of any possible bridges. So if you have 200mm of insulation above the roof make the timber upstand about 170mm, the Compafoam then is 150mm plus 30mm, plus any boards on to of the insulation and your roof finish, so about 200mm high Compafoam.

 

Yes

@JohnMo thanks for this - am still a bit confused with the makeup.. Is it like the below (tried to show it from a few angles). So build a tinber frame around the aperture, then fill between studs with compafoam with levels as you mentioned?

 

[JohnMo]

Have done hopefully a clearer sketch

[SBMS]

18 minutes ago, JohnMo said:

Have done hopefully a clearer sketch

Thanks - and in between the studs of the timber upstands goes compafoam (my section view 1) or could I infill with the PIR? 

[JohnMo]

41 minutes ago, SBMS said:

Thanks - and in between the studs of the timber upstands goes compafoam (my section view 1) or could I infill with the PIR? 

No

Compafoam goes above the wooden frame would have similar dimensions to the Compafoam upstand. The opening shown on my last sketch is the aperture for your skylight. So is showing the left and right of the aperture. You would line the aperture with 25mm PIR then plasterboard or what ever you want.

So nothing like your drawings.

[SBMS]

I get you. 
 

Could I make the upstand out of two layers of 150mm compafoam instead of a timber frame?