How to build insulated upstand

[pudding]

Hey all,

 

I've ordered a 3g roof light for our 'flat' roof extension, from here - https://www.customrooflights.co.uk/product/flat-rooflight-1000x2000/

 

Here's the installation section drawing - 

 

 

Our flat roof will also have 150mm PIR on top of the timber joists. I want to try and replace the as drawn 70mm wide timber upstand with something a bit more thermally efficient. I've thought about rather than solid timber, perhaps a 50mm timber frame, infilled with insulation, then another 20mm PIR outside it. Any ideas or tips?

 

Not sure about replacing the supplied rebated timber that the window sits directly onto either. I did consider perhaps as insulated bloc like compacfoam and then cutting it myself to form the rebate, but could be very pricey and not really worth it for the small amount of area? Has anyone tried cutting compacfoam? Seems like from here - https://www.greenbuildingstore.co.uk/product/compacfoam-200/ it'll be £30/m for 75mm blocks, and i'll prob need 7, so a couple hundred quid for the nice thermally broken rebated upstand. Maybe not as pricey as i thought.

 

Cheers.

Edited May 31, 2020 by pudding

[Dreadnaught]

I am designing the upstands for my rooflights now too. Mine are from a different company but are also triple glazed and are passive-house certified. I also have a PIR roof of similar thickness.

 

This is the upstand detail that I am following but my timber-frame designer and architect are converting it into something buildable offsite by my timber-frame manufacturer:

 

[pudding]

Ah, you've gone for roofmaker, i've got their installation drawing right here!

 

So what insulation is the dark grey, EPS? And why not just one box section, rather than the box and then what looks like a free standing piece of timber next to the plasterboard? How is that piece of timber fixed, what to? It looks like it's the edge of that single piece of timber, then the edge of the insulated box that at supporting the supplied insulated rebate. Is that right?  

[PeterW]

18 minutes ago, pudding said:

Not sure about replacing the supplied rebated timber that the window sits directly onto either. I did consider perhaps as insulated bloc like compacfoam and then cutting it myself to form the rebate, but could be very pricey and not really worth it for the small amount of area?

That is a frameless triple glazed unit you have ordered so to get the guarantee you’re going to have to follow the MIs which is timber frame to set the glass into. You will have to ask them if foam is acceptable and also how will you bond your roof covering up the sides of the up stand with foam ..?? 

[Dreadnaught]

5 minutes ago, pudding said:

So what insulation is the dark grey, EPS?

 

The type of insulation is not specified but I had assumed it was PIR. As I understand it, the inner leaf of insulation is intended to be continuous with the insulation inside the rooflight frame, and forms a thermal break. The weight of the rooflight is supposed by a combination of the exterior box frame and the interior single free-standing piece. It took me quite some puzzling and chat with the rooflight company before I worked it out.

 

In reality, I don't think we will follow these details too closely. Instead we will make something simpler but still much thicker than the typical upstand (including the one typically deployed by my timber-frame designer).

 

In my case I have nine rooflights, and almost each one will require a different upstand. Quite a complex design job and probably the only part of the overall frame design that really does require 3D.

[mvincentd]

...in my broadly similar scenario my bco saw my upstand from inside when skylight was fitted but no plasterboard was on, and he required me to to add a vcl behind the plasterboard.

 

[pudding]

So this is the sketch I've come up with:-

 

 

Thanks for the replies so far. I'd not really thought about any warranty for the rooflight and would hope a different rebated seat of the same dimensions wouldn't affect the actual rooflight and warranty, but I'm sure they would use it to wriggle out of any claim. I hadnt thought about adhering the roof covering, which at the mo is going to be EPDM to the compacfoam. Anybody any ideas about this and if it could/would work? I'll do some digging for that one. If i go down that route and the epdm wont stick to compacfoam, I could alter the sketch I've done and continue the 20mm PIR up to replace the outer 20mm of the compacfoam and make the rebated section slimmer down to 50mm.

 

Hopefully the VCL blue line I've drawn would satisfy any BCO and is in the right place.

 

[Mr Punter]

I have not seen the whole design.

 

How is the fall achieved?  I cannot see any firrings.

 

Often the adhered coverings need OSB to be stuck onto and there is none shown.  I am not sure you could fix EPDM to Celotex.  I sometime see the tissue faced insulation specified but it is very costly.

 

I would make the upstand out of 63mm x 38mm treated cls with 9mm osb sheathing nailed to the outside, insulated with 50mm Celotex.  Be much stronger than the tile batten and better insulated.

[pudding]

Fall achieved using tapered Kingspan boards. They are paper covered rather than foil so can be adhered to. I haven't yet had a cost from the builders yet but will need to chase them up before they order anything.

 

My initial proposal was for firrings and OSB on the top of standard foil PIR boards, especially as it'll be a green wildflower roof and we'll be walking up there every now and then to trim the plants, so with OSB on top I felt it would be a bit stronger, as I'm not too sure about walking on paper covered PIR boards directly. The builders are keen on tapered boards as everything in the roof structure can be flat and they simply plonk the Kingspan on top. It avoids the need for any extra long fixings for that top layer of OSB, which could need to 220mm+ so would be a lot quicker I guess saving some money there.

 

Thanks for your suggested design. I've sketched it out, so is it something like this, with the supplied rebated timber sat on top:-

 

 

 

 

 

 

 

Edited June 2, 2020 by pudding

[scottishjohn]

On 31/05/2020 at 20:24, pudding said:

 

 

 

 

 EPDM  would not be my choice i would use GRP and then you know it will never leak 

EPDM ,looks like a tricky layup with lots of joints  

grp there will be NO joints at all as you would lay it up around all these complicated sky lights  in one go 

 

[Pocster]

I am the upstand master ! ( That doesn’t mean I know anything mind ) .

For my walk on glazing ( stop laughing ) I had some firrings made to generate the fall . To insulate the upstand I’ll line it internally with aerogel.

[Nevoriana]

Only one of these configurations addresses the issue of the VCL, in particular where it should run around the kerb/up-stand area.  Is there a readily achievable solution to the conflicting requirements of vapour control and structural strength and stability?

[Simplysimon]

On 14/07/2020 at 08:26, Nevoriana said:

Only one of these configurations addresses the issue of the VCL, in particular where it should run around the kerb/up-stand area.  Is there a readily achievable solution to the conflicting requirements of vapour control and structural strength and stability?

propassive osb then p/board?