Timber frame internal vapour layer up wall onto warm roof?

[hotnuts21]

We have a Timber frame extension, part of it is one story with a warm flat roof, and part is a second story bedroom. Below this is one big kitchen diner. I've uploaded two photos, one is a wider view, showing the walls, the warm roof with the skylight on the left of a steel (supporting the upper wall) and the ceiling/floor of the second story.

The question I have is that the walls are going to have sheep's wool in them, so I'm going to put a low-e or VCL membrane over the walls, but I'm not sure how/where to finish it, should I take it up and across the warm roof, past the steel and attach it all the way along the wooden joist next to the beam. Or do I just end it attached to top plate of the wall? Although the warm roof has its own vapor barrier, I cant see any harm in putting the membrane across the roof to add an extra layer of protection to the warm roof and stopping any moisture going up and over the wall into the cavity.

For clarity, in front of the  membrane there will be a 25mm service void, if anyone can recommend a good low-e/reflective membrane that's used as low emissivity void. Can help increase u value
Note,
-  the gap above the TF wall will be filled with 140mm Celotex and foamed to create a seal from wall up to warm roof.
- The skylight has its own VCL, so will lap up and join to that, not just go across the gap 😉

[Nickfromwales]

If you've got the headroom, I'd do a continuous layer of 30mm (or more) of PIR across all the ceiling as well, and tape the joints with foil tape, as your VCL. Flat roofs are hideously cold, so focus on that well. Stopping the repeat cold bridging should be a priority.

 

Use Marmox boards to line the opening of the skylight, not plasterboard, as those upstands will also be a huge cold bridge. You can plaster straight on to the Marmox btw.  

 

Also, where do you think you'll get all the sheep wool from in Aberystwyth? LOL.

[hotnuts21]

8 minutes ago, Nickfromwales said:

Also, where do you think you'll get all the sheep wool from in Aberystwyth?

I know a man, there's plenty round here 😄    Most likely taking a van to Celtic Sustainables in Cardigan to collect thermafleece amongst a lot of the other bits I need.

I did my bathroom with marmox so thats a good shout, might have some spare, top tip!!  The top half of that skylight upstand is insulated on the other side of the timber to 150mm.

Unfortunately I do not have the headroom, its a very tight 2100 with no floor covering, and I need to put two layers of PB over the beam.  The flat roof is a warm roof with 150mm of celotex above the joists, so im not worried about that bit being cold, my main cold bridge issue is the great big box section of metal above the doors and windows. Although I have 70mm of woodfibre board on the outside of the timber frame.

Edited August 19 by hotnuts21

[Nickfromwales]

Just now, hotnuts21 said:

and I need to put two layers of PB over the beam

What wingnut told you this??

 

[hotnuts21]

😄  Need to fireproof the steel, two sheets of pink plasterboard apparently to protect the steel from fire.

Because this adds nearly 24mm under the beam, I either need to double board the whole ceiling or put 12mm packers under the beams to ensure its on continuous ceiling if that makes sense.

[Nickfromwales]

1 hour ago, hotnuts21 said:

😄  Need to fireproof the steel, two sheets of pink plasterboard apparently to protect the steel from fire.

Because this adds nearly 24mm under the beam, I either need to double board the whole ceiling or put 12mm packers under the beams to ensure its on continuous ceiling if that makes sense.

Ok.

 

No, it does not need 2 x pink FR plasterboard. That's your BCO taking crack, after a week on the Jack & Jill's.

 

The steel requires 30 mins fire protection, and that is adequately provided by 1x 12.5mm regular PB with skim coat applied.

 

Go back and ask your BCO to show you the written regs and where this requirement is born from, and watch them shrink like my hotnuts when I jumped in the pool in the resort in Antalya last year.

 

"When two becooooooome one"