Air space above insulation - or not?

[The Nomad]

Just taken the T&G ceiling down in the kitchen (made of Cedar and stained mid/dark brown - don't ask like it when I moved in) and now know why it is so @#%$ing cold in the winter and hot in the summer - no insulation at all.

The roof is a flat one with a slight slope to the gutter side (obviously) and room for about 170mm of rockwool. I'll put a vapour barrier up on the warm side.

The question is - do I need to ventilate the area above the insulation or can I foam the gaps around the edge of the walls where they meet the fascia boards (well actually the blocks between the rafters on the inner leaf of the wall)?

Not a job for now (foam says not to use over 25C), and will take a while to work out where the lights, power etc. are going when I move the units around, and the wiring is pants - choc-blox every where etc. and how to hang some wall units over a work top/island where there is no wall to hang them on!

Many thanks for any answers.

[The Natural Philosopher]

If the space is vented, already at the soffts etc, then you should leave gaps. Otherwise seal up tight.

back to back on chrome poles. :-)

That's what most people do.

[The Nomad]

Not as such - just very poorly fitting fascias direct onto wall - no soffit so looks like out with the squirty stuff then.

Puts one in mind of 70's discos etc. I have been thinking how to hang from the bases (IYSWIM) as I know where the strong bits of the ceiling are (for now). Or to stand them on poles (not Poles).

Many thanks for any answers.

[Tim Watts]

The Nomad wibbled on Sunday 04 July 2010 18:43

Tricky to be definitive. It's a kitchen so there's higher than normal humidity and no matter how well you PB the ceiling with vapour barrier PB (which is recommended if you use plasterboard) some will get through.

So ventilation is prudent - but how much depends. Does any of the rest of the roof depend on air from here to ventilate it?

If not, you could probably get away with leaving an inch above the wool or none if it's not too long a length and relying on leakage at the fascia which in this case I would not seal up tight under any circumstances as that's inviting trouble.

I did a similar exercise with some bay windows that were causing condensation on the ceiling below, using 2" celotex and 2" air gap above with actual round vents added to the soffits. In this case, the bays need to provide a through path for air to ventilate the rest of the roof structure hence the full 2" gap as recommended by the building regs. I didn't have any vapour barrier PB to hand (read, I ordered the wrong stuff!) so I evo-stik'd some ali foil on to make my own.

The ceilings are considerably warmer with only 2" (about 4" equivalent of rockwool) so your 7" should make a huge difference.

I wouldn't be too pedantic about the 25C re foam unless you're working in direct sunlight on sun baked structures. I foamed the bay insulation in place in temperatures similar to now and it was fine.

HTH

Tim

[Dave Starling]

Can I suggest a slightly different approach. Put the Rockwool in. Are you holding it up with netting?? It might be easier, though more costly to wedge in 100mm celotex type insulation. Then board the entire underside with 25mm celotex. Foil tape the joins. Then fix regular plasterboard to that. I took a similar approach to a bedroom ceiling and the result has very effective, both in winter and summer.

Dave.

[The Nomad]

No soffits, only gaps are where fascia boards meet the wall (or not) - wasps have got in in the past - there are old nests there.

Wiring has been drilled through the middle of the beams ;-(

Had actually thought about plastic VB rather than foil lined PB

Worse no access - the roof is a flat one and I am NOT taking that off !