insulation

im doing an insulation job in my attic (cold roof). 110mm celotex between the rafters and 40 mm beneath. the rafters are very uneven so before plasterboarding ive take the opportunity to straighten them out with battons and spacers so the final plasterboard layer will be flat. however this means that in places the beneath the rafters layer of plasterboard will not be up against the plasterboard - there will be a small air gap. ive done what seems practical to eliminate any air ingress on the layer of insulation between the rafters (still allowing for 50mm air gap) - but will i be negating some of my insulation efforts to allow this air gap between the plasterboard and beneath the rafters layer of insulation - ie possibility of cold air getting in between the insulation

thanks

Reply to
mcmook
Loading thread data ...

Seal up all gaps..its not air thats te problem, its draughts.

Reply to
The Natural Philosopher

That is very good advice actually. People think that one gap and all the warm air will rush through it like water through a funnel. Fortunately the PB usually takes care of the draughts.

Reply to
Stuart Noble

You need to leave a 50mm air gap between roof felt and insulation and using

Reply to
ALex

Not if the felt is a breathable membrane, which I believe is the norm these days

Reply to
Stuart Noble

I do have a 50mm airgap. its an old building my rafters are 7". my question was having introduced a draught on the inside (aka ventilation) will i negate my insulation efforts it there are gaps between the layer of insulation between and over the rafters (caused by uneven rafters) ie the faces of the boards don't meet. i've done all that is practical to air seal the between the rafters layer of insulation, carful cutting, friction fit and using sealant. i was just wondering how airtight "airtight" really means... its always a balance between whats acheivable and whats recommended with refurbishment ...

Reply to
mcmook

Any *draught* will reduce insulation effectiveness.

That's not quite the same as no gaps tho.

Reply to
The Natural Philosopher

If the unevenness is a problem then use expandable foam but buy a gun it is so controllable you can get one on ebay very cheap,and the cans are only £5.00 approx and in the gun they last a long time,and will seal any gaps.

Been in the building game nearley 40 years and have never seen 7" roofing joists before,so that is why i replied to your orginal post the way i did. Must be quite a rarity,out of interest how old is the building.

Reply to
ALex

On Mon, 09 Jul 2007 07:12:10 -0000, a particular chimpanzee, snipped-for-privacy@googlemail.com randomly hit the keyboard and produced:

There should be no gaps around the edges of the boards. They should be cut to fit snugly between the rafters. Any air between the layers of insulation will then not be subject to convection, assuming you're talking about small gaps (

Reply to
Hugo Nebula

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.