On 14/03/16 23:51, Dave wrote:
Hi

I'm planning to insulate my loft with insulating board for occasional use as
an office.

Need some help on use of foil; backed insulation products. Looking at
Celotex website they recommend a 2" gap between old fashioned non permeable
roofing felt and the Celotex fixed in between rafters, to allow ventilation.
In my case with only 3" rafters means that I can only use the 25 mm
insulation board. Does anyone have experience of using a smaller gap say 1"
to allow thicker insulation between rafters and does this lead to
condensation problems.

Second I understand the foil on Celotex acts as both an impermeable membrane
avoiding condensation, and a thermal barrier by reducing radiation loss.

That is really almost irrelevant.

Yui can line with foil backed pboard if you really care.


Does this radiation loss reduction work when for example 2 celotex boards
are mounted on top of each other or is an air gap required for the foil to
work effectively.This to my mind also would give extra conductive insulation
if the air gap is sealed.


Forget the radaiation. Its am almost irrelevant issue.

Does anyone have experience on using multi layer foil insulation, it seems
to give only a small thickness but expensive, but main thing does it work.
the manufacturers seem to claim better insulation performance than board
products but only give very overall figures in combination with celotex
boards and not for foil used alone.


If you put celotex between and then celotex over it will be fabulous.

However even an inch is WAY better than nothing. and the key is toi
totally get rid of draughts from e.g. eave and ridge vents and let that
lot circulate above the 'tex.

so use decorators caulk, extending foam and the foil tape to really
eliminate all the draughts and the result will be well good enough for
occasional use even with an inch.

Id p'board over fill and sand and then use lining paper and cheap
emulsion for a basic 'room' finish



Regards Dave

Please note only respond by newsgroup as email not working.




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