On Tue, 30 Sep 2003 20:09:40 +0100, "L Reid"
wrote:



Thanks Andy. Did you replace existing insulation with it, and if so, how did
it perform thermally compared to the 'old stuff'? Think I'll make a point of
cutting it up outside, weather allowing. Did you just lay it flat, or did
you use tape to hold it in place?

Cheers!

Leigh



Leigh

I had rather different projects to you which was to insulate the roof
and walls of a garage with a pitched roof and the same for a cabin.

I looked at your original post and can't quite visualise what you have
and were the insulation would go.

Also, it is important to be careful that there is appropriate
ventilation of the timbers with whatever you do. You don't want to
endup with a situation where timber is boxed in with insulation and a
vapour barrier without being ventilated.

I suppose the closest situation I had to yours was the garage roof, so
I'll describe what I did there. This roof is pitched, has
conventional roof trusses, felt and then battens and tiles. For the
environment, which is a workshop/garage I wanted to have reasonably
good insulation to allow that the space could be heated to a
comfortable temperature (16-18) for working at reasonable cost.
I did the calculations and 50mm Celotex would give respectable results
for what I wanted. If you want to do something to achieve Building
Regulations levels for a new property, it needs to be rather thicker.
Details are on Celotex web site and the requirement for Scotland is
tighter than for the area occupied by the heathens to th south.

The Celotex web site shows a couple of options. One is to place some
of the material between the rafters and some on top (i.e. furthest
from the tiles) using two thinner sheets. The other is to put a
single sheet over the rafters. This is what I did because I didn't
mind losing 50mm of space. Where you use 70mm for example, then you
may think it's too much lost and want to do the two sheet arrangement.
There are dimension reasons as well. My rafters have a depth of
about 75mm so I could have put 50mm material between them and still
have had 25mm behind for ventilation. Had I wanted to use 70mm, it
wouldn't have been enough.

Anyway, my method of fixing was to cut the pieces and attach them to
the rafters using 70mm dry wall screws and 25mm penny washers with
small holes so that the screw would not go through the foam board.
I then taped over the joints to stop air flow from front to back.
The space behind next to the felt is ventilated by having a soffit
vent between each pair of rafters and making sure that the space
behind he Celotex next to the felt is open to that.

I don't think that using tape as a fixing medium is that good unless
you use thick duct tape - I could see the adhesive deteriorating in
hot weather. If you are going between joists or in any case , the
main purpose of tape is to seal and prevent air leakage through.


..andy

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