The Natural Philosopher wrote:
wrote:
On 8 Jan, 14:44, (Andrew Gabriel) wrote:
In article ,
� � � � The Natural Philosopher writes:



Thinking more about this, if you have the space, Id be tempted to try
and mount the stoff OFF the rafters altogether - to make a 'tent' of
insulation underneath, because I am concerned that condensation above
the insulation layer may in time affect the rafters: when you take a
I did this with a lean-to construction roof (over my bathroom).
I fixed the underside of the rafters with pressure treated roofing
battens at right angles, and then fixed the Kingspan to those (or in
most cases through those into the rafters. I provided a vent in the
gable
end above the Kingspan, and the roofing felt looped down enough to
provide further ventilation. The rafters showed some signs of rot which
had been repaired (before my time, probably when slates were replaced),
and I wanted to make sure they stayed very well ventilated.
My worry was not condensation, but any water ingress through the roof
which I would likely not notice one the Kingspan was in place, and
without ventilation might lead to serious rotting of the rafters.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Dear all, thanks for your replies. I am the posters other half. The
loft is actually an attic room that had a low ceiling with no
insulation behind it and a couple of plaster board dividers behind
which the tiles have always been exposed (not weight bearing walls or
anyhting just boards) we want to use the room as a bedroom and
insulate it properly, as it was too cold in winter and too hot in
summer. It has an original window in the side gable. So we have taken
the ceiling down (100 years of muck) so now we have a roof that needs
some insulation before we can plaster and redecorate so it is not
quite a conversion just a bit of updating. With that in mind. would
you give the same advice?,
thanks for your help!


Basically yes. All becomes clear. If you have the space, insulate under,
if not insulate between and in all cases make airtight and tape it all
up. Leave at least some gap above.

Be careful at the eaves..You MAY get water dripping off the top edge of
the celotex here. put some kind of plastic sheet to let it come out at
the eaves, not down into the walls.

My instinct would be to tape plastic to the underside of the insulation
and let it hang over the edges of the rafter bearer plates, before re
boarding the thing.







50mm rockwool slabs between the rafters makes a huge difference, and
Celotex even more so. Either would leave you with the recommended gap,
but the rockwool packs you can sling in the back of a car rather than
having to arrange delivery, and they're a fair bit cheaper.
I found the key to a tight fit was to slightly overcut the width, then
wedge one end in and run a hand saw flat against the side of the joist,
cutting the insulation at the same time. That way any variation in width
is accommodated.