On Sat, 31 Jan 2004 19:53:49 +0000, The Natural Philosopher
wrote:



Only if you want a warm loft space. Otherwise why not use the ceiling as
the iinsulatin barrier. Less area to cover with expensive celotex. AND
you can use cheaper rockwool

Just to save a bit of trouble really, the loft has a modicum of
fiberglass insulation and is part boarded, it just saves removing the
boards.


This is what I thought, a sort of dry lined area on the sloping part
of the ceiling?


Thats true for teh sloping bits, bu don' feel you have to carry on on
teh slope.

I meant only the sloping bit exposed in the bedroom.

My house is very similar - sloping ceilings and a flat bit in the middle.

What the BCO came up with was celotex up the slopes, with an air gap
above to allow eaves ventialtion to circulate, and then rockwool over
foil backed plaster board on the flat parts of the ceiling.

Lost me again there, my roof has a soffit (and a fascia to hold the
gutter) and no visible ventilation in either.


I had wanted to avoid removing the lath and plaster, I had hoped to
"glue" an insulating board to the old ceiling and feather it in at the
edges.



Do you mean inside the room?

Yes

You could do that with celotex.. Otherwise
pushing slabs down the top of the slopes is fairly acceptable, if hard
to get perfect fits.

There just does not seem to be the space to do this, I will go up and
look again tomorrow.

Again, I queston teh need to do it this way rather tha insulate the flat
portion of the ceilings.

Again it avoids disturbing the boars forming the loft floor, not to
mention moving the junk.


At this stage the cost outweighs the benefit as my fuel costs are low.
I can still not quite fathom why a ventilation path, to prevent
condensate settling on the roofing timbers, cannot be formed by
fitting the celotex in between the rafters as described but allowing
an internal gap at the bottom and top. a convection current would be
set up from the warm apex down the cold roof (under the tile+felt and
between these and the celotex) and then vented pack at the eaves and
over the ceiling??



I cant see where the gap at the bottom is coming from.

I would leave the gap where the rafter meets the joist and floor
boards, for the outside vent Peter gave a gap of 5mm, I assumed the
same internal gap would work.

You need eacves vents of some sort, otherwise there is no way for air to
get to the base, unless you are going to let cold air run down the front
of the celotex, which meanas its not insulating the room anymore.

It is what I meant and I know it would be lossy, I considered it a
possible compromise as the air changes between the underside of the
felt and the celotex would be small.

AJH