"Tim S" wrote in message
news
Hi

[Preamble, Questions at end]

We're going to move in with my Dad next year - we're redoing bits of the
dormer loft conversion of his bungalow.

Now, upon inspection, the current insulation in the roof voids is manky
glass wool - yuk. Broken, falling away and very dusty.

I hate glass wool, partly as I a) have to get around the voids to fix some
electrics + install networking, and b) I'm going to use the voids as
supplimentary storage space for light items. I find it unpleasant and
a skin irritant. I also don't want the fibers going anywhere near my
baby daughter. Also, it's too knackered to be doing much good.

I also want to insulate the roof, not the floor as I want the voids to run
warm to protect the stuff I'm storing.

So I thought about using either Celotex/Kingspan to 50mm, leaving 50mm
breathing space in the rafters under the tiles - or rockwool slabs.

Rockwool in slab form is possibly less disgusting than glass wool
- at least once fitted (anyone care to comment?) but I believe from
reading around I'll get better insulation with Celotex or it's like at
50mm.

[Questions]

a) What's celotex like to cut - use a knife or a saw?

b) In a fire, does it pose any risk of giving off noxious fumes?

c) Does having an endothermic but still combustible material like
celotex packed around electric cables bother you?

Thanking you kindly :-)

Timbo

Have from the inside: plasterboard and a vapour barrier under. between the
vapour barrier and the rafters have a layer of Celotex. Between the rafter
have Celotex. Between the Celotex and the tiles/felt have a 25mm
ventilation gap. This arrangement must continue down to the eves, so air can
enter the ventilation gap, but not into the loft space.

Have the internal plaster, VB and insulation form a flat section at the top
of the loft, leaving a triangular section inside the loft at the apex.
Then, if two gable walls, install a vent in each gable at each end of the
triangular section. Then air from the eaves rises up the between the
rafters, enters the triangular section out via the ends through the gable
vents. If no gable ends then have ridge tile vents.

Have the loft "sealed" from air ingress via the ventilation. A highly
insulated loft should result, without any fear of condensation occurring
anywhere.