"Christian McArdle" wrote in message
t...
I'd been wondering how I would hold the insulation between the rafters.
It
strikes me that if I get another lot of kingspan/celotex of about 20mm
thickness (if the cost doesnt prove prohibitive), then I can install
that
over the top of the rafters (well, on the underside - ie on the
loft-space
side)

Indeed. Doing so is strongly recommended, and verging on the compulsory
for
new build/loft conversions. Keep the lower layer of insulation at or below
the thickness up the upper layer to avoid condensation issues. I would put
50mm between and 50mm underneath. Ensure that the top layer is foil
covered
to give a reflective surface for radiated heat from the tiles (you'll
probably find that the boards come fully foiled anyway).

Note that you should cover the entire lot in 12.5mm plasterboard. This not
only provides an aesthetically pleased surface, but has other benefits,
such
as making the space lighter and providing much needed fire protection to
the
insulation.

snip

Thanks, Christian. After reading the Kingspan K7 product pdf it seems that
the 12.5mm plasterboard can be substituted by Thermawall TW56 zero ODB
boards, which would solve the vapour barrier issues and fire protection
requirements & provide me with that extra insulation in one go.

Loads of diagrams on that pdf, and that's just confirmed all that you've
said.

Of course I haven't got around to pricing this lot up yet, so plans may well
change!!

Now, if I can just convince my wife that this is hell of a lot better
solution than one of those bloody silly portable air conditioners that she
wants at the moment, then I'm onto a winner all round.

--
Richard Sampson

email me at
richard at olifant d-ot co do-t uk