On Sat, 06 Sep 2008 23:57:42 +0100, John Rumm
wrote:

A "normal" block wall is about 4" (10cm) plus at least half inch of
plaster either side. Yours may be a thinner block I suppose.

There's about 10mm on the side I have "investigated", so possibly you
are right: about half an inch each side. I shall have to measure the
width across the door frame again.

I did wonder about chasing the external wall. This is thicker but of
course some of it's depth is cavity. Are both sides of a cavity wall
load bearing? I would think the outside bears the weight of all the
bricks above and that the inside bears the weight of the joists? I
presume joists do not cross the cavity? Wouldn't that defeat the point
of the cavity?

Depending on how the pipe runs that may or may not matter. (in fact
even if the pipe has a little water left in it, it does not usually matter.

In which case a lockshield with drain would be the easiest way to go.
Would it matter there was only a drain on one side of the radiator
though? Would I need a drain on the TRV side too?

In the past, I have tee'd off, into a service valve, then straight
through the wall into the gully the other side

I had not realised you were taking the tee outside; what a good idea
(where possible).

Regarding chasing for electrics, which is what the thread was about
before I hijacked it, when fixing oval conduit does it matter if you
use solvent adhesive? I use the cheap Tool station glue screws. I
wasn't sure if I had to use the solvent free version or whether the
solvent version would damage the plastic? I think the solvent version
sets faster so would be preferable if it is compatible with the
conduit plastic?

Thanks,
Stephen.