wall chasing

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?

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?

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.

potentially... the inner leaf will carry the joists, and quite possibly the roof load as well.

In modern places the joists do not piece either leaf of the wall - they terminate in joist hangers that are either bolted to, or more commonly, built into a mortar line the wall.

One side is fine. That will let you drain the pipe and the rad. You can then remove the rad a drain the other leg of pipe if you want straight from the TRV.

Not an idea I take credit for - remember seeing someone doing it on TV many years ago (may have been a tomorrow's world special on houses of the future), but it works well. Just a quick turn with a screw driver lets you drain down without any mess and no titting about with hose pipes or leaky drain valves etc.

This is just for getting the conduit to stay put in the chase I presume? Yup any glue is fine, as would be a couple of large head clout nails (for the avoidance of doubt, knocked in beside the conduit with the head holding it it place - not driven through it! ;-))