Just starting to realise how complicated this whole energy flow analysis is.
Unfortunately, our outside wall of the upstairs bedroom is sat on top of a steel I-beam, which in turn rests on the patio doors of the kitchen.
The outside of the I-Beam is filled with bricks, so definitely a cold spot.
You can see the white area labelled 'A' in the following image, which is the area of concern:
Obviously this is a cold spot with a potential for internal condensation to form. I don't see any benefit to cover in a water proof membrane as water would just collect on this on the inside of the steel.
If we fill the cavity with rockwool, we're concerned it will absorb this moisture from the I-beam surface, and get damp. But at the same time we want to heat up the area.
Currently we've decided the best course of action is to consider this cavity as outside the building envelope, and thus we would insulate above and to the left of the cavity with rockwool between the joists, and just under the top lip of the I-beam, attached to the underside of the floorboard.
Any suggestions on the best course of action are welcomed
Thanks in advance