Steel goal post clearance to top of rafters

[nghakrmyk]

Hi there - I’m looking for some guidance on an extension that is ongoing. There has been a deviation from the original plans and I’m unsure if the builder’s / architect’s solution is going to address the issue (or if I’m asking the right questions). 

I am extending a Victorian semi with an apex-type wraparound - a steel goal post is to support the existing rear wall. In the drawings / structural calcs, the goal post beam was not cranked and it was intended the top of the beam would sit below the bottom of the rafters. Cold bridging at the top of the steel would have been managed, as I understand, as we’re using a ventilated warm roof. However the builders have now put the steels in, added the rafters and the top corner of the steel beam (where it meets the steel column) is 10mm below the top of the rafters. I had to raise it with the builders (not sure why it wasn’t spotted) and we have now been trying to find a solution. We are also limited in the extent to which we can add height to the roof due to existing 1st floor windows - this gap (ie from the top of the rafter to lowest window cill) is currently c.178mm. Lastly, the roof is setup at a 16 degree pitch. Not much flex as the builders don’t want us to go lower as we’re putting normal veluxes in.

 

A picture is attached which shows the steel corner pinch point.

 

The architect’s suggestion was to add a batten (eg 38mm high) to the rafters to allow for c20mm PIR over the pinch point and a 28mm air gap to the vapour membrane. Then counter battens + battens for slates. This leaves c.80mm to the window cill for flashing - TBC if we could possibly use thinner battens to make it 90mm. I’m concerned 20mm PIR is not much of a solution and that 28mm is not sufficient, but absent changing the beam to a cranked beam so it sits below the rafters, there don’t seem to have many options?

 

Any thoughts would be much appreciated. 

[nod]

The easy option would be to pull that insulation out a wrap and tape the steel with multi foil 

[Russell griffiths]

I would get two cans of illbruck fm330, squirt it in to every little gap and fill it proud of the rafters, then when it’s gone of cut it flush. 

[saveasteading]

Jam all the gaps with PIR and squeeze in foam, as above. 20mm will make a big difference, and the extra heat loss will be a few £ a year.

10mm tolerances are acceptable in house specifications... prob no blame.