Loft conversion - Ridge Beam

11 Feb 2009
Reaction score
United Kingdom
I have other threads running regarding a predicament over Building Control plans - and their lack of suitability for the job.

I've tried to keep it short, and with the minimum qty of steels ;) sic

Plans are approved and ready, but I would like to raise the ceiling joists in the flat roof, on plan they bear into the webbing of the steel support beam just below the ridge, with a warm roof, as per 'd' on the diagram, I would get better ceiling height if arrangement 'c' was used, but I am concerned the BC officer would'nt allow such a change without new structural calcs being required.
If 'c' was accepted, would I run the 115mm Cellotex Temp Check Deck over the steel beam (plans require this on top of the ceiling joists) to satisfy insulation requirements. (to be under highest point on the roof - for planning purposes - is that the ridge beam or the ridge tiles)
If 'c' wasn't accepted, and I had to accept the beam in position 'd' could I bolt timbers to the steel beam, fix joists hangers and hang joists - higher than the steel.

Sponsored Links
They won't need new structural calcs. None of the member spans or loads will change so the calcs will still be OK.
That will raise the (approved?) dormer roof height and will also alter the ridge height and appearance which may not be acceptable to planning.
So moving the ridge up (200mm approx) and to the right (100mm) to option 'c doesn't effect calcs :)

The 'approved' dormer roof height is incorrect:
- an adjacent completed 'approved' development on an identical property, and my measurements indicate I can go up to the ridge and be within 50cu mt.

But with this arrangement I'm now presented with the problem of insulation and venting of condensation, (a warm roof steals 115mm of height - which would be good to avoid doing), I have read somewhere - if the voids between rafters are filled completely with insulation - there is no room for condensation - I assume voids are to trap air which is an excellent insulator - joists are 175mm thick - surely the underside of 175mm of insulation would remove the likely hood of any thermal bridging, or am I barking - up the wrong tree.
Sponsored Links
Out of interested for option C - how would you install this and keep the rafters in place? I can see how the option D steel would be install with the current roof in place. However option C looks like you’d need to take down both sides of the roof, then rebuild the front/rafter side? Therefore Surely Option C costs considerably more to achieve
It was all striped back to just rafters, and part of that pitched Roof incuded a small gable was retained, but the rest of the pitched roof was rebuilt,
I recently completed another loft and the whole of the pitched roof was replaced, with new treated (and straight) C24 timbers, bit more money, but its a roof, very important.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local