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There will be a minimum of 50mm air gap between the insulation and the OBS boards. Venting strip will be added to soffit. Not sure if Abutment Vent is a necessity so would be grateful to hear views on this also (is there a decent kit on the market) ?

Hi, I'm having a cold flat roof installed. 100mm PIR board to be inserted between the joists and some form of insulation with plasterboard will need to be fitted to the ceiling. I understand a vapour barrier needs to be fitted between bottom of joists (where the 100mm is inserted) and the...

Perhaps send a screenshot of a worked formula and I should be able to work it out. If you could annotate, that would be helpful.

The original passed off drawings had a 'lean to' roof with a vaulted ceiling. Because it seems too high (I have neighbour and the extension is built close to the boundary) I'm looking at a flat roof. The inspector seems ok with a flat roof (in principle). Hence, I'm working to the same joist...

I looked up EC5 document, the formula looks complicated - I don't have a structural engineer, is there a simple way to work this out? (perhaps an online tool)? Alternatively, I can oversize the beam and then notch. Thanks

That would be the easier way, but the builiding inspector may raise an eybrow or two ;)- Is it documented in building regs?

That looks perfect :) Thank you I can drill into the rsj and put those bolts in. Looks about 2m appart, if the joists are 450mm centres.

Sorry, terminology mixup, the flange is 100mm deep.

Regarding masonry hangers, I've found a 50mm x225mm which may work, does it get bolted on the top of the steel (as part of the steel has no bricks above it) ? https://www.travisperkins.co.uk/joist-hangers/simpson-strong-tie-masonry-supported-joist-hanger-225-mm/p/9000218842 The steel is a 203 x...

The web is 100mm deep. Part of the rsj has bricks on top (existing property), whilst the other section has nothing on top. How will I make the fixings ?

Hi, I'm building an extension with a flat roof and I have a question about the joists. Its a cold roof system. The walls are coming out on the back of the house and the builder put in a steel. Normally the joists fit into the web of the steel and the other side rests on a wall plate. The...

Hi, I'm installing a flat roof on a single storey extension. I'm installing the first rafter and unsure how far it should be from the adjacent wall that runs parallel. Is there a set distance or does butt up to the internal wall ? I will be adding insulation in between the rafters so not sure if...

Hi, I'm working on a single storey extension which has a 3600mm bifold door to be fitted in a 100mm cavity wall. The weight on the lintel will be: 1 course block (up to wall plate) 50mm x 150mm joists boarded and felted. The one side of joists will be on hangers fixed to the original build...

The OP here with another update. The builder convinced me to make the ceiling 2.6 and thus have no offset, but instead place the joists inside the web of 178 steel. But he did not use a straight edge to line up the end of the joists and as you may have guessed, he cut 3 of them short! These 3...

Hi, Thanks for the help - The reason why I wanted the 178 x 100 a little lower is because I wish the Existing ceiling height to be dropped from 2.6m to 2.5m. The 178 fits into a larger steel 203 x 203, once the 178 is tropped then so can the 203. On the new parts of the single storey extension...

Hi, I'm having a 178 x 102 rsj (160 x 45 internal web) fitted to support an existing wall and want the existing joists (50 x 150mm) to be attached slightly higher than the rsj. The usual designs I've seen are where the joists rest on the rsj or the joists fit inside the rsj (sometimes with a...

Hi, I'm having built single storey extension with a bifold leading to the patio. It will have a flat roof, so not much weight. The opening is 3.6m brick to brick, thermalite inside and concrete block outside, 100mm cavity. I assume this is too wide for a pre-stressed lintel so considering a...

Ahh, so I can use a lintel and not a padstone - something like this I suppose to be extra secure, rather than a lintel, why not add a 900mm long steel (178x102x19). Then I could bolt the 203 onto it ?

I can't find a suitable padstone size - I can get hold of a 600 long x 100 wide x 140 deep (This reduces bearing to 1.2 N/mm2), will this work or does it need to be 225mm deep also? About the 0.4h check- there are no openings in the wall and wondering if this check is needed? Applogies, but...

Originally on the inside there was a brick column, this is how the calcs were created. The Architect then removed it and did not update the padstone size. Nor by the looks of it the calcs. I have asked the architect several times about this but he does not respond. :(