Yorkshireman

Morning folks, We're looking to convert a 40ft x 16ft double skin brick garage with no internal pillars into living accomodation via PP. The current flat roof is being replaced with a 150mm PIR warm roof EPDM covered green/living roof and the span is 4.8mtr. Joist size, we are considering 220 x 75mm spaced at 400mm ctc intervals with a rise of 4inches from back to front for drainage. Would the joists be substantial enough, or would you suggest 2 x 220 x 50mm joists bolted together every 3ft for greater structural integrity? Any help and advice on this self-conversion would be appreciated, thanks folks.

I've looked into the EPS beads which I think could be inserted in the cavity via the open top once the roof comes off for full replacement and full planning permission will be submitted as we intend to build an additional room joining the main bungalow to the 'annexe'. We had considered EWI but due to the building being built on the actual boundary we opted against this due to additional factors related to the neighbour. We are looking into the internal condensation/ventilation risk with all windows having maximum trickle vent allowances for their sizes and the same with the french doors but will also look in to having the ICRA done as soon as we can, so thanks for that. The bathroom/en-suite will have an external through wall [between joists] extraction system and the same for the hob, but we are aiming to achieve the best possible U value we can.

It's double skin brick with a cavity [4inch?]

Hi, We have a 40ft x 16 ft double skinned garage we are looking to convert in to living accomodation. We're aware we need 90/100mm floor insulation and 150mm warm roof insulation but we don't know if there is any form of cavity insulation. What, if any recommendations, would you make regarding internal wall insulation? Cheers for your help.