Gordo

Good point. If using 9mm osb best use a large head nail at 150mm max crs. If using a nail gun I’d suggest must closer crs best.

9mm osb is plenty adequate for structural stud walling. It is only to provide racking resistance ie diaphragm/bracing. Many people recommend ply which offered a little more moisture resistance. TBH I wouldn’t bother

Agreed. But every week or so need to heat up to near 60 to kill bacteria I’d say.

That’s encouraging. I’m sure you will make it work

Haven’t seen that trim before. Big improvement on what I saw in past. Not a fan of EPDM flat roofing due to the weakness sealing joints. You will need a ballast also to hold it down if I recall correctly. Haven’t seen this used much nowadays. Best go for PVC or GRP in my humble opinion. Particularly PVC where I have experience of giving 40 years leak free service

9mm osb is plenty adequate for structural stud walling. It is only to provide racking resistance ie diaphragm/bracing. Many people recommend ply which offered a little more moisture resistance. TBH I wouldn’t bother

You are brave. Strongly advise you find someone with first hand experience to discuss the issue they had and how to avoid them. Don’t reinvent a wheel

I’d avoid any gap as you risk thermal bypass to unconditioned voids. If you have gaps best seal to avoid thermal bypass.

I would suggest you build stud off the concrete screed, leaving a small gap between screed & walls at perimeter with DPM below wrapped up and over screed (under the sole plate of stud) this will allow a drainage trough just in case. If at all possible (I know it’s probably too muck an ask) provide a few low level drainage/vents at low level with some insect screening.

BTW the existing A frame roof structure looks a little ropey. Are your walls still plumb or have they been pushed out any? Is it a tin roof? Be very careful about adding ANY additional loading without thinking about improving the roof structure

I’ve seen this principle used in portal frame buildings where the engineer provided a ridged UB picture frame instead of bracing to brace the end bay.

The England guidance is different to NI guidance on depths of IC. ICs are not intended for people to enter where as MHs are. That’s why they have to be larger. In England they accept ICs at greater depths with a restricted opening at top to stop people trying to enter it. You have to use remote tools for clearing a blockage. a dropped MH could have rodding access to the vertical stack so you can rod down to lower level drain.

Very basic heating engineer question this. The convection currents mean cold air falls and warm air rises. Therefore if you put radiators below windows this heats the cold air at window it rises to ceiling, travels along ceiling to far wall and falls as it cools, then travels along floor towards window wall and cycle continues. window walls are always the coldest by quite a margin. So always best to place radiators under windows. If you place on far wall the drafts at floor level will be colder. Second choice is a flanking wall

38mm pre insulated plasterboard VCL on 50 x 50mm treated studs at 600mm crs. 75mm gap to walls with stainless steel brackets from studs to walls mid span. 100mm drytherm 32 semi ridged mineral wool between studs. Leaving 25mm gap to walls. This will give a U value about 0.25 roughly. The gap should be left open to vent condensation into ventilated roof void. Best to fit a horizontal intumescent cavity barrier at top of cavity (fixed to horizontal timer with 50mm gap) just in case there’s a fire this will allow for ventilation. The studs aren’t structural just need firm grounds support timber at tops fixed to US rafters. do not pump the cavity with any form of insulation period. there are indeed minimum U values requirements for renovated external walls

I have no idea what the spans are to get an idea of size but would imagine it should be adequate. The fixing of the posts needs to be ridged enough and the pad foundations needs to be large enough to resist overturning of the unbraced framework. You could also add some rigidity to the joint between posts and horizontal member to create a more ridged box. This could be with bulldog tooth connectors and bolts or better still a large metal gusset or elbow flat iron plate. Just a thought. Maybe over engineered but without an engineers input best to over engineer

A door shouldn’t really swing over steps. BC likley to accept if it is a single step flush with the door, but door should ideally swing in away from step

If plans are approved with contravention then so long as you build exactly as per approved drawings then a completion certificate can not be withheld on this issue. However plans approved with an omission in information or detail gives no such assurances when inspected. For example if the drawings do not mention nails should be used to fix the rafters to the ceiling joists, the inspector would obviously be correct to insisting adequate fixings are provided, before they would approve the work.