ETC

Is the roof built? - if not change to a warm flat roof. If built can you drill holes through the cross members?

I’ll do it tomorrow when I’m at work.

If the radon maps says there’s radon in the area put a radon barrier down. What benefit is spending a shed load of money on an “assessment” which will more than likely be a desktop exercise using the same maps!

Rubbish. It’s the cost of a 1200 gauge DPM with all joints sealed and a few top hats. Put it under the slab and you don’t need any radon proof DPCs at all.

Very simple - set your road as 100.00 and measure everything from that datum - up for dropped kerb, higher for the grass. Keep it simple.

Madness. If there’s radon in the place where you are building put down a radon barrier. Why do you need a report to say that one is needed. Either a 1200 gauge membrane UNDER the slab or a radon proof DPC (Visqueen CPT) sealed to the DPM to the perimeter of the dwelling ABOVE the slab. If you need a sump - put one in - what is so complicated about this - I see it every day. If you want a detail let me know and I’ll post one.

Road=100.00. Dropped kerb=100.025. Grass=100.150.

https://historicengland.org.uk/images-books/publications/eehb-insulating-solid-walls/heag081-solid-walls/

If your church is old please get proper professional advice before you apply any type of insulation - internal or external. The external wall - depending on it’s construction may have been designed to “breathe” and adding insulation ad-hoc may cause more problems. Having said that if you want to see what U-Value you can achieve with certain insulation types there are many online U-Value calculators that will give you what you need.

Might be an idea to post a plan.

Only if it’s an inner room.

And is the cavity wall it supports insulated?

Why on earth is the cavity wall still at FFL? - you will save space by removing it. Also: You have no access between the garage and the house - why? Your GF WC is too small and does not comply. Try and get the GF back wall to tie up with the FF back wall. Put a flat roof on the back part.

Are the beams within the thermal envelope?