Mr Punter

I think that is the only one available.

Did or could they suggest an alternative foundation design?

I think a trial dig near the wall make sense. Don't do it near where you may be keeping the nibs of the existing wall. You may find that the existing wall foundation bears onto very stable base. Try to avoid underpinning.

I assume this is all for below ground? Is this foul, combined or surface water?

Maybe base it on extract rate of 10l/s and temperature difference of 10 degrees, year round.

If there is a smell it is more likely the pipework letting gasses in. An open end on a washing machine connector or something connected the wrong side of the sink trap?

The Velfac and IdealCombi trickle vents are very similar. They are not visible externally. Internally they are metal and flush with the sash when closed and protrude when open.

I have just had gas combi boilers fitted in 3 small new build flats. Much cheaper to do, customers know where they are regarding costs, very little space used, no outside units. I appreciate that ASHPs have their advantages, but they are not always the best solution.

It is a bit tricky as traditionally t&g floorboards were nailed down and there was expansion available between each board, which could be 5mm. If they are glued together the 5mm no longer applies and has to be multiplied by the number of boards which would be too much over 4.5m. Maybe the battens min 45mm will be better.

I doubt glue down will be good, so battens fixed to the floor with concrete screws. You could run cables in steel conduit if you need to. Floating floor could also work but you would need perimeter expansion allowance and tongue securely glued to groove.

If they are inside the shed I think you will be OK. You can always lag them a bit. In the unlikely event that it does get very cold, turn off the water and go to the launderette.

For clothes drying, a dehumidifier in a small, insulated room works really well.

They look very useful. I have used straight ones with a 45 either end, but that meant extra fittings, more cost and more space.

A few small points: Maybe look at a fire resistant membrane on the walls. The box gutter may fail at some stage and possibly rot out the walls. The Kingspan phenolic insulation is good (better insulation and fire rating) but expensive.

PIR inside, glass wool outside.