Starting from scratch.

[Windbag]

I have a mate who has had water damage to the ground floor. The insurance company are ripping it all out to dry out and replace.

So he had a blank canvas (in an existing house) for an energy rethink.

He has, space for log boilers, solar, batteries, thermal store etc etc.

What would you recommend?

[MrPablo]

Hi Windbag, could be interesting to see a floorplan and general build-up of the house at the moment.

[Stig]

Insulate the floor? It's normally really disruptive to do which is why almost nobody does it but now sounds like a perfect time. He could internally insulate the walls too but that means making all the rooms a bit smaller, maybe no big deal in something big & Victorian but would be in something small & modern.
He'd want to know the heat demand before specifying any new heating system so why not improve the insulation first.

[openspaceman]

Insulate the floor? It's normally really disruptive to do which is why almost nobody does it but now sounds like a perfect time. He could internally insulate the walls too but that means making all the rooms a bit smaller, maybe no big deal in something big & Victorian but would be in something small & modern.
He'd want to know the heat demand before specifying any new heating system so why not improve the insulation first.

Yes and surely it would be cheap at this stage to get a pipe layout designed and put the plastic pipes in the screed. A definite benefit to using a heat pump as well as keeping a gas boiler in condensing mode, although modern requirement mean radiators must be big enough to do the same now.

I snagged a gasifying wood boiler which ran a thermal store and underfloor heating, it only fired once a day.

[wookey]

He really need to do his PHPP sums and work out a whole-house plan.

But for the floor alone, dig it out, put down 200mm XPS (but make sure you find the low-embodied carbon stuff - some of it can be absolutely shocking) then preferably a lithotherm clay floor with UFH pipes in it. This again is dramatically lower-carbon than 150mm of confrete/cement which is the standard way of doing floors. Foamglass is a greener insulation than XPS but it tends to be effing expensive in the UK.

What sort of heating you put into said floor doesn't really matter too much - can be GSHP (if they have enough ground or don't mind paying for a borehole) or ASHP. The issue here is that the pipe spacing depends on the heat load and heat load depends on the rest of the building. Is it a draughty barn or a passivehouse? Factor of 10 difference in heat load.