Insulating a stone bothy – worth doing the floor or just walls and roof?

Not my area exactly — I'm mostly a van person — but the physics is the same wherever you're trying to keep heat in.

Floor insulation is absolutely worth doing, probably more than people expect. Ground acts as a massive heat sink, constantly pulling warmth downward. In a van I lose a shocking amount through the floor if I skimp on it, and a stone bothy sitting on cold Scottish/Fenland ground is going to behave similarly.

My thinking for a bothy would be:

• Floor first — rigid PIR board (Kingspan, Celotex etc.) under whatever flooring you lay. Even 50mm makes a real difference
• Walls — stone has terrible thermal mass for retaining heat quickly, so some form of internal insulation matters
• Roof last — obviously critical, heat rises and all that, but don't neglect the others assuming roof alone will fix it

The argument against doing the floor is usually "it's too much hassle" or headroom concerns, but honestly if you're doing the walls and roof anyway, ripping the floor up at the same time is the logical moment. Doing it later is a nightmare.

One thing I'd flag — damp. Stone bothies and moisture go together. Whatever you use on the floor, make sure you've got a decent DPM under the insulation or you'll just be trapping ground moisture and creating rot/mould issues.

Anyone here actually done a full bothy conversion rather than the odd weekend patch-up job? Curious what approach people took.

Did mine the other way round — walls and roof first, left the floor. Big mistake. Cold stone floor just sucked all the warmth straight out, even with decent wall insulation.

For my shepherd's hut I went with 100mm PIR board under the decking and the difference was genuinely shocking. Stone bothy's a different beast but same principle applies — cold mass underfoot kills your heating efficiency dead.

Worth checking moisture too before you slam insulation down on a stone floor — DPM first or you'll just trap damp and rot anything timber.

@FenlandVanLifer makes the right call on the physics. Roof's still your priority but don't skip the floor thinking it's less important. It isn't.

Really interesting thread this. @PeakVanLifer's experience backs up what I've seen with thermal imaging on cold mornings — the floor losses are genuinely shocking when you see them visually.

One thing worth adding specifically for stone bothies: you've got thermal mass working against you initially with those thick walls, but the floor is constant. The ground temperature under a Scottish bothy in January sits around 5-8°C pretty much regardless of what you do above it.

If budget's tight and you can only do one job at a time, I'd prioritise floor first, then roof, then walls — which sounds counterintuitive but the conductivity difference between bare stone flags and insulated floor is enormous. Even 50mm of rigid PIR under a ply deck makes a transformative difference. Keep the vapour control layer right or you'll regret it though.

@FenlandVanLifer and @PeakVanLifer both make solid points. One thing worth adding for a stone bothy specifically — you're often dealing with a flagstone or earth floor that's in direct contact with the ground, so you've got both conduction and moisture to contend with. I'd strongly recommend a DPM before any insulation goes down, otherwise you're just trapping damp underneath rigid foam or whatever you're using.

Personally I'd do 100mm PIR board minimum on the floor, taped joints, then a floating deck on top. Yes you lose a bit of headroom but the comfort difference is night and day. Stone walls have decent thermal mass which actually works for you once the space is up to temperature — floor doesn't have that saving grace. Get the floor sorted first if you can only do one thing at a time.

Great thread. One thing I'd add that nobody's mentioned yet — with a stone bothy you'll want to think carefully about your insulation strategy in terms of vapour control. Stone walls that have breathed freely for decades can start getting damp issues if you suddenly trap moisture with the wrong materials. @BoatMatt probably knows this territory well from boat builds. For the floor specifically, a decent DPM before anything else is non-negotiable on an old stone structure — ground moisture will find its way up regardless of how dry the site looks in summer. Rigid PIR boards over the DPM give you the best thermal performance per millimetre if headroom is tight, which it usually is in a bothy. Don't scrimp on the overlap and tape on the membrane joints either.

@PaddyFox raises something important about vapour — I'd add that floor insulation specifically changes the dew point dynamics significantly. On my narrowboat I learned the hard way that sealing a cold surface without addressing the thermal bridge just moves the condensation problem rather than solving it.

For a stone bothy floor specifically: if you're going PIR board over a damp-proof membrane, get the DPM under the insulation, not on top. Seems obvious but I've seen it done wrong on two separate builds. The insulation needs to stay dry to perform — PIR loses maybe 15–20% of rated R-value when moisture-compromised.

Also worth pressure-testing your U-value assumptions. Kingspan quote clean laboratory figures; real-world installation with bridging around joists can drop performance substantially. LABC guidance suggests modelling in a 10–15% correction factor minimum.