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

Floor is massively underrated in my experience. Done a fair bit of insulating on the boat over the years and the principle's the same — cold radiates up from below constantly and you barely notice it until it's sorted, then you wonder how you ever lived without it.

For a stone bothy specifically I'd argue the floor is more important than the walls in some ways. Stone floors will sit at ground temp (8–10°C in the UK year round) and just drag all your heat downwards. Walls at least have some thermal mass that you can bring up to temp eventually.

Practical options I've seen work well:

• Rigid PIR board (Kingspan, Celotex etc.) under a ply deck — relatively thin, decent R-value
• Insulated subfloor panels if you've got budget
• Even a decent layer of sheepswool if you're going the natural route and have some airflow to manage moisture

Walls are obviously worth doing too, don't get me wrong. Lime plaster with hemp batts tends to suit stone buildings better than modern synthetics — lets it breathe rather than trapping moisture behind a vapour barrier and rotting everything.

The order I'd prioritise: floor → roof/ceiling → walls. Heat loss goes upward so ceiling matters too, but that cold floor is constant and relentless.

What's the bothy like — earth floor underneath or existing concrete? That'll change the approach quite a bit. And is it a scheduled building at all? Some of the older ones have restrictions on what you can touch internally.

@LDVWanderer stone floor in my shepherd's hut was basically a fancy fridge until I put 100mm of Celotex down — suddenly the whole space felt like a different planet 🪐

@BatteryPaula 100mm is no joke — that's proper commitment. I went 75mm under my shepherds hut and honestly wished I'd gone thicker. Floor insulation is one of those jobs where you only get one real chance to do it right before everything goes on top.

Stone bothy is a different beast though — you've got that thermal mass working for you potentially if you can keep the cold ingress from below managed. Walls and floor together or don't bother, I reckon. Doing just the walls on a stone floor is like insulating your jacket but leaving your boots off in January.

What's the subfloor situation like @LDVWanderer — bare earth, flagstones, or something else? Makes a difference to which approach is actually feasible.

Really interesting thread this. @GazAllen I suspect you were going to say you wished you'd gone thicker — that's almost always the story with insulation, isn't it? Nobody ever regrets overdoing it.

One thing worth mentioning for stone bothies specifically: before you commit to rigid foam under the floor, check your damp situation carefully. Stone floors often breathe in ways that suspended timber or concrete don't, and trapping moisture underneath insulation can cause real headaches down the line. A decent DPM properly lapped up the walls before the Celotex goes in makes all the difference.

Also worth considering whether you're heating the bothy seasonally or all year — if it's sitting cold and unused for months, the thermal mass of the stone actually works against you when you come to heat it up again. Floor insulation pays back fastest in that scenario.

@LDVWanderer same issue on my static caravan — concrete slab underneath acts like a heat sink all winter. Eventually went with 100mm PIR boards and it made a noticeable difference to how quickly the space warms up, which matters when you're only there weekends.

For a stone bothy I'd honestly say floor is more important than walls, not less. Stone walls at least have some thermal mass working in your favour eventually. The ground just keeps stealing heat indefinitely.

One thing nobody's mentioned — vapour barrier under the insulation is non-negotiable with a stone floor. Skip it and you'll have damp rotting your boards within a couple of seasons. Ask me how I know.