Insulating a stone bothy for winter use — worth the effort or just get a wood burner?

Done both on different projects — insulation wins every time, but it's not either/or really.

Stone has terrible thermal mass behaviour in cold climates. It sucks heat out of a space for hours before it starts giving anything back. A wood burner into an uninsulated bothy is basically heating the walls indefinitely. Inefficient and you'll burn through a serious amount of wood.

On my tiny house build I used 50mm PIR board (Celotex GA4000) against the walls before battening out. Transformative. Same principle applies to a bothy — even a basic 25mm layer with a vapour barrier makes a massive difference to how quickly the space gets up to temperature and how long it holds it.

Practical order I'd suggest:

1. Tackle the floor first — cold floors kill warmth faster than anything
2. Ceiling/roof void — heat rises, obvious losses there
3. Walls — even partial coverage helps
4. Then fit the wood burner

The stone walls themselves aren't going anywhere so you're not fighting them, you're just lining the inside. Rockwool between battens works fine if PIR feels like overkill for a bothy.

One thing worth flagging — moisture. Stone buildings trap damp badly if you seal them without thinking about breathability. Make sure whatever system you use accounts for that or you'll have a mould problem by spring.

What's the bothy footprint roughly? And is it a weekend-use situation or longer stays? That'd change how much effort is genuinely worth it.

@CaddyProject interesting point about the thermal mass — hadn't really thought about it that way but it makes sense.

Slightly different angle here: I've been wrestling with similar questions on my static caravan and narrowboat setups. The caravan especially — thin aluminium skin, basically a fridge in winter. We went with 50mm PIR board internally before anything else and the difference was night and day before we even lit anything.

Question for anyone who's done a bothy specifically though — does the breathability issue with stone walls change your insulation choice? I've seen people mention that trapping moisture in stone is a nightmare long-term. Do you go with something like wood fibre board over PIR in that situation, even if it's slightly less effective thermally?

Genuinely asking because if I ever get a small outbuilding sorted I want to do it properly from the start rather than retrofit later.

@CaddyProject had the same issue in my static — took ages to warm up until I sorted the insulation properly. Stone's even worse I imagine.

One thing worth mentioning: a wood burner without insulation just means you're constantly feeding it to compensate for the losses. Gets expensive and exhausting fast.

If budget's tight, prioritise the roof first — that's where most heat escapes. Even basic 100mm PIR up there makes a massive difference before you touch the walls.

Then get your burner in. Both together is the goal, but if it's either/or short-term, insulate first, use a small electric heater temporarily.

Really good thread this. @CaddyProject makes a solid point about stone behaviour — I'd add that the direction of heat flow matters too. An uninsulated stone bothy in a Scottish winter isn't just slow to warm up, it's actively pulling heat toward the cold external face the entire time your burner's running. You're essentially heating the hillside.

What's worked well for me is a warm-side membrane with a small air gap before your insulation layer — keeps moisture from getting trapped in the stone, which is where a lot of bothy projects go wrong long-term. Damp insulation is basically no insulation.

Budget-wise, even 50mm of decent rigid PIR board makes a noticeable difference before you've spent a penny on firewood. Do the fabric first, then size your stove accordingly — you'll likely need something smaller than you think.

@CaddyProject nailed the core issue but I'd throw in one thing nobody's mentioned — air sealing matters as much as the insulation itself.

Did my bothy two winters ago. Slapped in 100mm PIR between battens, felt smug about it. Still freezing. Turns out the stone walls were basically a wind tunnel through every gap and mortar joint.

Went round with a cheap thermal camera on a cold morning and the results were... humbling. Fixed the air leakage properly and the difference was night and day before I even lit the stove.

So yes — do the insulation, absolutely. But don't skip the detective work first or you'll be burning through firewood wondering why it's not working. Draughts are silent budget killers.

Wood burner still essential though. Some of us just like the ambience and nobody's taking that away from me. 🪵