Insulating a stone outbuilding — worth the hassle or just go with a log cabin kit?

Spent three weekends wrestling with 600mm stone walls and a borrowed SDS drill before I finally admitted the outbuilding had won and ordered insulated plasterboard like a sensible person — 0 out of 10, would not recommend doing it the hard way.

That said, the thermal mass of stone is genuinely unbeatable once you've got it properly lined; my garden office holds temperature overnight without touching the Victron, whereas my mate's log cabin kit is basically a crisp packet in January.

Here's the honest breakdown though:

• Stone outbuilding — brutal to insulate, expensive upfront, absolute weapon once done
• Log cabin kit — up in a weekend, looks lovely, leaks heat like a sieve unless you're spending serious money on the good stuff

The question nobody asks is what's your usage pattern? If you're out there 9-to-5 every day, stone wins hands down. If it's occasional weekend use, you'll be waiting two hours for a stone building to warm up and questioning all your life choices.

Also worth considering: planning permission headaches are usually far less with an existing outbuilding than a new structure, depending on your local council's mood that particular Tuesday.

What's the actual footprint you're working with, and are you mains-adjacent or fully off-grid? That'd change my answer a fair bit. Others on here with log cabin setups — genuinely curious whether you've cracked the insulation problem or just accepted higher battery drain in winter?

@BayFrank mate I feel this deep in my soul — did something similar in my van conversion where I assumed "oh it's just insulation, weekend job" and then discovered the actual geometry of a real vehicle versus the YouTube van has absolutely nothing in common.

Stone walls are a different beast entirely though. The moisture-vapour dynamic in a 600mm rubble wall means you genuinely cannot just bung Kingspan against it without thinking through your condensation plane — insulated plasterboard on a properly drained cavity is honestly the correct answer, not the lazy one.

What product did you go with? The Celotex PL4000 range has decent lambda values but the Rockwool Flexi Slab with a separate vapite board handles the hygroscopic nature of stone better in my reading. Curious what your wall-tie situation looked like too.

@BayFrank stone walls: 1, humans: 0, the score since roughly 1,200 AD and nobody's closing that gap anytime soon.

@BayFrank 600mm solid stone is genuinely brutal — thermal mass works for you eventually but getting fixings in without shearing SDS bits is a rite of passage nobody mentions.

Insulated plasterboard is the pragmatic call, but watch your dew point carefully. With that wall thickness you're sitting on a decent U-value already, so going too aggressive on internal insulation thickness shifts condensation into the wall-plasterboard interface. 25mm PIR bonded board is usually sufficient; 50mm risks problems unless you're dot-and-dab with a ventilated void.

Also — calcium silicate board on any particularly damp sections before you board over. Stone outbuildings almost always have one corner that weeps in winter.

If you're running solar into this space, thermal mass actually helps buffer temperature swings which is a genuine advantage over a timber kit. The stone wins eventually; might as well use it.

@BayFrank ha, the borrowed SDS drill is doing a lot of work in that sentence — there's always a moment with old stone where you realise the drill isn't the problem, you are, and the wall has simply been waiting 200 years for this exact confrontation.

Genuine question though — what thickness insulated plasterboard did you go with? I went down the warm batten route on a similar job last year and ended up with a hybrid approach that I'm fairly happy with. The thermal mass @LH_Marine mentions is real, took about three weeks of heating before the walls stopped pulling heat out of the room like a sponge. Stick with it, the stone will eventually come round to your side. Mostly.

@BayFrank insulated plasterboard on battens is honestly not the defeat it feels like — done properly with a decent vapour barrier you'll end up with a warmer, drier space than most people manage with full wall insulation on stone anyway. The real enemy in those buildings isn't the walls, it's the floor and the roof losing heat while you're busy fighting the masonry. Get those sorted and the thermal mass @DaleLover mentioned actually starts earning its keep rather than just being cold and smug. What are you planning for heating — that'll make or break how comfortable the space ends up being off-grid.