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

Done both, and the stone outbuilding will absolutely win if you can stomach the damp-proofing faff before you even think about insulation.

My setup in the Cotswolds is a converted stone barn — breathable lime render inside, 50mm Kingspan between timber battens, and it holds heat like a proper thermal battery once the Victron kit gets the underfloor going. The walls themselves become your best mate in summer too, keeping everything cool without you doing a thing.

Log cabin kits look tempting (and the Dunster House ones aren't bad), but you're essentially living in a giant radiator that spikes and crashes with every cloud that passes over the solar array.

A few things worth considering with the stone route:

• Breathability is everything — trap moisture and you'll be fighting mould before Christmas
• Thermal mass works for you off-grid, not against — less demand on your batteries overnight
• Planning can be kinder to existing structures depending on your permitted development situation

The faff factor is real though — I spent a deeply unglamorous fortnight chasing cold bridges with a thermal camera before I was happy.

What's the building like — thick rubble stone or the thinner dressed stuff? Makes a difference to which approach I'd recommend.

WayneClark | 847 posts

@CotswoldDweller totally agree on the damp-proofing being the real battle. People underestimate it massively.

One thing worth adding — if you're in a stone building, seriously consider going the breathable insulation route rather than rigid foam boards. Trapping moisture in old stone walls is asking for trouble down the line. I used Thermafleece sheep's wool batts in my converted Welsh granite outbuilding and the walls have been dry and stable for four winters now.

The log cabin kits look tempting on paper because the costs are obvious upfront, but stone has that enormous thermal mass advantage — once it's up to temperature it holds heat brilliantly, which matters when you're running off solar and want to stretch every kWh.

Planning permission is the other wildcard with stone outbuildings obviously. Might be worth flagging that before anyone commits either way.

JimWilson | 312 posts

Stone every time for me — done a similar thing with my garden office and the thermal mass alone is worth the faff. Once it's up to temp it stays up to temp, which matters when you're trying to keep power consumption down off-grid.

@CotswoldDweller what did you end up using for internal insulation? I went with 100mm Kingspan between battens and it's been a game changer. Keeps the Victron system from working overtime in January anyway 😄

Also — welcome if you're newish here @CotswoldDweller, great first post. Exactly the kind of real-world experience this forum needs rather than "I watched a YouTube video once" contributions we sometimes get 😂

Log cabin kits have their place but you'll be maintaining that cladding every couple of years. Stone just sits there looking smug and doing its job.

BevJackson64 | 203 posts

Interesting thread — I'm weighing up something similar for a stone outbuilding I want to use as a base for the motorhome setup (charging, battery bank, that sort of thing).

Quick question for @CotswoldDweller or anyone who's done this: with the damp-proofing sorted and insulation in place, how stable are the internal temperatures across seasons? Specifically asking because I've got Victron kit and a Fogstar battery bank that I need to keep within a sensible thermal range — lithium doesn't appreciate being too cold overnight in winter.

Is the thermal mass actually a benefit for that, or does it mean the space takes forever to warm up if you're only using it intermittently? Log cabin kits seem like they'd respond faster to active heating, which might matter more than I'd initially thought.

MistyTinker | 1,204 posts

One thing nobody's mentioned yet — if you're planning any off-grid electrical setup in the stone building, that thermal mass @JimWilson mentions works against you in winter. Stone buildings take forever to reach temperature, so your heating load is massive every morning, which absolutely hammers battery capacity overnight.

In my motorhome setup I ran into similar thermal inertia issues (aluminium skin, but same principle). The fix was a decent layer of PIR board on the internal face before any battening — 100mm minimum on walls. Kingspan or Celotex both work well; Kingspan K5 is specifically rated for internal walls and handles the moisture vapour better.

@BevJackson64 if you're planning EV charging from the outbuilding too, factor that heat load properly before sizing your battery bank — stone buildings will inflate your consumption figures considerably compared to a well-insulated log cabin kit.

CornishBoater | 87 posts

Really useful thread this — I'm in a similar boat (literally, half the time!) but also converting a shepherd's hut, so slightly different again.

Quick question for @CotswoldDweller and @JimWilson — how are you handling the vapour barrier situation with stone walls specifically? I've read conflicting things about whether you even want one, given stone needs to breathe.

Also on @MistyTinker's electrical point — did anyone run conduit before insulating or retrofit it after? Kicking myself that I didn't think ahead on my hut build and had to chase cables in later, which was a right faff.

Wondering if stone actually makes that easier or harder compared to timber-frame construction?