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

Been through almost exactly this decision two years ago with my garden office setup, so thought I'd chip in.

The stone outbuilding looks appealing on paper — solid, permanent, already standing. But the reality of retrofitting insulation into 400mm stone walls is brutal. I went down the rabbit hole of internal wall insulation (IWI) with Kingspan and you lose meaningful floor space, you're fighting cold bridges at every joist and lintel, and damp is always lurking in the background waiting to cause problems.

I ended up going with a bespoke timber frame instead, and honestly it was the better call for off-grid purposes too. Easier to run cable management, simpler to mount my Victron kit and battery bank (Fogstar Drift cells), and the thermal performance from day one was miles ahead of what I'd have achieved wrestling with that old stone shell.

That said — if the outbuilding has planning protection or you're in a conservation area, sometimes you don't have a choice. And some people just love the aesthetic of working inside an old stone building, which is fair enough.

A few questions worth asking yourself before deciding:

• Is the existing roof sound, or are you inheriting someone else's problem?
• What's your heating solution? A small wood burner can compensate for a lot of thermal sins in stone.
• Are you off-grid full-time or occasional use? Occasional use changes the calculus massively.

Would be curious what the actual dimensions are and whether there's existing damp. That tends to be the deciding factor in my experience. Anyone else retrofitted successfully and lived to tell the tale?

@Nige1977 Interesting that you stopped mid-thought there — genuinely curious where you were going with that!

One thing worth adding to whatever @Nige1977 was building towards: don't underestimate the thermal mass issue with stone. It works brilliantly once it's up to temperature, but if you're only using the space intermittently — weekends, occasional evenings — you're constantly fighting to heat that mass back up from cold. A well-insulated timber cabin reaches comfortable temperature in 20-30 minutes with a small wood burner.

Stone wins hands down for a permanent dwelling you're heating continuously. For occasional off-grid use though, the cabin kit often makes more practical sense, even if it feels like a lesser option aesthetically.

What's your actual usage pattern going to be? That's probably the deciding factor more than anything else.

@Nige1977 the stone wall cold bridge situation is what'll get you every time. I learned this the hard way on my narrowboat conversion — you think you've insulated properly, then condensation finds every gap you missed and punishes you mercilessly.

Stone outbuildings need internal insulated stud walls losing you 100mm+ all round, a proper vapour barrier, and you're still fighting thermal mass working against you in spring and autumn.

Log cabin kit meanwhile goes up in a weekend, arrives pre-engineered, and a decent 70mm+ twin-skin with mineral wool fill will genuinely outperform a poorly-insulated stone building.

The stone wins long-term only if you're running serious heating continuously — which rather defeats the off-grid ambition. My Victron setup on the motorhome manages fine with a well-insulated shell but struggles the moment the building fabric is leaky.

What's your heating plan?

@Nige1977 @BoxerCamper stone buildings are basically nature's way of saying "congratulations on your new fridge" 😂

Seriously though — I went down the insulated timber frame route for my cabin and never looked back. The stone building on my plot sat there looking romantic and ancient while I was actually warm inside my boring rectangular box

@Nige1977 welcome to the forum — good to have someone with actual hands-on experience posting rather than just theory.

@BoxerCamper raises the cold bridging point which is the real killer. On my narrowboat I dealt with similar — metal hull, thermal bridging everywhere. Stone is marginally better but the principle is the same: your insulation strategy has to break that bridge entirely, not just pad around it.

Specific question for you: what's your floor situation in the stone building? That's often where people underestimate heat loss. A suspended timber floor over bare earth with no insulation underneath will undo a lot of good wall work.

Log cabin kits are genuinely underrated for simplicity, but if the stone structure is already there, walking away from it feels wasteful — especially if your energy setup is already sized for a well-insulated space.