Has anyone insulated a shepherd's hut with sheep's wool batts? Wondering if it's worth the extra cost

I've been slowly converting a 10ft shepherd's hut and I'm at the point where I need to commit to insulation. I was originally going to go with Kingspan or Celotex between the ribs (they're 75mm deep), but I keep getting drawn back to sheep's wool batts on principle — it just feels right for a shepherd's hut, doesn't it? Thermafleece CosyWool seems to be the most talked-about brand, coming in at roughly £8–10/m² for the 75mm thickness, which is noticeably pricier than PIR board.

My main concern is moisture. The hut lives outside year-round in rural Wales, so it sees proper damp. I've read that sheep's wool handles humidity buffering well and won't rot, but I've also read it can compact over time and lose some of its stated U-value. The walls are corrugated steel over timber ribs, so there's already a condensation risk in that assembly without adding a wool product that might hold moisture against the frame.

Has anyone actually used it in a similar build — especially in a wet climate? Did you use a breather membrane on the cold side and a VCL on the warm side, or did you go vapour-open throughout? I'm also wondering whether the thermal performance difference between 75mm sheep's wool (roughly 0.039 W/mK) and 75mm PIR (around 0.022 W/mK) is noticeable in practice when you're heating a small space with a little Hobbit stove.

YEL_Marine | Posts: 847

@CraftyGrafter I fitted sheep's wool batts in my timber cabin a couple of years back and honestly don't regret it despite the cost premium. The key thing nobody mentions is how forgiving it is in a shepherd's hut specifically — those curved corrugated roofs create condensation challenges that sheep's wool handles brilliantly because it absorbs and releases moisture without losing performance, unlike rigid PIR boards which can cause damp pockets if your vapour control isn't perfect.

With 75mm ribs you're looking at roughly λ0.039 with good quality batts, so thermally comparable to Celotex at that thickness.

One practical tip — the batts cut with scissors rather than a dusty knife, which in a tight curved space makes a genuine difference.

What's your heating setup? That might influence the answer more than the insulation choice itself.

GlenKelly | Posts: 312

@CraftyGrafter Worth considering that sheep's wool handles moisture brilliantly - it can absorb and release humidity without losing much thermal performance, which matters in a shepherd's hut where condensation can be a real issue given the metal shell.

One practical point though: 75mm ribs are fairly shallow, so whichever route you go you'll want to think about a thermal break layer across the face of the ribs afterwards, otherwise you're losing a fair bit through those steel contact points. A layer of 25mm Kingspan over the top of your wool batts would actually give you a decent hybrid solution - natural material doing the breathable work, rigid board dealing with the cold bridging. Might make the cost difference feel more justifiable too.

What are you using for the ceiling? That's often where shepherd's huts lose the most heat in my experience.

ThistleKen | Posts: 1,203

Did the same in my van — Kingspan won the battle of the tape measure but sheep's wool won the battle of not waking up in a tin sweat box at 3am.

Paddy | Posts: 2,156

One point nobody's raised yet: in a shepherd's hut specifically, you've got a steel chassis and often steel ribs creating thermal bridges that will absolutely undermine any insulation regardless of type. Before committing to either product, I'd strongly recommend addressing those cold bridges with a continuous layer — even 10–15mm of Recticel or similar across the face of the ribs before your internal lining goes on.

On the 75mm depth: sheep's wool batts are typically sold in 100mm thicknesses and compress reasonably well, but you'd be installing them at reduced specification. Worth checking the manufacturer's declared lambda value at compressed depth rather than nominal.

@CraftyGrafter what's your primary use case — year-round habitation or occasional use? That significantly changes whether the sheep's wool premium is justifiable versus two layers of 50mm Celotex with staggered joints.

GlenChild | Posts: 156

@CraftyGrafter One practical thing nobody's mentioned yet — sheep's wool batts are genuinely forgiving to fit around the curved ribs of a shepherd's hut. Rigid foam like Kingspan needs fairly precise cutting to avoid thermal bridges at the edges, and those curved profiles can make that fiddly. Wool just compresses and conforms a bit more naturally. I've seen poorly fitted Kingspan in similar builds that ended up with more gaps than the "inferior" alternative would have had. Given your 75mm rib depth, you'll likely get a better real-world fit with wool even if the headline U-value looks slightly worse on paper. Whether the cost difference is worth it really depends on how much you're heating the space and how long you plan to keep it.

LindaCross66 | Posts: 847

@CraftyGrafter I insulated my 12ft hut with Thermafleece about three years ago now and honestly haven't looked back. One thing worth knowing — sheep's wool is remarkably forgiving if you've got slightly irregular rib spacing, which in older huts is pretty much guaranteed. It compresses and expands to fill gaps in a way rigid board simply won't.

On cost, I found buying direct from the manufacturer rather than through a builder's merchant saved me a fair bit. Also worth checking whether any local farms near you sell raw fleece insulation through agricultural suppliers — I got a portion of mine that way for considerably less.

The smell when damp is genuinely negligible in my experience, nothing like wet dog as some people claim. Three winters in and the hut stays remarkably comfortable with a small log burner. Well worth the premium in my opinion.