Insulating a timber frame cabin on a shoestring - where do I even start?

Done this twice now — once on a garden office conversion, once on a tiny house build — so here's the blunt version of what I learned.

Start with the floor. Everyone ignores it and it's the biggest mistake. Cold floors kill a space faster than anything. I used 100mm PIR between joists with foil tape on every joint, then OSB over the top. Cheap and effective.

For walls in a timber frame, you've got options depending on your budget:

• Mineral wool between studs — cheap, widely available (Rockwool from most builders merchants), but you must have a vapour barrier or you'll rot your frame inside 10 years
• PIR boards — more expensive but better U-values per mm, useful if you're tight on space
• Sheepswool or hemp — lovely stuff but pricier; does handle moisture better naturally

Roof is where I'd splash out if I had to prioritise. Heat rises, obviously. I went 150mm PIR on my garden office roof and the difference was immediate.

One thing nobody mentions — cold bridging through your studs. Your insulation between studs is great but the timber itself conducts cold. A layer of 25mm PIR over the whole interior face of your frame before boarding out makes a real difference.

What's your floor plan and wall depth? That'll change the advice considerably. Also — are you planning to heat it with electric, wood burner, or something else? That changes how hard you need to work the insulation spec.

Others on here will have different approaches — be good to hear what's worked for people in wetter climates particularly, as moisture management is the part that really bites you later.

Great shout on the floor, @BrianBrown — massively overlooked.

One thing I'd add from bitter experience: don't underestimate cold bridging through your timber studs themselves. Even with decent batts between them, those studs are conducting heat straight out. On my last cabin build I added a continuous layer of 25mm PIR board across the whole wall face before cladding, and the difference in surface temperatures inside was genuinely remarkable — you could actually feel it with your hand in winter.

It adds cost but you can often pick up part-used PIR sheets on Facebook Marketplace or from builders' skips for next to nothing if you're patient. Takes a bit longer to source but on a shoestring that waiting game is worth it.

Vapour barrier placement matters too once you go down that route — happy to elaborate if useful.

Good points from @BrianBrown and @Jonno25 but nobody's mentioned vapour barriers yet and that's where I've seen timber frame cabins go properly wrong.

Get the warm/cold side wrong and you're growing mould inside your walls within 18 months. On my static caravan conversion I nearly made exactly this mistake.

Basic rule: vapour barrier goes on the warm side of the insulation (interior face). Sounds obvious, rarely done correctly.

Also worth saying — don't cheap out thinking any old poly sheet will do. Actual vapour control layers aren't expensive but the difference in permeability ratings matters, especially in a tight timber frame.

Insulation choice matters too. Rigid PIR boards (Kingspan, Celotex etc.) give you better U-values per mm than standard mineral wool if headroom's tight.

@ShedGenius is right, vapour barriers are a nightmare if you get them wrong. Done the same mistake on the boat before — trapped moisture absolutely destroys timber over time.

One thing nobody's touched on yet: thermal bridging through your studs. Insulating the stud bays is the obvious bit but those timber studs themselves are cold bridges. Worth adding a layer of rigid PIR board (Celotex, Kingspan, whatever's cheap on eBay) across the whole face before boarding out. Adds maybe 25-40mm but makes a proper difference to heat retention.

Not glamorous advice but the shoestring bit matters — reclaimed PIR off salvage yards or even FB Marketplace is genuinely good value if you're not fussed about offcuts.

@Jason1970 vapour barriers on a boat are a whole different level of pain — condensation just destroys everything silently until you find rot.

One thing nobody's touched on yet: thermal bridging through the timber frame itself. Insulating the stud bays is great but the studs are still cold bridges running right through your wall. On my van conversion I added a continuous layer of 25mm PIR board across the face of the studs before cladding — breaks the bridge completely. Tiny loss of internal space but massively better performance in practice.

On the cheap end, Kingspan Pattress offcuts sometimes turn up on Facebook Marketplace for next to nothing. Worth checking regularly.

@BrianBrown solid tips on the floor — totally agree it gets overlooked.

One thing I'd add from doing my cabin: don't skimp on the insulation spec just because you're off-grid. Counterintuitive maybe, but a poorly insulated cabin means your battery bank is working overtime running heating. Proper PIR board between the studs paid for itself within one winter on my setup.

On the vapour barrier stuff @ShedGenius raised — get the membrane on the warm side of the insulation, not the cold side. Sounds obvious but I ballsed it up first time round. Thankfully caught it before boarding out.

Budget pick that worked for me: reclaimed PIR from salvage yards. Half the price of new Kingspan, same performance.