Converted an old shepherd's hut last summer - worth insulating the floor first?

Done both a shepherd's hut and a motorhome conversion so can speak to this a bit.

Short answer: yes, absolutely do the floor first. Once your cladding and furniture are in, you've lost the chance. I left it too late on my first hut build and regretted it every winter.

For the hut I used 50mm rigid PIR board (Celotex) between the floor joists, then a layer of foil-backed bubble wrap as a vapour barrier before the ply went down. Made a noticeable difference — those metal chassis frames are basically a giant heat sink otherwise.

A few things worth considering:

• Moisture rising from underneath is the bigger enemy than cold in a lot of ways. Don't skip the damp-proof membrane under the insulation
• Thermal bridging through the steel frame is real — you can add a thin layer of Kingspan on top of the joists before the ply if you want to go further
• Ground clearance matters too. More airflow underneath = more heat loss

What type of chassis is yours on? Some of the older traditional huts sit quite low and you've got more limited options. Also worth checking if there's any existing material between the joists already — some come with basic mineral wool which is basically doing nothing useful.

Anyone else tackled this on a hut with a wooden chassis rather than steel? Curious whether the thermal bridging issue is as bad.

@FrostySocket makes a solid point that's easy to ignore when you're excited to get the walls up.

I'd add — don't just think about thickness, think about moisture barrier placement. Shepherd's huts sit on those iron wheels/chassis and the underfloor void gets brutal airflow. I used 100mm Kingspan with a proper vapour barrier on the warm side in my garden office build and it made a noticeable difference to floor temperature in winter.

Also worth checking whether your chassis has any steel bridging directly to the floor joists — thermal bridging there will quietly undermine even good insulation. Bit of a pain to address later but manageable at build stage.

What flooring are you going over the top? Some options are less forgiving of movement than others if you're on uneven ground.

@FrostySocket nailed it — did my shepherds hut floor with 100mm Celotex between the joists and it's the difference between a cosy retreat and a very expensive freezer.

Quick tips from bitter experience:

• Tape every single joint — draughts find gaps like my dog finds sausages
• Rigid PIR foam (Celotex, Kingspan, Recticel) beats mineral wool in a floor — moisture resilience matters when you're sitting inches off damp ground
• Fit a vapour barrier on the warm side or you'll be fighting condensation forever

Also worth thinking about now — run any cable conduits through the floor void before you button it up, or you'll be weeping into your Fogstar battery wondering why you didn't think ahead. 😅

@FrostySocket is right and people consistently underestimate floor heat loss — it's not glamorous insulation work so it gets skimped on.

One thing nobody's mentioned: vapour barrier placement matters on shepherd's huts specifically. You're typically sitting on wheels with airflow underneath, so you've got cold moving air attacking the floor constantly — worse than a static build on blocks or a concrete pad.

Did mine with 100mm PIR between joists plus a proper foil-faced membrane on the underside before boarding it up. Total faff to do properly but I'm glad I did. Ground-mounted solar and a small Victron setup means I'm out there year-round and a cold floor in January would be miserable.

Also — if your joists are shallow, consider furring them down to get more insulation depth before you lose access forever.

Seconding everyone here — and speaking from bitter experience on the narrowboat where I didn't do the floor properly first. Spent an entire November wondering why my diesel heater was running flat out and my feet were still freezing. Turns out I'd basically built myself a very cosy radiator pointing straight at the Trent & Mersey Canal.

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