Insulating new shed floor (concrete base, 38mm bearers)

7 Nov 2022
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United Kingdom
I am buying a 5m x 3m shed and have a nice flat concrete slab to put it on. shed is pre fabricated and will be assembled on delivery.
I have requested damp proof course and 22mm t&g flooring. There is no option to insulate under the floor so am trying to work out how I could add insulation before they put the floor down and build up on top. in particular dont want to do anything which could cause moisture issues.

The floor comes in 5 premade sections and they provided a sketch and a photo (attached). they advised the floor bearers are 3x2 with 2" height from the ground.

Would it make sense to cut 25mm thick insulation board to slot into the gaps when the floor arrives and use compatible glue to stick to the floorboards? (twenty 25mm x 21" x 38" + five 25mm x 16.5" x 38")

do I need to ensure ventilation gap? I have lots of aluminium foil tape but not sure if this is any use if the floor is already mounted to the bearers?

any advice on ventilation? is anyone able to suggest any alternative?
I have lots of 1.2m width foil/radient barrier. does it make any sense to lay the on the floor under the shed facing up?


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Yes, hoping I can use as home office in future. Keen to sort floor before it is built as I know once once shed is build I will only be able to add insulation on top of existing floor which is not ideal.
I can't see there will be a lot gained if you insulate under the floorboards in between the bearers, as the bearers will be the source of cold and 25mm won't do a lot anyway.

You might be better laying the insulation on top of the floor and floating a floor covering on top.
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you may be right but I dont want to miss this opportunity to put something in and if more is needed, I can add later on top.
is there anything I can put under the bearers to help reduce conduction?
If I did want to add insulation underneath, is this going to cause moisture issues?
should I lay down the radient barrier below to reflect thermal radiation back at the shed floor when it gets warm?
I'm confused, do they just plonk those floor panels on your slab? You'd be far better building up an insulated subframe for them to put it on.

If you want to live in a shed, you need to either leave it as is and accept the heat loss or upgrade it to a habitable standard. Have you considered infra red heating where it heats the occupants and not the space?
As far as I can work out..

If I build an insulated subframe and they mount those floor panels on top with the 2x3 bearers, would the air gap not comprimise the insulation? Should I then also add insulation to fill the gaps?

Thanks for the infra red heating suggestion, ill look into that

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