Shed base / floor - insulation and damp proofing?

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Hello,
I'm building a 9ft x 14ft shed/workshop and i'm after a little advice as it's the first time I've done anything like this.

I've excavated and prepared a base consisting of, weed control/driveway membrane, 5 inches of compacted type 1 then a screeded 50mm sharp sand/cement 6/1 dry mortar mix, then finally laid a combination of 2x2 and 3x2 50mm "council" concrete slabs covering exactly 14ftx9ft.

The shed base I'm planning using 4x2 pressure treated timber framework (16" on center) with 18mm exterior grade plywood as the final floor surface. This will all be resting (screwed down on to) on an undecided number of 4x2 (laid flat) pressure treated "bearers" running the long length of the floor, perpendicular to the 16" on center timbers of the shed floor framework, the idea being airflow under the shed?

Ok, I hope that's all ok so far, please advise if I've missed something critical?

My questions are mainly around damp proofing the floor whilst adding insulation.

I'd planned buying and cutting big sheets of 50mm Celotex and fitting these neatly between the floor framework but this is where I'm coming up to my limit of knowledge.
  • Do I leave an air gap between the Celotex and the 18mm ply floor covering and if so how much?
  • Do I have the foil side of the Celotex pointing up towards the floor?
  • Is it ok to leave the back of the Celotex directly exposed to the air underneath the shed floor framework (which is only two inches off the ground)
  • Finally, do I need some sort of damp proof membrane in my floor structure given the whole lot is going to be pressure treated timber and if I do when where should I have it?
I'd really appreciate any advice anyone can offer!

Thanks!
 
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With insulated spaces you either full fill them and don't ventilate or leave a gap but then the gap must be vetilated.

I would put your celotex between your joists and then plywood tight on top. Leave the underside open. Foil face up.

I would avoid dpc's but if you do want some strips the place for them would be to seperate the floor joists from the 4x2 bearers.
 
Facing same questions. Sounds like I leave the timber base as it is, then insulate between the joists right underneath the floorboards.

Good idea to put DPC between floor joists and the timber frame.
 
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Hello,
I'm building a 9ft x 14ft shed/workshop and i'm after a little advice as it's the first time I've done anything like this.

I've excavated and prepared a base consisting of, weed control/driveway membrane, 5 inches of compacted type 1 then a screeded 50mm sharp sand/cement 6/1 dry mortar mix, then finally laid a combination of 2x2 and 3x2 50mm "council" concrete slabs covering exactly 14ftx9ft.

The shed base I'm planning using 4x2 pressure treated timber framework (16" on center) with 18mm exterior grade plywood as the final floor surface. This will all be resting (screwed down on to) on an undecided number of 4x2 (laid flat) pressure treated "bearers" running the long length of the floor, perpendicular to the 16" on center timbers of the shed floor framework, the idea being airflow under the shed?

Ok, I hope that's all ok so far, please advise if I've missed something critical?

My questions are mainly around damp proofing the floor whilst adding insulation.

I'd planned buying and cutting big sheets of 50mm Celotex and fitting these neatly between the floor framework but this is where I'm coming up to my limit of knowledge.
  • Do I leave an air gap between the Celotex and the 18mm ply floor covering and if so how much?
  • Do I have the foil side of the Celotex pointing up towards the floor?
  • Is it ok to leave the back of the Celotex directly exposed to the air underneath the shed floor framework (which is only two inches off the ground)
  • Finally, do I need some sort of damp proof membrane in my floor structure given the whole lot is going to be pressure treated timber and if I do when where should I have it?
I'd really appreciate any advice anyone can offer!

Thanks!
Muzza80, I'm going through the exact conundrum and was thinking of doing exactly the same. How did it work out in the end?
 

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