Insulating a pre bought shed floor before assesmbly

[heyrob]

Hi,

I have had a little snoop around the web but haven't found what I am after.

I have a 8x12 shed on order which has a T+G floor.

I have made a timber frame for it to sit on out of 3x2 which is sitting on concrete piers and over the old small concrete slab.

The shed will be mostly to store tools and be used as a little workshop, so I would like to future proof it buy insulating the floor when I install it. Then likely insulate and heat the inside in the future. I don't really want to take away headroom with a floating floor inside. The way I see it I have the following options / problems:

Flip the T+G floor over and insulate between the joists (will likely be thin) or pin bubble wrap etc over the joists. Both would leave the ends open? would these need to be closed to create a sealed air gap?

Put insulation between the timber frame joists sitting it on batons. Again when the pre fab floor sits on top it will leave a gap and the edges are exposed surely this would reduce its effectiveness. Also do you need to board out / membrane the underside of the joists to stop, bugs / animals using the insulation? The videos I have seen seemed to leave polystyrene underneath open and board on top for the floor?

any help advice would be appreciated.

 

[Seafarer1966]

You could try floor insulation board. The type that goes underneath a laminate floor. I got mine from B and Q. It's about 10 mm thick or thereabouts and comes in panels that jigsaw together with one side metallic foil. You'll need to lay board on top of it. I'd use an exterior grade ply for durability and longevity.

 

[Seafarer1966]

Sorry I meant to add. Use aerosol foam filler for any gaps or hard to do bits? It cuts lovely with a sharp blade when it's cured and you could pretty much do anything with it.

 

[r896neo]

Its hard to envisage the exact setup you have regarding your 3x2 and piers but the general principle is you want the insulation absolutely tight against the underside of the flooring. The underside of the insulation can be left open. Its essential not to leave a void between the insulation and the floor or you will create the possibility of condensation in this gap.

 

[REEMS]

You could raise your 3x2 and put 100mm insulation onto the concrete so to fill in the void under the shed.

 

[heyrob]

Excuse the bad sketch but this roughly shows:

Piers added to existing concrete slab.
3x2 frame sitting on top of those
T+G prefab shed floor on top of that

So the only way to have it tight to the shed floor would be to insulate between the t+g floor battons.

 

[big-all]

if you are within 2m off the boundary make sure your below 2.5m total height from the natural ground height it covers to avoid the need for planing permission

 

[REEMS]

I see what you mean depending on how even or uneven your concrete is you could use 50mm and 25mm celotex or recticel it may protrude passed the 3x2 or it may sit flush with the top you,d have to measure see if you have enough room.
And its foil both sides.

 

[heyrob]

Yep I checked, should come in at max 2.4m

If I use Celotex I would still have an air gap when the T+G sits on top? that's what I cant get my head around, Unless I celotex between the T+G floor joists as well as between the 3X2?

 

[big-all]

from the ground level ??

 

[REEMS]

Why dont you put it between the T&G floor joists first before you put it down on the 3x2 if you cut it so its a tight fit it should stay there till you put the floor down, i,ve just been using recticel in studing if you put it in tight you cant get it back out without damage.

 

[heyrob]

from the ground level ??

Yep Its a pent shed so is only 2010mm high so have 490mm to play with for piers and framing

thanks Remeguy seems the most sensible option, will cost it up

 

[big-all]

have you put felt or dpm between the concrete and timbers to give a moisture barrier

 

[Diver Fred]

Why do you not put the floor section of the shed in it's final position; Lay insulation over the top of it then lay another wood floor over that, then errect the shed sides and roof finishing off by sealing around the insulation edges.

That way you maintained the ait gap underneath the shed and have you insulated floor.

 

[motorbiking]

I think you are over thinking this.. you need to insulate the walls, door and roof too, I think I'd use 20-50mm celotex and cut to fit between the joists and then either clad with ply or plasterboard. The route you are going it would be cheaper and easier to buy a SIPS shed or build your own.

Given the life of a shed, its going to be cheaper to burn the extra power than recover the cost of insulation. Particularly since you will have a single glazed window ? with a U of over 5 and perhaps a door too?