Insulated shed subfloor question

[GCarnegi]

I want to build a workshop / shed in a corner of my triangular garden, so will be building from scratch rather than from a bought kit. Shed will be right angled triangular in shape. Sides will be 5m + 5m + 7m "hypotenuse".
I want it to be as heat efficient as possible, so was curious about the floor / subfloor / base construction.

I have a bunch of 2x10 joists from a recent demolition which I was going to use for the floor, but am I best to build a block work foundation around the perimeter and hang the joists off that, or just build some sort of timber "decking" base? Should I have a concrete base poured or leave it dug out and filled with chuckies?

Should I insulate between the floor joists with loft insulation, and if so, how do I keep it dry?

Any and all tips appreciated.

Guy

 

[holmslaw]

There's no point in insulating a shed unless you're going to pemanently heat it, and that will cost more than the house heating bill.

What you need is good ventilation, this will prevent condensation and keep the shed bone dry.

My shed has an approx 20mm gap at the top of two opposite walls and it is perfectly dry. If I need to use it in the winter I use a fan heater and the shed is warm in a few minutes.

 

[GCarnegi]

Fair enough. Thanks for that- it makes sense. So would you still recommend building over an earth base, laying slabs underneath, or pouring concrete?

 

[Deluks]

There's no point in insulating a shed unless you're going to pemanently heat it, and that will cost more than the house heating bill.

Not if the shed is better insulated than the house. He didn't say he wasn't going to heat it.
If you wanna insulate it, go for it. But you should do walls and ceiling too. Easiest way would be concrete base, dpm, polystyrene or foil backed board with chip or plywood flooring on top. Can do joists if you want but will need to dig out quite a bit and fit airbricks in perimeter walls.

 

[GCarnegi]

I'd probably have a Super-Ser in there or an infra red thingmy.

Walls were going to be built something like below, and I haven't really thought about the ceiling / roof yet.

Untitled

• GCarnegi
• 26 Sep 2011
• 1

Would probably add the insulation and internal boarding at a later date, but obviously I can't do much about the subfloor / base at a later date, so have to get that right off the bat.

Should probably have added that it is already dug out to around 12" depth as I was planning to put decking there but never got round to it (plus it's always in shade sho not really a good place for decking)

 

[Deluks]

You can do away with the osb sheathing, unless security is a massive concern, and plywood the inside instead with the money you save. 2x1 treated battens will be more suitable than 2x2, and cheaper. You should use a polythene vapour barrier on the internal framework, before boarding out. (walls and ceiling, and tape all overlaps)
Couple of closeable vents fitted to opposing walls.