Insulating a garden shed/summerhouse advice needed

Colmustard

Hi all,

I have done some research on this subject but have an underlying query, when insulating a garden shed or summerhouse, some people say use a vapour barrier on the warm side, others say leave an air gap, I am confused as to what is the best option.

I am building a 3.5m x 2.5m with a height of around 2.1m summerhouse (personally I would just call it a big shed) with the plan being to have treated featheredge cladding on the outside with a stud work frame, and on the inside, either plywood or osb, the whole thing will be raised at least a foot above the ground as there is no concrete base to sit it on, there will be four main corner posts concreted into the ground at a depth of about 2 foot/60cm and the floor will essentially be the same as the walls but with a damp proof membrane, this is where I need advice;

(I will use a 'sandwich' layer type of analogy starting from the outsides of the walls/floors etc)

1. I assume the floor 'sandwich' would be as follows, please correct me if I am wrong: damp proof membrane (wrapped underneath then over the top of outside floor joists) then plywood or osb panel then insulation then another panel?

2. When considering the insulation, should I just fill the whole cavity with board insulation cut to size (I would rather use a 'greener' insulation alternative if possible) or fill it with roll insulation? Or instead should I leave an air gap? If so, how would the 'sandwich' be for this?

3. Would Warmcel 100 flooring insulation be suitable to use on the walls also? It is loose fill but I can pack it in bit by bit, I ask as it is very cheap and if it can be used for a loft floor, why not a shed wall? I believe it is also quite Eco friendly as it is made from recycled newspapers.

4. How would the sandwich be for the roof? A flat, slightly angled roof, to channel the rain into a gutter.

5. When I concrete the corner posts in, will this prevent moisture damage and rot to the corner posts that are in the ground or do I need to protect them even more?

If any of this is confusing I am sorry, I tried to keep this short but as you can see, I that didn't happen.
I can draw up a diagram if this is needed.

Thanks a lot in advance.