shed insulation and air gaps

[antihero]

Hi guys,
Have received my pre-built shed and I'm now ready to begin buying materials to insulate.
Now,I know the basics thinking and order of insulating,from inside out,Int cover,Vapour barrier,insulation,air gap,vapour breathable cover,ext cladding.
My questions are thus,
My all studs are only 50mm thick so this is all the room I have to include all these layers so to speak unless I want to add more timber to the studs resulting in less overall room(shed is only 61/2ftx14ft so space is precious) so how much of an air gap do I have to leave?Will 25mm insulation be worth the hassle?
Couldn't I bung in 50mm rockwool and forget about the air gap and the vapour breathable layer.....after all my shed walls have no air gaps in them for air to circulate so surely if I insulated and left air gaps between the insulation and cladding this would just create pockets ???
Then surely I'd have to put vents?? at top and bottom of all the sections of the walls to ensure there was air flow??

So confused,please advise?
Will add pics of my walls if it helps

 

[9fingers]

If you use an insulation material that is closed cell and wont absorb moisture, I'd scrap the air gap and fill the 50mm with insulation.
polystyrene eg jablite is cheapish or better still if money is not tight is kingspan or similar.

Remember that draughts can negate the effect of insulation in no time at all.

Eliminate these as a priority.

Bob

 

[antihero]

9fingers,thanks for the reply(41 views and 1 reply),
I was hoping to use 50mm Rockwool(not closed cell but I can get it cheap),
Could I still use this if I included the vapour permeable layer to the cladding and then still left no air gap,would this prevent the insulation from getting damp?
So it would go,Int cover,Vapour barrier,Rockwool,(no air gap)Vapour permeable barrier,Ext cladding?
Would that work??
Thanks again.

 

[9fingers]

You will possibly be ok with rockwool. Ideally you want plenty of air circulating round the outside of the shed. If it is in a corner against a fence or wall, then some polystyrene near ground level on the sheltered faces will ensure that the rockwool does not retain any moisture that might collect.

Try and resist attempts by local management to grow plants up the outside!!

Good Luck

Bob

 

[woodman47]

Remember that different materials have different Insulation values. Rockwool is half as effective as the same thickness of PU foam (Kingspan). And as you can miss out one of the membrane layers you save money there. Alternatively there are newer multi-layer mat-type materials that are thinner still for a given U-value.