How to Stop condensation in out door building

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I have recently moved in to a new house and in the garden is a well built garden shed 8M x 4M.
It was built with stud work /flat felt roof ,all new.
The wall studwork has vapour barrier on the outside held on with batton and shiplap timber on the outside of that.
The shed is water proof but i want to use it as a home cinema room and want to insulate all the walls and roof then board it over.
Can i just put rockwool in between all the stud work to rest against the vapour barrier or will i have to make a air gap somewhere on the inside boards so condensation won`t appear.-
thanks,
jo
 
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Sounds like it will sweat badly it should have a breather membrane were the vapour barrier is, and I would use insulated plaster board.
 
Are you sure that its a vapour barrier?, i.e. a tarred paper or plastic sheet? If it is, its not a vapour barrier but a secondary protection against water ingress due to knot holes/cracks in the shiplap. So you must make this layer permeable to air or you will have a problem.
How it works is that as you go from the inside to the outside of a wall the components should get more porous to air. This is because you breathe out moisture and as it percolates through the wall, the air gets colder and the water that starts of as a gas condenses into real trickles, which will pool up and cause rot.
So to meet this criterion, from the inside, plasterboard/ other boarding, VCL, insulation, outer layers (brick or wood). If its something like shiplap, then a secondary water proofing layer should be used such as breather membrane with a venting space to the inside of the shiplap. This will give you the same arrangement as a flat roof.
An idea (my own!!), would be to try and replicate vertically hung tiles. This is so penetrating water will drip down and outwards while providing some gaps for air movement. This basically slash the existing membrane in a defined pattern. Push through bits of square plastic film that hang down on the outside and up in the inside where its taped. Soo water dripping on the outside continues down but the inside where you have cut the film air can get in or out. So your pattern of bits of plastic shield the lower one from water ingress. A small piece of rolled up plastic could be pushed through the cut so as to let more air through.
Frank
 
Thanks ,the prince of darkness,
I have been and looked closer, it is thick plastic /polythene sheet used, however if i look up from under neath between where the sheet drops down by the outside floor beams i can just look up between where the sheet touches inner stud work and see the inner roof area.
Also from inside i can see down and see the ground.
If i were to give the sheeting some separation maybe with a batton to create a gap from the inner stud work from roof to floor so as to create a wind movement past the inner stud work would that work?
Thanks,
jo
 
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Looks as if the person who built the shed may not have understood the principles of condensation. Beneath the shiplap on the outside should be a breathable membrane (Tyvek or similar). The prevents stray water getting in, but allows any moisture that gets into the structure from the inside (or the outside) to evaporate. If you were to insulate on the inside, a vapour barrier (plastic sheet, or foiled Celotex with joints taped) should go on the inside to prevent moisture in the warmer air from penetrating into the wall structure and condensing onto the timber. That is, the vapour barrier goes on the warm side of the insulation.

Assuming there is no prospect of removing and replacing the shiplap, you're right in that creating airflow between the insulation and the inside of the vapour barrier you do have should be effective.

Cheers
Richard
 
You did not mention the floor.

If it is a concrete slab in contact with the ground, with no DPM, water will pass through it and evaporate into your shed. It will be particularly bad if rain falls off the shed and onto the slab.
 
You did not mention the floor.

If it is a concrete slab in contact with the ground, with no DPM, water will pass through it and evaporate into your shed. It will be particularly bad if rain falls off the shed and onto the slab.
Hi John,
No the shed is built on a wooden frame mounted on adjustable big plastic feet sitting on a old patio.
So it is up off the ground water free.
jo
 
You did not mention the floor.

If it is a concrete slab in contact with the ground, with no DPM, water will pass through it and evaporate into your shed. It will be particularly bad if rain falls off the shed and onto the slab.
Hi John,
No the shed is built on a wooden frame mounted on adjustable big plastic feet sitting on a old patio.
So it is up off the ground water free.
jo
Might be worth insulating the floor then, if it isn't already insulated. You could chuck 50mm Celotex or Jablite on it and some plywood on top of that
 
You did not mention the floor.

If it is a concrete slab in contact with the ground, with no DPM, water will pass through it and evaporate into your shed. It will be particularly bad if rain falls off the shed and onto the slab.
Hi John,
No the shed is built on a wooden frame mounted on adjustable big plastic feet sitting on a old patio.
So it is up off the ground water free.
jo
Might be worth insulating the floor then, if it isn't already insulated. You could chuck 50mm Celotex or Jablite on it and some plywood on top of that
Hi, Looked underneath and someone has already suspended under the green floor sheets between the joists celotex on tin brackets.
jo
 

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