Shed Condensation/Cladding

[RobLyon]

My apologies if this is a bit off topic so please feel free to delete if not allowed.

I'm in the process of building a large timber framed shed (pent roof) that will be clad in plastisol sheet. I've read that metal sheds can be terrible for condensation so i've been looking into ways to avoid it. I've read that insulating the roof is a good start and ventilation is key. I've already bought non breathable membrane with the hope that any condensation will fall off the metal cladding and onto the membrane rather than the floor/ceiling. Will the condensation now just form on the membrane though?

I'm looking at using loft insulation between the purlin's. and boarding the ceiling with plasterboard. I've also decided that it's worth fitting a breathable membrane to the side walls before fixing the batons and cladding panels as retro-fitting would be a nightmare.

Should i return the non breathable membrane and just do the whole lot in Tyvek?

The timber frame went up over the weekend so if I don't sort something soon its going to hold up the build.

Thanks in advance,

Rob

[Bearbonesnorm]

I'd use a breathable membrane everywhere except the floor. I don't see any benefit to using a non-breathable membrane as both are waterproof and as you say, ventilation is key to helping combat condensation.

For insulating the roof, I'd probably use Kingspan boards.

[Taylor]

What he said. ^^^^^^^

[psling]

Stu and Taylor are right, sort of...

Questions:
What base/floor are you using? If concrete, have you used a damp membrane (non permeable)?
Will the shed have any form of heating?
Will there be any water pipes/gas boilers/water storage in the building?

Two potential causes of damp - 1/ sweating of the metal cladding relative to other materials used and 2/ condensation.

Sweating can be prevented / reduced by insulating against the inside of the metal panels. A breather membrane should be between the insulation and the metal cladding. If you are boarding the insides (especially the roof) the addition of a vapour control barrier to the room side of the insulation will also help.

Condensation (gross generalisation) can form against a surface colder than the internal temperature if internal humidity is close to / exceeds saturation point. So, insulation and ventilation are your friends as Stu & Taylor say.
Humidity is kept lower if the base is waterproof, dry, & insulated and there are no or minimal water sources e.g. cold water pipes/un-flued gas appliances/etc..
Ventilation is best if there is a flow between low level and high level.

This may be overkill if it's just a shed; lots of holes and gaps may be sufficient!

Bit like a tent really

[RobLyon]

Hi,

Thanks for responses.

I have ordered a roll of Tyvek and will return the non-breathable membrane.

The base is 2" concrete pavers coated in garage floor paint (not sure if that helps?). There is a DPC stapled to the base of the timber frames and the whole lot will be sat on some off-cuts of ceramic tile to leave a ~8mm gap. There is no water or gas in the shed/workshop. I'm not sure on heating or if the walls will be insulated yet, i'm trying to leave the option open if I decide at a later date that its too hot/cold/damp etc

Thanks,

Rob

[psling]

The 'floor' will be your biggest source of moisture into the shed then and plenty of ventilation sounds like the best thing for now; the 8mm gap under the walls will give good ventilation (and plenty of cold draghts in winter!!).
Some high level ventilation (through the eaves) will also help.

[Trail-rat]

why board with plasterboard ?

Id not go with loft insulation either.

MY garage suffered this issue with the metal clad roof.

i went with Kingspan seconds from fleebay cut and between joists to tight fit and filled the gaps with expanding foam.

That fixed my issue.

Ventilate - ventilate and ventilate.

[RobLyon]

My dad has suggested creating a skirt around the perimeter using the DPC, it should stop water coming in but will reduce the ventilation/draught. The highest point of the roof can be left exposed as it is 1m away from the house so should never get driving rain or wind.

Plasterboard was mainly because its cheap and easy but any condensation could leave marks.

The build is being done in phases really over the next 6 months. As mentioned the timber frame is up and hopefully the cladding should be up in the next 2 weeks so hoping it should be waterproof. Then i'll look into insulation, wiring/lights and finally heating if required. I'm not sure if its worth just paying the extra for the insulated roof panels.

[Jamesh]

Some sound advice here.
Been undertaking a similar project but on a slight differing scale. I've been renovating my farm workshop of late.
Have cut to fit recticel/celotex 50mm, butted close to the exterior metal cladding inbetween the cross beams. Filled all gaps with expanding foam. Then lined on top with 3/4 ply mounted on some 2x2s bolted in on the cross beams to bring it in line with the original block walls. Currently building a mezzanine when light fades

Satisfyingly simple job which has made a big different to the space. Though alarming how quickly a significant bill can accumulate