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We've got an 8*8 shed used to store stuff. In spring earlier this year we noticed that the stuff inside was getting a bit due to condensation: at one point there was a sheen of mould on a chunk of stuff. I opened up the soffit vents and added a ventilation panel at the bottom of the door, which seemd to help: the mould wiped off an didn't seem to come back and the condensation was not an issue
as we're getting into winte we're seeing the condensation again, what's the best course of action? I'm seeing conflicint suggestions, some say seal up vents to prevent cold drafts, others saying you need airflow.
I can add a couple more vent holes easily enough. Is it worth getting a solar powered extraction fan? (There's no main power to the shed)
Any recommendations especially for specific models / items / sensible courses of action will be gratefully received
What's the shed made of? has it got a box profile steel sheet roof? or is it a standard garden shed. If so I would say there's a leak.
Ventilation is your friend. We had similar problems in a fully sealed room we made at the back of our garage, but I've added a door vent and a vent into the garage for good airflow, and now no problems. It's cold, but that doesn't matter.
it's a wooden shed with a 2-part wooden roof covered in roof felt with plenty of overlapÂ
loads of ventilation. As much as you think and double that. Preferably where you get a bit of wind. No need for fans until you try the 'free' passive route properly first.
I wouldn't have thought a wooden shed like that would be sealed enough to get condensation. Condensation doesn't tend to form on wood only metal sheds. Likely to be some ventilation through the albeit small gaps around the door, between the panels etc. Unless you have insulation and or a membrane lining the inside and the roof.
But no harm in putting in ventilation and seeing how it impacts the moisture levels. My money is on water getting in there. Get in there with a torch and have someone spray a hose pipe over the top.
Does the shed have guttering?
Ventilation +1
The more the better.
The problem with trying to seal it, it it's impossible. So some moist air gets in, condenses, moisture accumulates, and before long at all you've got enough moisture to be at 100% RH all winter and mold sets in.
Whereas with enough ventilation the inside of the shed should never get to 100% RH as it'll be slightly warmer than the outside overnight, and airflow during the day will be <100% RH.
Struggling with my new summerhouse at the moment as the floor is a ~66x44mm frame on a concrete base with boards on top, water creeps in off the (larger than the shed) concrete pad, gets trapped and breathes in through the floorboards. The inside of the building is fine because it's ventilated but there's mold under the floor. It's only a problem inside where I have a rubber matting gym floor that doesn't breath. It's soaking wet underneath.
In hindsight I should either have made a 1/2" screed pad the exact size of the shed so water couldn't run under it (the sealing it option), or changed the floor so the joist only ran one way and open at the ends (the ventilation option, which I would now prefer).
In the meantime I'm going to take the floorboards up and put in a layer of superquilt with taped joins. Hopefully that's sufficient insulation/vapour barrier to keep the floorboards dry and trust the treated wood of the frame to last despite the damp. If it survives a decade then either we'll have to jack it up from the corners and re-do the floor, or will have moved house 😂.
Unless you have a heat source and the ability to retain a bit of heat you should ventilate. It would need to be airtight to be good enough to prevent condensation via sealing.
Under certain climatic conditions you'll get condensation irrespective of the amount of ventilation.
At my old house I had a sectional concrete garage with an asbestos roof - it would drip horrendously all winter, stuff would get mouldy even when covered up. I removed the roof, replaced it with a pitched roof covered in shingles with open eaves and it was never damp again.
Ventilation. We had the same, I put two vents in at opposite ends at the highest point of the roof, worked a treat.
Nothing clever vent wise, just two of this kind of thing
https://www.screwfix.com/p/map-vent-fixed-louvre-vent-matt-anthracite-229mm-x-152mm
Was a doddle with an electric reciprocating saw. Specifically Martyn's reciprocating saw, which I still have if you want to borrow it 🙂
Ventilate! at opposite ends of the shed, underneath the eaves at least. The more ventilation the merrier!
If you seal you'll just be sealing the damp in and making matters worse.
I have two sheds, one is timber standard garden thing, on gravel with air space underneath. One door, freezer inside, electric light etc. no ventilation other than gap around doorZero damp.
Second shed is stone built with concrete floor and corrugated plastic roof. Loads of ventilation. Condensation is bad on cold ie frosty mornings
Make of that what you will!
Apart from improving ventilation, which is a good call, what's it resting on? I had a crappy shed at out last house that was resting directly on paving slabs. Water would find its way up the joists and into the OSB floor where it would spread out and steam the place. I emptied the shed, lifted it onto secondary joists with a barrier between the two and the problem went away.
"Apart from improving ventilation, which is a good call, what’s it resting on? I had a crappy shed at out last house that was resting directly on paving slabs. Water would find its way up the joists and into the OSB floor where it would spread out and steam the place. I emptied the shed, lifted it onto secondary joists with a barrier between the two and the problem went away."
Good point! What's it resting on?
Base is paving slabs, with the joists resting on regularly spaced chunks of paving blocks to lift them clear of the slabs
So plenty of space for air circulation under the shed floor.Â
What's around the shed? Is it in a sheltered corner or is it exposed to a regular wind?
whats in the shed?
Does it but up to a neighbour? I once found that the neighbour had wacked a bunch of nails in my shed to hang a plethora of bird feeders. Firstly the nails were angled so that any rain on them trickled into my shed and then rain that hit the feeders bounced off and down the wall