Mould in shed. Too much ventilation maybe?

lozcozard · 25 Mar 2021

I built a shed last October. Couple of months later the contents are getting mouldy and I can see mould spots on ceiling.

everything I’ve read says ventilation is key. Keep it ventilated. Well I’ve got plenty. The roof beams sit on top of the wall frames. This means between the roof beams there’s a 3” tall gap. Space between beams is maybe 12”. I haven’t filled them in. The roof overhangs a bit from the wall so you can’t see right out.

the only thing I can think of is during the last horrible wet winter the damp outside has come in through these big gaps.

So could too big a gaps be an issue? It’s letting too much damp air IN?

I’m wondering if I do fill them in but leave a much smaller gap for ventilation.

Photos attached.

I haven’t insulated it. It’s tongue and groove on outside of frame. I did put membrane in to keep damp out in case o do insulate it. The overhang has tongue and groove under it so actually there’s not massive gaps on the front. The back hasn’t.

big-all · 25 Mar 2021

what flooring do you have??
is the shed used regularly??
what material is the mold on ??
pictures below will help

lozcozard · 25 Mar 2021

Roof and floor is OSB

floor osb sits on 3x2s that span across gravel, secured in place by those plastic mesh things.

Some mould on the roof osb but can’t see any floor, although I have carpet cut offs on the floor.

mould is on garden furniture cushions, but also office equipment like monitors (I built the shed to store my office equipment as I closed my office due to the pandemic). Mould on various other things.

I am in and out of the shed often. Every other day maybe. Sometimes a few times a day as it’s where I store all my tools too.

further pics of shed attached but I don’t have mould pics at the moment.

lozcozard · 25 Mar 2021

During winter it felt damp inside a little. The monitors had condensation on them.

If something was wet inside I can’t think what. Although thinking about it could be from when the floor osb was wet during construction as it was in the rain for some time before I finished the roof and walls. I hope it is that which means the damp is short term and it’ll dry out.

big-all · 26 Mar 2021

wet wood drying out will be part off the explanation as the temperature cannot move the moisture in the structure at any speed
non permeable surfaces like plastic hard nylon and glass will show condensation where as other surfaces will absorb moisture but spread it around so its below the the level mould will grow but its still there
if you dont have windows for both solar gain and to attract the moisture it can be difficult to shift the damp

lozcozard · 26 Mar 2021

I’m thinking of putting Windows in in the future when I don’t need to store my office in there anymore and use it more. That’s when I was going to insulate it. I didn’t think a window would help like you mentioned so maybe I should put it in sooner rather than later.

I’m also going to hope it was the moisture in the floor and will dry out and see what happens.

thanks

big-all · 26 Mar 2021

you can under value windows
the power off the sun is immense so quite a bit off heat input
is there any sort off heating at all to help move the dampness ??
Moisture will just circulate until enough heat to drive it out the fabric then removed by airflow
insulation on its own wont dry it out as it does nothing more than average the temperature out over several days you need some heat input via windows or heater to shift the damp

lozcozard · 26 Mar 2021

No there’s no heat. I assumed sheds can stay dry without it. I have 2 other flat pack overlap sheds (so loads of gaps!) and they don’t have mould.

Sunshine and warmth are nearly upon us so am sure it’ll dry naturally soon then I can wait and see if the mould comes back.

MisterBoy · 26 Mar 2021

Is it obviously draughty when you're in with the door shut? I would wonder about maybe having a fan to keep air moving around.

Jowwy · 26 Mar 2021

If you got power in there, then plug in a USB fan to aid air movement. I also think you need proper vents

lozcozard · 26 Mar 2021

You can feel air moving a bit because there’s a lot of ventilation around the eves

what would proper vents be? So instead of a gap put a vent there which is like plastic with holes in?

Jowwy · 26 Mar 2021

I would put a vent top of side wall.....and a vent low down, so cool air comes in at the bottom and pushes the warm air out at the top. The fan will help that happen

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Mould in shed. Too much ventilation maybe?

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