Why does my shed get went under things?

[JP_]

I noticed this weekend that water accumulated under items in my shed.
It first, I thought it was just items on the floor, but then same happened with something on a shelf. The shed has a single large air gap and the door is not exactly a tight fit, so air flow should not be a problem. It sits on a concrete base that does not have a damp membrane in it. The base is close to the house soak away, of that is relevant ... but not right next to it.

Could excessive moisture build up underneath be a problem? Should I make some air gaps under the shed, as the base is "closed" and no air gaps (this shed was originally built on sleepers on a lawn so would have had airflow below)

Was wet under punch bag:

And wet under a bucket (bucket did not have a hole!)

 

[JohnD]

wet patches under things on a shed floor are very common when there is no dpc.

the ground is always damp, so the floor can only be dry if water evaporates off it faster than it permeates through. Putting things on the floor obstructs evaporation. This can also be seen on damp floors and walls inside a house.

it sounds like the void is unventilated, so fix that before the rot gets too bad. there is also a wet corner that might be due to a faulty or absent gutter and downpipe.

Even if the slab does have a dpc, the shed must overlap it, or rain will fall on the exposed surface and make it wet.

The shed bearers appear to be standing on the exposed slab, so they will be damp and will rot.

I can't see a picture of the wet shelf you mention.

 

[JP_]

I was thinking of drilling holes around the shed base for ventilation - any reason why I shouldn't do this?

Didn't take a photo of the shelf, only spotted it later in the day. Was a metal shelf with something on it - at first I assume it was all from the floor, but that made me think maybe humidity in the shed was too high.

 

[big-all]

is the shed off the ground with no timber in contact with earth or concrete ??
ok just noticed your pictures and it needs to be off the concrete with airflow underneath

 

[JP_]

Hmmm, wondering how I am going to lift it and get something under it ... could I not just drill air holes all around it?

Here's the base - I put 5 litres of wood preserve on it before building it, so hope I can save it!
I wouldn't be able to get round the back though, so could only make holes in the front end...

 

[big-all]

is it fully sitting on chippings ??
as in earth topped by chipping and ply fully in direct contact ??

 

[John D v2.0]

it's not really related to ventilation directly, the outside of our car is covered in condensation every morning, as are our windows on some days.
Without heating or dehumidification you'll always get this problem to some degree, due to temperature changes. It even happens inside unoccupied houses.
Basically during the night all your stuff in the garage, and the garage itself cools down. Then as the (thermally light) air warms up and the dew point rises, your (thermally heavy) stuff is now cooler than the dew point, so the water duly condenses all over it and runs off onto whatever's underneath.
You'll notice it a lot more under hard things that are vertical, than absorbant horizontal things.
Add heating or dehumidification and it will help.

 

[Harry Bloomfield]

I was thinking of drilling holes around the shed base for ventilation - any reason why I shouldn't do this?

It will not do much harm, but neither will it do much good. You need a good free air flow under there. On a dry day, remove everything in there, then use a scaff pole with a flattened end to gradually lever it up off the ground, a bit at a time, working round and round the perimeter. You should aim to have it clear of the ground the height of a house brick, laid flat down. You will need several of them.

 

[JP_]

It will not do much harm, but neither will it do much good. You need a good free air flow under there. On a dry day, remove everything in there, then use a scaff pole with a flattened end to gradually lever it up off the ground, a bit at a time, working round and round the perimeter. You should aim to have it clear of the ground the height of a house brick, laid flat down. You will need several of them.

Problem is, it has another shed to the left and a fence behind, and a small greenhouse to the right, so not sure I can lever it up from anywhere other than the front

 

[JP_]

is it fully sitting on chippings ??
as in earth topped by chipping and ply fully in direct contact ??

No, it's on a concrete base

 

[Odds]

JohnD makes a good point about condensation occurring naturally at this time of year. On every frosty morning i have to wipe down windows because the cold glass and warm air create a fog, just as it does along the river valley where i live.
A dehumidifier would help to some extent and a larger gap under the shed would've been more helpful but there's not much more you can do: lifting the shed sounds like a great deal of work for little effect.
Apart from suggesting a Jumbo bag of silica gel, i can't think of a way to solve small patches of damp.

 

[JP_]

Yeah, but I have 3 sheds, and it is only this one that has this problem. The other 2 are always dry.

I don't see how a dehumidifier would work, more moist air would be drawn in through the air vents quicker than the dehumidifier could remove it.

I think the solution is probably to try not to leave too much on the floor like that. Support things a bit in this shed. Maybe drill some holes underneath..

Funny, as last summer, one day I had a bunch of slugs climbing up the shed towards my strawberries - reckon they are living underneath it now. Must by nice and damp down there ...

 

[Harry Bloomfield]

Problem is, it has another shed to the left and a fence behind, and a small greenhouse to the right, so not sure I can lever it up from anywhere other than the front

You need a small toe jack - Lift it up a little way at the front, so you can insert a toe jack gradually to lift it along the sides.