Frequently Asked Questions on Damp in Sheds

by John Coupe

Questions on Damp in Sheds – I get asked a lot of questions about Damp in sheds and so I have pulled together a lot of these onto one page for you to browse. Hopefully, you can find an answer to your question in amongst these.

If not please visit my Shed Questions page and ask away.

My only request before you do this is to take the time to submit several pictures and write a good summary your problem. I am keen to help but if I just get a one-liner saying - “I need some help with my shed roof!” it takes a lot longer to help you get to the root of the problem and find a solution.

I look forward to hearing from you if you don’t find an answer to your question below:

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How to protect stuff from damp in my shed.

by Matt
(Southern England, UK)

John, I have a shed provided by our housing association. It's basically a long block, brick built building, that has been split into 6 sheds that have a concrete base. Each brick shed has a wooden door. I think the roof is possibly a type of concrete covered in roofing felt. There's no ventilation I can see, other than the fact that the door doesn't sit perfectly in the frame.

In the shed, I currently store my bass amplifier, which has a paper cone (15inch). I've made a plastic cover for it but am obviously concerned about damp. The reason I don't keep it inside the flat is that it weighs 50kg and I'm on the 4th floor, and there's no lift.

What can I do to improve the damp proofing in the shed, that doesn't involve structural work (which we're not allowed to do)? I wondered if I could build an insulated frame sitting inside the shed - plastic membrane on the floor, thin insulation on the walls and door?

Any help much appreciated.



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Protecting your equipment from the damp
by: John

Hi Matt,

Thank you for your question. Three things that will help to lengthen the life of anything that you are storing in your shed are temperature, ventilation and humidity.

It sounds like you may not have power to this shed as it is basically a brick shell so heating it does not sound like much of an option. If you did have power I would recommend insulating the shed to minimise the power usage. Increasing the temperature would encourage any damp to evaporate but this would also require ventilation.

Ventilation - installing some sort of wind driven fan or a small battery operated fan (possibly with solar recharging?) would encourage a through flow of air and so help to prevent pockets of stale air where mildew could thrive.

The final option is to reduce the humidity. The normal route for this would be to use a dehumidifier , however as you may not have power to the shed then the powered route is not an option.

Another possible solution,, depending on how often you use this amplifier, would be to create an air-tight container/box to store it in. You could then place the amplifier in the box with some dessicant crystals which would absorb any remaining moisture in the air. Over a few cycles the dessicant crystals would become saturated with moisture, but they could be regenerated in the oven to burn off the absorbed moisture. To make the crystals last as long as possible the volume of the box should match the size of the amplifier as closely as possible.

This is the same sort of approach that suppliers of electronic equipment use when they insert those small sachets of crystals into the packaging of new electronics.

I hope that the above suggestions give you some food for thought.


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Damp proofing shed floor

by Ronda
(McHenry, IL. USA)

We have an existing shed. It was built using wood timbers cemented into place and has a wood floor. There was no moisture barrier put into place below and there is really no way of getting under the shed. It is the size of a 1 car garage with a full attic. we insulated the celing of the first floor so the attic is good but the main floor everything gets moldy in the damp seasons. What can we do to solve this problem and prolong the life of our shed?

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Shed mould
by: Tim baber

I once read a really good book about building when I was living for 6 years in a shed made of hardboard. It said there are three things that you must do. INSULATE, VENTILATE and HEAT.

It worked for me, so without offering details try these three things.

I would do them in that order of importance, looking for no more than 1 air change per hour with the ventilation (possibly) to save on any heating you find is necessary.

An old saying from the English countryside is that a building needs a good hat and boots. Sounds and looks like you have a good hat, but you are going to need the boots now!

A couple more questions to help get to the root of the problem.
by: John - Admin

Hi Ronda,
Thanks for your question and thankyou Tim for your input, I like the analogy about "the good hat and good boots".

Ronda, could you tell me a bit more?

You say that the shed is formed from timbers cemented into the ground, does this mean that this is a pole barn where the main vertical posts are concreted into holes in the ground and the rest of the structure is supported off this frame?

Also could you say a little more about the floor construction? Is it boards or plywood? Are the timbers that the support the floor in contact with the ground?

What I am trying to do here is identify the source of moisture as I believe that is one of the main reasons that the mold/mildew is enabled to grow. Reducing the moisture content of the air and increasing ventilation are the main two prongs of attack. Some form of heating, as Tim mentions, could help to reduce the moisture content of the air once we have stopped the moisture getting in to the building at source.

Knowing a little more about the problem may help to identify an appropriate solution.



Answer to Questions
by: Ronda

Sorry for the delay in these answers.
Yes, it is a pole barn. The floor is plywood. The shed is on a slight incline, so the front of the shed the support under floor touches ground but the rear of the shed is above. But not enough for us to get under.

Ventilating the shed floor
by: John - Admin

Hi Ronda,

Thanks for the extra information. I think that you need to check that there is plenty of ventilation beneath the floor so that moisture can't build up beneath the floor. This would take the form of holes in the siding on each side of the shed below floor level to allow cross ventilation. The holes would be trimmed and covered in mesh to keep out pests and critters.

The other two factors to pay attention to are then heating and insulation. The purpose of this is to keep the inside of the shed warm and dry. Most likely some form of low power electric heating, just enough to stop the mildew growing.

How does this sound?



Thank you
by: Ronda

Thank you for your help, We will get started on insulating and working out a heating system this summer and hopefully be ready for next winter. But one more question... If we do heat it like you said. What is the minimum temp do you think we can leave it set at to avoid condensation?

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Shed for storing magazines!

by Colin

Hi, I need to buy a shed for storing my large colection of magazines. Obviously I am worried about keeping them in good condition. I have seen advertised 'garden buildings' that come with built-in insulation (e.g. those made by Lifespace, Solus, Waveney) but compared to conventional sheds they are very expensive!

Is it necessary to buy something like this, or would adding insulation ourselves (fibreglass?) be good enough?

I hope you can offer me some helpful advice! Thanks in advance!

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Must read manga!
by: GreenBoy

Well before goign further you need to make some choices on how you want to use your shed.

Do you just want to store the magazines or do you also want to use it as a plce for reading them, cataloging etc?

If its pure storage i would say then you could go for any well constructed shed and insulate it with rockwall of expanded foam.. In a dition i would suggest if power is available to put in a black heat tubular heater - these are very low power and if combined with a frost stat will help stop the temperature dropping so condensation starts.

Ventilation is another aspect to consider as idealy you would have some sort of vent - but you may want to consider security so just having an auto opening window (as you see on greenhouses), you may want to put a vent axia type extractor in (again assuming power) with buit in humidity stat. to help keep things dry.

Drynes is CRITICAL - so ensure not only you buy a quality structure but also that you errect it properly.

If you are going to use it as a library as well as a store then it may be more advantageous to save up and go for something more akin to the Solus Leisure buildings which are insulated, and probably double glazed.

Hope this helps, but please feel free to post follow up qustions.

I am also sure John will have some great advice also.


Storage shed for magazines
by: John - Admin

Hi Colin,
Thankyou for your question. Great advice by Greenboy. I am not an expert in paper storage but I would think that the key factors to think about are temperature, humidity and ventilation. The reason for temperature being important is that as the temperature drops and the 'dew point' is reached water will condense out on to cold surfaces which would probably include your magazines. Greenboys suggestion of insulation and a source of heat is a good way to combat this. Another possible route is to purchase a de-humidifier which lowers the moisture content in the air and so the posibility of condensation forming. I think that humidity control is an important factor in museums and libraries.

With regards to the shed structure the main thing I would have thought is that the shed is well insulated and as air tight as possible. This probably will push you towards the more expensive end of the range. Alternatively if you are at all practically minded building your own shed/storage building is a way of saving money. There is however a fairly large investment of physical labour and time involved.

I hope this of some help. I would be very interested to know the sloution that you adopt.

All the best.


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