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The Home Depot

How Do I Prevent My Shed From Becoming Damp?

Pro Referral > Home Guides > General Contracting > How Do I Prevent My Shed From Becoming Damp?
How Do I Prevent My Shed From Becoming Damp?

Metal sheds are more prone to a damp buildup than wooden sheds. Once a shed becomes damp, it’s difficult to get it dry again. In a typical damp shed, the walls run with water and there is a growth of mildew and mold. The water can get inside any items placed inside the shed such as your tools, lawnmower, your furniture, toys, and appliances. The damp will damage these items and, in time, erode the material of the shed itself. Let’s take a look at how damp build-ups up inside your shed and ways to prevent it.

  1. 1.Condensation

    When you drink hot tea or coffee in the winter near a window, you can see the steam rise and condense on the glass. The steam will then cool and begin to run down the glass as water. The same goes for the warm moisture in a shed.


    Metal sheds are almost airtight, which prevents the air inside from escaping. During the morning and afternoon, when the sun is shining, the air, both inside and outside the shed, becomes warm. The water vapor inside the air is also warm at this point. When the outside temperature cools, at night and in the early morning, the air inside the shed remains warm, as it has been prevented from escaping.


    However, the metal of the shed is a salient conductor of heat. It becomes cold to match the temperature outside. The warm air inside comes into contact with the metal surface of the shed, which then sucks in the warmth from the air, causing it the moisture in it to cool and condense. The moisture then begins to run down the walls of your shed.

  2. 2.Preventing Condensation: Wall Ventilation

    One of the ways to stop condensation form forming on the walls is to make sure your shed is ventilated properly. Small holes can be made in the walls of the shed, which allows the moisture bearing air to escape outside (warm air rises). These holes should be just right; too small and the moisture will remain inside the shed, but too large and it’ll be difficult to keep your shed insulated. Also drilling holes in the shed wall will mean the metal is now more susceptible to rust. The holes also have to be sealed and covered with plastic angles to prevent water inside if it ever rains.


    Sometimes a decent ventilation system will involve punching holes in walls facing each other, which will allow a breeze to flow inside and clear the moisture-laden air.

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  4. 3.Preventing Condensation: Floor Ventilation

    Another way to ventilate your shed is to build a wooden floor on top of the existing foundation. Why? Warmth rises from the ground in the evening, when the temperature has begun to cool. This warmth seeps inside your shed through the floor and becomes trapped inside, then cools later to cause your shed to dampen. To prevent that, a material that doesn’t conduct heat as readily can be used as a buffer. For example, if your shed has a concrete foundation, timber sheeting can be placed on it as insulation to prevent the warmth from entering inside. Sometimes water from the ground can also seep inside the shed. You can see why a shed would benefit from wooden flooring.


    Another way to ensure proper floor ventilation is installing damp-proof floor membrane on the existing foundation.

  5. 4.Preventing Condensation: Spraying the Underside of the Roof

    Some people prefer to spray the underside of their metal roofs with an underbody sealer, used in cars, to prevent the moisture from building up there. Other people spray the sheeting of the metal roof with methylated spirits then let it dry out. After that, they stick polysterene tiles to the underside of the roof. This is a permanent way to eliminate moisture on the underside of the roof, but it doesn’t help the other areas of the shed.

  6. 5.Preventing Condensation: Quick Tips

    Drying a damp shed is harder than you would think. There are several factors responsible for a shed becoming damp in the first place. The first factor, as we’ve discussed, is condensation. The second is faulty design. If a shed has been constructed poorly, there is nothing to prevent condensation from forming inside.


    To dry a damp shed, all the water inside has to be let out in some way. The first step is correcting the faulty design of the shed. In many cases, damp sheds do not have a raised floor. Have that fixed, if possible. A quick fix is to install thick metal sheets on the base of the shed that will raise it a little and prevent the moisture from getting inside. Another way to fix the problem is adding ventilation beneath the shed, which allow the air below to flow away and not attempt to force its way inside the shed.


    A combination of suitable ventilation, wooden flooring, and corrective design measures will stop your shed from becoming damp in the future.


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