How to damp-proof your shed

How to damp-proof your shed

Damp-proofing your garden shed helps to stop moisture from damaging the fabric of the building and destroying your tools and equipment. Here we cover routine maintenance, insulation, ventilation, heaters, dehumidifiers, and more. Everything you need to know to keep your shed dry and damp-free. 

At a glance

  1. Shed maintenance & repairs – take care of your shed roof, windows, walls & doors
  2. Install sufficient insulation in the walls
  3. Ensure adequate ventilation in your shed
  4. Heat and / or dehumidify your shed
  5. Invest in quality storage solutions for your garden building

Water ingress and condensation create a damp atmosphere in your shed which promotes rust and corrosion. To avoid damage to expensive tools and equipment, and to stop your shed rotting, it’s vital to make sure it’s water and damp proof. Here’s how to do it. 

Shed maintenance & repairs

Check the roof

Damaged roof felting on a wooden shed
Damaged shed roofing felt is easy to repair
Image: Waltons

When was the last time you gave your shed a good once over? Check the roof first – many sheds are covered with roofing felt or felt shingles. This bitumen-based product is cheap and cheerful, but deteriorates over time. Pay particular attention to potential stress points like the ridge line and eaves. 

Patching a felt roof is straightforward: use gutter sealant to secure patches in place and to repair minor tears in roof shingles. When the time comes to replace the felting, you may wish to consider going for EPDM, a rubber sheeting solution which is made to measure and lasts for many years without maintenance. Your shed roof takes the brunt of all weathers.

Treat walls, doors & windows

Treating side of wooden building with wood preservative
In sunny weather, apply an annual coat of preservative to protect the wood.
Image: Shutterstock

Apply wood treatment every year. Even if you’re buying a new shed which comes with a guarantee against rot, it’s very important that you give it an annual coat of wood stain. Stopping rot before it starts is by far the best way to prevent your shed from getting damp and mouldy. To make a colourful statement with your shed, apply an outdoor wood paint with a built-in preservative to your garden building. 

Check windows and doors for decay and damage, and repair as necessary. Over time wood can expand, shrink and crack, so apply filler such as silicone sealant around your windows as necessary to make sure you have adequate rain and draught exclusion.

Install sufficient insulation in the walls

Installing insulation in Waltons Insulated Garden Room
Insulation will help to keep the temperature in your shed more stable
Image: Waltons

The dew point is the temperature at which humidity in the air condenses. Without insulation, cool surfaces like windows and metal tools get wet when the temperature drops, and soft furnishings, wood and paper grow damp, swell and become the perfect growing medium for mold. 

Even without heating, if you install insulation to your garden building you’ll trap any available heat inside your shed, helping to keep the temperature more stable. Basic insulation like silver backed bubble wrap will help, but if you can, go for a really effective insulation product like Kingspan or Celotex – solid foam insulation available in a range of thicknesses. Treat shed window frames routinely with wood stain. 

Ensure adequate ventilation in your shed

Wooden shed with double doors open
Open the doors of your shed often to allow air to circulate.
Image: 12 x 8 Overlap Double Door Apex Windowless Wooden Shed from Waltons

Stop moisture buildup by making sure your shed is well ventilated. Even opening the door and windows every few days will help keep moisture levels down. That’s because moving and replacing the air in your shed stops damp building up. To get the air flowing, you need a minimum of two vents, ideally installed into opposite walls. 

For smaller sheds, a couple of static vents are all you need, but for sheds over 12’ by 8’, consider installing a solar or mains-powered vent. To stop bugs setting up home among your tools, make sure that any vents are mesh-backed. Putting small vents in opposite walls of your shed keeps air moving. 

Heat and / or dehumidify your shed

Wood burner in log cabin
A wood burner will keep your garden building cosy
Image: Waltons

Along with ventilation, heating your shed works wonders for keeping damp under control. If you have mains power to your shed, it’s worth thinking about buying a tubular heater which you can wall or floor mount and set to emit background heat to help keep the temperature above the dew point. 

Even if you don’t have a 240V electricity supply, you can still install a heat source. A professionally installed wood burner (with a carbon monoxide detector) is one option, a solar powered air heater is another – but avoid paraffin and Calor Gas heaters because as well as producing heat, they pump out moisture – just the thing you’re trying to eliminate. 

As well as a heater, you might want to install a dehumidifier, particularly if your shed is located on damp ground, if you live in a particularly rainy part of the country or you’re near the coast. Electric heaters help to keep damp at bay

Invest in quality storage solutions for your garden building

Black toolbox full of tools
Lock away your tools and equipment to protect them from damp
Image: Shutterstock

If despite your best efforts, your shed still suffers from damp, invest in quality storage boxes, cupboards and drawers and there’s every chance you can still prevent your tools and equipment corroding. 

Anything left lying around deteriorates, so always put your tools away after use – preferably in sealed containers with a silicon gel sachets inside to keep them dry and undamaged ready for the next time you need them. 

A shed which is unventilated, unheated or leaky, will quickly grow damp and mouldy. But with regular maintenance and by paying attention to insulation, ventilation and heating, you can make sure your shed stays warm and damp-free this autumn and winter. 


Visit Waltons for a wide range of garden sheds.

If you need help finding a new shed, just call our friendly sales experts on 0800 029 1000.

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