How to waterproof a shed

Jul 15, 2022

Waterproofing your garden shed will help keep the building itself and whatever you’re storing in it in good condition. Too much moisture or water ingress can rot wood, build mould and mildew, and it can even rust your metal tools.

Thankfully, it’s simple to waterproof your shed! Follow our guide below to ensure that your shed stays safe, secure and water-free for a longer lifetime and safer tools and supplies.

How to waterproof a shed

1. Choose the right shed

You get what you pay for when it comes to sheds. A low quality shed (made with sub par materials or inappropriate craftsmanship) will simply not last as long as a higher quality alternative - no matter how well you waterproof it.

2. Pick the right location

The first step towards a waterproof shed is picking the right location. Chances are you’ve already got a spot in mind, but let’s make sure it isn’t going to do your shed any harm.

  • Avoid low-lying areas where water pools and where the ground is constantly wet.
  • Choose an area that gets a decent amount of sun, which will help any natural moisture evaporate.
  • Avoid areas that have things like hollows or holes in the ground, as this is where water will pool.
  • Avoid areas with soil that doesn’t dry out quickly and fully after it rains.

Starting with the right location for your shed will make a big difference to how much water seepage and ingress you experience from environmental moisture.

Outpost Shed with spouting and gravel base


3. Lay the right base

Most farm and garden buildings will either need a base or will need to be raised off the ground. This is to ensure that moisture doesn’t creep into the building simply from being in contact with a wet ground.

For a permanent structure, a concrete base can be a good choice. This will help keep your shed clear of groundwater seepage, particularly when combined with a waterproof membrane. Another cheaper option is to lay a gravel pad to ensure good drainage and raise your shed up above any ground moisture. 

If you’d prefer your shed to remain portable but still have solid waterproofing, all of our kitsets come mounted on tough timber skids. These allow them to be dragged and moved around your land, but also provide airflow under the shed and keeps the floor from touching the ground directly. This ensures you can keep your shed nice and dry and free from rot without having to pour concrete.

4. Insulation and ventilation

Insulating your shed will help regulate the temperature and keep it below the dew point, reducing the chance of condensation. When combined with adequate ventilation, either through the installation of air vents or through regular airing out, this ensures that your shed doesn’t have a build up of moist air that can contribute to rot in a timber shed.

Outpost Buildings kitsets can be easily ventilated and insulated - in fact, we’ve specifically designed them that way.

5. Waterproofing paint and/or stain

Wooden sheds are usually constructed from treated timber, providing them with some protection from the moment they’re constructed. However, to make them truly durable, you should apply some wood preservative (like a paint or a stain) or use waterproof shed paint.

Ideally, this should be applied after construction and should last for five or more years if you use a high quality paint or stain - though if your shed gets scraped or beaten by the weather, you may need to do some patch work. 

How do you waterproof the inside of a shed?

You can waterproof the inside of a shed the same way you would the outside by applying a wood oil, stain or paint designed to provide waterproofing. If you discover water on the inside, you should check for any gaps or holes that have appeared since the first build. These may be letting in rain, and can be filled with waterproof sealant.

Water on the inside is not likely to be condensation like you might find in a metal shed. Timber sheds (like the kitsets we provide) are designed to have improved internal airflow and so are far less likely to have internal condensation.

Garden shed with trees overhanging

6. Remove vegetation

If you’ve got a garden or farm shed, chances are that they’ll be near plants. It’s right there in the name, after all. However, proximity to plants can reduce air flow and increase dampness in the soil, making your shed less waterproof. There’s also a chance that, if you don’t have a great shed foundation or you’ve ended up with a cheap, flimsy shed (i.e. not one of ours!), tree root structures may damage the base and result in cracks or collapse.

As part of preparing your site or after construction, make sure to cut back on plants that are touching the walls around your shed. A foot or so of clearance is a good measure. Keep an eye out for climbing plants like ivy - these can be particularly damaging if they latch onto the structure.

Good news on the grass side of things though. Your lawn is unlikely to cause any issues, as long as it’s kept fairly short in the vicinity of your shed.

7. Waterproofing maintenance

Door and windows

Even the best waterproofing efforts can still have minor issues that build up over time. The better the quality of your wooden shed, the less likely this is to happen, but there are a few common trouble spots you can keep an eye out for.

For most old wooden sheds, this is the doors and windows. Check old door frames regularly for gaps and fill them with sealant, expanding foam or builders’ caulk. For old window frames, check for signs of rot - these will be unusually soft sections of the wood. Dig them out with a screwdriver and fill them with a wood filler, then sand down the area and repaint or restain.

Outpost uses high quality aluminum joinery for any windows in their designs so you won't have to worry about rot. The framing around the windows is also protected with a sealant during assembly, so you can rest assured that they are weatherproof and maintenance free.

Settler Shed with gutters and roof flashings


The roof of a wooden shed is another common trouble spot for waterproofing. After years in the wind, rain and hail, they can become damaged, especially if the roof isn’t made from durable materials designed for the high-impact weather that New Zealand sometimes experiences.

Maintenance and waterproofing will depend significantly on the roofing material that you use. Roofing felt can be replaced, and shingles of a variety of materials can be fixed with sealant.

Unlike many wooden sheds, our kitsets use corrugated iron roofing for improved durability and elimination of the chance of rot. We use genuine Colorsteel or Zincalume in our kitsets, which are recognised as high quality options for steel roofing. They come with an 18-year manufacturer’s guarantee and are generally maintenance-free. If your property is near the coast, we recommend using Colorsteel Maxx for added protection against saltwater erosion.

Outpost sheds also have roof flashings which cover the joins between the roofing and the timber framing. These flashings prevent water from getting inside and provide extra protection for the timber. The roof flashings on our buildings are made with Zincalume or Colorsteel to match the roofing.


If your shed comes with gutters, these will help prevent puddles from appearing around your shed and will reduce the chance of moisture getting inside. Soggy ground and standing water are a surefire sign that your shed is going to become damp and potentially may experience rot. 

Keep your gutters free from leaves and other debris to keep the water flowing away from your shed. You may also want to look into digging a trench around the outside wall and filling it with gravel. This will help the water drain away even faster.

Need more advice on waterproofing your shed? Get in touch with the Outpost Buildings team to discover our range of built tough portable kitsets and how you can keep them in tip top, waterproofed condition.

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