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a homeowner demonstrating how to waterproof a shed

Typically, garden sheds are used to store the lawnmower, the BBQ and assorted garden furniture. But these days, sheds serve various purposes —there’s the workshop shed; the summerhouse shed; and the pub shed!

In recent years we’ve also been getting more questions around converting sheds into home offices. We’ve also seen an uptick in orders for our larger and more luxurious sheds. As the way people use sheds evolves, the humble garden shed is becoming popular. A quick look through ‘shedditors’ (a forum for shed enthusiasts) is evidence of this.

With more people choosing to keep valuable (and electronic) items inside their garden sheds, we thought it a good time to highlight the damage that water can do to the structure and contents of a shed.

This guide explains how to waterproof a shed, giving practical tips for building a long-lasting base and a watertight roof.

How to spot water damage

Before we get into how to go about waterproofing your shed, it’s important to understand what you’re aiming to prevent.

Most wooden garden sheds now use high-performance polyester roofing felt and pressure-treated Scandinavian timber that’s resistant to water absorption. However, the timber used on the inside of your shed, such as the flooring and frame, can be susceptible to water damage.

Even if you can’t see obvious signs of water ingress such as a drip, water can gradually seep through the roof, walls or base of your shed. Over time, this water is absorbed by the wood which is what causes problems.

There are 3 telltale signs of water absorption in wood:

1.     Discolouration

The early sign of water absorption is wood that has begun to take on a darker colour. If the water absorption continues, this discolouration spreads like a shadow that gradually masks the natural grain and golden colour of the timber.

2.     Moss and algae

Over time, water absorption leads to wood becoming saturated. The growth of organisms such as moss and algae, which tend to thrive in damp areas that don’t receive sunlight, is a sure sign of saturation. Like discolouration, moss and algae cause superficial damage that can be reversed, as opposed to lasting structural damage. However, some cases can lead to a lingering musty smell developing.

3.     Rot

Prolonged water ingress can lead to the growth of mildew, mould and other fungi. Mould is a major problem as it indicates the early stages of wood rot. Rotting occurs in heavily saturated wood and can lead to complete structural failure. Fungicides are only a treatment —the only way to stop rot from occurring is to prevent water or moisture from getting into your shed.

a wooden shed that has been waterproofed

How to make a shed watertight

A watertight shed relies on a well-built roof, but other parts of the structure like the base and windows shouldn’t be overlooked. We’ve also included some helpful tips on ventilation and the use of wood preservers.

Build on a solid foundation

To avoid groundwater seepage, it’s essential to build your shed on a solid foundation or footing. Failure to separate the base of your shed from the ground will result in huge amounts of water being absorbed through the walls and floor of the shed.

In the UK, waterproof sheds tend to be built on a concrete footing, such as paving stones or a level patio. Alternatively, you can build on top of decking or plastic shed base.

At Estate Sawmills, our prefabricated sheds use heavy-duty floor joists that are attached to the underside of the floor, effectively lifting the sheds off the ground and improving airflow.

Keep your shed clear of vegetation

Maintaining a plant-free border around your shed improves its longevity. Plants and vegetation draw in and hold moisture. What this means is that, where your shed is in contact with vegetation such as bushes or long grass, it’s in contact with moisture.

As well as reducing contact with moisture, keeping your shed clear of vegetation improves air circulation around it. In the absence of sunlight, good air circulation will keep your shed dry, reducing the risk of mould and mildew.

Seal the window frames

Another area where moisture can enter your shed is around the window frames. It’s therefore important to use a good silicone or expanding foam that creates a watertight seal around the frames.

Over time, the seal around the window frames will degrade. If you do spot a gap around a window frame, remove the silicone with a stanley knife and reseal with silicone, caulk or expanding foam.

Ventilate your shed

As well as maintaining good air circulation around your shed, you should ventilate the inside of it. As mentioned, good air circulation improves the evaporation process, allowing moisture to escape before it can be absorbed.

Windows that you can leave ajar are one method of ventilating your shed, but rely on dry weather and you remembering to open or shut them. Wall vents are a more convenient ventilation method. For optimum ventilation, position the vent high up on one of your shed’s gable walls.

Apply a shed preserver

The outer cladding that makes up the wall of your shed is designed so that water streams off it. Quality shed cladding also uses pressure-treated timber that is resistant to water absorption. Even so, you can make the walls of your shed watertight by treating them with a shed preserver.

Apply the shed preserver immediately after completing the build and once a year thereafter. As well as helping to waterproof the walls of your shed, a preserver protects wood from insects and fungi, preventing rot and decay.

how to waterproof a shed roof

How to waterproof a shed roof

Not only does the roof receive the most rain, it is also most exposed to wind damage. The best way to waterproof your shed’s roof is to use quality materials. Use a high-performance polyester felt or use corrugated roofing sheets.

Check the roof of your shed for any signs of wear and tear. If using a felt roof, pay close attention to ridge lines and the edges of your roof as these areas bear the brunt of the elements. Many factors affect the lifespan of the roofing felt, but we recommend a full replacement of the felt every 3 years.

Keep the gutters clean

If your shed has gutters, it’s crucial that you keep them clear of leaves and other garden debris. Blocked and overflowing gutters are the most common cause of water damage to shed roofs and walls.

You can usually get away with clearing the gutters over winter once trees have shed their leaves. It’s also worth checking the condition of the gutters after storms and windy conditions.

A good garden shed is a waterproof garden shed

As well as prefabricated wooden sheds, we stock first-rate shed timber and construction timber for custom garden shed builds. Our range of shed materials includes ship lap and log lap cladding boards, heavy-duty tongue and groove boards, roofing felt, sheets and ridges, plywood insulation boards, and various fixings.

Whether you plan to build a cosy nook, a stylish bar or somewhere to store your growing collection of gardening equipment, we provide everything you need for a custom build.

And of, course, if you have any questions about an outdoor project –whether it’s a garden shed (or a garden bar) –you’re more than welcome to contact the team here at Estate Sawmills HQ.

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