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By Amy Hanlon on 06 Feb 2024

Are wooden sheds waterproof?


You want to answer one simple question: are wooden sheds waterproof?

The short and simple answer is no, wooden sheds are not waterproof. But that doesn’t mean you should rule them out of your shed search.

There’s a slightly longer and more complicated answer that’s well worth reading, and not just because I wrote it! 

Here at Gillies & Mackay, we’ve been making timber garden buildings for the past 35 years, and keeping water out has always been at the forefront of our minds. So we’re definitely biased towards timber as a shed material, but if you read on you’ll find out exactly why that is, and why, even though they’re not waterproof, a timber shed is an excellent choice.

What does waterproof mean?

“Waterproof” describes a material that is impervious to water. “Impervious” means that fluid cannot pass through a material. If something is waterproof, water cannot pass through it.

Think plastic bottles, painted steel and glass. If you make a container from these materials, anything inside will stay 100% completely dry. Not a single molecule of water will pass through any of these materials.  

Why isn’t timber waterproof?

A Gillies & Mackay wooden potting shed, painted pale grey. It has two large fixed windows and an opening window, and a steel box profile roof.

Timber is not impervious to water. It will actively take in water. Timber comes from trees and a tree’s ability to take in water is a matter of life or death. The network of pores and channels that transports water through the tree continues that same job once the timber is cut. 

Different species of trees have slightly different structures, meaning that some types of timber take in water more easily than others. This is why it’s important to know what type of timber a building is made of.

How do I make timber waterproof?

A man painting a timber panel with pale green paint. He is wearing a white t-shirt with a "Shedonism" logo on the back.

This part is important: you don’t want your shed walls to be waterproof.

Wait…what? Why not?

There’s a multitude of different shed materials out there these days. As well as timber, you can buy metal sheds, concrete sheds, and plastic sheds. But all of these other materials have one key problem that doesn’t affect timber sheds: condensation.

Why does condensation happen in metal and plastic sheds?

Condensation happens when water in the air hits a surface (like a shed wall) that’s colder than that air. The water condenses as droplets onto that surface, and if the surface is waterproof, it stays there. If there’s enough of it, it will run down the surface and pool at the bottom. If this surface is a shed wall, you now have water on your shed floor, or at the very least on its framing. 

Pooled water inside a shed is a perfect invitation for mould, and depending on the material of the shed, may also lead to rot or rust. 

What are the benefits of breathable walls?

If you have timber shed walls, you have better protection against condensation. 

This is because any water that condenses on the inside or outside of your shed is less likely to linger on the surface of the walls or to pool inside the building. The timber absorbs the water, which makes its way to the outside of the building easily. 

Breathable walls allow the transport of small amounts of liquids and gases and their main benefit is that water and air don’t become trapped inside the building, leading to a stuffy, mouldy atmosphere.

If your shed has mould inside, you risk the contents of the shed becoming mouldy too. Breathable walls prevent condensation and ensure that any moisture inside the building has an easy way out.

What are the drawbacks of breathable walls?

However, if water can pass out of the building from the inside it can also pass into the building from the outside. That’s why it’s so important to paint your shed. We recommend water-based paint that maintains the breathability of your building but also minimises water ingress.

What is water ingress?

Water ingress happens when there’s a dramatic amount of moisture in the air, so much so that it penetrates the walls of your shed. 

By a dramatic amount, I’m talking about days and days of rainfall, which unfortunately we do experience in this part of the world fairly reasonably. 

Water ingress is always a possibility in a single-skinned building, and if the weather is wet for a prolonged period, it’s extremely likely that your shed won’t stay 100% watertight.

For most people and most sheds, this is not going to cause any major problems. There are several ways to minimise water ingress and to ensure that it doesn’t impact your building.

But if you’re expecting a single-skinned shed to stay absolutely bone-dry in Scotland, it’s likely that you’ll be disappointed. 

What if you buy a really fancy shed? Or if it’s a super-expensive shed? What if it has super-thick cladding?

Because we all know that there are sheds and there are sheds. Buying a good shed needs some insider knowledge. A good shed will be far less susceptible to water ingress than a shoddy shed. But at the same time, a single-skinned shed is always susceptible to water ingress, especially if the weather is extremely wet. 

What does water ingress look like?

Here’s a photo from a customer whose shed was experiencing water ingress:

A close-up of a Gilles & Mackay shed where water has penetrated through the wall and stained the framing of the building.

As you can see, this isn’t a dramatic, terrifying deluge of water. It’s a small stain indicating that water has soaked into the timber. If you ventilate your shed regularly, any remaining moisture will dry out and it won’t cause any issues. Because the shed is solid and well-built, this problem will happen only during very wet weather.

Can I have a watertight wooden shed?

If your garden building has to be 100% watertight, are you doomed to have a condensation-ridden plastic monstrosity ruining your otherwise beautiful garden?

Absolutely not. Because we know so much about water ingress, we know exactly how to prevent it. That’s how our 3-Tier Sheds were born. These layered buildings evolved out of our watertight Garage specification, and if water ingress is a problem you want to avoid, they’re the perfect solution. 

3-Tier Sheds have a breathable outer layer of pressure-treated timber which is still permeable to water as any other Shed wall is. But the air gap stops any water that permeates the cladding, and the breather membrane provides an extra barrier. This means that the OSB inner layer stays dry. These buildings are ideal for workshops, studios, or for storing anything that has to stay completely dry. 

Why aren’t all wooden sheds waterproof?

You might be wondering why we don’t make our sheds 3-Tier as standard. The simple reason is that most garden sheds don’t have to be 100% watertight. 

If you’re storing garden equipment and some miscellaneous bits and bobs that have outgrown your home, it’s really not the end of the world if the building occasionally experiences water ingress. As long as this isn’t happening every single time it rains, your building will be just fine.

But if you’re not aware that water ingress is a normal occurrence, and you’re expecting your single-skinned shed to remain absolutely bone dry, you’re bound to be disappointed. And the last thing anyone wants is disappointment.

Should I buy a wooden shed?

A wooden Gillies & Mackay pent shed painted pale blue, with a single window and access door and steel box profile roofing.

If you’re aware of the potential for water ingress and you know how to minimise any impact that this has on your building and its contents, a well-built wooden Shed is just what you need. 

If you need a building that won’t experience any water ingress, no matter what the weather, take a look at our 3-Tier Sheds

And if you still have questions, book a consultation with one of our team. There’s no obligation, and we’ll make sure that you have all the information you need to buy your perfect Shed. 

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