The Best Way To Waterproof A Shed

Waterproofing outdoor wood such as decking, fencing, cladding and sheds is essential to prevent swelling, rot and long-term damage. This is especially important for sheds, as keeping them dry protects both the structure and its contents. That’s why our experts have created this guide to help you waterproof your shed and keep it clean, dry and protected long term.

In this guide we will cover:

• Why do you need to waterproof a shed
• How to waterproof a shed

Why Waterproof A Shed?

Protecting outdoor wood is essential because it is highly porous and easily absorbs moisture. Bare, untreated wood is vulnerable to water ingress, which can damage the structure over time.

Wooden sheds are often not waterproof, so applying a waterproof treatment is vital to keep them protected and in good condition.

The main effects of moisture on untreated wood are rotting, organic growth and discolouration.

Rotting

Rotting is common in outdoor wood exposed to UK weather and is caused by a fungus that thrives in damp, moisture-saturated timber. As the wood absorbs and holds water, the fungus feeds on it, weakening and breaking it down. Once rot starts, it will continue to worsen unless the moisture source is stopped. Preventing water ingress is the most effective way to protect against rot.

Organic growth

Moss, algae and lichens thrive on damp wood and other natural surfaces once they become saturated. While they don’t always affect structural strength, they can ruin the appearance of the timber and hide its natural grain and colour.

Discolouration

How Do You Waterproof A Shed?

The process of ensuring that your wooden shed is water-tight and the building and its contents are in good condition can encompass a number of things. Here are the steps you must take to fully waterproof your shed and reduce the amount of moisture entering the structure.

1. Create a base

Moisture can enter a structure through the ground or the walls. Wet ground holds rainwater, which can transfer moisture into surfaces in contact with it. Homes use a damp-proof course (DPC) to block this. For sheds, a raised foundation such as a plastic base or concrete pavers is essential to lift the timber off the ground and prevent moisture transfer.

2. Choose a waterproof treatment

To protect a shed from rain, apply a waterproofing treatment to the wood. Options include wood paint, wood stain, wood oil, wood sealer, and wood waterproofer, each offering different levels of protection. True waterproof products must be water repellent; labels like “weatherproof” or “weather-resistant” may still allow moisture in.

Wood paint – opaque colour, mainly aesthetic

Wood stain – adds colour while keeping the grain visible

Wood oil – nourishes timber without changing appearance

Wood waterproofer – clear, repels water, reduces rot, discolouration and organic growth

All treatments must be highly breathable to allow water vapour to escape. Low-breathability coatings trap moisture, causing rot, peeling and blistering. Look for an SD value below 1.

Unlike sealers that form an impermeable surface, Emperor Exterior Wood Waterproofer chemically bonds to the wood pores, repelling rain while allowing water vapour to pass through. This creates long-lasting, invisible protection. Independent testing shows it maintains performance and appearance for at least 25 years under harsh conditions.

Read more: Lifetime guarantee 

3. Apply the waterproof treatment

Preparation

Before applying any treatment, ensure the shed wood is dry and clean. Moisture or dirt can reduce the effectiveness of the waterproofing and affect the finish.

• Heavy dirt – use a power washer to remove surface debris.
• Light dirt – hot soapy water and a soft brush is usually enough.
• Deep grime – sand with 180-grit paper to remove ingrained dirt.

Cleaning Treatment

Cleaning alone may not remove all organic growth. Applying a fungicidal cleaner ensures moss, lichens, and fungi are eliminated before waterproofing.

• Apply Emperor Exterior Cleaner with a brush, roller, or pump sprayer.
• Leave to dry for 2 hours.
• Kills organic growth and lifts remaining dirt from the wood grain.
• Protect surrounding surfaces with masking tape, window film, or dust sheets to simplify cleanup.

Waterproofing

Once the wood is dry and clean, apply a waterproofing treatment to protect it from water, rot, and discolouration.

• Use Emperor Exterior Wood Waterproofer, a one-coat, easy-to-apply treatment.
• Application options – brush, roller, or pump sprayer.
• Coverage – 5m² per litre.
• Drying time – 1–2 hours, touch dry within 1 hour.
• Leaves an invisible, water-repellent finish that maintains the natural look of the wood.
• Being water-based, tools can be cleaned with water.
• Remove masking tape and dust sheets after application.

Frequently Asked Questions

Is there any other steps I need to take to waterproof my shed?

Before waterproofing, check the shed for any defects that could let moisture in. Inspect the roof for leaks, examine the timber for damage, and ensure drainage is adequate so all areas are protected.

Can I apply Emperor Wood Waterproofer to treated wood?

Emperor Exterior Wood Waterproofer needs to absorb into bare wood to chemically bond. Previous treatments like paint or oil can prevent this. To apply, either remove the existing coating or use a compatible product designed for treated wood.

How do I know if a wood treatment is waterproof?

A truly waterproof treatment must be water repellent. Products labeled “weatherproof” or “breathable” may still allow moisture to penetrate. Look for treatments that are both highly water repellent and highly breathable to prevent trapped moisture and protect the wood.

How do I know how many coats to apply?

Check the product instructions. Generally, wood paints, stains, oils, and waxes require at least two coats for full protection. Emperor Exterior Wood Waterproofer is a one-coat treatment, as it absorbs and chemically bonds to the wood.

We hope we have answered any questions you may have had regarding the best way to waterproof a shed. If you have any other questions, feel free to get in touch with our team of experts who are on hand to assist you. Contact them today by emailing [email protected] or calling them on 01254 936121.