The Ultimate Guide to Keeping Timber Garden Buildings Dry
Introduction
This guide breaks down the three most common problems new timber garden building owners face:
• Splashback water sneaking in at floor level
• Mould and condensation building up inside
• Moisture soaking into your timber
And because we like to make life easy, we’ve also included simple maintenance tips, customer-friendly explanations, and clear solutions you can follow at home – no builder’s degree required.
Splashback Rainwater: The Sneaky Culprit Behind Damp Floors, Walls and Doors
When rain hits hard surfaces, it bounces straight back up, splashing onto the building and underneath the walls and doors. This is one of the biggest causes of:
• Damp patches along floor edges
• Water stains on the bottom of walls and doors
• Water sneaking under the door
How to Fix It
1. Paint the underside edges (properly!)
This is the most commonly missed step. The underside of bottom boards where they join and overlap the floor, as well as the underside edges of doors, need a good-quality waterproof exterior wood treatment. These areas take the most splashback and are easily missed because they’re hard to reach.
2. Fit gutters
A simple gutter kit stops the roof dumping water down the sides of the building. Less water on the walls = less water bouncing back into your shed.
Bonus points for fitting a water butt to the downpipe – great for saving water and money in the long run.
3. Fit a weather or storm guard
Adding a protective weather strip to the bottom edge of the door or the door cill helps reduce the amount of water that can bounce through the gap, keeping the floor inside your shed dry.
Mould & Condensation: Why Sheds Sweat More Than a Gym Class
This is the big one – especially in winter, and especially with new buildings.
During the day, your shed warms up (even slightly). Inside, the air becomes humid from stored items, damp ground, natural moisture in the air, or the timber itself. This is often worse when a building is new, as pressure-treated timber is still drying out.
At night, temperatures drop and all that warm, moist air condenses on the coldest surfaces, usually:
• Roof boards (because the roof is covered with felt or rubber)
• Behind items pushed tight against walls
• On the items themselves
Cue mould, staining, and that “wet dog” smell no one asked for.
How to Fix It
1. Ventilate during the daytime
Open windows or doors for an hour on dry days. Fresh air in → moist air out.
This is the most important step, especially straight after your new garden building has been installed.
2. Fit proper vents
We install one vent as standard on all our sheds and summerhouses (unless they’re having internal insulation and cladding). Additional vents can be purchased and installed if required.
3. Keep wet items out
Don’t store soggy boots, sponges, car-washing equipment, wet decking cushions, or anything that belongs on a clothesline. They steam your shed up like a shower room. Make sure items are fully dry before storing them.
4. Consider insulation (done correctly)
Insulating your walls and roof helps keep surfaces warmer, reducing condensation. Use breathable materials and a vapour-permeable membrane.
This is especially important if you’re using the building as a summerhouse or hobby room, as soft furnishings need to be kept dry.
5. Treat mould promptly
Use a suitable mould cleaner and wipe surfaces clean to prevent it spreading further.
Timber Moisture Absorption: Why Wooden Buildings Need Treatment
Let’s say it loud for the people in the back:
Wooden sheds are not waterproof.
Timber naturally absorbs moisture like a sponge, which is why treatment isn’t optional – it’s essential. Without proper treatment, timber will:
• Darken with damp
• Warp
• Show patchy wet spots
• Eventually rot in exposed areas
How to Protect Your Shed
1. Allow pressure-treated timber to dry first
When a new building is installed, the pressure-treated timber will still be quite damp. We recommend allowing at least 3–4 weeks for it to fully dry before applying paint.
2. Apply two coats of exterior paint or stain
Once dry, apply two coats of a proper exterior waterproof coating designed for sheds and garden buildings.
Cheap water-based colourants alone aren’t enough.
We recommend (and sell) Protek Royal Exterior Superior Wood Finish.
(Make sure to follow the manufacturer’s guidelines regarding drying times and application)
After around six months, apply a third coat, as the timber will have slightly shrunk and you may see unpainted lines along board edges.
3. Don’t forget end grain and bottom edges
Cut edges absorb water quickly. Seal them well.
4. Recoat regularly
Most quality products recommend annual inspections and re-coating every 1–3 years, depending on exposure.
The Protek range states 2–5 years, depending on the building’s location and exposure to the weather.
Other Common Issues and Solutions
- Doors swelling or sticking
Usually caused by moisture. Recoat the door, paint all edges (especially the bottom), and adjust hinges on summerhouses and garden rooms if required. - Knot holes and shakes
Knots are natural and can form holes if they dry and shrink.
Solution:Secure loose knots with epoxy or filler and use a knotting solution or specialist primer to prevent resin bleed.
Shakes are splits along the grain that occur naturally or during seasoning.
Solution: Fill with wood filler and paint once dry.
- Leaking windows
Silicone sealant can dry out, lose elasticity, and crack over time due to age, weather, and movement. This can allow water to seep in around the glass.
Re-applying silicone around the window and frame (inside and out) should resolve the issue.
Condensation can also make windows look like they’re leaking, as water can run down the glass and pool on the inner window cill. This is resolved by ventilating the building as outlined above.
Final Notes
If any of the above issues persist, please contact our Customer Services team:
Email: cs@solidsheds.com
Phone: 01695 51442 (press “2” for Customer Services)