How to Stop Damp in Summer House: An Expert Guide


If you’re wondering how to stop damp in your summer house, you’re not alone. While it’s usually not a concern in the warmer months, once there’s more rain – which isn’t unheard of in the UK, we know – you may start to have issues with damp. 

Let’s have a look at what causes dampness, how to protect your summerhouse against it, and what to do to fix these issues.

Table of contents:
Why Does My Summer House Get Damp
Untreated Timber
Water Ingress
Rising Damp
Damp-Proofing Your Summer House
Wood Treatment
How to Choose the Perfect Summer House

Why Does My Summer House Get Damp?

There are a few different ways dampness can develop in a garden house. Here are the most common ones.

Untreated Timber

Untreated timber gets damaged when it’s exposed to humidity without receiving a protective layer first. One of the most important things, if not the most important thing, is to always treat wooden buildings or structures on time – right after they are installed. We can’t stress enough how crucial this is.


You’ll see condensation accumulate when moist air comes into contact with a cool or cold surface – like your summer house window. Because the cold outside air is in direct contact with the window it creates the perfect surface for condensation. 

It’s good to know that single glazed windows are much more prone to condensation than double glazed windows, which have better insulation. When choosing between single vs double glazed windows consider the pros and cons.

Condensation problems can lead to mould and mildew growth, which can ruin the window frames and the air quality inside. Condensation issues can be solved with enough ventilation or occasional heating during the colder seasons.

Water Ingress

Water ingress is a pesky problem and refers to when water makes its way inside the wood the summerhouse is made of. Another word you may hear used for a certain type of water ingress is penetrating damp – meaning when water penetrates the walls of a building and reaches inside.

Rising Damp

Rising damp is a similar concept to penetrating damp. The damp gets into the building, but as you may guess from the name, it’s coming from the ground below. 

How do you recognize it? You can spot it on the walls by tidemarks or damp patches, rising from the floor. To avoid rising damp your summer house foundation should be built with a damp proof course (DPC), a vapour barrier or with a foundation type that raises the garden building off the ground – such as ground screws or a pedestal foundation.

Damp-Proofing Your Summer House

So, how do you go about damp-proofing your summer house? Let’s have a look.


The best way to let moisture move out of your garden house is by ensuring there’s enough air movement. Ventilating your summer house by opening windows or doors regularly is the simplest way to go about it. 

It’s good to be aware that even when you’re not using your summer house, moisture does build up in it. If you’ve ever stepped into a building that hasn’t been used for a long time, you will notice that the air feels humid. This is because all buildings are designed to keep warmth inside. The warm humid air will accumulate inside any home or garden room and turn into condensation if it’s not ventilated.

Depending on your situation, you may also consider adding additional vents to your summer house. These would usually be added to the gable ends of the building on opposite sides.

Wood Treatment

Remember to consider how important it is to treat the timber of your log cabin or summer house and to protect it from the elements. When you don’t treat the wood it becomes vulnerable to any kind of moisture – even from a fog or a light drizzle. Without a protective barrier, the water is free to seep into the wood and cause dampness. 

The story may not end here though. The moisture that gets into the wood can lead to fungus growth and dry rot of the timber. Once the fungus is present, it will steadily grow and spread across the timber, ruining it in the process.

Luckily preventing this from happening is simple. All you have to do is treat the timber periodically with a waterproof seal. You apply it first immediately after putting up your structure and then reapply every few years, according to the product and manufacturer.


Inspect your summer house regularly and repair any damaged seals, cracks or gaps that you find. Take care to also check your garden building after a storm, heavy rain or snowfall. Check the roof, walls, windows and doors. You want to catch any damages or leaks as fast as possible and fix them. 

This reduces the chances of you having to deal with a bigger problem later on! While it may seem like a small thing initially, a tiny leak or crack in the wood can be the start of issues with damp and dry rot.

It’s also good to know that timber doors and windows shrink over the years, which can affect their effectiveness in weatherproofing. When you check on them make sure all parts are properly sealed.


Heat is the best way to beat moisture. With the colder months comes an increase in rain and humidity. You may start to notice condensation build up on the windows, which signals there’s too much humidity. 

The easiest and by far the best solution is to use any kind of heater you prefer to warm up the summer house and the air inside. This drives out the moisture along with the warm air. Make sure that the air has openings it can escape through – like an open window.

Worried about energy bills? You don’t need to heat your summer house constantly. Every now and then during the weekend is enough. The important thing is not to leave any garden building shut up and unattended for too long.


Are you planning to use your summerhouse around the year? Or maybe you want a layer of additional comfort? Consider adding insulation. It will help keep the temperature on an even level and lowers the chances you’ll have to deal with dampness caused by rainy weather.

Even a thin layer of insulation will help keep the temperature inside your garden room on a more equal level during cool summer eves, making it less likely that there’s condensation build-up.

How to Choose the Perfect Summer House?

Consider what you’re looking for: is it a cosy she-shed or a robust man cave? Do you love the sleek modern look or traditional styles? Summerhouse24 has a range of high-quality prefabricated garden buildings fit for any taste. 

All Summerhouse24 summer houses, log cabins and sheds are expertly crafted from the highest quality slow-grown Nordic timber using German technology and superior components. 

Why not take a look at our best-selling Modern Garden Room Olivia or Garden Summer  House Eva E with Veranda today or browse our vast summer house selection here.


Stopping damp in your summer house comes down to the reason why it’s there in the first place. Is it the lack of ventilation? Remember to keep those windows and doors open. Is there a leak that needs to be fixed? Repairing it quickly will save your summer house from issues down the line. With a bit of detective work, you can find both the cause and the solution to your damp problem.

Frequently Asked Questions

How do I treat mold in a summer house?

First take out all the furniture and fixings. Then use either bleach, a bleach solution or mould cleaner. Apply it using a spray bottle, then scrub down the surfaces and rinse with clean water. Don’t forget about your safety – wear appropriate protection like rubber gloves and a respirator and keep the door and windows open while working.

Leave the building to air out for a day, after which you can treat the wood with an anti-fungal solution. Once the building has had another day to dry out, you may want to paint the inside if there’s any staining.

How do I seal a summer house?

You can use caulk to weatherproof your shed. It’s great for sealing any gaps around doors and windows, and prevents water from entering the summer house.

How often should I treat my summer house?

Wooden garden buildings made from softwood (like pine, fir or spruce) should be treated immediately once they are installed and then about every 3-5 years.

How do I stop damp coming in through my shed floor?

There are a few different things you can do here. Raise your shed up from the ground, seal any leaks, add insulation, use a concrete vapour barrier or install a damp proof course. The right option will depend on your specific circumstances.