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(Under 12m2) Specification

This article is about our former summerhouse specification, which has since been replaced by our brand-new Garden Rooms (under 12m2). It's worthwhile reading, but to jump straight to learning more about the new spec, click on!

By Amy Hanlon on 30 Jul 2023

How To Stop Your Summerhouse Getting Mouldy.

Ah, Summer! Long, glorious days to bask in the sunshine…then get soaked in the downpour. The Scottish Monsoon is great for gardens unless your washing is out, and while there have been some really cracking rainbows, one thing it’s not great for is summerhouse upkeep. Maybe you’ve noticed the odd creeping patch of black spots or some unwanted fluffy walls. So how do you stop your summerhouse getting mouldy?

Why does my summerhouse get mouldy?

Mould, or fungus, is an entire microscopic world of tiny organisms that live anywhere that’s warm and wet. If there’s water and there’s warmth, mould can thrive. This is bad news for summerhouse owners at this time of year because there’s plenty of both around. Hot sunny mornings followed by summer showers, followed by yet more sun mean that any mould spores in your summerhouse will grow and multiply and have themselves a good old time.

Most summerhouses are single-skinned buildings, with one layer of timber forming their walls. This means that they are seasonal buildings and that there is always the potential for water ingress. While you can take steps to minimise water ingress, even the most solid single-skinned construction has the potential to let water in through the walls.

The most reliable way to prevent water ingress completely is to start with a building that has layered walls. This is the construction we use for both our Under 12m2 Garden Rooms and our Blackstone Garden Rooms to make them suitable for year-round use.

How can I prevent mould from getting into my summerhouse?

The bad news is that, like bacteria, mould is present to some degree in most environments, including your summerhouse. This isn’t anything to worry about – you’d need a microscope to find it – but rather than thinking of mould as something you can completely eradicate from your summerhouse, think of it as crowd control. What you want to avoid is an overgrowth of mould.

How do I stop mould from growing in my summerhouse?

The first two tools you have against mould are sunlight and airflow. If you’re at home and you notice it’s raining, once it stops, get out to your summerhouse and open up all the doors and windows. As long as the rain doesn’t start again, keep them open to give the building a really good airing. Don’t leave doors or windows open overnight, but make sure you get plenty of air into the building.

Timber is a natural material that will always take in moisture to some extent. Your job is to make sure that when this happens, there’s enough airflow to let the moisture out again.

We often hear customers saying, “I haven’t been in my summerhouse since last year, and when I opened it up this summer there was mould inside!” This isn’t surprising at all – timber buildings need regular airing to keep everything ship-shape. If you ignore them for months at a time, problems will pop up.

Will paint help prevent mould in my summerhouse?

A can of Sadolin SuperDec paint.

The next weapon in your fight against the black stuff (or green stuff, or white stuff – will it never end?) is paint. A good coat of paint will help prevent excess moisture from getting into your summerhouse. Less moisture means less chance of mould.

Make sure that you choose a good quality, breathable paint like Sadolin. While this isn’t the only water-based exterior timber paint out there, it’s the one we recommend for all our buildings.

Paint the outside of your building according to the instructions on the tin of paint. You should also make sure that the inside edges of your doors are painted all the way around – as well as keeping moisture to a minimum you’ll also prevent the doors from swelling or shifting.

Are there any other ways to stop my summerhouse getting mouldy?

As well as airing your building and painting it every few years, think about what’s inside the building.

If you bring moisture into the building, you’re increasing the risk of mould. Let’s say you have cushions in your summerhouse, and the kids have been playing with them out on the wet grass. Make sure that they’re thoroughly dried out before putting them back into the building and closing the doors.

The same rule applies to anything that you store in your summerhouse – if you put anything damp inside the building, that moisture isn’t going anywhere until you air it out. Spillages count here too – make sure to clean up any spilt liquids really thoroughly, and get as much air and sunlight into the building as often as you can.

If you feel like there’s just too much rain to keep up with, you can also buy dehumidifier pots like these. They’re easy to find online and are often sold in supermarkets and discount stores. These sit inside your summerhouse and collect any excess moisture from the air. They’re especially useful in the winter when it feels like there are no dry days available to air out the building.

Or, if you have electricity in your summerhouse, you could invest in a powered dehumidifier like this one.

How do I get rid of mould in my summerhouse?

This could definitely be a whole post by itself. Preventing mould is definitely easier than treating mould, which can be surprisingly hard to get rid of.

If you have hayfever or allergies, mould may make these worse, so dust off your COVID masks and make sure you’re protected. There’s a common misconception that bleach will kill mould, but all this does is lighten any areas that have been stained; it doesn’t get rid of the culprit.

Most of the chemicals used to remove mould are pretty serious stuff, like this Mould Remover Kit from Permagard. Make sure you follow all the safety instructions and cross everything that you won’t have to repeat the treatment.

Top tips to prevent your summerhouse getting mouldy.

  1. Prevention is definitely better than cure.
  2. Air and sunlight are the best ways to prevent mould. Make sure your summerhouse gets plenty of both.
  3. Painting the outside of the building will help prevent mould.
  4. Don’t store anything damp or wet inside the building.
  5. Clean up any liquid spillages thoroughly and air the building afterwards.
  6. Use a dehumidifier in the winter months if necessary.

Single-skinned buildings will always need regular maintenance to stay at their best. If that feels like one extra job too many, and if you want to use your garden building all year round, come and see our brand new Under 12m2 Garden Rooms. They may look similar to our previous summerhouse products, but they have a whole new specification to keep them warm, dry and mould-free! Come on down and see them and us at our Show Area in Errol.

Further Reading:

How to fix summerhouse doors that won’t close.

How to get rid of condensation in a summerhouse.

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