How to build a garden room - garden room damp proofing & waterproofing guide

Garden rooms have surged in popularity, especially with more people working from home following the pandemic. They still allow you to keep work and home separate, while cutting out the commute. And they’re not just for garden offices, either. Garden rooms also provide extra space for hobbies, exercising and socialising - essentially, a garden room can be used for whatever you like!

When it comes to garden room construction, you have options to purchase a pre-made structure, build your own from scratch or convert an existing structure. In our guide, we’ll be focusing on waterproofing and damp proofing of garden rooms to ensure longevity.

What is a garden room?

A garden room is a stand-alone building that’s separate to your house. Providing extra space, often for a specific purpose, they make a valuable addition to your home. Garden rooms are given a plethora of names including studios, summer houses, log cabins, outbuildings. They can be built from a range of materials, including wood, stone or brickwork.

Garden room ideas

There are countless things you can do with a garden room. Some of the more popular garden room uses are::

• Home offices
• Art studios
• Gyms or yoga studios
• Bars and social spaces
• Game rooms
• Cinema room
• Craft workshops
• Music studios

Or, you can simply create a space to retreat to whenever you feel like it.

DIY Garden Offices

One of the most common uses for a garden room is an office. Now that more people are working from home, they’ve become more popular than ever. Home offices in the garden can be purchased pre-fabricated, built from kits or from scratch using a range of materials. It’s also possible to convert an existing workshop or garage into a garden room.

It’s important to note that with a garden home office, you would need electrics installed in the building as well as broadband. For this, you would need a professional electrician to ensure everything installed correctly.

How much value does a garden room add?

Garden rooms add value as they increase the square footage of usable space. While the amount can depend on the quality of the build and insulation, garden rooms certainly create an attractive feature and selling point for your home.

Replacing or converting an existing structure or installing an extra, external space is appealing to many home buyers. Garden rooms also provide usable space all year round.

Garden Room Regulations

Usually, you do not need planning permission to build a garden room. However there are exceptions, such as if someone will be sleeping in the building and it becomes a habitable space. You may also need planning permission if you live in/near a listed building, national park or an area of outstanding beauty.

Overall, the general rule is that you don’t need planning permission if:

• The maximum eaves height is 2.5m, or
• The max roof height is 4m with dual pitched roof

If you’re unsure, always check with your local council.

Garden Room Conversions

When building a garden room, you won’t always be starting from scratch. If you already have an old outbuilding or a garage, you can convert it into a garden room instead.

Please note that you still need to ensure your room has the right damp proofing in place. For more info, please read our sections on:

Damp proofing and waterproofing
Garden room ventilation
Green roofs for garden rooms

Converting an outbuilding into a garden room

An outbuilding is an ideal option for being converted into the garden room you desire. This is a cost-effective method as it’s an available space and pre-existing structure just waiting to be transformed.

Depending on the material, your outbuilding may be cold or prone to condensation or damp, so it’s important to fully appraise the structure before deciding how to insulate and damp proof your garden room.

Garage to garden room conversion

Some people opt to convert their garage into a garden room. This can be a great alternative if your garden is small and you don’t use your garage that often.

Garage to garden room conversions are great for:

• Offices
• Gyms
• Toilets
• Home cinemas
• An extra living space

If you’re considering converting your garage, then take a look at our garage conversion guide.

Garden Shed Conversion

Many homeowners initially consider converting their shed into a garden room. This is usually because it’s a cost-effective method and they already have the space. Sheds are often quite small and only provide enough space for certain uses, such as garden offices, bars, game rooms and man caves.

However, with a garden shed conversion there are a number of issues that might not make it the best long term solution. You will need to waterproof your shed effectively and prevent draughts from entering the building - sheds can be particularly cold and you won't want to stay in there for long if you don’t do anything about it. This guide covers ways you can keep your shed to office conversion warm and protected from damp.

How to build a garden room from scratch

Before you decide to build a garden room from scratch, it’s best to consult with a professional builder and understand what, if any, elements you can do. We’ll take you through each step below, focusing on waterproofing and damp proofing.

It’s important to note that, before starting any garden room DIY, you should always double check if you need planning permission first.

Building a garden building

Now that you’ve got a budget and decided on the design, it’s time to start building your garden room.

Garden Room Foundation

The first step is laying the garden room foundation. Without a strong foundation, your structure will struggle to remain structurally sound and withstand adverse weather conditions.

Garden rooms do not need the same foundations as a house. The main thing is that the base needs to be 100% level and slightly larger than the building itself.

There’s many garden room foundation options you can go with:

• Concrete slab
• Plinth
• Ground screws
• Concrete piles - mix of concrete slab and plinths

Using a concrete slab is an easier and more popular method. You can easily install a damp proofing system, whether you’re using an existing concrete base or starting from scratch.

When building a new concrete base for a garden room, you can incorporate a damp proof membrane (DPM) that prevents groundwater from entering your garden structure. The 1200 Gauge DPM is designed for use in concrete floors, providing long-lasting protection for years to come. Its durability means that it will not be damaged by foot or site traffic, although care must be taken during installation.

The DPM is added beneath the concrete slab, and a vapour control layer (VCL) can be used over the top. So, your garden room flooring build up would look like:

• Hardcore
• Compact sand (sand blinding)
• 1200 gauge DPM
• Concrete slab
• Insulation
• VCL
• Screed

If you’re building on an existing concrete base for a garden room, you can install an epoxy flooring damp proof membrane, if a plastic DPM is not already incorporated in the concrete or a previous DPM has failed. An Epoxy DPM is hard wearing and easy to install, preventing damp from travelling up through the floor. It’s a particularly good option if you’re planning on having heavy equipment, such as exercise machines or an office desk.

To learn more about applying epoxy flooring, read our guide here.

Damp proofing / waterproofing a garden room

Like all buildings, garden structures are prone to damp and condensation, so you will need to put the right measures in place.

One cost-effective damp proofing method is tanking. This method prevents water ingress by coating the substrate with a cement-based coating, known as tanking slurry, that forms a waterproof barrier. It is easy to apply and effective.

To tank a wall, you need to first prep the surface and remove any dirt or debris. If there are cracks in the wall, you’ll also need to fill them in beforehand using PermaSEAL Fillet Seal. You can then simply mix the PermaSEAL Tanking Slurry with water and apply directly with a brush. We go into more detail about tanking in our waterproofing a garage guide.

If you’re building an independent stud wall, then we recommend using a waterproofing membrane instead, such as PermaSEAL 8 Clear Waterproof Membrane. This offers a more flexible option, better suited for new builds to cope with settling. Our membrane allows air to circulate between the wall and structure.

Our PermaSEAL damp proofing mesh membranes will also provide a key for rendering, if you aim to plaster your garden room walls directly. For example, if you’re building solid 9" brick or stone walls, these can be rendered or take dot and dab plasterboard for internal finishes when the membrane is applied.

External Waterproofing for a garden room

If you are building a brick garden structure, then you should also protect exterior walls from water ingress. Your garden building will be exposed to wet and windy weather throughout the year. Protecting the brickwork will help minimise water and structural damage, such as penetrating damp, making cracks worse, and freezing thaw issues.

PermaSEAL Facade Cream is designed to protect your home from the elements. It’s long lasting and easy to apply, suitable for brickwork and masonry (but not blockwork!). Its cream consistency means that the product will not run down the walls as it soaks into the bricks, so nothing is wasted and your garden room will experience better protection. You’ll also improve your energy efficiency, as the facade cream reduces heat loss by up to 28%.

Another protective layer you can add to your garden room is cladding. Cladding protects the exterior of a building by helping to reinforce the structure. It provides some weather resistance and insulation, and can add an aesthetically pleasing element to your building. For cladding materials you have many to choose from, such as composite, wood or plastic.

Do I need a vapour barrier in my garden room?

Vapour Control Layers (VCL) are a requirement in some circumstances, such as including a stud wall or adding garden room insulation. As you build insulation into a building, you leave a space between that insulation and the outer wall. This may increase condensation later on. VCLs put a stop to this by controlling how much moisture can pass through your garden room.

Installing a VCL is a relatively simple job, but you need to make sure that it’s sealed properly, including the ceiling and floor joints. You can seal all parts of the VCL with Radbar Single Sided Tape Foil. For step-by-step instructions and more detail about vapour control layers, click to read our VCL installation guide.

Garden Room Ventilation

A lack of ventilation can lead to serious problems for your garden room and even health issues, such as condensation & mould growth, and musty smells. Ventilating your garden room can be as simple as opening a window, but this isn’t always convenient, especially in the winter. If your garden building has lots of windows, then internal air can become heated, creating a humid, stuffy space that’s prone to damp and mould. Garden room ventilation is even more important in these circumstances.

For one-room ventilation, our Perma-Vent passive vent is a great option. It has a simple, unobtrusive appearance that’ll fit in with any garden room design. It tackles condensation and mould growth by allowing moist air to leave the building, without letting any draughts back in.

You can also try the Vent-Axia Heat Recovery Unit, which helps you stay on top of condensation issues by introducing fresh, filtered air into your garden room. It helps reduce allergens from the room and has a heat recovery rate of 84%, reducing your carbon footprint while also avoiding cold draughts. Its sleek design won’t interfere with your interior design. With improved air quality and ventilation, you’ll minimise condensation and mould growth throughout your garden room, saving you from future issues.

Building a Garden Room with a Green Roof

Building a garden room with a green roof can turn your structure into even more of a feature, and can bring many benefits to your home and the local environment, including:

• Being environmentally friendly, creating green spaces for wildlife in urban areas
• Reduces energy use - cooling for summer and keeps heat in winter
• Sound insulation

There are two types of green roof systems, intensive and extensive systems. Extensive systems are easy to install and require little maintenance, so you don’t have to spend a lot of time looking after it. You can install a green roof system for both flat and pitched roofs (although flat roofs are easier), meaning you can easily fit them into your garden room design.

Permagard offers complete green roof systems, ideal for building a green garden room as well as instant sedum green roof trays. Whether you’re working on a flat or pitched roof, we provide all you need to install an efficient green roof, including:

• Polyshield Liquid Roof Membrane for your primary waterproofing layer - although your garden room should already have a waterproofing layer as part of the build.
• Root barrier membrane
• Drainage membrane, which also has a filter layer for ease of installation
• Or, we also have a separate filter fabric available
• Green roof substrate and wildflower seeds

It’s important to install a green roof correctly to ensure efficient drainage, preventing your plants becoming waterlogged and hindering growth. Read our green roof construction guide for step-by-step instructions and installation tips.

Waterproof your own garden room with Permagard

Building a garden building from scratch can be an easy and rewarding job that’ll bring numerous benefits to your home. Here at Permagard, we have the tools you need to build your own garden room, from epoxy flooring, ventilation units and green roofs, ensuring your building is properly ventilated and protected from condensation and damp.

To find out more about our product range, or for technical advice regarding your garden room design, speak to our expert team by calling 0117 982 3282 or send an email to: [email protected].