How to Build a Fully Insulated Garden Room

Building a garden room is a fantastic way to add functional space to your home while increasing its value. However, hiring a professional for the job can be costly. In this step-by-step guide, I’ll show you how to build your own insulated garden room from scratch, using proven DIY construction techniques that ensure durability and year-round comfort.

Whether you need a home office, creative studio, gym, or games room, this timber garden room is designed to industry standards, using high-quality insulation and materials for a professional finish. Best of all, by taking on this project yourself, you can save up to 50% of the total cost compared to hiring a construction company.

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Garden Room Plans – PDF Guide, Step-by-Step Instructions & Interactive 3D Models

My detailed instructions and interactive 3D model for this build are now available in my shop.

Use code wood10 for an additional 10% off all shop items!

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I will jump straight into the DIY garden room build and provide links to other important information such as planning permission and a full materials list at the end.

Step 1: Preparing the Ground and Laying a Solid Foundation

There are a number of ways to achieve this but I’m going to show you how to build a wooden frame base that will be suitable for most builds. Whether your plot is on a slope or even surface this will provide a good solid base to support your garden room.

1. Start by clearing the ground where your garden room will be situated. Remove debris, plants and any type of vegetation. Leave a suitable 500mm gap between any boundaries and obstacles.
2. Measure the area and mark the four corners of your building plot. You can use sticks, bricks or spray paint to achieve this.
3. Use string and spikes to mark out the perimeter of the building. Adjust the corner spikes by measuring equal distances from corner to corner.
4. Once the foundations are in place use a weed protective barrier to cover the floor. This will prevent invasive plants from growing into your building.

Garden Room Foundations

You can build the wooden frame on one of these foundation types:

Ground screws

These can be screwed into the ground and adjusted according to the required level.

Breeze block or concrete block pillars

These can be useful for gardens with sloping terrain.

Wooden post supports

These are the quickest and cheapest option for your garden room foundation but must be treated with creosote to protect from rot.

Step 2: Constructing the Timber Frame Base for Your Garden Room

The timber frame is constructed from a kiln-dried 47x150mm C24 construction timber. This should be made to your specific size requirements. Try and make sure the spacing is roughly 360mm and spaced equally to support the OSB boards (1220x2440mm) which will be secured to the top of the frame.

The timber can be secured in place with 100x6mm screws. Joist hangers should be used on joists but the noggins can be secured using screws.

If using ground spikes. Ensure good coverage with a spike at least every 1m.

For the other two foundation options (timber and breeze-blocks) mounting points can be every 1.5m – 2m

Insulating the base

I’d recommend using a 100mm thick insulation board. These can be cut using a panel saw and pushed between the joists. I recommend using these Celotex insulation boards:

Finishing the base with boards

The final job for the garden room base is to secure durable flooring. The are two options here. An 18mm OSB board or a thicker TG4 chipboard flooring. The TG4 flooring offers better moisture protection but is more expensive. (TG4 is recommended for a garden room)

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Step 3: Constructing the Timber Frame Walls for Your Garden Room

With the foundations and base in place, it’s time to move onto the timber frame walls. Think about what doors and windows you want and order them prior to the build. This will ensure you have the correct dimensions for your openings. Ensure your supplier has them in stock. The last thing you want is to resize the openings because you end up with different-sized windows and doors.

Timber size can either be 47mm x 100mm or (I have selected a slightly cheaper) 38mm x 89mm timber for my drawings.

When measuring for windows and doors, add 5mm to each edge so they are easy to slot into the openings. Packers can be used to square off when in place.

The overall height of your garden building cannot exceed 2.5m. (Without planning permission) Therefore the height of the wall timber frames should not exceed 2000mm. For a single-pitched roof, I have made the front wall a little taller.

Complete one wall at a time, securing each to the floor with 70mm x 5mm screws.

The wall frames should line up with the edge of the base.

Step 4: Constructing the Timber Frame Roof for Your Garden Room

The roof frame will need to be constructed on top of the walls. Trying to lift a frame this size onto the roof will be near impossible with heavy lifting equipment.

The roof frame is constructed using the same timber as the base. 47mm x 1500mm C24 construction timber.

The rafters can be lifted into place first and the rest of the frame can be constructed around these. Two people may be required for this part.

The roof frame can be secured in place with screws or metal angle brackets. This completes the timber frame for the garden room.

When planning your build, one of the most important considerations is the roof. Choosing the right timber sizes, rafter spacing, and understanding load calculations will ensure your structure is safe and long-lasting. For a detailed breakdown, see my guide on garden room roof timber sizes, spans, and load calculations.

Step 5: Fitting the Outer Walls and Roofing Boards

The outside walls and roof now need to be covered with an 18mm OSB board. These can be cut to size and fixed to the frames with 40mm screws. The same will need to be fitted to the top of the roof.

Breather Membrane

With all the boards in place on the walls it’s now time to cover them with a breathable membrane. (On the outside) This will prevent moisture from reaching the OSB boards and allow any moisture to escape the building.

The breather materials can simply be stapled onto the boards. Ensure a 100mm overlap between layers. Normally available in 1.5m x 25 or 50m rolls.

Step 6: Installing Electrics in Your Garden Room

Now is a good time to think about installing the electrical system in your garden building. If you’re not qualified or are unsure how to install sockets and lighting then it’s best to hire a qualified electrician. Get them in at this stage, before starting on the interior insulation and boarding.

Step 7: Fixing Furring Strips for Cladding

For the next step in this guide, we’ll take a look at the furring strips. These will be essential to support the cladding and will allow for ventilation between the boards.

When installing vertical cladding, furring strips are installed in two parts, vertically and horizontally. (If you decide to install horizontal cladding then you will only require vertical furring strips). You basically want to avoid having horizontal furring strips fixed to your breather membrane to prevent the build-up of moisture on the strips.

The first set can be installed like this.

The second set is installed horizontally.

Step 8: Cladding Your Garden Room with a Durable timber

The first step for cladding is to select a suitable material. There are loads of options when it comes to cladding so the choice will be yours depending on the budget. If you can afford Western Red Cedar it is worth it. It is a very oily wood with great natural moisture-prevention qualities. It will still need to be treated but will outlast most alternatives. More affordable options will be your standard pressure-treated pine in both loglap and shiplap styles.

Western Red Cedar example image

Start with the roof underside for the cladding.

Now move onto the walls.

Step 9: Installing the Garden Room Doors and Windows

As you can see in the above image I’ve fitted the windows and doors. These can simply be lifted into place and secured to the frame. You will need to ensure the doors are fitted correctly so that they open and close smoothly. To doo this you may need to square off the frame using packers which normally come supplied with the doors.

A sealant can then be added around the frames to seal any gaps.

Follow the manufactures installation guidelines for the perfect fit. Here I have fitted a 14mm x 79mm timber strip around all the edges.

Window and Door Trims

To finish the doors and windows it’s important to finish the edges with a thin timber trim.

Step 10: Fitting the Waterproof Roofing Material

To ensure a watertight seal on the roof you will need to fit EPDM rubber roofing. you can buy this in a kit form which includes a large rubber sheet, glue and any trim required to secure the edges. It is best to follow the manufacture’s guidelines here for installation. Here is a great example video I found which demonstrates the installation clearly.

Finishing the edges of your roof can be done with the EPDM fitting kit or your choice of timber finish.

Step 11: Finishing the Garden Room Interior

So far we have learnt how to build a garden room structure and make it water tight, but now it’s time to turn your attention to the interior. Hopefully, you now have all the electrics installed and can start fitting the insulation and plasterboard.

For the insulation, I’d recommend using two types. The first has great thermal protective properties whilst the second is great for acoustic insulation.

1. Celotex insulation board – GA5040
2. Rockwool RWA45 40mm

Proper insulation is key to ensuring your garden room is comfortable and energy-efficient all year round. Several insulation materials are available, each with its own benefits. For a detailed breakdown of insulation options and techniques, check out this guide on how to Insulate a Garden Room, Summerhouse, or Shed.

To help demonstrate how the entire wall looks I have created this cross section diagram.

This cross section view from the interior shows the following materials. Starting from the outside:

• Western red cedar cladding
• Furring strips (horizontal)
• Furring strips (vertical)
• Breather membrane
• 18mm OSB 3 board
• CLS timber frame (38x89mm)
• Celotex GA4050 (50mm thick)
• Rockwool RWA45 (40mm thick)
• Polythene vapour barrier
• Plasterboard (12.5mm thick)
• Skimmed plaster
• Paint of your choice

The same type of insulation can be used for the roof. The polythene vapour barrier is essential to stop any moisture reaching the plasterboard and plastered walls. This is available in large sheets and can be stapled to the walls and ceiling.

Electrical wiring can be cut into the insulation allowing for socket backboxes etc.

Here you can see a before and after the plasterboard has been installed.

I tend to leave plastering to the professionals but you can always try this yourself.

The final jobs left to do are to paint the walls and ceiling, install suitable flooring like laminate and add skirting boards.

Flooring Options

For this garden room, I used a 5mm gold underlay paired with laminate flooring, but there are several other excellent flooring options to consider. While hardwood flooring is not ideal due to the temperature and humidity fluctuations typical in garden rooms, the following alternatives can suit a variety of uses:

• Luxury Vinyl Flooring (LVT): Durable, waterproof, and available in various designs, LVT is perfect for garden rooms exposed to temperature changes. It provides a comfortable surface underfoot and is easy to maintain.
• Rubber Flooring: Ideal for a garden room gym, rubber shed flooring is slip-resistant, durable, and absorbs impact well. It can handle the wear and tear of gym equipment and workouts while providing sound insulation.
• Engineered Wood Flooring: If you love the look of wood but need a more stable option, engineered wood flooring is a great compromise. It’s designed to withstand temperature variations better than solid hardwood.
• Interlocking Foam Mats: Another gym-friendly shed flooring option, foam mats are affordable, easy to install, and provide cushioning for activities like yoga, Pilates, or light workouts.
• Carpet Tiles: For a cosy garden room setup, carpet tiles can add warmth and insulation. They’re easy to replace individually if damaged or stained.

This completes the garden room construction. Just remember to treat your exterior cladding every couple of years to ensure it lasts and looks great for years to come.

Download the Full 3D Drawing and Guide

Take a look at my shop where I have the full step-by-step build guide and 3D drawings available for download. These plans cover every aspect of the build in detail to make building this garden room as easy as possible. Simply print the materials list for your local hardware supplier and get started right away.

Materials List for Self-Build Garden Room

Here are all the materials required to complete this build. Use the links to find current stockists.

Material	Meters	Quantity
Ground Spikes		28
OSB3 board 2440×1220 (18mm)		25
Treated timber 47x150mm (4.2m)		20
Treated timber 47x150mm (3.6m)		5
Treated timber 47x150mm (4.8m)		9
CLS treated timber 38x89mm (4.8m)		12
CLS treated timber 38x89mm (2.4m)		50
Treated sawn batten 50 x 25mm (4.8m)		32
Celotex 100mm GA4100 2.4m x 1.2m (insulation)		6
Celotex 50mm GA4050 2.4m x 1.2m (Walls)		12
Rockwool RWA45 40mm 1200x600mm (Walls)		24
Rockwool RWA45 50mm 1200x600mm (Roof)		10
Breather membrane (1.5x25m)		1
Polythene vapour barrier  2.5m x 20m		2
Square edge plasterboard 12.5mm 2440x1220mm		17
Western Red Cedar Cladding 135mm x 18mm	260m
EPDM Roofing kit 3.5m x 4.5m		1
Fascia Board UPVC – 9mm thick, 150mm wide x 5m		4
Fascia corner trim join 450mm		2 (cut in half)
Plastic headed pins 40mm		50
LPD AluVu Left Handed Grey Aluminium Clear Glazed Folding/Sliding Door		1
Crystal Left Hand Side Hung Grey uPVC Casement Obscure Glazed Window		2
70mm x 4mm wood screws		300
40mm x 4mm screws		600
35mm lost head nails (or nail gun)		600
Staples for staple gun		200
80mm Turbo gold screws (5mm)		80
64mm Kreg washer screws		178

The above list includes all items required for the build listed in my full garden room guide.

Before starting your build, it’s important to plan out the design, gather the right materials, and understand the best construction methods. For a more detailed breakdown with a PDF guide and interactive 3D model, take a look at this Self-Build Professional Garden Room Guide.

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My Top Five Timber Frame Garden Room Construction Techniques

Building your own garden room is a rewarding project but it could be short-lived when the structure is not constructed correctly. Here are my top five construction techniques to ensure a robust build.

One. Ensure your timber frame is raised off the floor with suitable drainage around the building. Any water buildup on or near the timber will dramatically reduce the life of your garden room.

Two. Ensure you use a breathable membrane on the outside of the timber frame walls. This will allow your garden room to ventilate correctly and prevent mould growth within the walls.

Three. Larger garden room buildings will require additional foundation support. Ensure your garden room has a sufficient number of ground anchor points to support the overall weight without any sinking of subsidence.

Four. Use the best quality timber cladding you can afford. Western red cedar is considered the best timber for cladding due to its naturally high oil content. It naturally repels insects and moisture.

Five. Treat your timber cladding annually. To ensure a long lasting structure, ensure you treat the exterior timber annually with a suitable oil, stain or paint. If you don’t have time, hire someone to do this for you. It will increase the life of your building to over 50 years.

Self-Build Garden Room Questions and Answers

Here are answers to some of the most common questions I get asked with self-build garden rooms.

Is it cheaper to build your own garden room?

Certainly! Building your own garden room can be a cost-saving option. By eliminating labour costs, you can save a significant amount of money. For instance, if you were to hire a four-person construction team to build the garden room in approximately five days, you could potentially save between £8,000 and £25,000 in labour expenses, depending on the complexity and size of your design.

If you possess the necessary skills, tools, and enthusiasm, building your own garden room is definitely worth considering. With the guidance provided above and in my detailed guide, you can confidently undertake the project and achieve results that match the standards of a professionally constructed garden room.

Is a garden room cheaper than an extension?

Whether a garden room is cheaper than an extension depends on various factors, including the size, design, materials used, site conditions, and the specific requirements of the project. In general, garden rooms tend to be more cost-effective compared to traditional house extensions for several reasons:

1. Construction Costs: Garden rooms are typically smaller in size and have simpler designs compared to house extensions. This can result in lower construction costs since less labor, materials, and time are required.
2. Foundation and Site Preparation: Garden rooms often have lightweight construction and may not require extensive foundation work, unlike house extensions that may require more substantial foundations. This can help reduce overall costs.
3. Building Regulations: In many cases, garden rooms can be constructed within the permitted development rights, which means they may not require planning permission. This can save costs associated with planning application fees and time required for the approval process.
4. Utility Connections: Garden rooms can often be connected to existing utilities, such as electricity and water, without significant additional expenses. In contrast, extensions may require more complex utility connections, which can add to the overall cost.

However, it’s important to note that the cost comparison between a garden room and an extension is not always straightforward. Customisations, high-end materials, complex designs, additional features like plumbing or bathrooms, and specific site conditions can all impact the cost of a garden room and make it comparable to or even more expensive than an extension.

When you take into consideration how to build a garden room compared to building an extension there is a key cost saving when taking on the job yourself. You’re instantly saving up to 50% of the costs of labour. This is a serious saving that can’t so easily be recouped on an extension.

Do you need planning permission to build a garden room?

Most garden room builds will not require planning permission but be sure to check with your local planning authority before you get started. Visit the planning portal to check if your design fits within what is known as permitted development.

Here is a brief summary of the restrictions:

1. Any outbuilding situated ahead of the main wall of the house is not allowed.
2. Outbuildings and garages must be single-storey structures with a maximum eaves height of 2.5 metres and an overall height of four metres if they have a dual pitched roof. For structures with any other type of roof, the maximum overall height should be three metres.
3. If a building, enclosure, or container is located within two metres of the property’s boundary, its maximum height should not exceed 2.5 metres.
4. Verandas, balconies, or raised platforms are not permitted, except for platforms that do not exceed a height of 0.3 metres.
5. The combined area of additions or other buildings on the land surrounding the “original house” should not exceed half of the total land area.
6. In National Parks, the Broads, Areas of Outstanding Natural Beauty, and World Heritage Sites, the total area covered by buildings, enclosures, containers, and pools located more than 20 metres from the house should be limited to 10 square metres.
7. Planning permission will be required for buildings, enclosures, containers, and pools located at the side of properties on designated land.
8. Within the grounds of listed buildings, any outbuilding will require planning permission.

You can read my definitive guide on planning permission for garden rooms for further details and information.

What is the maximum size I can build a garden room?

Footprint – The size limit for a garden room, without the need for planning permission in the UK, is no more than 50% of the land around the original house.

Height – For gable designs, the maximum permissible height of your garden room, including the roof, is 4 metres. For all other designs, the maximum height is 3 metres. However, if you plan to construct your garden room within 2 metres of a boundary, the total height, including the roof, must not exceed 2.5 metres unless you obtain planning permission.

How thick should garden room walls be?

In the aforementioned example, the main timber framed walls have a thickness of only 89mm, which represents the minimum width I would suggest. If enhanced insulation is desired, I would recommend opting for slightly thicker timber frames. By increasing the thickness of the timber frame, more insulation can be incorporated, resulting in a more energy-efficient structure.

While thicker cladding can be employed, its impact on thermal efficiency is minimal. However, thicker cladding offers advantages such as improved acoustic properties and increased durability, making it a worthwhile investment, particularly for projects involving sound studios. You could in some cases make your timber garden room walls thicker but this will add significant cost to the build with no major benefits.

What is the lifespan of a timber framed garden room?

The lifespan of a garden room can vary depending on several factors, including the quality of materials used, construction techniques, maintenance practices, and exposure to environmental conditions. A well-built and properly maintained timber garden room can have a lifespan ranging from 10 to 50 years or even longer.

Timber-framed garden rooms can last for several decades if the timber is treated, regularly inspected for any signs of decay or damage, and properly maintained with appropriate finishes or coatings to protect against moisture and pests.

Other materials commonly used in garden rooms, such as metal or uPVC, can also have a long lifespan if they are of high quality, installed correctly, and maintained properly.

It’s important to note that the lifespan of a garden room can also be influenced by factors like local climate, usage patterns, and the level of wear and tear it experiences. Regular inspections, repairs, and maintenance can help extend the lifespan of a garden room and ensure its continued functionality and durability.

For more permanent options you could consider used 20ft shipping container garden rooms.

How long does it take to build your own garden room?

The design proposed in this article should take one person about 2-3 weeks to complete by themselves. When hiring a professional to build your garden room expect the job to be completed by a team of about 4 people in one week.

These assumptions exclude any groundwork preparation which can add days or weeks to the build.

Are garden rooms warm in the winter?

Garden rooms can be made warm and comfortable during the winter months with proper insulation, heating systems, and design considerations.

Insulation: Adequate insulation is crucial for maintaining warmth in a garden room. Insulating materials can be added to the walls, roof, and floor to reduce heat loss. Common insulation options include foam insulation, mineral wool, or natural materials like sheep’s wool. Insulating the windows and doors with double or triple glazing also helps retain heat.

Heating Systems: Various heating options are available for garden rooms. Electric heaters, underfloor heating, or even wood-burning stoves can be installed to provide warmth. The choice of heating system depends on factors such as the size of the garden room, power availability, and personal preferences.

Design Considerations

Design features can contribute to the warmth of a garden room. Large windows that allow natural sunlight to enter during the day can provide passive solar heating. Proper ventilation is also important to prevent excessive humidity and maintain a comfortable indoor environment.

It’s worth noting that while garden rooms can be made warm, they may require additional heating compared to the main dwelling, as they are separate structures and may not benefit from the central heating system of the house. Energy-efficient practices, such as using insulation, sealing drafts, and using heating systems wisely, can help create a warm and energy-efficient garden room during the winter months.

If you’re unsure about the best size for your garden room, a 5m x 4m layout offers plenty of space for an office, studio, or home gym. For a ready-to-use guide, you can view these Free 5m x 4m Garden Room Plans that include all the materials, tools, and step-by-step instructions you’ll need.

Can you have a bedroom in a garden room?

In the UK, it is possible to have a bedroom in a garden room, but there are specific regulations and requirements that need to be met to ensure compliance with building regulations and planning permissions.

Building Regulations: If you intend to use a garden room as a habitable space, including a bedroom, it must comply with the applicable building regulations. These regulations cover aspects such as structural stability, fire safety, insulation, ventilation, and electrical installations. Meeting these requirements ensures that the space is safe, comfortable, and suitable for occupancy.

Planning Permission: Whether you need planning permission for a garden room with a bedroom depends on several factors, including the size, location, and intended use. In some cases, you may be able to use permitted development rights to construct a garden room without planning permission, provided it meets certain criteria. However, if the garden room is intended to be used as a separate self-contained living space, such as a permanent dwelling or an independent annex, planning permission will be required.

Read my full garden room construction planning and building regulations guide here.

Strictly speaking you cannot sleep in your garden room without planning permission.

Conclusion

By following this step-by-step guide, you can successfully build your own insulated garden room, creating a versatile and comfortable space that can be used year-round. Whether you’re constructing a DIY garden office, studio, or hobby room, this timber garden room is designed to industry standards, ensuring durability and efficiency. With the right materials and techniques, you can complete this project at a fraction of the cost of a professional build, adding value to your home while enjoying a custom-built space tailored to your needs.

Further Reading

There are more questions you might have regarding this build. I’ve covered some of these in the below articles but if you can’t find the answer please feel free to leave a comment and I’ll get back to you when I can.

• How to build a base on uneven ground
• Do I need planning permission for a garden room?
• How to prolong the life of your garden room
• How much does a garden room cost?

How to Build a Budget Garden Room

Like many, you might be looking to create your own garden room on a tight budget. If the above project isn’t right for you and you need to cut back on the overall cost of your garden room project then take a look at my pre-fabricated garden office build.

Within this project, I managed to build a fully insulated garden room for under £7k. Thats quite remarkable considering the above project could cost in excess of £14k. That’s half the price.

Read the full guide here: https://wood-create.com/billyoh-log-cabin-review-build-guide/

Read how I insulated this building here: https://wood-create.com/how-to-insulate-your-billyoh-garden-office-log-cabin/

Thanks for reading and good luck with your build.