Free 5m X 4m Garden Room Plans

Hello and welcome to my free 5x4m (16x13ft) garden room plans. I’ve spent hours drawing up these garden room plans to share with like-minded DIY enthusiasts like you. If you have access to a handful of basic tools, some spare time and a reasonable budget, then this is the right place to get started on your dream garden room. This guide will walk you through this professional build, fully insulated garden room from start to finish. It captures all the best techniques and building standards to ensure you can build a long-lasting, durable structure in your garden.

What’s Included in These Free Garden Room Plans?

Within this article I will show you a step-by-step guide to complete this garden room. I’ll also include a list of tools, materials and some detailed drawings and plans so you can see some of the finer detail in the creation of this amazing building. Before getting started on you garden room build, be sure to check if you need planning permission.

What’s not included in the free version:

• Access to the interactive 3D model.
• A full material and cut list for each stage of the build.
• A full printable materials list and quantities for the whole project. (To send to suppliers for up to date cost quotations).
• A printable garden room plan PDF document, guide and instructions.
• Detailed step-by-step instructions for each stage of the build process.
• Email support. If you get stuck or have questions about the build you can contact me for guidance.

How Much Will it Cost to Build This 5x4m Garden Room?

Before I scare you will the cost for this garden room, please bear in mind the total cost will include:

• Foundations and ground works
• Timber (Framework, sheet materials and cladding)
• Windows and doors
• Insulation
• Electrics (Sockets and lighting)
• EPDM roofing
• Internal finishing (Plaster, flooring and painting)

I’d also like to point out the potential savings here on labour. If you decide to take on this challenge yourself then you will save roughly 50% of the total cost. For a garden room of this size and professional quality finish, you should expect to pay between £15,000 and £20,000. Hire a professional garden room company and you could be in the region of £40,000. That’s a saving worth considering. That’s why I think my full paid guide is worth considering. It’ll give you everything you need to complete this build on your own.

How to Build a Garden Room Base

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. You’ll also need to ensure good runoff and drainage. I personally would recommend another option as the life expectancy of this method will be far less than the other methods.

Building the Base Frame

The timber frame is constructed from a kiln-dried 47x150mm C24 construction timber. Spacing between rafters will be about 400mm. The timbers are 4.8m and 4.2m long joined with 3 large 100mm screws. The top is finished with 18mm OSB boards or if you want a higher standard finish, 22mm Egger Protect boards.

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 flooring boards

The final job for the garden room base is to secure durable flooring. The are two options here. The cheaper 18mm OSB board or a slightly more expensive TG4 chipboard flooring. I would recommend TG4 for a garden room.

or

Building the Garden Room Walls

Once the foundations and base are complete, it’s time to construct the walls. We’ll use 38x89mm CLS timber. Again, the spacing between timbers will be 400mm. A steel hollow beam is used above the large bi-fold doors to ensure the roof’s weight can be supported without impacting the doors.

The front walls are 100mm taller than the back walls to ensure there is suitable water run off on the roof. The window openings are set 5mm wider (in each direction) than the window frames to allow for easy installation.

Building the Garden Room Roof

Due to the large roof span and height restrictions (2.5m) we need to double up some 47x150mm C24 timbers. The timbers will be bolted together using 100x8mm nuts and bolts located in equal spacing along the beam.

Noggins and an outer frame can be added once the main support beams are in place.

Now, the roof boards can be secured onto the roof frame. For this, we use 18mm OSB T&G boards that measure 2400x600mm. The boards can be secured using 50mm screws in several locations.

Adding the Wall Boards, Doors and Windows

The walls need to be boarded using 18mm thick OSB3 boards. Simply attach the boards to the exterior walls and secure in place with 50mm screws. Cut out sections for windows and doors as required using a jigsaw or circular saw.

The doors and windows can be added at this stage and secured to the wall frames. Read the supplier’s installation instructions for the correct fitting. Use tech screws to secure the doors to the steel beam. Tech screws are self-tapping screws designed for easy installation into steel.

Electrics for Your Garden Room

Now is the ideal time to consider installing the electrical system in your garden building. If you’re not confident or qualified to handle tasks like wiring sockets and lighting, it’s safest to hire a professional electrician. Make sure to bring them in before you begin installing insulation and interior wall panels.

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 air circulation.

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

Furring Strips for Cladding

In the next step of this guide, we’ll focus on furring strips, which are crucial for supporting the cladding and ensuring proper ventilation between the boards.

For vertical cladding, furring strips are installed in two layers: one set vertically and the other horizontally. If you’re installing horizontal cladding, you’ll only need vertical furring strips. It’s important to avoid attaching horizontal furring strips directly to the breather membrane, as this can trap moisture and lead to issues over time.

Cladding the Garden Room

The first step in cladding your garden room is choosing the right material. There are plenty of options available, so your decision will largely depend on your budget.

If your budget allows, Western Red Cedar is an excellent choice. It’s a naturally oily wood with outstanding moisture-resistant properties. While it will still require treatment, it tends to last much longer than other materials.

For a more budget-friendly option, pressure-treated pine is a solid choice. It comes in both loglap and shiplap styles, offering a durable and cost-effective solution.

The Window and Door Framing

Using a 22mm thick timber, measure and cut four pieces to fit into the window frame for a tidy finish.

Fitting the Waterproof Roofing Material

To achieve a watertight roof, you’ll need to install an EPDM rubber roofing system. These systems are available as kits that typically include a large rubber sheet, adhesive, and edge trim for securing the perimeter. For the best results, follow the manufacturer’s installation guidelines carefully. Here’s a helpful example video that clearly demonstrates the installation process.

Materials and Tools Needed

• EPDM roofing kit (rubber membrane, adhesive, and edge trim)
• Soft-bristle broom
• Roller and brush for adhesive
• Utility knife
• Measuring tape
• Protective gloves

Step 1: Prepare the Roof Surface

1. Clean the surface – Ensure the roof deck is clean, dry, and free of debris. Sweep it thoroughly with a broom.
2. Inspect the deck – Check for any loose boards, nails, or damage, and repair as needed. The surface must be smooth and secure.

Step 2: Measure and Cut the EPDM Membrane

1. Unroll the EPDM membrane over the roof, allowing it to overhang the edges by at least 150mm (6 inches).
2. Leave it to rest for 30 minutes to relax and reduce any wrinkles.
3. Trim the membrane to size using a utility knife, but keep the overhang intact.

Step 3: Apply the Adhesive

1. Fold back half of the membrane to expose the roof surface.
2. Apply the adhesive evenly across the exposed roof deck using a roller or brush, following the manufacturer’s instructions.
3. Allow the adhesive to become tacky (as per guidelines) before carefully laying the membrane back into place.
4. Smooth the membrane with a soft-bristle broom, working from the center outward to remove any air bubbles.
5. Repeat the process for the other half of the roof.

Step 4: Secure the Edges

1. Apply adhesive to the edges and fold the membrane over, ensuring a tight seal.
2. Attach the edge trim supplied in the kit to secure the membrane along the perimeter of the roof.

Step 5: Finishing Touches

1. Trim any excess membrane with a utility knife.
2. Inspect the entire roof for any wrinkles or air pockets, smoothing them out as needed.
3. Check the edges and seams to ensure they are fully adhered and sealed.

Tips for a Successful Installation

• Perform the installation on a dry day with mild temperatures.
• Avoid stretching the membrane too tightly; it should be laid flat but not under tension.
• Follow all manufacturer instructions for adhesive curing times and application techniques.

Finishing the 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

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.

Materials List for this 5x4m 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
OSB3 board 2440×1220 (18mm)
Treated timber 47x150mm (4.2m)
Treated timber 47x150mm (3.6m)
Treated timber 47x150mm (4.8m)
CLS treated timber 38x89mm (4.8m)
CLS treated timber 38x89mm (2.4m)
Treated sawn batten 50 x 25mm (4.8m)
Celotex 100mm GA4100 2.4m x 1.2m (insulation)
Celotex 50mm GA4050 2.4m x 1.2m (Walls)
Rockwool RWA45 40mm 1200x600mm (Walls)
Rockwool RWA45 50mm 1200x600mm (Roof)
Breather membrane (1.5x25m)
Polythene vapour barrier  2.5m x 20m
Square edge plasterboard 12.5mm 2440x1220mm
Western Red Cedar Cladding 135mm x 18mm
EPDM Roofing kit 4m x 5m
Fascia Board UPVC – 9mm thick, 150mm wide x 5m
Fascia corner trim join 450mm
Plastic headed pins 40mm
LPD AluVu Left Handed Grey Aluminium Clear Glazed Folding/Sliding Door
Crystal Left Hand Side Hung Grey uPVC Casement Obscure Glazed Window
70mm x 4mm wood screws
40mm x 4mm screws
35mm lost head nails (or nail gun)
Staples for staple gun
80mm Turbo gold screws (5mm)
64mm Kreg washer screws

I’ve managed to cover a high level of information in this guide which should give you enough to plan and start your project.

Do You Need Planning Permission for This Garden Room?

All of my garden building designs keep within the permitted development height and size restrictions. To check if you need planning permission for your specific house and garden visit me comprehensive guide: Do You Need Planning Permission for a Garden Room?

What you get from my full paid guide:

• Access to the interactive 3D SketchUp model.
• A full material and cut list for each stage of the build.
• A full printable materials list and quantities for the whole project. (To send to suppliers for up to date cost quotations).
• A printable garden room plan PDF document, guide and instructions.
• Detailed step-by-step instructions for each stage of the build process.
• Email support. If you get stuck or have questions about the build you can contact me for guidance.

Thanks for your support