If you frequently want more space in your home, an extension is a great idea. Unfortunately, extensions are normally limited to extending the space you have against the back wall of the house – normally the kitchen.
So, for everyone who wants more space but not a larger kitchen, a garden room extension is a better option. This separate room is fully distinct from your home and allows you to add more indoor space, without extending the kitchen.
In most cases, the average cost of a garden room extension is £1,500-£2,000 per square foot. In addition, you’ll pay from £1,500 including labour, materials, wiring, and basic interior finishing. Depending on the materials you use, those costs could more than triple.
Topics
Why Extend Your Garden Room?
A garden room extension allows you to build a new room in your garden, without extending from the back wall of your house. This means you don’t have to extend your kitchen.
It also means you don’t have to block light from whatever room you do have there. Providing you just want a hobby room, gym, office, or other similar space, there’s no real reason why you would need the building connected to your home.
=> Looking for a custom house floor plan? Click here to fill out our form, a member of our team will be in touch.
Garden rooms are:
- Standalone structures
- May be connected to your home’s existing heating system
- Do not need a structural engineer if under 10×10 metres and more than 20 metres from the home
Extensions are:
- Built into the house by knocking the back wall out
- Are connected to your home’s existing heating system
- Always require a structural engineer
Conservatories are:
- Built against the back wall of your home
- Primarily made of glass and brick
- May not be connected to your home’s existing heating system
- Likely do not need a structural engineer
This means that a garden room extension adds a lot of value in a few very specific scenarios. If you want extra room, but do not want it to be part of the current back room of the house, and want to retain light in the back room of your home, a garden room extension is a great call.
On the other hand, if you want to increase the size of a room in your home, you’re better off with a traditional home extension.
Garden Room Extension Cost Estimates*
Garden room extensions will cost roughly £30,000 or more with all work taken into account. That starts out at around £1,500 per square foot. However, you can always increase costs by increasing the quality of the materials or paying for more design details.
For example, if you’re taking the simple route of building without requiring planning permissions, (A 10×10 metre garden room installed 20 metres from the home with a roof that caps out at 3.5 metres, you can expect roughly the following costs:
| Costs | Hours | Total | ||
| Hourly Rate | £10- £50 | £656- £6,730 | ||
| Pouring Slab | 4-8 | £40-£300 | ||
| Bricklaying | 48-60 | £480- £3,000 | ||
| Roofing | 4-8 | £40- £350 | ||
| Electric Work | 2-8 | £50- £150 | ||
| Glazing | 2-4 | £100- £250 | ||
| Heating | 4-8 | £40- £480 | ||
| Drywall | 4+ | £40- £180+ | ||
| Insulation | 4-12 | £40- £720 | ||
| Building Regulation Approval for Notifiable Work | £0- £690 | |||
| Materials & Fittings | £18,740 – £26,556 | |||
| Brick | £12,000- £14,500 | |||
| Cement | £120- £396 | |||
| Roofing | £825 – £1750 | |||
| Insulation | £3,000- £6,000 | |||
| Heating | £2,500+ | |||
| Drywall | £100- £500 | |||
| Light Fixtures | £50+ | |||
| Electrical | £145- £860 | |||
| £19,396- £33,286 | ||||
*Please note, these costs were based on price averages at the time of writing in April 2023. Actual rates are subject to change and may be different at the time of reading.
Extending Garden Room Price Factors
The largest cost factor in extending a garden room is normally the cost of materials. However, you can also pay a considerable amount for labour. The following price factors will impact the total cost of your job.
Materials
Materials can be the largest cost of building a garden room. However, different materials cost vastly different sums of money. Brick is one of the most popular building materials in the UK. It’s also one of the most expensive.
For example, you need roughly 120 standard UK metric sized bricks per square metre of double brick wall. This means that for a 10×10 building, you’ll need over 6,000 bricks. However, different materials vary significantly in cost-to-build.
| Material | Cost per M2 |
| Brick | £100-£160 |
| Metal (Steel) | £35-£42 |
| Stone | £100-£270 |
| Glazing | £1,200-£3,400 |
| Softwood (Pine/Fir) | £30-£80 |
| Hardwood (Oak) | £450-£850 |
Of course, you’ll also have to pay for other materials.
- Concrete Footings – Expect £120-£150 including pouring and polishing
- Roofing – £132-£255 (gable or flat, with clay or concrete tiles)
- Doors – £150-£690 per door
You’ll also have to consider cost factors like electrical work (e.g. wiring, spurs, fittings, switches), plumbing and heating (e.g. radiators, hot water lines, taps, sinks, baths, showers, etc.) For example, if you want to fit your garden room with a bath, you can probably add about £8,000+ to the above estimate.
Labour
Labour is another significant factor in the cost of building a garden room. Most labourers have a rate of about £10- £60 per hour. It’s not uncommon to find day rates between £150 and £350.
Here, you can expect to spend different amounts of time and money based on the building material you choose. For example:
- Prefab Metal/Wood Building – 14-20 hours
- Brick – 1 day per 1,000 bricks (40-60 on average)
- Custom Wood – 8-20 hours
In addition, many bricklayers will offer total rates for 1,000 bricks. For example, 1,000 bricks (material and labour) for £1,000- £1,500.
It’s also important to note that you might be unable to find a single contractor or firm to do all of your work. You’ll need a registered plumber to do the radiator. You’ll also need a registered electrician to do the electrical work. Otherwise, you could end up spending much more on notifications.
Size
The larger your garden room, the more it will cost. However, you will often find that there’s a sweet spot where building larger is significantly cheaper per square metre than building smaller.
In addition, if you build over 10×10 4etres or higher than 4 metres, you’ll need planning permission and a structural architect. That can greatly complicate your build process and add weeks to the process.
Excavation and Foundation
In most cases, you’ll have to excavate and prepare the foundation before you can build a garden room on it. The foundation doesn’t have to be the same as the house.
However, it should be rated to support the weight of the building as well as any furniture you have inside. In most cases, foundation preparation costs £200-£260 per square metre.
Wiring
Wiring and electrical work will cost anywhere from £800-£3,000+ depending on what you want. If you just need a light and heating controls, you can probably get away with a simple spur off the spur in the kitchen at the back of the house.
However, if you want a workshop, are running a high power PC, or are otherwise drawing extra power from your garden room, you’ll want to spend more to get a 20 amp spur that can support the room.
Plumbing
You can legally put a garden room on the same heating system as your house, which means you can extend your radiator system. That means hiring a registered plumber to do the work.
It will normally cost from about £800 – but costs can be much higher depending on what’s involved. In addition, if the garden room is too far from the main house, your plumber may recommend that you install a new boiler system instead.
Planning Permission
If you build against your home, closer than 20 meters to your home, larger than 10×10 metres, or higher than 4 metres, you’ll need planning permission. That will cost £190-£206 depending on your region. But, it also means you’ll need structural planning.
Of course, you’ll also need structural planning at any point when you have a building over 4×4 meters in size. This means you may already have the engineer as part of your project budget.
In fact, your construction firm probably has one to hand to handle everything you need for that. Therefore, planning permission may be a relatively small part of the added costs.
On the other hand, it can take 6 or more weeks to get planning permission, which means you may see significant delays in making your garden room extension a reality.
Notification Cost
You’ll have to notify City Council/Building Control of your new building, including any electrical or plumbing works. This will cost £170-£690 depending on your location. In most cases, if you have a Part P registered construction team, they will handle notifications for you.
In addition, if they are Registered Competent Persons, they can also self-inspect and submit the necessary safety inspections as well. If not, you can expect to add £1,000+ in total inspection costs from Building Control to the end-total of the garden room.
Planning Permission and Building Regulations Needed
Your garden room will require:
- Planning permission
- Part P Certification
- Building Control Notification
You can often skip planning permission for a garden room. However, that may not be the case. You can normally skip planning permission if your building meets the following requirements:
- The building is not more than 10 metres by 10 metres
- A gabled roof is not taller than 4 metres
- The building is further than 20 metres from your home
- Your building is not intended to be heavily trafficked
- The building does not include plumbing
- Your building does not contain a sleeping space
- The building does not take up more than 50% of the total area around the house
- Your building is not more than 1 storey
- You have no plans for a balcony or veranda
- The building does not exceed 15 square metres
- You do not live in a listed building
If your planned garden room meets those requirements, you can typically skip planning permissions. Otherwise, you will need them.
However, you’ll always have to notify building control. The only way you could skip doing so is by keeping your building under 2 x 2.5 metres, not having plumbing, and not having electrical work. Because that’s inconvenient, you probably don’t want to.
However, you can get around most of this hassle by simply hiring a Part P Certified contractor to do the work. This means they will notify building control for you. The £170- £690 cost will be included in your rate.
In addition, they’ll be able to self-inspect, which means they can provide the necessary safety certificates you need. That will save you considerably over hiring someone else to come out and do the inspection for you.
Garden Room Uses
A garden room can be a great way to extend your home with another room. For example:
- Teenagers’ bedroom
- Home gym
- Hobby room/workshop
- Socialising space
- Outdoor kitchen
- Home spa
- Guest room
In almost every case, you should have a very good idea of what you want to do with a garden room before you invest in one. After all, knowing whether you want to install a kitchen or a sleeping area will greatly impact costs and design.
Project Checklist
Planning a garden room is a straightforward project but there are many complications that may come up.
- Research materials and options
- Set a budget
- Select building materials and designs
- Research and compare local contractors
- Ensure that your building materials and design actually work
- Get designs approved by a structural engineer
- Apply for planning permission
- Prepare the site (Excavate the foundation, dig trenches for plumbing, etc.)
- Lay plumbing
- Pour the foundation
- Build the walls
- Build the roof
- Install electric
- Add insulation and any underfloor heating
- Install drywall
- Lay flooring
- Get the structural inspection
- Add electronics
- Get the electrical safety inspection
- Paint and finish
- Notify Building Control
In most cases, with planning permission, you can expect the full project to take 6-8 weeks. The actual build time should be 2-3 weeks, depending on the weather, the number of people on the job, and the size of the project.
To End
A garden room can be a great way to expand your home without extending the kitchen. In addition, as a fully insulated room, garden rooms can be part of your existing heating system. However, with costs averaging at £1,500 per square metre, they can be quite expensive.
If you want a garden room, the best option is to compare your options and choose the one that best aligns with your project goals and needs. Use the form at the top of the page to request local quotes from contractors in your area.