Garage conversion costs: How to calculate what your project will cost

An architectural drawing of plans for a garage conversion
(Image credit: Getty Images)

Understanding garage conversion costs is the first step in transforming your underutilised garage into a functional living space. A garage conversion is an affordable way of expanding your home and adding value to your property. It’s far less expensive than moving house and can be done for less than the cost of an extension of the same size — after all, the foundations, walls and roof are already there. 

Over time lots of garages become storage spaces for unwanted junk or household tools. So it pays to unlock the potential of these wasted spaces by converting them into additional bedrooms, offices, or home gyms. 

In this article, we’ll look at the average cost of a garage conversion, and how this price tag is impacted by a range of factors. 

Are garage conversion costs worth the expense? 

A garage conversion is the most cost-effective way of adding space to your home. Being an existing – and often adjacent – structure it requires less planning and intervention than a brand new extension. But there are many other benefits to opting for a garage conversion: 

  • You won’t lose any of your garden space by converting your garage, and the works are far less likely to be disruptive. 
  • If your garage is detached, you could be gaining a self-contained annexe for your home. This could be used as an additional living space for a loved one or a place to work from home. 
  • Garage conversions can add from 10 - 15% to the value of your home depending on their purpose and design. However, be aware that parking spaces in certain locations can be incredibly valuable and removing your garage (if you don’t have alternative off-road parking) could actually devalue your home.

A home garage with an open garage door

If your home garage is rarely used, consider converting it into a living space (Image credit: Getty Images)

What is the average cost of a garage conversion?

As a ballpark figure you can expect a typical 16m2 garage conversion to cost on average £15,000. That’s a great amount of extra space for an average cost of £950/m2.

The type of garage you have - integral, attached or detached - will impact conversion costs. The cheapest type of garage to convert is an integral garage, as this will already have a connection to the house and is likely to already have an electricity supply for lighting. You should budget around £12,500 for these projects, based on average costs. An attached garage would fall in the middle of the cost scale at an average of £15,000, with a detached garage being the most expensive type to convert at around £20,000. 

It's worth remembering that all of these options are still cheaper than building the same sized extension for the same purpose.  

A bedroom and a bathroom with white walls and grey carpets

Converting a garage into a bedroom is a great way to add value and space to your home (Image credit: Future)

The main factors that will influence costs

Before you start browsing garage conversion ideas, you may want to dig a little deeper into the factors that will impact your budget: 

1) The cost of flooring 

Garage flooring is not finished to the same standard you would find in an internal room, so as a minimum you’ll need to budget for digging up the existing floor and laying a new concrete base at a cost of around £1,000. The flooring will also need a suitable damp-proof membrane to satisfy Building Control. 

2) The cost of garage insulation 

A typical garage won’t have any insulation, so budget around £1,000 for basic options. 

3) Filling in garage doors and adding new windows 

The cheapest way to fill in the hole left by the garage door would be with blocks/bricks/render to match your existing façade, but this isn’t necessarily the most attractive option. Most conversions will have at least a half wall and new window at the front for aesthetics and maximising light in the new space. You may also opt for a further window or possibly patio/bifold doors at the rear, depending on the purpose of the space. Budget around £1,000-£1,500 for a new wall and standard uPVC window.

4) Extending and introducing new services 

Your garage may have an existing electricity supply which will need to be extended to provide sockets and additional lighting. It’s unlikely to have any supply of water or gas, so these services will need to be introduced and the cost will increase depending on how far away the source is in your home. Budget between £1,000 and £4,000 depending on whether you require the basics or full services. 

5) Plastering and decorating

Allow £600-£900 for plastering and £500-£750 for painting and decorating. 

A kitchen with a white kitchen island and a garage conversion beyond.

Convert a garage into a multifunctional room to maximise on space (Image credit: Future)

Other garage conversion costs to consider

Do you need planning permission to convert a garage? 

Generally, unless you are changing the existing building by increasing the size or adding another storey, you won’t need planning permission as the conversion will fall under Permitted Development rights. However, if you are increasing the size of the garage, or your property is listed or in a conservation area, you will need planning permission from around £200 depending on your local authority. Beware, your garage may also be subject to restrictions under your deeds, which mean the use for parking cannot be changed.

Do you need building regulation approval for a garage conversion? 

Building Regulation approval will be required as the conversion needs to be inspected for fire safety, insulation and ventilation, and structural stability, including a damp-proof course. Unless you are using a contractor that can self-certify the works, you should contact your local authority prior to any works commencing. Budget between £500 and £1,000.

Design costs 

You are unlikely to require professional design advice if your plans are simple, such as adding an extra bedroom. However, if you are looking to reconfigure your home layout using the extra garage space, design professionals can provide a range of options you may not have considered. You can obtain basic design advice from around £300-£400 and plans from around £500 to £1,000. 


If you are using a builder, check that they have the necessary insurance in place. If you are planning on doing the work yourself, you must contact your own home insurance provider as you will need conversion insurance to be covered for the work. 

A bedroom with white walls and a double bed

Converting your garage into a bedroom is a cost-effective way to add value to your home (Image credit: Future)

Converting a garage into a bedroom

Converting a garage to a bedroom shouldn't be too expensive, as it requires only basic services like lighting, sockets and a source of heating (radiators or underfloor options). Modern garages will probably have an existing electricity supply for things like lights and possibly some sockets, which will be cheaper to upgrade than installing a new supply. 

For a simple bedroom conversion of a typical 16m2 garage you can achieve a conversion for under £10,000 for an integrated or attached garage and £15,000 for a detached garage. If you are very skilled at DIY there is scope to make savings, but you will need a qualified electrician and be able to satisfy the building control requirements. 

If you want to add a bathroom to this space, then you will need to add the cost of the plumbing/drainage works and the bathroom suite so you should budget an additional £2,500- £5,000 for this 

Tim Phillips is an experienced senior quantity surveyor and estimator and has worked in the construction industry for over 35 years. He has worked on many varied projects in this time, for corporates, public bodies and private residential clients, managing multi-million budgets. 

For the past 13 years, Tim has worked on a freelance basis, whilst managing his rental property portfolio. He has extensive experience of undertaking his own full-scale house renovations. He is also a speaker and expert at the Homebuilding & Renovating Shows.

With contributions from