Garage Extension: How to Extend a Garage?

Robert Kinney

By Robert Kinney

Last Updated on February, 2025

Thinking of building a garage extension? You’re not alone. 

Custom garages are a popular DIY project for homeowners in the UK, and building an extension is one of the best ways to enhance your property–both in size and value.

Moreover, the versatility of a garage extension lets you turn yours into pretty much anything: an office, a home gym, a living space, or even a studio dedicated to your favourite hobby. 

Maybe you can already envision it, but imagining the perfect garage won’t make it magically appear. Building a garage extension requires much work and planning, whether a bump-out addition or a new structure. 

But worry not! This article will guide you through the process, from selecting a location and materials to final construction and finishing touches. 

Rest assured, our guidelines will cover all the bases and help you build the garage extension of your dreams. 

Ready to get started? Then let’s begin!

Quick Summary

  • Building a garage extension requires thorough planning, including selecting the location, consulting with an architect, and ensuring compliance with local zoning laws and building codes. Ignoring these can lead to fines and project delays.
  • Whether building a bump-out or a detached garage, specific tools and materials are needed, like plywood, wooden beams, and concrete. The construction process includes setting foundations, creating walls, and ensuring proper drainage and insulation.
  • A garage extension can increase a property’s value by 5-10%, provide additional storage, and protect vehicles. The extension can also be converted into a living space, gym, or studio, enhancing functionality and appeal to potential buyers.

How to Build a Garage Extension?

Extended garage door with a car port

Breaking down the garage building process into phases can simplify it. This will give you a linear set of tasks and make it easier to track the overall progression of your garage project. 

Let’s have a look!

Planning

When planning a garage extension, you must consider location, design, zoning laws, and more factors. These will largely depend on whether you’re building a garage addition or a detached garage away from the main house. 

We recommend consulting an architect to determine the ideal option based on your property’s layout.

Ensure sufficient distance between the existing garage wall and your patio for a garage bump-out addition. The wall should also be away from outside fencing to provide enough room for your extension. 

Once you’ve decided on a wall, the next step is clearing out your existing garage. Tools, vehicles, and lawn equipment can interfere with construction, so it’s essential to free up as much garage space as possible.

Dispose of any junk or broken machinery you’ve always meant to throw away but could never find the time. 

With the garage cleared out, you can begin construction. Since it’s an attached structure, you’ll want to ensure its design and aesthetics match your home’s exterior. This will create uniformity and prevent your extension from standing out. 

On the other hand, building a detached garage requires picking a new location. As such, you may need to cut down trees or shrubbery to make room for the structure. 

In addition, you’ll have to factor in its distance from the main house, exposure to sunlight, and drainage. Installing gutters is essential, but you can also use the planning stage to decide on other additions to your new garage, such as plumbing or special lighting. 

Another consideration is whether your existing driveway can accommodate the new building. Depending on your needs, you might need to widen your driveway or pave a new one.

Neither option is cheap, so you should plan for them beforehand. Nothing derails a project faster than surprise expenses! 

In addition to location and design, you will also have to consider local zoning laws. These may apply to new structures and additions to existing garage walls. 

Local building codes dictate the height of your garage, how far it can extend about your property line, and when you will need to apply for permits.

Violating these rules can lead to heavy fines, so contact your local building department and gather information before commencing work on your garage extension. 

Since they depend on several factors, local zoning laws in the UK can get confusing. If you are unsure how the regulations apply, consider hiring a professional garage builder during the planning stage. They will help you avoid setbacks and stay on the right side of the law. 

Construction 

Now comes the fun part–once the prep work is done, gather your tools and get to work! 

The joy of garage extension projects lies in their DIY nature, but that doesn’t mean you have to do everything yourself. While you may be able to DIY certain parts of the construction process, others might be too complicated without prior experience. 

Unless you’re building a basic garage extension for some additional space, you’ll need the help of a professional contractor and a few extra hands. Getting the proper assistance will ensure a smooth building process and the best outcome for your home improvement project. 

Below, we’ve outlined the different approaches to building a garage bump-out addition and a new garage from the ground up. 

Building a Garage Addition 

A garage door extension that has two doors

Building a garage addition requires eliminating an existing wall. Before this step, add wooden beams and double trimmers to support the roof. Ensure that it is not a load bearing wall, as breaking that could cause structural issues.

Next, select the area of the wall you want to remove and outline the size of your extension. 5 x 12 feet is the recommended size if you want adequate storage space or use it as a one-car garage. Centering the bump out is up to you and is not a requirement. 

With the outline in place, mark it so that the wall opening is 7 inches narrower than the width of the garage addition, and mark 3 inches on either side of the opening. 

Install king studs between your wall’s top and bottom plate. They should be almost the same size as the width of your extension. For example, if your garage addition is 12 inches wide, the ideal stud size is 11 feet and 11 inches. 

Then, use a reciprocating saw to cut two 10-inch headers and affix them with 10d nails. Complete the header by nailing a 2×4 to the bottoms of the 10-inch pieces. 

Reduce the upper wall studs to 11 and a half inches and remove nails, sheathing, or any remaining stud pieces to fit the new header. Then, you can knock out the existing garage wall to make an opening for your extension.

To create the base of your garage bump-out addition, nail plywood to the existing wall, ensuring it hangs 18 inches above the garage floor. The recommended size for the plank is 12 feet.

Dig two holes, each 1 foot deep, to erect posts for the extension. Fill each hole with eight inches of concrete and wait for it to set. 

Once it does, fix two four-by-four posts and cover each base with soil. As a precaution, you can apply wood sealer to the joists to prevent moisture damage and keep them from rotting.

Attach the two posts with a wooden beam and secure it using concrete anchors and metal hurricane ties. Measure the distance between the beam and your existing structure, then use four pieces of plywood to create the floor of your bump-out addition. 

Leave a three-foot gap between the boards and pour concrete into each. Level it using a two-by-four to complete the foundation and attach the floor of your extension to the shared garage wall. Lastly, fasten the header with hurricane ties for support. 

Next, use the garage floor’s flat surface to make walls for your extension. Start by building the taller, 12-foot wall.

To get accurate measurements, add seven inches to the width of the opening and three inches to its length. Following these measurements, cut two wooden beams for the width and two for the length. 

Outline stud locations on the top and bottom plates for the taller wall. Afterward, connect the longer and shorter beams with 16d nails and straighten the assembled wall to stand upright.

To build the two 5-foot walls, measure the length of your extension from the existing garage wall to the taller one you just assembled. Cut four wooden beams according to these measurements to make the top and bottom plates for the shorter walls. 

Nail the walls to your new garage floor and ensure the corner studs are aligned correctly before nailing them as well.

Finish off by installing tie plates to secure both walls and ensure they don’t overlap.

With the walls and foundation in place, you can now move on to the most important part of your garage bump-out addition: the roof. 

Mark an outline for the rafters by fastening a pair of two-by-six pieces parallel to the garage roof. Use chalk to indicate the centre of the garage extension and the roof overhang distance. Install a two-by-six between the two rafters to create a ridge. 

This outline will help you create the frame for your roof. 

Nail rafters to the ridge and strengthen the tie plates with metal hurricane ties. Install roof trusses to the ends of the rafters and add plywood sheathing over the frame.

Complete the roof by adding roofing felt and attach shingles with a staple gun. Ensure that it matches the roof of your existing structure to create a coherent look. 

Wrap up the construction of your bump-out by adding vinyl siding to the walls. Move upward from the foundation and use chalk to mark the top of the first row. Ensure the alignment for the following rows is correct before nailing them into place. 

Once the structure is covered, attach wall channels where the siding ends to support the corners. 

Building a Detached Garage

Detached garage in a house shape

Constructing a detached garage poses a different set of challenges compared to a garage bump-out. Not only will you have to build a new structure from the ground up, but you’ll also have to consider positioning, drainage, electricity, and plumbing. 

Hiring professional help is strongly recommended for this project. It may seem costly, but doing the job right will allow you to save money on repairs in the long run. 

Start by creating your garage foundation. This should be elevated appropriately and consist of footers and a concrete slab. If you plan to use the garage as a parking space, we recommend building a sloped floor to allow water or snow tracked by the vehicle to roll out. 

It is also recommended to slope the ground near the overhead or access door to prevent water from entering the garage during a downpour. The concrete team will ensure the garage floor is even, but remember to let them know if you want other parts sloped. 

Your contractor will pour the concrete and let it harden over several weeks before resuming the work. 

Once the concrete sets and you have a solid foundation, the construction crew will create the outline of your garage building.

This involves cutting the wall plates, marking the corner stud locations, and making the door and window openings. After straightening the walls and nailing them together, the team will begin work on the exterior. 

You can use plywood or OSB (oriental strand board) for the sheathing. The latter is cheaper and environmentally friendly, but plywood is more moisture-resistant. Consult with your contractor to decide which type of sheathing to go with. 

Next, add a layer of house wrap and siding to finish the exterior. Vinyl siding is generally considered the best option due to its aesthetic appeal and affordability, but you can also choose steel or fibre cement siding, depending on your budget. 

You may be able to build the roof of the garage extension yourself. However, considering the risk of injury, only proceed if you have adequate experience with roofing materials and procedures. 

A construction crew typically employs a crane to position gable trusses before nailing them down to the frame. They then complete the roof by adding roofing felt and shingles.

You will need new gutters and drainpipes for your garage extension, which the building team will connect to your existing drainage system.

This is one of the most critical parts of the process, as stormwater during the rainy season can disrupt the soil around your garage and cause structural damage. Ensure that the gutters are correctly sloped for adequate runoff. 

The team will then install the garage doors and windows. Depending on the size of your extension, you may have one window opening or multiple. Similarly, you can choose to install two single garage doors or one double garage door; it’s totally up to you. 

Another vital part of construction is adding drywall. This is to make your garage walls fire-resistant and more durable. The good news is that drywall is highly cost-effective to install and repair.

While it’s possible to DIY the installation, we recommend getting a professional’s help to ensure that the sheets are correctly positioned. 

Following this, the contractor will add electrical wiring and plumbing fixtures. This will depend on your requirements, such as using the garage as a living space or a workshop. Installing plumbing will require insulation, as you don’t want your pipes freezing during the winter. 

However, even if you only intend to use the garage for extra storage, we still recommend insulating it to protect from pests and adverse weather. 

Final Steps 

With most of the work done, you can now focus on adding the finishing touches to your garage extension. This includes painting the walls, applying trim, adding floor sealant, installing light fixtures, etc. 

For added security, consider installing an automatic garage door opener for your garage’s primary entry point. 

The look of the interior and what appliances you add will depend on the purpose of your garage extension. For some, this is the most rewarding part of the process, as it lets you customise the space and make it truly yours. 

Relevant guides:

Things to Consider When Building a Garage Extension

Garage extension with car parked on it

Building a garage extension is a great way to increase the square footage of your property, but there are some factors to consider before starting work. 

Let’s see what they are! 

Garage Type 

When planning an extension, you generally have two options: an attached garage or a detached one. 

In the case of an attached garage (also called a garage bump-out), you will add another building to your existing house or garage. This often means removing an area of a wall to expand your property. 

On the other hand, detached garages are structures separate from the main house. While they are often built within close proximity to the home or existing garage, they are not connected to them and, therefore, need to be constructed from the ground up. 

Since attached garages are often smaller and already insulated by the shared wall, they tend to be cheaper to construct. Conversely, detached garages are more costly but give you more conversion options. 

Purpose of Extension

The purpose of your extension will influence the type of garage you need. 

In most cases, attached structures are built to add more space or expand the existing building into a two-car garage. Building an extension is an excellent way to create extra room if the main storage area is too cramped to keep power tools or new equipment. 

A separate garage may be a good idea if you want a more extensive storage area, especially if the layout of your property doesn’t allow for a large bump-out. A detached structure is also better to create a living space, a workshop, or a studio. 

In such cases, special consideration should be given to electricity and plumbing during construction. 

Garage Size

The size of your garage will depend on many factors, including the size of your vehicle, how many vehicles you want to park, and how much storage space you need. 

When determining your garage size, it’s generally recommended that you make it as large as your budget allows. Your garage space may fill up before you know it, and you’ll want to ensure enough room for your vehicle to pass through without incident. 

A single garage should be able to accommodate a small car with extra space for another vehicle, such as a motorbike. For more than one car, you may want to consider a small or medium double garage.

Garage Door Type

Your garage door is one of its most vital components, so picking the right type is essential. 

Sectional and roller doors are the most popular types in the UK, mainly due to their high levels of security and insulation. The former is more aesthetically pleasing, while the latter is generally more affordable. 

If you choose a manual door, ensure it can be converted to an automatic system. A garage door opener adds convenience and reduces the risk of burglary. 

Materials Needed to Build a Garage Extension

Building a garage extension

Here are the building materials you’ll need:

  • Plywood
  • Wall studs 
  • Wooden beams 
  • C20 OR C30-mix concrete for the garage foundation
  • Wood sealer
  • Double trimmers
  • Vinyl siding 
  • Roofing felt 

Along with the above materials, you’ll need these tools to get the job done:

  • Ladder
  • Reciprocating saw
  • Hammer drill
  • Concrete anchors
  • Tie plates 
  • Level
  • Gloves
  • Safety goggles 

Do You Need Planning Permission to Build a Garage? 

Planning and building permits are crucial considerations for any extension project in the UK. Depending on your project’s size, complexity, and location, you may need to obtain specific permissions from your local council. 

Some garage extensions will be eligible for permitted development rights, provided they meet specific criteria.

Under permitted development, the garage addition cannot take up more than 50% of the land around the property. If you’ve added extensions in the past, the square footage available to you may be used up or reduced. 

Additional limitations exist on how far you can extend your property to the rear. Detached properties cannot exceed 8 metres, while other property types have a threshold of 6 metres. 

You will also require a building permit if your garage height exceeds 4 metres. While this applies to a garage bump out, you cannot add another story to a detached garage. Doing so will put you in violation of permitted development laws. 

Another thing to consider is whether your property is affected by an Article 4 direction. This is usually enforced in conservation areas but can still affect outside properties. You can contact your local planning authority or consult a garage builder to learn more. 

If Article 4 applies to you, you will need to obtain planning permission before any work can begin. 

Costs of Building a Garage Extension

The size and complexity of your extension will significantly influence the total cost. 

A garage bump-out is generally cheaper to build compared to a new structure, as having a shared wall simplifies the process. Moreover, detached garages require additional utilities that increase the cost of materials and labour. 

A single garage with a pitched roof costs around £9,500, while a double garage can cost upwards of £20,000. 

Obtain and compare multiple quotations to ensure you don’t overspend on materials or labour. 

Benefits of Building a Garage Extension

Modern garage and a car port extension

Building a garage extension is a great way to add extra square footage to your property. This addition provides numerous benefits, not just in terms of functionality but also as an investment. 

Here are the advantages. 

Increased Storage Space: The most common reason homeowners feel they need a garage is to expand their storage space. Over time, your household can accumulate many things, including sports equipment, antique items, seasonal decorations, etc. 

A garage extension provides a dedicated space to store these items, helping keep your home and garden clutter-free. 

Vehicle Parking and Protection: If you own multiple vehicles or are in the process of purchasing a new one, a garage extension may be a necessity. 

It will protect your vehicles from harsh weather conditions such as hail and heavy snowfall. This is crucial as continued exposure to the elements can cause significant damage. 

A garage extension also ensures that your vehicles don’t catch the eyes of potential thieves. With carjacking being a huge concern in the UK, having your car out in the open is a risk you don’t want to take. A well-secured garage extension offers the perfect protection against robbers. 

Raises Your Property Value: When constructed and designed well, a garage extension can add functionality and improve aesthetics. These factors will significantly increase the value of your property and impress potential buyers. 

It will allow you to sell your house more easily in a competitive market–not to mention at a higher price than before you had the garage extension constructed. 

Conversion Options: Depending on the type and size of your extension, you may be able to convert it into a living space, a home gym, or even a guest house. 

Tips to Maintain Your Garage Extension

Constructing your extension or garage bump out is only half the battle, as you must also keep it in good condition.

Repairs can be annoying and costly, especially if you have to do them frequently. Carrying out regular maintenance will help you avoid issues with your garage doors, floor, and outer walls. 

Here are some steps you can take. 

Clean the exterior: Dirt and dust can ruin the look of your garage exterior. Wash the outer walls once every 2-3 months with a garden hose. For tougher stains, use a pressure washer. Remember to use a lower setting so as not to damage the paint job. 

Use dishwashing liquid and warm water to remove grime on the garage door. 

Service the garage door: Garage door issues can inconvenience you when you least expect them. This is especially true for automatic garage doors, whose mechanical components can malfunction over time. 

Have a professional inspect your door at least twice a year. They will lubricate the door tracks and replace faulty springs to keep the door working properly. 

Garage floor maintenance: Regularly sweep or vacuum your garage floor to keep it clean. Minor concrete cracks will be unavoidable, mainly if you use your garage as a parking space or to store heavy equipment. 

However, you can still use caulk sealant to fill the gaps. For issues such as moisture damage, contact a cleaning service for assistance. 

How Much Value Will a Garage Add to Your Property? 

Glass garage door and an extension

Adding a garage extension will raise your property value due to numerous reasons. 

Most home buyers will be attracted to an extended house as it provides a readily available storage solution. Beyond giving extra space, a garage extension also assures protection for their vehicle. 

As such, even something as small as a one-car bump out holds tremendous value. Meanwhile, a two-car garage will also appeal to buyers who don’t have multiple vehicles, as they can use the additional space in other ways. 

Overall, your garage extension will increase your property value by 5-10%. However, that number could climb considerably higher with a well-designed studio or living space. 

Conclusion 

A garage extension can be a versatile addition to your home when built right. It will expand your storage area, allow for vehicle parking, and increase the value of your property. 

Building one may seem daunting at first, but careful planning will go a long way to simplify the process. After that, it’s just a matter of hiring the right people to help you out, and what seemed challenging at first will soon become a rewarding project. 

So follow our guidelines and get started! 

Good luck! 

FAQs

Garage extensions can’t exceed the front elevation of the house. Rear extensions can go up to 8 meters for detached properties and 6 meters for others.

Yes, bump-out additions are generally cheaper to construct than detached structures. 

Prefab garages are cheaper and quicker to build but less secure, durable, and add less property value compared to professionally built garages.

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