Extending Over A Garage - Your Guide
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Extending over an attached garage is an obvious way to add additional space to a home, which can be used for an extra bedroom, bathroom or study. Building into this wasted space can also improve the look of the house too, making it appear more balanced.
Although extending over a garage appears a simple option, there are many structural implications which need to be considered before you simply add on an extra floor.
We look at some of things to think about before you extend above a garage, including the cost and structural considerations.
If you are thinking about extending in the near future and need some help with where to start with your project, try our renovation advice session.
Renovation advice session
Will The Foundations Support Extending Above The Garage?
You will first need to check whether the existing foundations can cope with the additional load from the extension above.
If your home is relatively new, you may be able to obtain copies of the drawings of the original home and garage to find out the size of the original foundations, this will give you an indication of how easy it will be to extend above the garage.
A building control inspector will want to assess the foundations of the garage which you should do early in the process to check the feasibility. The building inspector may also take a sample of the soil to ensure it can take the load.
In order to check the existing foundations, inspection holes will have to be dug which will be around 1 metre squared in size - your builder will be able to do this for you and the structural engineer or building inspector will confirm where these should be.
If the foundations are not adequate, the main option is to underpin the existing garage to provide the support. At this stage it may be more cost effective to knock down the existing structure and rebuild it, particularly if you need to carry out additional structural work to ensure the existing walls are also adequate.
What About The External Walls Of The Existing Garage?
Another important consideration is whether the external walls of the garage can bear the load of the new extension. Commonly, a garage exterior wall is made from a single skin brick, where the wall is a solid brick instead of a full width cavity wall.
If the exterior wall of the garage is a single skin, then you will need to strengthen the existing wall to ensure it can support the weight of the new extension.
You will need to work with a structural engineer to ensure the walls can bear the additional weight with solutions including widening the walls and fitting steel beams. Their solution will depend on the structure of the extension, for example a timber frame extension would not require the same support.
How Much Does It Cost To Extend Over A Garage?
A common misconception is that it should be a cheaper extension as the existing foundations and structure are already there.
However, as there are structural changes required including removing the existing roof and joists and potentially include underpinning and strengthening of the existing walls, the cost of extending over a garage is broadly in line with any other extension rather than a cheaper alternative.
Working with a structural engineer to look at the options for your garage will help determine the cost of the extension. The builder will need structural calculations to provide an accurate estimation.
Our extension cost calculator will give you a high level view on the cost, which will vary depending on your location in the UK, the specification and which rooms you are including in the extension.
Extension cost calculator
Do I Need Planning Approval To Extend Over A Garage?
A first floor extension above the original garage will require planning permission. Your local authority will consider how close the extension above the garage is to the boundary to avoid a terracing effect with your neighbours - they would be looking for around 1 metre to the boundary.
It's always best to chat with your local authority to find out any rules in your particular area as it can vary depending on the council.
What Professionals Do I Need When Extending Over A Garage?
An architect or architectural designer will be able to help with the design of the new extension, including how it flows with the existing home.
You will need a structural engineer to ensure that the existing structure will be able to cope with the additional load, including the additional steel and support required. Your architect will normally recommend a structural engineer that they work with.
You will also need to find a recommended local builder who has experience with similar projects to carry out the construction, as well as to dig the inspection holes to check the foundations.
If you are thinking about extending in the near future and need some help with where to start with your project, try our renovation advice session.
Renovation advice session
Published: February 3, 2022
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