Extending over a garage (already part extended)
I’m looking at buying a detached house with a 3m wide garage attached to the side. I have posted a separate question about the same house re the loft.
The garage has been built on at some point in the past to creat a first floor bedroom and en-suite. The floor level (and roof level) is about 80cm lower than the first floor of the rest of the house. The roof at the front elevation is sloping and there is a single velux. At the rear (above the garage) there is a full brick built extension with a large window. We could gain quite a lot more space and make this extension more fluid with the rest of the house by raising the floor level to meet with the existing house and by either putting a dormer on the front or by building a proper 2nd story with a pitched roof instead of the sloping roof at the front.
Question:
- so long as building control sign off was given for this extension, can I assume that the foundations of the garage are adequate to allow the for extra weight of raising the floor (and ceiling as a result) and either adding a dormer to the front or a ‘full’ extension with a pitched roof in line with the roof of the main house.
- does having this part done extension save on costs vs just building over a garage with nothing on top?
The house is in Cardiff. I hope I’ve made this clear
Thank you in advance
Advice from 7 local tradespeople
You need to find architect who designed that house and ask what type of foundation is there and how much it can hold. Building on week foundation will ruin your work above
Hi, you shoud not assume that, have the builders to dig a hole to check the depth of your garage foundation (if is not mentioned in any documents).
We a had similar challenge with a client in Watford - London and needed to reinforce the foundation in order to be able to build up the extension, also the external wall was a single brick layer so make sure you have checked that out as well!
Regards,
Ana
Call me I'm god builder
Yes will much cheaper if you can build and do something with the existing one.
you need to do a trial pit to examine the foundation of the garage, then forward the information to structure engineer for accurate decision
If the garage already has a previous extension that received building control approval, you can’t automatically assume the foundations are adequate for a further storey — but it is a good sign.
However, for a new first-floor extension you generally need to:
• Check the foundation depth and width (trial pit)
• Confirm the existing walls can support extra load
• Bring the floor levels in line with the main house
• Replace the sloping roof with a dormer or pitched roof, depending on design preference
The fact that part of the garage has already been extended usually makes the project easier and can save costs, but you still need a structural check to confirm suitability. This is very common work and is usually feasible with the right design.
you need to do a trial.pit and consult a structural engineer for that.
