Can I build on top of a garage?
Discussion
We had single skin garage attached to the side of our house. Wanted to build above it so got an architect in. The single skin didn’t have sufficient foundations along the outside wall.
The solution was to dig a big hole In the “weak corner” fill it with concrete then use steels (One vertical and two horizontal tying into existing strong walls).The upstairs walls were then built off the steels.
Main advantages from my point of view were that we wouldn’t need to worry about party wall changes (the wall is right on the boundary and the garage interior of the garage doesn’t loose space due to the additional interior wall.
The solution was to dig a big hole In the “weak corner” fill it with concrete then use steels (One vertical and two horizontal tying into existing strong walls).The upstairs walls were then built off the steels.
Main advantages from my point of view were that we wouldn’t need to worry about party wall changes (the wall is right on the boundary and the garage interior of the garage doesn’t loose space due to the additional interior wall.
Biggy Stardust said:
Terminator X said:
^^ engineers design to factor of 3 don't they so it should be able to support more load.
TX.
That factor of 3 is there for a reason.TX.
TX.
elanfan said:
Builders tend to dig one set of foundations for the whole plot and so are the same all round. You’ll have to dig down to check.
^^^ This.It's nonsense to talk about whether the engineers originally 'designed' it for two storeys and what safety factors were used. It's a house, not an aircraft or Formula 1 car.
Broadly speaking, foundation depth is irrelevant to the loads the foundations can take. It's the width that counts, and in practice that depends on the bucket of the JCB... it's not slimmed down to the last millimetre based on engineer's calculations, and they won't usually vary it around the foundations - the whole plot will be dug the same (the exception would usually be where they were hand dug).
Similarly, the walls. You will need to get a Struct Eng to do a stability check (the wide opening/small reveals of the current garage door will probably mean it doesn't offer enough buttressing for the loads of an extra storey above, but that would be fixed by installing steel wind posts or sway frames), but beyond that the compressive strength of the masonry will undoubtedly be fine... we don't use special, extra-weak masonry to save a few pence where we know it's going to be single storey; it gets built in the same stuff as the rest of the house. (ETA: single skin masonry is obviously a different case, but again that comes down to a stability check by the engineer, and in this case we've been told by the OP that it's dual-skin).
Edited by Equus on Saturday 12th June 12:39
Take up a paving slab at the rear and dig a test pit there to check the foundations.
Whether you need new foundations or not will not make any difference to obtaining planning. It is more a building control and cost issue, you could just work out budgets for building with existing and new. As mentioned if you are going wider you will be putting at least some new in anyway so possibly a design using a new supporting flank wall with steel beams across to the house to take the upper story would negate the foundation issue.
Whether you need new foundations or not will not make any difference to obtaining planning. It is more a building control and cost issue, you could just work out budgets for building with existing and new. As mentioned if you are going wider you will be putting at least some new in anyway so possibly a design using a new supporting flank wall with steel beams across to the house to take the upper story would negate the foundation issue.
Aluminati said:
Not all. I priced a loft conversion in Feb, 130k. Due to material increases, I advised client to hold off ( Leaving me with a hole) to see what way the market goes. The recommendation I will get from that will fill the hole.
Builders on checkatrade May be different…
£130k for a loft conversion???Builders on checkatrade May be different…
We did something similar as part of a more general extension. Based on the fact that similar houses nearby had built above their single skin attached garages, we figured it would be possible.
First conversations were with an architect who drew up plans and secured permissions. From memory, it was a structural engineer who confirmed the suitability of the garage foundations by getting the builders to cut out a section of concrete floor in the garage. They had to do it there because the garage sits on the boundary.
Anyway, the engineer seemed satisfied and an assortment of steels arrived later. These were used to support the inner leaf of the cavity walls of the room built above the garage.
First conversations were with an architect who drew up plans and secured permissions. From memory, it was a structural engineer who confirmed the suitability of the garage foundations by getting the builders to cut out a section of concrete floor in the garage. They had to do it there because the garage sits on the boundary.
Anyway, the engineer seemed satisfied and an assortment of steels arrived later. These were used to support the inner leaf of the cavity walls of the room built above the garage.
We built above an attached single garage in our last house ( over 20 years ago,).The only complication was due to the wall on the outer side being single skin. A second skin was needed and it would have been too close to the edge of the foundation. We had to underpin to enable the second skin to be built. It was not a big problem and not expensive. An inspection hole was dug to check on the wall/ foundation situation for Building Regs purposes and their underpinning requirement made then before any work began. We had a good builder and no problems.
Fire safety regs were an important part of the design.
We had great neighbours. A big plus!
Fire safety regs were an important part of the design.
We had great neighbours. A big plus!
Had the same dilemma about 7 years ago.
Bulider was pretty certain the foundations wouldn't be strong enough, and said I should check the plans. These were available on line at our local council - no fee.
Not sure if yours will be the same, but might be worth a check?
By the way, ours wasn't strong enough - 1970's build.
Bulider was pretty certain the foundations wouldn't be strong enough, and said I should check the plans. These were available on line at our local council - no fee.
Not sure if yours will be the same, but might be worth a check?
By the way, ours wasn't strong enough - 1970's build.
Zarco said:
Terminator X said:
^^ engineers design to factor of 3 don't they so it should be able to support more load.
TX.
You think all garage foundations are designed by an engineer? TX.
Z
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