i'm wanting to build on top of a garage. how do i know if the foundations are o.k?

Get yourself a structural engineer to check it out:thumbsup:

or a cheaper option is to get a copy of the consents for the existing structure (might be with the solicitors etc), and you may find in there a drawing of what was proposed when the structure was built. show it your builder, and they should know if you have enough depth and width on the footings depending on the soil type, to build over the top of. dare i say, most are suitable to build on.

if it was put up purely as a garage with no foresight for a conversion, then you might have problems, or indeed if it is a lean-to type garage, which might have 300mm foundations on the outermost wall.

Yeah as above ....you may need to demolish garage and then rebuild garage with extension on top if current foundations inadequate for 2 storeys and current regs !!

To be honest I would be very surprised if you are able to build on top of existing garage as chances are foundations won't be deep enough!!

You may also need to look at redefining boundaries as some garages are built right up to the boundary but extensions are required to be about 6 inches in from boundary to allow for guttering.

If existing garage is in good condition and is worth keeping underpinning the existing foundation may be an option - it is not always as expensive as it seems.