Is a garage conversion cheaper than a loft conversion?

Usually, yes. A garage conversion reuses the existing garage, including the walls, roof, garage floors and foundations, so it is typically one of the lower-cost ways to add liveable space compared with a loft conversion or a full extension. It also tends to be quicker and less disruptive, because you are improving existing space rather than building a new structure. If you only need to use part of the garage, a partial garage conversion can turn one section into a functional room while keeping the rest as storage.