Extending above a garage

When can or can't it be done? Chartered surveyor, Ian Rock, answers one common question about adding a single storey to a garage, and firm foundations are key

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Q We're planning on building a single-storey extension above our garage but our builder has told us that we might have to knock the garage down and replace it. Is this the only option if the foundations are weak?

The big unknown with any project that involves building over garages or extensions is whether the existing structure is up to the task of supporting the additional loadings.

A lot of older garages were cheaply built with little by way of foundations, so the advice from your builder may turn out to be correct. But in my experience, builders often feel happier taking down and rebuilding old walls, ceilings and outbuildings etc rather than tackling renovation work with the risk of hidden costs. From the builders' perspective it obviously makes sense to stick to what they do best. However, if it is possible to retain your garage you could reap significant savings in lower wall construction and groundwork.

HOW OLD IS THE BUILDING?

To judge whether a garage is worth incorporating as part of the new extension a lot will depend on its age. As a rough guide, garages built within the last 30 years are more likely to be fit for purpose, particularly if they were constructed as an integral part of the original house with the same depth of foundations.

THE RIGHT TYPE OF WALL