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Q: My old garage needs to be replaced. Can I use the old concrete slab?

A: This is a common question, particularly in neighborhoods with older homes. The viability of an old slab depends on how the slab and foundation were built and whether you are staying in the same footprint as the old garage. It is usually most expedient to pour a new foundation and slab, especially if you are expanding the footprint. And in most cases, the old foundation and slab are rarely in good enough condition to use again.

Building a garage sounds simple enough. Before you start, however, you need to figure out if you can build the garage where you want it and as large as you would like it to be. Some jurisdictions only allow garages to be built in certain parts of the yard, or require fire-rated material on the side closest to the property line. Also, garages are often figured into lot-coverage restrictions and can have height limits, which could impact how big the new garage can be and how much storage you can build into it.

Once you have determined any restrictions in size and location, the next step is to design the garage and have the structure engineered. If you live in an Environmentally Critical Area (ECA) with considerations like a steep hill or the property being in a liquefaction zone, you may need more detailed engineering work than would be required in a location with a simple, flat lot. If you are going to be building in an ECA, plan on higher building costs due to the foundation and structural requirements. Then it’s time to obtain a building permit.

Depending on possible neighborhood association rules, you can design a new garage to match the siding, trim and window detailing of your house or go in a completely different direction. Garages can be built very simply, with open-stud walls, no windows and minimal electrical, or they can be finished out with running water, insulation, Sheetrock and built-in cabinetry. A storage loft can be created in the attic space, depending on how the roof system is framed, with access by a pull-down ladder.

In the city of Seattle and in some other jurisdictions, it’s possible to build a complete living unit above the garage, although these backyard cottages have a number of restrictions on size and height. But there is an opportunity to permit them so they can be rented out as a studio apartment.

As you plan your garage, keep in mind that if you want power, you will need to make a connection back to your home, usually via conduit in a trench. If you want water, you have to make connections to both the water supply and the waste lines, and if you would like heat, that may require running a gas line.

Depending on size and location restrictions, the possibilities are endless for building a garage — from simple protection for your vehicles to essentially a second mini-home.

Anne Higuera, owner of Ventana Construction, is a member of the Master Builders Association of King and Snohomish Counties’ Remodelers Council. HomeWork is the council’s weekly column about home care, repair and improvements. If you have questions about home improvement, send them to