Retrofit Improvements: Wall-to-Foundation Attachment

In older homes, the connection between the house sill plate and the foundation wall may be inadequate to withstand either a lateral force from wind or earthquake or an upward force from wind catching cantilevers or overhangs farther up the face of the building. Installation of additional bolts will not only provide a stronger connection between the foundation and sill plate, but it will also provide a link in the structural load path which under static conditions travels from the roof to the foundation, but changes direction with seismic and wind movement.

Typically, 1/2” to 5/8” diameter anchor bolts with 3” × 3” square plate washers are specified on spacing at 24” to 36” apart to secure the sill plate to the foundation. As with other hardware which secures the components of a house along the load path, each piece of installed hardware costs under $10 to install in a new house. This cost, however, assumes that there is direct and simple access to the sill plate foundation, which is not often the case in an existing house. But, unfinished basements and garages – and some remodeling projects – present the opportunity to strengthen the connection at the foundation more simply. The sill plate and foundation can be drilled and filled with expansion bolts or epoxy adhesive and a threaded rod. Hardware that connects along the face of the foundation and framing member has been developed for seismic retrofits. Consult your contractor about the necessity and feasibility of this and other safety details that will add value and peace of mind to your home improvement project.

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