This Seismic Risk US Reference Map was scanned from the IRC (International Residential Code). It shows the relative risk factors for earthquake – represented in graduated shading for severity of the risk. High-risk areas are shown darkest and light to white, least or no risk. This information is used in the structural design of buildings and their foundations. The letter designations tie the shade level to risk levels A, B, C, D1, D2, referenced in the map’s legend.(you can cursor-over and click map to see larger version)
Most garage plans by Behm Design apply prescriptive measures for Braced Wall Construction per IRC and are thus suited for building in the A, B, AND C risk level areas on the map. A few plans exceed size limits for C so may only be prescriptive for A and B level areas. Because the map shown is in small scale it is best for you to verify with the local building dept. what your local seismic risk level is. If local risk level is more severe than C you can have plans certified by local architect or engineer.
Braced Wall Construction
The IRC (International-Residential-Code) is the basis code for US states’ building codes, excepting FL and CA. Every 3 years the code is revised and most state governments legally adopt the code as its own. States can amend or not. In turn, counties and cities can adopt their state’s code. So, complying with the IRC code usually means complying with your local code for building. It prescribes construction methods and materials for building strong and safe structures which will resist the lateral, as well as overturning, forces acting on the building structure due to earthquakes and wind. This prescriptive approach is called “braced-wall-construction” and it works well for many buildings which use conventional, light wood framed construction. This enables the designer and builder to comply with earthquake and wind requirements of the code without engaging the professional services of a state-licensed engineer or architect.
There are seismic risk categories assigned to all of the US, rating A (less risk) to E (greater risk). A, B and C are no risk to a moderate level and the code allows prescriptive compliance. The D and E categories always require the design and plans be certified by a state-licensed professional.
All of the garage plans by Behm Design utilize conventional, light wood frame construction and have exterior wall sheathing of either 7/16 inch O.S.B. or 1/2 inch plywood panels. This method complies with the Braced-Wall-Construction of the IRC. Braced wall panels, alternate braced wall panels, and portal frame walls are all part of the IRC methods. Larger garages will feature interior braced wall panels if required and they can be seen as perpendicular short walls inside of the outside walls. Braced walls are anchor-bolted to the concrete foundation below. Shorter braced wall panels (called “alternate braced wall panels”) are often anchored to the foundation with additional steel strap/anchors or special anchor bracket and bolt systems. All of the braced walls are acting as ‘shear walls” which resist lateral forces and keep the building wall from racking and/or collapse.