Seismic Reference Map
by Jay Behm - This map was scanned from the IRC 2009 building code. It identifies the areas of seismic risk as determined by the ICC and can help you determine if seismic risk is an issue for your garage project. The darker areas signify the more severe risk areas and the lighter areas, less severe. Clearly, most parts of the continental US are category C or less in severity. Most of our garage plans are prescriptively compliant, designed for use in category areas A, B and C. (Some of our larger plans are usable only in A an B and are identified as such) Our D designated plans are usable in D1 and D2 areas.
If your location appears to be in one of the more severe areas you can verify the required category with your local building dept. or inspector. The quality of this image is not suited for precise definition near the shaded category boundaries.
Braced Wall Construction - The Prescriptive Approach
by Jay Behm - The IRC code provides various construction methods which strengthen a building to resist seismic (as well as wind) lateral forces. In conventional light wood frame construction it is possible to design the building to be usable in seismic categories A through D without having to use the engineered approach, thus not requiring additional engineering services. Since most of the US is within categories A, B, and C designing our garage plans to those prescriptive construction methods allows the plans to be used in most areas of the US. We do offer a limited group of plans designed prescriptively for category D (more severe) which is typical for western areas of Washington and Oregon (Washington State Plans).
The methods of construction used in Behm Design garage plans include OSB (oriented strand board) sheathing (or equivilent structural sheathing panels) fastened to the wall framing. This creates "braced wall panel" construction and is a conventional method in most parts of US. Sheathing is required for all of the exterior walls and is covered with any code compliant siding products. Alternatively, textured OSB or other structural grade siding panels may be used without the added siding layer - and that saves cost. Some walls don't have enough length of wall on the foundation (i.e. garage front wall with garage door openings). For that condition walls are designed as "alternate braced wall panels" which require less wall length but require anchor straps to the foundation. Where available wall length extremely minimal the front wall can be built as a "portal frame" which makes the garage door header beam(s) extend extend over/into the adjacent bracing walls which make the entire wall rigid to resist lateral forces. This method may or may not require added straps to the foundation.
This approach to design allows using conventional light wood framing methods which allows the buildings to be built economically and without expensive complications. However, the application of the design methods/measures involve the many tables, ratios, dimension, and certain limitations which are realized in the building design. It is advisable to ask the local inspector if they allow modifications in critical wall areas to make sure that it is allowable. You can also call Behm Design at 1-800-210-6776 if you have questions.