Wood naturally shrinks as it dries. These changes in dimension are of importance to anyone designing and constructing a multi-story building. Based on environmental factors and the type of framing, incremental shrinkage can be up to ¼” or more per floor. In a five or six story wood frame building, shrinkage can add up to more than 1- ¼“, plus the addition of settlement incurred when a building is fully loaded.
Conventional hardware does not address settlement and wood shrinkage issues that occur in wood frame structures. Historically, conventional strap solutions have been known to loosen and buckle on structures with multiple floors, which can cause exterior finish issues that allow water infiltration.
As larger wood frame multi-residential structures are being built with four, five and six floors, it’s important to design correctly for the accumulated shrinkage caused by wood drying. Here are a few steps to ensure your building is prepared to compensate for wood shrinkage.
- Calculate Shrinkage – Estimating the shrinkage of each wood member in the wall and floor assembly will help you determine the overall impact of shrinkage. Moisture changes are perpendicular to grain, so in lumber these changes are expected across the grain and usually occur at the inter-floor framing level. There are several online tools to help you calculate wood shrinkage. Check out the wood handbook at http://www.fpl.fs.fed.us/ for mechanical information and calculations.
- Replace Conventional Hardware with Continuous Rod Tie-downs – Rod systems allow for wood to shrink. Threaded rods run continuously from the foundation to the top plate through drilled holes at each floor assembly within the wall cavity. As wood members at each floor shrink, the threaded rods maintain tension without causing structural issues. For more information on replacing conventional hardware read CLP vs. Conventional Hardware.
- Restrain Rod System with Take-up Devices – Since rod systems allow for movement caused by wood shrinkage, it is important to compensate for the incremental changes with a take-up device to maintain tension on the building. A take-up device is a cost-effective shrinkage compensation solution and is installed at the floor level to eliminate slack in the rod system caused by shrinkage.
To learn more about anchor tie-down systems using threaded rods, contact CLP Systems today and schedule a lunch and learn. At CLP Systems, we understand the design and installation difficulties you experience. We have worked with over 2,500 projects to revolutionize how tie-down hardware is designed and installed, ensuring long term structural integrity of wood frame buildings while making it quicker and easier for framers to install hardware. Ultimately, helping customers keep projects on time and under budget.
