To keep houses from shaking apart in earthquakes or being blown away in hurricanes, engineers and architects specify hold-downs, metal framing connectors, and plywood shear paneling. The idea is to use metal connectors and plywood to create a continuous "hold-down path" that ties the structural wooden frame together from foundation to roof peak. In California, where I live and work, every set of house plans addresses the issue of tying the structure to the foundation.
Scan the Plan
Every piece of hold-down hardware, whether it’s a simple 1/2-inch J-bolt or a custom metal clip, will be marked on the foundation plan and in the structural details. When reviewing a set of plans, I use a colored marker to highlight every hold-down and shear panel anchor bolt. As I mark each one, I keep a running count of each type and familiarize myself with their locations. Hold-downs are typically called for in pairs, located, for instance, at each end of a shear wall or on both sides of a window or door where the shear wall is interrupted by the opening (see Figure 1).
Scanning the Plans
Figure 1. Hold-down installation begins with a careful review of the plans. An overlooked hold-down bolt or embedded strap can turn into a costly retrofit once the slab is poured. The author uses colored highlighters to locate every piece of hardware specified by the engineer. With experience, it’s pretty easy to find (and even memorize) the location of the hold-downs. Although we usually keep an extra supply of the most popular clips in the storage shed, it’s expensive to go back and do a special installation of an omitted hold-down, especially for the larger, more costly anchors. So if you are new to these kinds of anchor systems, be prepared to do a close examination of the plans to avoid a costly retrofit installation. Nevertheless, this is a common problem, especially on a complicated set of plans. If you do omit a hold-down, ask your structural engineer for a solution. For example, a common fix for a missing foundation anchor is to drill into the foundation or footing and install a retrofit bolt or a length of threaded rod, secured with epoxy. The plans I get from architects are very specific, and it’s my job to locate the foundation hardware and to see how it will connect to the shear walls, and to the door and window openings. I look for places where some other building component, such as waterlines or power conduits, might interfere with the installation of the hardware. If the house has a second story, I’m careful to note any connection called out between floors so that my framer can adjust the stud and post layout to accommodate the connecting hardware. I then turn to the roof framing plan and note how the engineer has created a hold-down path up to the roof diaphragm. These systems can be complicated, so if anything is unclear I notify the engineer and ask for guidance. To avoid confusion between subs, I meet with our lead framer and foundation foreman to discuss the plan and to note any changes.
