Some houses are simple. You have a shoebox shape to work with, there aren't too many big window or door openings, and you're not in a seismic zone or high-wind area. But some builders work in seismic zones, and some builders work in hurricane country. In those regions, any structure—high-rise or house—has to be designed for lateral loads, the sideways force of wind pressure or earthquake action.
Whether it's of a Florida beach, a Los Angeles hillside, or a Colorado mountaintop, homeowners love a beautiful view, and designs often call for high ceilings, walls full of windows, and large open rooms; and, of course, there's always the garage door. The result is structural situations where an extreme wind or seismic load has to be handled by a very small amount of solid wall. Facing that challenge, a typical stud-and-plywood wall—or even a site-built shear wall—can't always do the work.
If that's your situation, your engineer is likely to specify manufactured shear walls and moment frames—most likely supplied either by Hardy Frames (Panel or Brace Frame components and engineered Moment Frames), Simpson Strong-Tie (Strong-Wall panels and Ordinary Moment Frame or Special Moment Frame assemblies), or, in parts of the western U.S., Shearmax (the Shearmax panel system).
"I kind of see manufactured components as a necessity now, to design what people actually want and to give them the structural integrity that they need," says Santa Barbara, Calif., framing contractor Don Gordon. "You've got an ocean view and you need a big window, but that only leaves you room for 8 feet of plywood. Well, in 4 feet, these things can give you the equivalent of 16-feet worth of site-built shear wall."
In this story we'll survey the whole field—wood shear-wall components, steel shear-wall components, and steel moment-frame assemblies. We'll look at how the products are the same and how they're different, and take a look at the issues you'll want to be aware of when you frame with them. We'll also discuss which product type is best suited for which situations, including both new construction and retrofits of existing structures.
Understanding Lateral Loads
When the ground moves in an earthquake or the wind blows against the walls in a hurricane, houses in seismic or wind zones experience a "lateral force." To remain standing, walls have to withstand this force and transmit it into the foundation. The fine points of wall performance vary depending on whether the design accounts for wind, earthquakes, or both (see Seismic Versus Wind). [BB: But in general, engineers look at four issues: Shear—will the wall rack? Overturning—will the wall topple? Sliding—will the wall slip sideways? And uplift—will the anchors pull out?
The narrower the wall involved, the more problematic these forces become. A narrow wall has less material available to pick up the shear load, and fewer locations for anchoring to the foundation to prevent sliding. And as walls become narrower, the "aspect ratio"—the ratio of height to width—becomes higher, which increases the risk of overturning. That, in turn, creates greater leverage at the base of the wall, which applies a greater uplift force to the wall anchors.
David Lopp, who handles product support for Hardy Frames, explains: "As a panel gets narrower, the uplift on the hold-down bolt, and the compression on the other corner of the panel—that overturning force goes up. If you put a panel in the wall that is 12 inches wide, or you put a Brace Frame in the wall that is 44 inches wide, when you push with the same force at the top, the uplift on the narrow panel is going to be much greater than it is on the wider frame."
All the big suppliers offer a variety of pre-built panels and frames, in a range of widths. And because the narrower components need to do more work and be more securely anchored, the narrower the component, the more it is likely to cost.
The Makers
Most of the manufactured-shear-wall industry is made up of two top companies: Simpson Strong-Tie, headquartered in Pleasanton, Calif., and Hardy Frames, based in Ventura, Calif. Both of these big players ship components nationwide and offer extensive design and technical support. Simpson Strong-Tie also manufactures hangers and connectors; and Hardy Frames has been acquired by a larger company, MiTek, which also owns United Steel Products Co., the makers of USP Structural Connectors. So both Simpson and Hardy Frames can help engineers specify a complete solution for a home's structural load path, tying together roofs, walls, floors, and foundations to resist all the applied loads.
Shearmax, a much smaller company, is important in the California market and also ships panels to Utah and some other western states. Like Hardy Frames, Shearmax started out life as a framing company in Southern California; company engineer Tim Timmerman II (son of the founder, Tim Timmerman Sr.), credits that background for the company's emphasis on making a user-friendly panel.
Hardy Frames' Lopp makes the same argument for his company: "We started out as a production framer. You have to be efficient, you have to be effective, and you have to be the low price. And there are a lot of things we know how to do that will save money in the framing while still using these high-capacity panels."
Making the panels cost-effective and easy to use is on Simpson Strong-Tie's radar as well. For example, after acquiring the Trus Joist TJ Shear Brace system (a laminated strand lumber shear-wall component) from Weyerhaeuser this year, Simpson started addressing complaints from the field about the product's anchoring method. The system, re-branded by Simpson as the Strong-Wall SB Shearwall, allows framers to make top cuts in the field to fit a roof height and rake angle. But accessing its attachment hardware at the bottom can be awkward.
Competition among the top suppliers is keen. As a result, every year brings improvements to product lines, and companies put a lot of energy into technical support for their products—on site, as well as over the phone. For the smaller companies, it's personal: Hardy Frames' Lopp says, "If somebody calls with a question, they can talk to me." And California builder David Moore says that when he got into trouble with a Shearmax installation, Shearmax president John Jenkins came out to the site to help him set panels. "He figured out what to do in a half hour," Moore says. "It would have taken me half a day."
Choices and Challenges
All the products in the market are designed to do the same job—strengthen the building against lateral loads. And their code listings, based on verified testing, are evidence that you can rely on all of them to perform as advertised (as long as you follow the directions when you install them).
Depending on the situation, a framer might prefer working with one or the other. Unfortunately, however, framers—or even builders—who are working in high seismic zones aren't usually the ones choosing which product to use. Bay Area builder and remodeler Jeff Kerr says, "It depends on the engineer who's actually specifying it, based on the seismic requirements. The architect draws his plans, which are basically a wish list. Then he sends the plans to an engineer who determines the loads and specifies the products. Our job is just to price it out and install it."
Typically, framers set the shear-wall panels directly on the concrete foundation or on the first-floor frame before they start stick-framing the surrounding walls. Kerr describes the installation process: "You form for your concrete (we do most of our own concrete work), you get all your rebar in, and you get a set of drawings from your engineer. All the panels come with a template, and you attach the template to the forms. Then from the template, you hang off your threaded rod or your anchor that is going to get embedded in the concrete in the forms. You just have to follow the instructions. … Once we've poured it, it only takes two guys a couple of hours and they're in. Then you just frame around the thing and attach it."
Sometimes, however, because of delivery issues or job schedules, wall framing is completed before the panels are installed. You can set a shear-wall panel into an already framed wood wall, but it may be a little fussier and slower (see photos, next page), so framers usually prefer to set the panels first.
"Probably the most critical thing is to get the bolts in the right spot to start with," Gordon says. "You have to use the templates. We've had bolts misplaced a couple of times, to where the panel is sitting outside of the wall."
Kerr agrees. "You better do your layout carefully, and be sure you've looked at all your framing members so that you've given it enough space to fit, you've put it in the right spot, you've set the template just so, and you've set the right bolts and hardware in place. If you blow it there, you can take care of it, but that's only going to cost you time and money. If you missed a bolt, you have to drill a new bolt and epoxy it in. If you've got something in the wrong spot, well, you might be chopping the whole thing out."
That happened more when the products were new and unfamiliar, says Simpson Strong-Tie's Don Simon, a trainer who helps manage the company's builder education outreach. "In the early days, we had guys in the field all the time helping builders fix mistakes," he says. But these days, it's old hat, at least on the West Coast.
Carpenters have one good reason to like Simpson Strong-Tie or Hardy Frames moment frames, Gordon notes: It puts the ball in their court. "It becomes my work, not the structural-steel guy's work," the framing contractor says. "So I buy the $2,000 moment frame, charge profit on the materials, and then charge labor to install it."
But shear-wall panels aren't that expensive, Kerr says: "I just priced a pair out for a master bedroom addition with a large patio door. They were $330 apiece, plus tax."
Where a builder does have control over design and product specification, there's a lot of variety to choose from—and what you select depends on what you care about. If you want to be able to trim panels in the field, you have two options: Simpson's Strong-Wall SB Shearwall or Shearmax. If you need the maximum wall opening possible, you'll have to choose a moment frame. If you have a lot of wall area to work with, you can use a less expensive and wider component, such as a wood Simpson Strong-Tie Strong-Wall or a Hardy Frame Brace Frame.
What you don't have to worry about—if you install the panels right—is performance. Consulting engineer Zeno Martin says, "They've all been engineered to do what they say they can do. You've taken engineering out of the equation. So for a builder, I think it all comes down to cost and lead time. How much am I going to have to pay for it, and how long is it going to take me to get it?"
