Preston Press & Charter, January 2008
Wall Panelization Grows Up
Ryan Reed, Builder News Magazine
Factory wall panelization is the black-sheep stepchild of the component industry. While the use of manufactured components in residential framing has been on an upward path for decades—67% of residential roofs now use trusses, 37% of floors use engineered I-joists or open-web trusses—most homebuilders remain skeptical of preassembled walls.
Wall panelization has in fact surged in popularity several times over the past three decades, usually to meet temporary demand spikes, only to drop off when the market cools. In recent years, between 5% to 10% of residential walls have been panelized.
Wall panels have some decided advantages that balance the cost of transportation: accurate and tight framing, accelerated erection times and reduced field labor. Multifamily and large homebuilders, who benefit most from the economies of scale and repetition, have been its biggest users. But panelization has had trouble finding wider acceptance by single-family builders.
One challenge is the misconception that panelization makes sense only for relatively simple, low-end homes. Off-site framing is in fact particularly appropriate for more complex walls. “The more complicated the house, the better it is for panelizing and the more money you’ll save,” says Jim Armstrong of Armstrong Lumber based in Auburn, WA. “Panels really shine in chopped up, complicated houses.”
Armstrong also disputes the belief that only large-scale production builders stand to benefit. His company in fact consumes most of its panel output on its own custom homes.
“People can be shocked that we’re assembling their $1 million home in panels,” says Armstrong. “They have it in their head that prefab is inferior, when in fact it’s better.”
Very few houses resist panelization, he says, although a home with many tall walls over ten feet won’t be economical to factory frame.
While there are many cost advantages to factory assembly, including controlled conditions, better worker oversight, better inventory and tool access, and in some plants automated marking and sawing tools, wall panels still can’t compete on price alone. As with I-joists and other components, the benefits are indirect:
- Speed. In 1996 a demonstration project at the Builder’s Show of side-by-side 2,600-square-foot houses, the site-framed one required 93 hours for walls alone, the panelized one 26-1/2. Less time on site means fewer accidents, fewer weather delays, and faster time to dry-in.
- Clean jobsite. In the 1996 project, the site-framed house generated 17 cubic yards of waste, the panelized one, four (including roof and floor framing). With very little scrap to deal with, cleanup crews, dumpster costs, and tipping fees can be minimized.
- Less area required on tight work sites. You need a crane for a day or two, but no area to store stacks of framing lumber.
- Jobsite theft. It’s hard to walk off with a 20-foot framed wall section.
- Quality control. The controlled environment is one thing. Manufacturers are also less likely to use studs with bows or wane because the inventory is handy, and they usually have a ready use for scrap.
- Value and structural analysis. Virtually all wall panel makers use software to create layouts, and can analyze framing for redundancies and structural deficiencies that can cut material costs and improve a building’s thermal envelope.
Most panelizers are material suppliers or truss manufacturers. While many suppliers have recently added wall panel capacity, or plan to, many also fail; competing against stick framers is a tough business—particularly in slow times. Several companies have succeeded by taking framing in-house, avoiding the inefficiencies and scheduling problems that arise from working with a separate framing contractor.
Shipping is a big cost of using panels, and longer distances can add more per lineal foot, and proper shipping is tricky. Assembling a load involves balancing efficient use of space, shipping stability, and trying to keep walls in the order they’ll be used on site.
Factory-built wall panels differ little from site-built framing. Exterior walls are sheathed, but otherwise left open for plumbing, wiring, insulating, and finishing on site.
If a crane will be used to set the walls, lengths up to 40 feet are possible. More common are 16-foot lengths, which can be craned onto a floor deck and slid into place by a small crew, or set with a skid-steer. Two-story jobs are usually phased a few days apart to allow for floor framing.
Since wall panels are difficult to modify to fit, slab-on-grade foundations need to be square and level, or an intermediate plate can be used. Top plates are added on-site to splice panels together.
Wall panels are designed with specialized software and fabricated on long lines of tables and jigs. The level of automation varies considerably. In some shops, walls are marked and assembled largely by hand; in others, walls can be “extruded” nearly hands-free from a series of machines that mark, nail, cut, and rout out openings.
Over the past decade new technologies have arrived to drive wall panel costs down. Automated laser marking systems take the place of manually storyboarding framing layouts. Automated axis saws to cut out window and door openings are replacing the routers currently used. Laser etching marking technology, computerized saws, optimizing sheathing use are gradually cutting costs.
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