[Editor’s note: Roger and Lynn Normand are building a [no-glossary]Passivhaus[/no-glossary] in Maine. This is the 25th article in a series that will follow their project from planning through construction.]
Even though the concrete is still fresh in the Logix ICF block foundation, and the material for the main floor deck has yet to arrive, it’s time to think about walls.
Our main floor walls are not structurally complicated. The illustration at right shows a cross section of the walls.
The floor plan consists of four rectangles and one trapezoid joined together to form a tilted “T.” We will use 24-inch-on-center studs, with 2-stud corners to maximize the insulation cavity. We’ve got lots of big windows on the south side of the house that will use headers made of standard LVL (laminated veneer lumber). All exterior walls are framed with 2×4 studs, except for the garage which is framed with 2×6 studs.
Huh? The house is framed with 2x4s but the garage uses 2×6 studs?
Yes. We hate getting into a cold car on a winter morn, and wanted the extra depth of a 2×6 wall to better insulate the garage.
The walls will be 14 inches thick
I should also say that the exterior wall on the house is really a double-stud wall, i.e., two parallel 2×4 stud walls spaced 7 inches apart. (Building geeks call the outer wall the exterior wythe, and the inner wall the interior wythe). Our outer wall is load bearing. The 7-inch spacing between the outer and inner wythe, plus the 3 1/2 inch depth of each wythe, gives EdgewaterHaus a 14-inch-deep cavity that we will completely fill with aptly named dense-packed cellulose, for an R-53 exterior wall.
Most homes are “sticked-framed” on site. After the main floor deck is in place, the lumberyard delivers a mountain of 2-by lumber and sheathing to the job site. A framing crew then spends weeks cutting studs, assembling wall sections with exterior sheathing on the floor deck, and lifting the completed wall panel into place. They brace and nail the panel to the floor deck, then start on the next wall section.
I think there’s a better way to frame a building, one that can speed the process, improve quality, reduce waste, and perhaps save money.
Our wall panels will be built off-site
Somewhere between manufactured housing (completely built in a factory) and typical stick-built homes lies panelized walls built in a factory. The wall panels are then trucked and erected on site. Some panelized walls can include electrical, plumbing, insulation and exterior and interior finishes. We chose the more modest approach of factory-built studs and sheathing only.
There were a couple of nearby companies that panelize walls. We chose Hancock Lumber in Windham, Maine.
The advantages of panelization
I think factory-built walls have many advantages over stick-built walls:
Reliable, predictable assembly time. The panels are built in a controlled environment unaffected by weather delays. The panels are delivered on the day needed, ready for immediate assembly.
Concurrent wall production. It takes six or more months to build a home. Many parts of the construction schedule are sequential; one of the longest is wall framing. Factory-built walls panels are built concurrently offsite without interfering with onsite construction.
Quality. The wall panels are designed using 3D CAD software with error-checking software. We splayed most window rough openings to maximize daylighting the interior. We wanted our interior walls 5/8 inch shy of the ceiling plane, so we could apply 1/2-inch plywood across the ceiling plane to conduct our first blower-door test.
We also cut 5/8 inch from the length of interior walls that intersect the inner wythe, so that we could later slide drywall through the intersection to achieve an airtight drywall installation. (We gleaned this detail from an excellent article on airtight drywall by Myron Ferguson in the Aug/Sept 2012 issue of Fine Homebuilding Magazine.)
The CAD software helps to visualize how all these walls come together, and automatically produces a detailed cut list. A specially equipped workshop and an experienced crew like at Hancock Lumber can consistently and efficiently produce high-quality wall panels.
Much faster building dry-in. When combined with factory-built roof trusses, the framing crew can erect and dry-in the entire building in a matter of days, not weeks or months. That reduces the likelihood of framing delays affecting the scheduling of future tasks.
Less exposure to weather. Completing the building shell quickly reduces the likelihood of weather damage from mold, mildew, warping, or delamination of sheathing.
Environmental. There is likely much less waste. Because wall panels are built every day, cutoffs that would otherwise be thrown away can be used for other wall panels. It is also much easier to capture and recycle sawdust and short framing pieces.
Worker ergonomics. The panels are assembled on a waist-high table. No bending down to floor level to nail the top and bottom plates to the studs.
Theft concerns. There’s not a tempting stack of lumber or plywood on site for weeks that tempts someone to “borrow” a few pieces.
But the foundation has to be perfect
Panelized walls is not, however, a panacea.
The method places a premium on the foundation. The wall panels are built according to the architectural plans, under the expectation that the “as-built” foundation and floor deck will also achieve the same level of precision. A stick-built wall can more easily accommodate foundation and decking irregularities.
The method limits adjustments. Once in production, panels can’t be easily re-framed if the owner wants to subsequently relocate a door or window.
Are there any cost savings?
Does panelized walls save money? I believe so. A 2011 study commissioned by the province of Alberta, Canada, compared construction of two identical side-by-side homes: one was stick-built and the other used panelized walls. The panelized home had a 40% shorter build time, 55% less lumber waste, 60% less sheathing waste.
We started working with Gary Plourde, director of the Panelized Wall section of Hancock Lumber, last year and have been exceptionally pleased with his professionalism and insight.
I recently drove to Hancock Lumber in Windham to watch Gary and his crew build the wall sections for our main floor, garage, and three-season room. I was very impressed with how the wall panels were designed and assembled. I’m amazed more homes don’t use factory-built walls.
Check out this video of the process. Check in with us later to see whether the “as built” foundation and floor deck meet the design expectations!
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