Energy-Efficient Framing, a.k.a. Advanced Framing
Use Less Material and Build a Better House
Saving materials through advanced framing takes some planning
Here are some rules:
Frame walls with 2x6s on 24-inch centers rather than 2x4s every 16 inches can save a lot of wood and increase the energy performance of a house because it makes more room for insulation.
Stack the framing
Aligning framing members between floors transfers loads efficiently. This means that you can omit the double top plateIn wood-frame construction, the framing member that forms the top of a wall. In advanced framing, a single top plate is often used in place of the more typical double top plate. in favor of a single one. It also means a better-quality nailing job of the plywood that spans these transitions.
Place doors and windows on the grid
Moving door and window openings so that they line up on the 2-foot grid reduces waste and, again, leaves more room for insulation.
Use less wood in the corners
Exterior corners can do well with fewer studs and more insulation in them. The same goes for where interior partition walls meet exterior walls — less wood, more insulation.
Omit unnecessary headers
Walls that don't carry roof loads — for example, most gable-end walls — don't require structural headers over windows or doors.
Steel strapping, hangers, and clips
Advanced framingHouse-framing techniques in which lumber use is optimized, saving material and improving the energy performance of the building envelope. requires only a few materials that may be unfamiliar to builders of conventionally framed houses. When windows are framed without jack studs, the headers are attached to the king studs with steel clips (for example, Simpson HH header hangers). When walls have a single top plateIn wood-frame construction, the framing member that forms the top of a wall. In advanced framing, a single top plate is often used in place of the more typical double top plate., steel strapping is used to tie partition top plates to intersecting walls.
Design with materials in mind
Plywood and oriented strand board (OSB) come in 2-foot increments, so why not plan for that in building dimensions? Research conducted by the National Association of Home Builders Research Center on this optimum value engineering concept revealed mixed results for floor plans done on 2-foot increments, but adjusting roof pitches/overhang dimensions to 2-foot increments significantly and consistently reduced materials and waste.
Some siding isn't compatible with 24 inch on center stud spacing. For example, the VinylCommon term for polyvinyl chloride (PVC). In chemistry, vinyl refers to a carbon-and-hydrogen group (H2C=CH–) that attaches to another functional group, such as chlorine (vinyl chloride) or acetate (vinyl acetate). Siding Institute requires that most types of vinyl siding be installed with fasteners spaced no more than 16 inches apart; fasteners must penetrate studs. The standard notes, "These distances may be increased if the manufacturer permits greater spacing based on wind load testing."
Planning for advanced framingHouse-framing techniques in which lumber use is optimized, saving material and improving the energy performance of the building envelope. can be challenging
Design preferences about the appearance and layout of a home can conflict with the goal of reducing the number of necessary framing members. This makes it really critical to consider optimizing framing material as early as possible in the design process, and to repeat that goal frequently. (Like many other design considerations, advanced framing is most successfully accommodated if it is part of the design, not an afterthought.)
The smaller the home, the more challenging it can be to use advanced framing techniques. Focus on those that deliver the highest lumber savings, such as spacing of repetitive members (studs, joists, and rafters).
Transitioning to advanced framing
Although advanced framing is often presented as a package of measures, some builders prefer to adopt some, but not all, advanced framing details. Some builders who quickly adopt two-stud corners still retain double top plates, preferring to tie partition walls to exterior walls in the traditional way. Others are happy to switch to single top plates but prefer 16-inch-on-center stud spacing because it permits more closely spaced nailing for siding.
It takes time and attention to learn how to frame a house in a new way, but the material savings can be big, and the energy performance of the house can be much improved.
Section 602 of the International Residential Code (IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code.) relates to wall framing. All code references are to the IRC unless otherwise specified.
With the rising popularity of advanced framingHouse-framing techniques in which lumber use is optimized, saving material and improving the energy performance of the building envelope. techniques, the IRC now has some exceptions to a few standard framing details. Two-corner studs are allowed if clips or wood cleats are used to support drywall [F602.3(2)], and single top plates are acceptable if 3x6-inch steel plates with 6d - 8d nails connect all joints [602.3.2X]. If you use a single top plate, joists, rafters, and trusses can only be offset from studs by 1 inch [602.3.2X].
The above information is from the book Code Check Building 2nd Edition. Buy it at the Taunton Press online store.
ABOUT ADVANCED FRAMING
Less lumber means more insulation
The whole point of advanced framing, also known as optimum value engineering (OVE), is to frame a house so that it meets its structural requirements without wasting material. A welcome corollary is that the same house will have more room for insulation inside the walls and will therefore be more energy efficient than a conventionally framed house. Minor downsides, for example, attaching trim in areas with less structural lumber, and wider spacing of siding fasteners, are easily overcome.
MORE ABOUT ADVANCED FRAMING
Load paths must line up
The main principle of advanced framing is to eliminate unnecessary lumber. For example, double top plates can be eliminated as long as each joist and rafter is lined up with a stud and partition walls are tied into intersecting walls with steel strapping.
Lining up framing materials in this way may require the designer to draw up a framing plan for each wall and floor.
Use more engineered wood
OSB, finger-jointed studs, laminated veneer lumber, and I-joists are all examples of reliable building products that can replace conventional plywood and large-dimension sawn lumber. Pressure on old-growth forests is reduced, waste is reduced, and better performance often results.
Omit needless wood
Using two studs instead of four in outside corners saves a lot of lumber. Instead of using the same header size over all openings, engineer each header for the load it will actually carry. Headers in non-bearing walls can be eliminated entirely.
Consider insulating sheathing
Building scientists recommend replacing OSB or plywood sheathing with rigid foam insulation. This reduces the transfer of heat and cold through wood framing, a phenomenon known as thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. . Diagonal bracing and shear panels can provide racking strength.
BuildingScience.com: Using Wood Efficiently: From Optimizing Design to Minimizing the Dumpster
- Chuck Lockhart/Fine Homebuilding #174
- Rob Yagid/Fine Homebuilding #197
- Daniel S. Morrison/Fine Homebuilding #174
- Code Check Building 2nd Edition
Sat, 11/02/2013 - 06:00
Fri, 11/01/2013 - 21:00