Checklist: Advanced framingBy Marcus Renner on 03/22/2010
Although contested, wood-framed buildings are a great American innovation. Developed 150 years ago, wood-framed (also called stud-framed or western platform framed) buildings now account for 90 percent of our homes. Framed homes are cost efficient made with a renewable resource and are relatively easy to construct, many times without the help of an engineer or architect.
As with all technologies, decades of use fostered innovation. One of the latest innovations for framed construction is now called Advanced Framing. Once labeled Optimum Value Engineered Framing, advanced framing addresses efficiencies in speed, cost, materials and energy. Redundant wood is eliminated, layout is simplified and insulation is increased — less wood, more insulation.
The advantages of advanced framing are numerous. By minimizing wood and increasing insulation, the materials and labor cost are reduced. Not only is the construction of the frame faster and less expensive, but the trades people — such as electricians and plumbers — have to drill and cut fewer holes, saving them time. Even the insulators are putting up fewer but bigger pieces of insulation, which means increased efficiency. Joe Lstiburek, preeminent researcher and principal of Building Science Corporation, offers these statistics for advanced framed homes: They use 5 to 10 percent less lumber, up to 30 percent fewer pieces of wood, and are 60 percent more insulated. Advanced framing is a less expensive, faster way to construct homes, saving more energy than conventional framing methods.
Model building codes accept all the advanced framing methods listed here. In the 1970s, a research collaboration between e National Association of Home Builders and the U.S. Department of Housing and Urban Development established what is now advanced framing. Since then, the methods have been allowed through model building codes. As with all nonstandard practices, however, be sure to consult with your building official before starting construction.
Below is a list of all the methods associated with advanced framing:
• 2x6 exterior stud walls, 24 inches on center
Increased room between studs enables more insulation. 24-inch centers (versus 16-inch centers) require less wood, even though the size has increased. Many builders are eliminating interior window and door trim and rounding the drywall to terminate at the window frame. Only a wood sill is installed, saving money.
• 2x4 interior walls, 24 inches on center
Non-structural interior walls don't need 16-inch spacing. Less wood means less work for the framers and trades people.
• Corners constructed with two studs, not three
Corners inherently carry less of a structural load than the wall. The only reason a third stud is installed is for connection of the drywall, but doing this creates a cavity which can't be insulated. Eliminate the stud and install drywall clips or a smaller one inch board to connect the drywall to. Recently, the building code started requiring two stud corners.
• Ladder bracing where partition walls meet exterior walls
Additional studs are traditionally placed in the exterior wall on either side of the last interior wall stud. These are placed there for the drywall connection. Ladder bracing is just as strong and allows insulation to be placed in the exterior wall. Small scraps of wood can be used.
• No cripple studs connected to jack studs under windows
Windows aren't heavy. Follow the framing layout for the small studs under windows but don't add additional wood at the jack or king stud.
• No jack studs for headers
Jack studs hold up headers. Jacks can be replaced with header hangers. Less expensive than wood, and quicker to install, header hangers allow more insulation in a wall.
• No headers in non-load bearing walls
If there is no load above a window, why put an expensive header that requires large boards and compromises the insulation? Frame out the opening with one flat 2x6. Non-load bearing openings are usually under gable ends.
• Single headers flush with the outside or insulated headers
Most homes never have the forces to require a double header. Eliminate the interior board. This will allow the insulators to fill the space in the header. Drywall is less likely to crack when not connected to the larger piece of wood. If you do need to install a double header be sure to fill the center with insulation before constructing and installing it, or stack the headers together and put the insulation in last.
• Raised heel trusses or rafter ends
Many times, trusses are often designed with no room above the top plate. Site framed homes often have the rafter sitting on the top plate next to the ceiling joist, also providing minimal space above the top plate. Insulation is usually compressed at the edge of the building. Raised heel trusses are designed to allow ample room above the top plate so the insulation can keep its luff. In a framed roof, a ledger board can be placed flat on top of the joist ends and the rafter sits on the ledger.
• In-line framing
Framing in a way that all the structural elements line up increases strength and minimizes wood. The layout of the floor joists, studs, ceiling joists and rafters are the same. The stud is directly over the floor joist, the ceiling joist is stacked on top of the stud and the rafter is on top of the ceiling joist. This more efficient and stronger way of building also looks better and gives a perception that the building is stronger, which it is.
• Single top plates
When doing inline framing, the double top plate can be eliminated and a single top plate will suffice. Metal plate or wood splice connections can be made at partition wall intersections and top plate butt joints. Although this is an easy way to minimize wood and increase insulation, many code officials won't approve this method, so be sure to consult with them.
• Floors and roofs framed on 24-inch centers
With the advent of floor decking that is ¾-inch thick, there is no need to use 16-inch spacing. Two foot centers with ¾ inch decking are faster and have a lower materials cost than other methods. Keep in mind that the trades people will also have less wood to cut or drill through when running plumbing, electrical or other services.
• Insulating sheathing
Although not a framing method, using rigid insulation as the exterior sheathing is an excellent way to increase the efficiency of the home. Framed homes have a break in the thermal insulation every time a stud is installed. If the walls are insulated with R-19 rated insulation, the effective R-value of the wall is actually around R-13 because of the wood break. Insulation as sheathing actually creates a thermal break and adds additional R-value to the wall. If the seams are caulked and taped, then the house wrap can be eliminated, saving money. Taping the seams also provides an air seal that stops air leakage, the No.one form of energy loss in our homes. Diagonal loading has to be addressed, and there are a number of ways to do it. Wood sheathing can be installed at corners or diagonal bracing of wood or metal can be nailed into the wall.
Advanced framing is an innovation that has many benefits. If we didn't innovate transportation, for instance, we may all still be traveling by horse. Framing with old methods is like traveling on a horse — slow, costly and inefficient. Building codes are slowly changing to reflect innovation, and soon all new homes will have to be framed with energy in mind. Get off the horse and into the hybrid. Get ahead of the code and do yourself and your customers a favor by using some or all of the methods listed here.
[Marcus Renner, LEED AP, NCGC, GPA, MA, RWE. Educator, consultant and building analyst, Marcus has kept abreast of the industry through in-the-field experience, research and tenaciousness.]