Information about best practices, framing materials and a transition guide give you an overview to some concepts that you can begin using today.
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One detail that is especially beneficial to the thermal performance of a house is a modified, two-stud corner that allows more insulation and blocks much of the thermal bridging in a conventionally framed corner. With less cold air inside the wall cavity, the chance of condensation and mold declines. Adding a layer of insulating sheathing to the outside of the building is an added benefit. Drywall clips or an extra piece of 1 in. x 4 in. catches the edge of interior drywall.
Optimum Value Engineering — or simply advanced framing — has two main benefits.
- It eliminates framing members that serve no structural purpose, thereby reducing waste as well as unnecessary costs for the buyer.
- It makes more room for insulation and eliminates cold spots, making the house more comfortable and less expensive to heat and cool.
Virtually every part of the frame is affected, and while some of the techniques may seem like small potatoes the cumulative savings can be substantial. Advance framing, however, is different, and for that reason it often challenges the long-held views of builders who are familiar with it. Changes takes time, but advance framing works. Here are some of the basics:
- Walls are framed with 2x6s on 24-inc centers rather than 2x4s on 16-in. centers to increase insulation depth and reduce thermal bridging.
- Corners are made from two studs rather than four to allow more room for insulation and to eliminate cold spots.
- Headers are sized according to the load they actually carry, not to conform with an arbitrary formula for building traditions.
- Roofs are built with trusses rather than framed conventionally, reducing the amount of lumber that's needed.
- Floors are framed with I-joists rather than sawn lumber, making for stiffer floors that use less material.
- Insulating sheathing replaces conventional plywood or oriented strand board, reducing thermal bridging and making the house cheaper to heat and cool.
Advanced Framing Reduces Waste
Most wood-framed houses are assembled one piece at a time at the construction site. And that's part of the problem. There is often too much framing—too many studs placed too close together, headers that are too big for the loads they carry, framing that gets in the way of insulation. Call it habit, tradition, or insurance on the part of the builder, but the bottom line is that these and other wasteful practices make building envelopes more expensive and less efficient than they could be.
In the late 1970s, during an energy crisis that was not doubt a practice run for what's to come, the National Association of Home Builders' Research Foundation conducted studies to identify what structural configuration was necessary to maintain superior strength and yet allow the maximum insulation in wall cavities to improve energy efficiency. The result was called "Optimal Value Engineering" (OVE). Researh showed that on average as much as 20% of the framing material used in traditional construction could be removed without compromising structural integrity. Today, OVE is just referred to as advanced framing.
It's easy for framers to throw another stud in the wall or to beef up a door header just to be on the safe side. After all, an extra piece of material here and there can't make that much difference. Or so it would seem. But it all adds up. Advanced framing brings order to this haphazard system, reducing the amount of materials used in the shell of a house and simultaneously allowing greater energy efficiencies when the house in insulated. Both are cornerstones of sustainable building.
Improving on Conventional Framing
If advanced framing seems like too much of a change all at once, there are significant ways to improve frames made the conventional way— from 2x4s on 16-in. centers. Building Science Corporation, working with the Building America program of the Department of Energy, found that wrapping the frame of a house with rigid foam insulation increased the overall R-value of the walls and reduced heat loss. This added layer of insulation makes detailing especially around door and windows, more complicated. But there are ways to accomplish this—by switching from conventional 3/4in. trim to deeper brick mold, for example.
Some builders have switched from 2x4 to 2x6 construction on the theory that it allows for deeper stud cavities and therefore more insulation, which is true. If you're using fiberglass batt insulation, the nominal R-value of wall insulation jumps from R-13 (R-15 for high-density batts) to R-19. But when builders continue to space 2x6 framing on 16-in instead of 24-in. centers the result is structural overkill. All the extra wood in the wall increases thermal bridging while decreasing space for insulation. You only frame a house once so it is best to create an envelope that's as energy efficient as possible