Building for Optimal Efficiency
Many products today (oxboard, engineered floor joists, etc) are designed to reduce our use of natural resources by using material that may have been previously considered as waste. But when we shift from production to use, most homes are built (framed) the same today as they were 50 years ago. Most have corner posts, partition posts, headers above all doors and windows, cripples, 16” spacing on wall studs and many other construction techniques similar to those used in the 50’s and 60’s. While these techniques built sturdy homes, they didn’t necessarily lead to energy efficient homes. As energy prices increase and we move to other, more expensive forms of energy (renewable), it may be time to rethink how we build homes.
The first place to look is at the framing layout pattern. Typically, floor joists and wall studs are on 16” centers while roof trusses are on 24” centers. While floor joists and wall studs typically use the same spacing, it doesn’t necessarily mean they line up with each other. Lining up framing members on 24” centers, called stack framing, ensures building loads are directly transferred to building members below with the use of less building material. Unfortunately, stack framing requires planning and therein lays the problem.
If homes and rooms are designed on a 24” center layout, doors and windows can be slid to the nearest stud, reducing the use of jack and other supporting studs. Wall board and exterior sheathing (four foot widths) would have less waste material. Using 2 x 6 studs ensure walls have sufficient structural stability and provide additional room for wall insulation.
Traditional corner and partition post construction was designed to provide wood corners so that wall board has a surface to be fastened to at all corners (figure 1). The problem is that all wood shrinks and all wood shrinks at different rates. This can lead to drywall cracks. Using drywall clips (figure 2) reduces the amount of wood used, ensures corners are fully insulated and reduces cracking. Full height partition posts can be replaced with horizontal ladders between adjoining studs to stabilize the wall while allowing for full wall insulation.
To achieve properly insulated walls and to prevent the growth of mold and mildew, cold spots in walls need to be eliminated. The use of structural load bearing headers over doors and windows in non-load bearing walls can be eliminated, allowing for increased insulation levels. When possible, header hangers should be used to support headers, eliminating “jack” studs, an additional 2 x inserted into the wall to support headers. Eliminate cripples (similar to jack studs) under windows that are used to support the horizontal windowsill as no structural loads are transmitted to these 2 x’s.
Finally, 1” extruded foam with an R-5 insulation level should be used for exterior wall sheathing instead of OSB or plywood. This does cause a need for alternative methods of providing shear strength, or the force to keep the home from twisting in high winds. Using ½” OSB or plywood at the corners with ½” extruded foam, installing diagonal metal bracing nailed to the face of the studs or inserting engineered sheer panels into the wall can accomplish the need for sheer strength.
As energy efficiency becomes the driving force behind the development of new construction products rather than ease of construction, new materials and building techniques will appear on the market. But even with better materials, planning ahead is the only way to ensure the efficiencies these new products offer are maximized. As Joseph Lstiburek, Ph.D. says, “What we have is an inefficient framing system that we are all doing incredibly efficiently. We need to refocus on a more efficient system.” To achieve that will require change and planning ahead.
