The Future of Framing is Rooted in the Past
Growing Interest in Energy Conservation Leading Builders to Look at Advanced Framing Techniques
There have been many innovative construction methods and products developed over the last decade but when people talk about advances in framing a structure you need to take a look to the past for the latest innovation – 40 years in the past to be exact. That’s when a collaboration between the U.S. Department of Housing and Urban Development (HUD) and the National Association of Home Builders Research Foundation delivered “optimum value engineering framing” or OVE framing. Today, the methods developed back in the 60’s and 70’s are referred to as “Advanced Framing” (AF). You may also here the terms “in-line”, “stack”, or even “smart” framing used to describe the process whose objective is to improve a structures energy efficiency while reducing material and labor costs. So why wouldn’t every builder in America sign up for those benefits? Resistance to change certainly plays into it. We may have an inefficient framing system but we are doing it incredibly efficient and have been for decades. Plus, introducing change to a builder’s jobsite can be complicated because other subcontractors can be affected by the changes. Also, it takes added coordination, forethought and potentially productivity setbacks during the learning curve of new product and new process introductions. So, the old adage, “if it ain’t broke, don’t fix it,” probably plays into builder’s resistance factor. Yet, today’s growing interest in energy conservation and green building processes is leading more and more builders to successfully adopt AF techniques.
Advanced Framing has been described as an affordable way to balance energy and structural building code requirements. AF is a great concept for builders who are trying to meet today’s strict energy code while maintaining a structure that is cost effective, durable and sustainable. In a nutshell, AF is about optimizing material usage by removing redundant and unnecessary framing members and replacing them with more wall cavity insulation. The combination can realize a 30% reduction in framing material used in a wall and a 12-14% gain in insulation space within the exterior walls. The Department of Energy estimates that a home with advanced framing will cost 5-8% less to heat and cool, which is a lot of money over the life of a structure. Throw in the added advantages that AF helps builders qualify for the Energy Star label, as well as LEED and green building standards points, and the process seems well worth investigating.
At its core, Advanced Framing replaces conventional 2 x 4 wall framing at sixteen inches on-center with 2 x 6 wall framing at twenty-four inches on-center. The change to a thicker wall section works out to be a financial wash since you are using fewer 2 x 6 studs by spreading out the spacing. It saves energy because it provides a 60% deeper insulation cavity* allowing for greater R-values in exterior walls. Other commonly used structural techniques can also be scrutinized like double top plates, three-stud corners, multiple jack studs, double or triple headers and unnecessary cripple studs. Advanced Framing incorporates single top plate, two-stud corners, single headers and minimal use of jack studs and cripples, and the elimination of redundant studs and unnecessary blocking and bridging. And while adopting the AF system holistically will enable the builder to realize the greatest overall results, introducing some techniques independently can also prove beneficial.
Before moving on to evaluate the details of incorporating Advanced Framing techniques in a structure’s walls, the other major AF concept that I want to discuss is “stacked” or “in-line” framing where all framing components, truss/rafters, walls, and floor joists align vertically. This provides a direct load path from roof to sill plate and results in greater overall structural integrity. Adopting this concept is a prerequisite for being able to use a single top plate. It also changes fundamentally how you view load transfer through a structure from a block/slab upward design to a truss member downward design. When you utilize stacked framing it all starts with truss/rafter design. Once again, this takes a little thought in the design stage but has many basic benefits throughout the construction process due to the framing elements being further apart allowing easier installation of services. The plumber, HVAC, electrician and insulator all should be able to save time with the wider, deeper, more consistent wall cavities.
In addition to the energy benefits of deeper wall cavities, minimizing Thermal Bridging is another advantage of eliminating framing members in the walls. A thermal Bridge, also called a cold bridge, occurs when heat is transferred through a building component at a higher rate than the transfer through the surrounding envelope. Wood is a poor insulator so studs, plate and headers link conditioned interior space and exterior environments and contribute to significant heat loss in heating months and heat gain in cooling seasons. Thermal bridging accounts for as much as a 37% reduction in a walls overall R-Value. Obviously Advanced Framing cannot eliminate thermal bridging but it does reduce it. If you are looking to maximize the R-value in your walls, in addition to AF, look at adding a layer of rigid foam over the OSB sheathing. A minimum of one-inch of foam can double the effective R-Value in a wall.
Incorporating Components of Advanced Framing
Even though builders routinely over-engineer homes, many builders electing to incorporate AF techniques incorporate them in stages rather than all at once and some may only utilize certain techniques that they are most comfortable with. Let’s look at the most common components of Advanced Framing and review details of how to implement them on your jobsite.
2 x 6 Wall Studs
Introducing 2 x 6 walls is the most widely adopted component of AF mainly due to the energy code requirements. The combination of spreading the wall out to two-foot on-center spacing is a natural progression for those seeking to take full advantage of energy savings and sustainable construction strategies.
In-Line or Stacked Whole-House Framing Alignment
For superior structural performance, implement a “stacked” framing alignment where trusses/rafters, studs and floor joist vertically align creating a condition where compression and tension loads are directly transferred through the framework of the house. When used with continuous wood structural panel sheathing (OSB or Plywood) for wall bracing, shear strength and exterior siding & trim nailbase, many experts believe the perfect balance is created between energy efficiency, structural performance, sustainability, and affordability. Note that two-foot on-center floor joist spacing may require an upgrade to thicker floor sheathing for a stiffer, more solid feeling floor.
Single Top Plate
In order to eliminate double top plates the structure requires vertical framing alignment from the roof through the floor joists. This typically requires an engineered wood floor system to optimize resource efficiency and can result in added design costs as well as the sourcing of non-standard length studs. For these reasons (and a few others) many builders elect to retain double top plates.
Two-stud corners decrease lumber use and allow full insulation placement in the corner of a framed wall. There are also several three stud corner details that permit for increased insulation levels and drywall nailing capabilities. Some of the details call out for drywall clips which permit for floating drywall corners. This reduces expensive drywall cracking repair costs but many builders reject using the clips due to subcontractor resistance and because many municipalities require an inspection of the clips after installation.
One area where Advanced Framing techniques really make sense is in window and door headers. Structural headers are often oversized or installed where unnecessary, largely for convenience. Each header should be engineered for the load it will actually carry and headers in non-bearing walls can be eliminated entirely. Proper sizing of headers allows better insulation and saves wood. In some cases, single-ply (single 2 x 6) headers can be used, allowing even better insulation around windows. Again, some forethought regarding design, specifically the placement of openings in load-bearing walls and the location of framing members above openings, have a significant impact on headers sizing for AF. Excessive common studs beside window openings and excessive jack studs and redundant cripple studs above or below openings are often unnecessary and promote thermal bridging. Framers tend to think structurally, not thermally. For them, more wood is better but they are typically not doing your customers any favors.
Interior Wall Intersections
Utilizing 2 x ladder blocking at T-Intersections requires less than 6-foot of blocking material verses the two studs at each side of the intersecting wall, or 16 feet of stud lumber plus additional blocking. If you place the blocking’s wide face vertical for maximum backing, it allows an insulation cavity behind the ladder blocking. A 3” x 6” galvanized steel plate is recommended at the top of the two intersecting walls to tie them together.
It is important to realize that dimensional considerations can play a significant role in a building’s design efficiency. Drawing a structure utilizing two-foot increments can allow for optimal material and labor usage. Take, for instance, the construction of a back-yard shed. It takes the same amount of material to build an 8’ x 8’ shed as it does a shed that measures 7’ x 7’. And, it actually takes more labor and time to construct the smaller shed, not to mention the generation of more waste for the landfill. It just makes sense (and cents) for city planners, developers and architects and builders to consider modular (two-foot design increments) and outside dimensions in the design process. Every jog, every bump added to a square or rectangle building’s footprint challenges framing and resource efficiency. Practical design doesn’t mean you’re relegated to building a box, it just means more attention could, and should, be given to maximizing framing material and framing layout in the design process.
In my opening paragraph, I mentioned builder’s resistance to change, even when an idea seems to make perfect sense, and I would like to go into a little more detail of why I think that is. In my experience, I feel that builders have had an exceptionally hard time realizing the “perceived savings” often associated with making changes, be it a new product, advertised as costing 10-percent less than the product it is replacing, or a better process, guaranteed to save labor and time...the proverbial “new mousetrap.” I think there are several reasons this is true. First of all, research conducted during the developmental stage of products and processes can be flawed, over-exaggerated, or unrealistic when compared to a real-life construction environment. This can relate to discrepancies in product performance, product pricing and labor savings. It is extremely difficult to get subcontractors to make price concessions back to builders when they are barely making enough money to survive. And then, in the builder’s eyes, is the savings or the performance advantages worth the risk of the delving into the unknown. Nearly every builder has been burnt one time, or another, by a product or process that did not live up to the lofty claims made going in. This is just an observation, not condemnation, from someone who has spent the last 35-years trying to introduce new ways of thinking and doing to the construction community.
Regardless of the level of reluctance or skepticism a builder possesses the benefits of using some, if not all, of the Advanced Framing techniques cannot be ignored. With growing emphasis on high-performance, energy efficient housing, the push to advance Optimum Value Engineering is quickly picking up momentum and thus, may be moving from mothballs into the mainstream.
*Building America Report – 1004, Joseph Lstiburek & Aaron Grin, November 15, 2010, Building Science Press
T-Intersection & Header Details
Details courtesy apawood.org