Advanced Framing, sometimes called Optimum Value Engineering (OVE), refers to framing techniques designed to reduce the amount of lumber used and the waste generated in the construction of a wood-framed house while maximizing the energy efficiency of the wall assemblies by making more room for high R-value insulation of R3 to R6 per inch instead of wood at only about R1 per inch.
The US Department of Energy has been responsible for the research that defines and supports Advanced Framing Techniques. The following chart was created by the DOE:
Click on the chart for larger view.
The most basic feature of Advanced Framing for a two-story home is changing the wall frame from 2x4s @ 16" on center to 2x6s @ 24" on center. Even though we use lumber that is 50% larger we actually are using slightly less lumber since we are using wider spacing and lots of techniques like two-stud corners which use fewer studs than normal. Here we have just tilted up the first 2x6 @ 24" on center wall section.
Optimizing the use of lumber can save significant cost. For example, the Uniform Building Code even allows 2 feet on center 2x4 stud spacing in one-story dwellings and on the top floor of multistory dwellings instead of the conventional 16 inches on center. Also, using two-stud corners can save as many as 40 to 50 studs in a house.
Advanced framing methods may reduce wood use up to 20% and improve wall thermal resistance values from 5 to 10%. Just the corner and wall intersections of typical homes can add up to 10 or more feet of wall that is not insulated.
This doesn't include the additional insulation value you get by filling a 2" deeper wall cavity with insulation. A standard 2x4 wall cavity would achieve R-13 when filled while a 2x6 wall cavity can achieve R-20 with the same fill materials. This is over a 50% increase in R-value, and insulation is pretty cheap.
The small window rough openings high on the long wall are sized to fit standard 24" o.c. stud bays so there are no extra studs used to frame the openings. This is another feature of Advanced Framing if you have managed to get the building designers on board from the start. Most of the windows in this home have been designed to fit a single or double wide stud opening ...no extra studs.
However, we are in earthquake country on this project so the structural engineers require additional studs for "hold down" connections to the foundation and horizontal blocking for metal straps above and below window and door openings. Even so, we still have more room for insulation and the wall cavity is deeper so it will accept more insulation. Enough to cover the horizontal blocking in this wall section and thereby reducing thermal bridging.
Here we have one example of an insulated header with some EPS foam on the exterior side of the header visible in this photo of an 8ft wide window opening. Below is another type of insulated header with EPS sandwiched in between LVL headers.
The house is just as strong as a conventionally built house. We save trees and money and we achieve a higher insulation content which yields increased comfort and energy savings. Additional construction cost savings result from reduced waste disposal, which also helps the environment. A win-win-win by all measures.
We will post some other stories with more details on the Advance Framing techniques we used on this project.