GreenDwellingSeattle

Now that we have the foundation in place it is time to move on to constructing the exterior walls of Columbia City Green.  To do this let’s first step back for just a moment to talk about how it is that we will connect the framing to the foundation. 

The most common method is to place “J Bolts” (so termed because of their shape) into the concrete of the foundation wall.  These bolts have threads at the top of the “J” while the other end serves as an anchor in the concrete and keeps the home from becoming dislodged from the foundation.  Over the top of these bolts is placed what is known as the sill plate or sole plate.  The sill plate in this case is a wooden 2 x 12 that has holes drilled in it to receive the “J Bolts”.  Nuts and washers are then fastened to the bolts securing the sill plate to the foundation. 

The most common technique used for framing a home in the United States what is known as the platform method.  This technique involves attaching the sill plate to the foundation walls, installing floor joists and then covering all of this with a layer of sheathing.  At this point the stud walls are constructed horizontally and tilted up and into place.  As we move to the next level, we repeat the floor joists and sheathing and follow with the stud walls for this level.  The point at which the stud walls of the highest floor meet the roof assembly is known as the top plate.  We will come back to this top plate in future posts.  Now let’s go back down and talk more about the framing. 

Case Design & Project Management chose to use what is called Advanced Framing in the construction of these homes.  Advanced framing is a collection of techniques that significantly reduce the material requirements (wood) while increasing energy efficiency and simplifying the layout of the framing.  Standard framing is based on wall studs and floor joists being placed every 16 inches, or 16” on center.  In advanced framing there is a stud or joist every 24 inches, or 24” on center.  The floor joists, wall studs, and roof framing are all stacked on top of one another thereby effectively transferring the load straight down to the foundation.  At corners, t-wall intersections (where interior walls meet the exterior) and window headers there are additional opportunities for material savings and increased insulation.  Advanced framing takes advantage of drywall clips instead of extra studs for fastening and benefits from the use of insulated headers instead of solid dimensional lumber.  A 2 x 6 stud on the exterior of a home has an R-value of about 6.  The Cellulose insulation they have chosen for these homes has an R-value of about 21.  With fewer studs on the exterior walls there is room for more insulation.  For the window headers the R-value jumps from approximately 7 for traditional headers to 18 for those made from rigid insulation sandwiched between two pieces of OSB (oriented strand board). 

Simply put Advanced Framing can save as much as 30% of the lumber that is required using standard framing and can also provide as much as a 30% increase in exterior wall R-value.  There is less construction waste, and taken as a whole, a considerable reduction in the embodied energy of the home.  Houses with advanced framing are just as stable, just as strong and offer superior performance with reduced environmental impact.  It can also save the builder and thus the homeowner money in the form of lower construction costs.  It should be the logical choice for homebuilding in many parts of the country.

If this is the first post you have read on this great project please take a few minutes to go back and read the few posts that have come before it.  For more information about Case Design & Project Management please visit their website at www.case-architects.com .  Next week we are going to talk in depth about insulation and its effect on energy demand and costs.  See you then.