Green framing is a terrific concept, not much debate in that. But is there a point of diminishing returns? Yes, of course there is. Remove too much wood, and strength suffers.
Take the humble top plate of a stick-framed wall, for example. For centuries builders have used the double top plate rather than the single top plate. But seeing as the single cuts the amount of top plate lumber precisely in half, any progressive, green-thinking framer ought to wonder why he or she should even consider the double.
I wasn’t around when the double was invented, but I bet I know how it became the standard.
For one thing, joining intersecting walls is easy: overlap and nail off. The same goes for in-line joining of the plate itself: just overlap 48-inches and slap in eight 16ds.And with a double top plate, you don’t have to worry about lining up rafter heels or joists with studs. The double plate can take those loads no matter where they fall.
Also, nobody cared much about saving trees.
Nowadays we’re deeply concerned with being green, making the single top plate a sexy option. But how to overcome the issues of joints and rafter/joist loads that fall between studs? Fortunately, the building code folks have burnt the midnight oil and conquered these predicaments. (See section 2308.9.2.1, 2009 IBC.)
In essence, a single can be used:
- On bearing and exterior walls when joists/rafters fall within one inch of a stud, andthejoints, intersections, and partitions are connected with a 3-inch x 6-inch galvanized steel plate with six 8ds on each side.
- On interior, non bearing walls. An interesting note here: Section 2308.9.2.3 says, “single top plate installed to provide overlapping at corners and at intersections with other walls and partitions.” So how do you overlap single top plates? The code does allow in-line joints to be connected with a 2x, 16-inch-long block, or “1/2-inch x 1 1/2-inch metal tie with two 16ds on each side of the joint.” That’s a tiny patch of metal with large 16d nails. I see those nails splitting the single and poking through way too far. Why not use a bigger plate and more 8d nails?
But wait, as with most things in the building code, there’s more! Should your building be located in a moderate to high seismic risk area (seismic design category D, E, or F—the entire West Coast as well as other U.S. areas) and the calculated shear force in your wall exceed 350 pounds per lineal foot (a modest value), you must use 3x or double 2x boundary members. This would include top plates, bottom plates, and at all sheathing edges. (See table 2306.3, footnote i, 2009 IBC.)
With all the rigmarole involved in using single top plates, I question whether it’s truly worthwhile. In rough numbers, given a 1,800-square-foot home, a person could save about 400 lineal feet of interior and exterior top plate material using singles. At 40 cents per foot, this works out to $160. But offset that with the cost of all those metal tie plates and the hassle of lining up trusses and joists and are you truly ahead? Not to mention that you can’t even use singles in many parts of the U.S.
If I’m making the call, I’d stick with doubles and rack up framing savings elsewhere, like right-sized beams, headers, posts, trimmers, king studs, cripples, wall studs, and foundations.
All that glitters isn’t green.
Tim Garrison, of ConstructionCalc Software, Inc., is an author, professional engineer, and speaker who lives and works in Mount Vernon, Wash.