Single versus double header for energy-efficient framing
ranson
| Posted in Green Building Techniques on
There are two headers that I could use for a short span in a 2×6 wall: one 2×10, or two 2×6’s. With the 2×10, I would fill the open space with cellulose on the inside. With the 2×6’s, I would sandwich in a 2.5″ layer of rigid foam. Since code would require the 2×10 header to be boxed in with 2×6 plates, it seems like the doubled 2×6 header will present less of a thermal bridge and use less wood.
Am I missing anything? I’ve seen a number of sources suggest single member headers to improve efficiency, but the code requirement for extra plates seems to make them worse.
–John
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Replies
John,
If you are correct that the code requires single 2x10 headers to be boxed in with 2x6 plates -- I was unaware of that requirement -- then you're right about the thermal bridging being worse with the 2x10 option.
It may be worth noting that the double 2x6 option (assuming the use of polyiso) also results in a higher R-value for the header area (ignoring the plates). The R-value of the insulation in this area (ignoring the R-value of the header lumber) is about R-16 for 2.5 inches of polyiso vs. R-14.8 for 4 inches of cellulose.
Hi Martin,
Thanks for confirming my thoughts.
FYI, the code reference for boxing in single member headers is IRC 2015 R602.7.1: "Single headers shall be framed with a single flat 2-inch-nominal (51mm) member or wall plate not less in width than the wall studs on the top and bottom of the header [...]"
--John
John. Are you using advanced framing techniques? That's what I did on my home and really didn't run into any issues with code enforcement. Of course, I didn't have to worry about snow load, hurricanes, or earthquakes (in all probability).
FYI. Martin has an article on advanced framing here: https://www.greenbuildingadvisor.com/blogs/dept/musings/pros-and-cons-advanced-framing
Hi Steve,
I am using advanced framing techniques. It sounds like I've got a few more worries where I'm building. We've got a 40psf ground snow load here, and the house will be on a 19 acre open field exposed to the wind.
I want my design to be pretty much entirely by the book so I don't have any issues with the building department. Breaking with tradition and building slab-on-grade is enough to get the stink eye here.
--John
John,
Code requirements aside, I'm having trouble imagining how you could frame an exterior wall using single headers without including a plate above and below them. The one above is needed to attach the cripples between it and the top plates, The one below to frame the opening.
Malcolm,
I agree. I don't see how a single member header would work without the plates. It seems like this portion of advanced framing is perhaps misguided.
--John
John,
Maybe it's because I came from a framing background but I don't think any of the benefits of advanced framing outweigh the downsides.