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Exterior wall “headers”

Jerry Liebler | Posted in Green Building Techniques on

I’m planning to build a one story ‘green’ energy efficient, net zero with PV panels, house in northern Michigan. I plan on using ‘advanced framing’ 24″ OC for my exterior double stud walls. I would like to use trusses specifically made to “replace” one stud or two studs (this may require some slight ‘repositioning’ of openings). The trusses bottom chord would be the top of the rough opening and it’s top chord would sit directly under the single top plate. In my situation, only two truss lengths would be needed , 46 1/2″ and 70 1/2″.. Since I’ll have 9′ ceilings and 6’10” door & window tops the trusses are about 2′ high. The trusses would be rather simple, having just two angled members, but designed to support the concentrated loads above them that occur 24″ OC. The advantages of this approach include much less ‘thermal bridging’ for higher “whole wall’ r value, greener because it uses less and smaller lumber.. While such trusses could be fabricated ‘onsite’ by reasonably skilled carpenters it is probably best to have them made by a truss manufacturer as the result would, no doubt, be stronger & more uniform . My questions: Is this commonly done? Should I expect “flak” from building inspectors etc? Any other issues?

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Replies

  1. John Klingel | | #1

    OK, you lost me. Got a sketch of your plan?

  2. GBA Editor
    Martin Holladay | | #2

    Jerry,
    I'm guessing that these proposed trusses are parallel to the wall, not perpendicular to it, installed within the wall at header height. Am I right?

  3. Expert Member
    Armando Cobo | | #3

    Do we understand you question correctly??? You plan to use 2' tall flat truss installed under a single top plate and continuously the whole length of the building? or, individual lengths per rough openings? Detail drawings would be helpful.

  4. Jerry Liebler | | #4

    Sorry for the confusion, I haven't figured out how to upload a sketch. These trusses would sit within the wall one above each window or door opening. A truss would replace a conventional header. They would be made of 2x4, as is the wall with the 4" dimension perpendicular to the wall as are the studs in the wall. The total of all window and door openings is about 10 % of the wall area.

  5. Expert Member
    Armando Cobo | | #5

    So you are making Truss Headers... I tried the same long time a go, but I've found that right sizing headers (per 2009 IRC R502.5) saves more lumber; it's cheaper and quicker. Depending on your bearing span, you need a 2x8 or 2x10 header with 1 or 2 jack studs: See R502.5 table. You can always use single LVL headers as well.
    You need to install outsulation to avoid wood sheating condensation, as we all should in any climate zone; but you are taking care of thermal bridging with the double walls.

  6. Michael Chandler | | #6

    Assuming you'll be using raised heel trusses you might check with your engineer to see if you can hang them on headers that run over the top plate and skip the header and jack studs altogether. You would have to work with your truss company to build the affected trusses shorter at the heels to accommodate the headers but it would give you full insulation in the wall all the way to the top with no limit on the insulation depth at the header as it would be in the ceiling insulation. We've been running headers in plane with the floor trusses for years.

    I'm with Armando that it's easier just to right size the headers (and we push them to the tops of the walls so they are in contact with the underside of the top plate for hurricane reinforcement) but you could push it a little farther.

  7. Jerry Liebler | | #7

    Thank you all for the comments. Since I have only two opening sizes to consider, 46 1/2" and 71 1/2", I'm thinking I can use single headers 2x8 for the smaller and 2x10 for the larger opening. the single headers would be flush with the outer edge of the studs, directly inside the sheathing and up against the top plate and secured to the studs at either end with metal brackets. The top of the opening would be a single horizontal 2x4 and notched 2x4 s would be installed vertically at the locations of the "missing" studs to provide nailing area for the sheathing. Since this wall will be insulated with mineral wool bats, accommodating the single headers adds a bit of cutting but is still relatively easy. It is certainly easier to get 2x8 & 2x10 rather than custom trusses and the cost is, no doubt, much lower as well. Though I haven't done a thermal analysis of both solutions I suspect the difference is negligible as is the difference in amount of wood used.

  8. Mike Eliason | | #8

    jerry,

    were you thinking of doing something like these trusses over the openings on the right?
    https://lh5.googleusercontent.com/-gg0XY9CXMX8/Tq7uNVPxivI/AAAAAAAAFZA/DGjd9kVHASc/s912/DSC_0272.JPG

  9. Jerry Liebler | | #9

    Mike,
    No, not anywhere near that scale!
    All,
    As to jack studs, I'd argue that doubling the studs at each end of the single header is all that is needed because, with that, there are the same number, or more, of studs as would have been without the opening. Even that may be overkill as wood is very strong in compression and the studs are braced against 'buckling' by the sheathing.

  10. Expert Member
    Malcolm Taylor | | #10

    "Even that may be overkill as wood is very strong in compression and the studs are braced against 'buckling' by the sheathing."

    Jerry, that is true but the requirements for wood frame construction already take its general properties into account, so deciding on structural sizing is best done either by following code requirements or subjecting any deviation you may want to do to calculations. For a large opening with significant roof loading on it, the governing factor may well end up to be the shear value of the header and more studs may be needed to provide a larger bearing surface.

  11. Jerry Liebler | | #11

    I finally got a look at the IRC code table R502.5 & realized there is much more to be considered, especially the 'building width and snow loads. I have a building width of 36 feet, allowing 10 #/sqft for ceiling & roof structure, 5#/sqft for insulation and 30#/sqft for snow load means each stud is supporting 1620#. From the table 2 2x10s for the 6' span & 2 2x6 for the 4' span with the 6'span requiring 2 jack studs. the 4' could legally be done without jack studs with approved hangers. I should be able to substitute a single 2x12 for 2 2x6s. But to make a single header equal to doubled 2x10 probably means 1 3/4 x16 LVL with 2 jack studs. The wood parts of the truss design will easily withstand the loading, but as with all trusses the problem is the connections. I have only 2 of the 6' openings and 15 of the smaller ones. I'm sure i can convince the authorities that a single 2x12 is stronger than 2 2x6 s but not so sure in the case of the LVL. geting the local officials approval may be easier with trusses designed for the point loads of the roof trusses.

  12. Expert Member
    Malcolm Taylor | | #12

    Jerry, again you don't have to convince the authorities of anything, you just show them the calculations or values from span tables. This isn't about opinion, it's straight engineering.

    Can you elaborate on this:

    "The wood parts of the truss design will easily withstand the loading, but as with all trusses the problem is the connections."

    I'm afraid I don't understand it.

  13. Expert Member
    Malcolm Taylor | | #13

    .

  14. Aj Builder, Upstate NY Zone 6a | | #14

    Let-in headers screwed in place, no jack, bullet proof as to shear..... Not code... Last home I put up had wood-foam-wood sandwiched jacks that I made. The headers landed on the wood of course. Inspector didn't notice my little twist on all. Also avoided double jacks mostly but not all together. Lvls do not require double jacks as often as SPF too if used instead.

  15. Jerry Liebler | | #15

    Malcolm,
    I use a book "Simplified Design of Structural Wood" by Harry Parker & James Ambrose. Basically wherever truss members meet the simple tension or compression in any member must be transferred to other members through shear. Developing the shear is the function of the connection and that is usually the weakest link, so to speak.
    FWIW Where I'll be building requires design for 70#/sqft snow loads. Using manufacturer supplied design information & my actual roof size,, including overhangs, I can meet the load criteria with 14" LVL on 5" bearing for the six foot opening and 9 1/2" LVL on 2 1/2" bearing for the 4' All with single 1 3/4" LVL.. If it really is "straight engineering", I'm ready.!

  16. Expert Member
    Malcolm Taylor | | #16

    I don't mean to belabour this as I'm not sure it is helpful to you, but manufactured trusses easily make the required shear values through engineered connections. It isn't something to worry about.

    The second part of your response comes back to my comments on the number of studs required to support your headers. You appear to need more than a doubled stud at each end to get the required bearing.

  17. Jerry Liebler | | #17

    Single headers do NOT work out! with my snow load! in fact 2x4 walls don't either because of the compression across the grain in the plates $ truss bearing area.. Fortunately 2x6 is within allowable stress but that means triple 2x6 headers for the small one's 40" or 38" span & 5 1/4 x7 1/4 LVL for the 6 foot spans. So I've got to redo my insulation plan & widen my walls a bit. But the LVL table shows an allowable reaction for 1 1/2" bearing under the 5 1/4 beam being 5906# well above my calculated 3680# for 80#/sqft roof load.

  18. Aj Builder, Upstate NY Zone 6a | | #18

    A load carrying wall in the middle carrying the ridge instead of trusses would drop your loads in half. 12/12 pitch is nice in snow country. A check payed for final engineering may be your best bet when you get done with your own ideas and number crunching Jerry.

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