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Thread: Joist inquiry

  1. #1
    Join Date
    Feb 2008
    Location
    Tennessee
    Posts
    105

    Default Joist inquiry

    Saw this in a detached garage that was built in the early to mid-eighties. Garage depth is 24' and joists used were two 12' 2x4's attached at their ends. Sagging has occurred with the storage above. Seller says, "well, okay, it's been like this for almost 30 years-what's the big deal?" My question is, what would the requirements be the joist size requirements over this span? I've included a photo of the garage for roof pitch visual as well as the joists. Thanks in advance.DSCF4259.jpgDSCF4258.jpgDSCF4241.jpg

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  2. #2
    Join Date
    Mar 2007
    Location
    Spring Hill (Nashville), TN
    Posts
    5,847

    Default Re: Joist inquiry

    Is that truss framing or did they just use the plates to attach the 2x4x12"s together?

    An unsupported span of 24' is more than twice the length for SYP of that dimension. No matter, it is wrong and with that much deflection I bet the teeth in those plates are pulling loose in several areas.

    Scott Patterson, ACI
    Spring Hill, TN
    www.traceinspections.com

  3. #3
    Join Date
    Feb 2008
    Location
    Tennessee
    Posts
    105

    Default Re: Joist inquiry

    Quote Originally Posted by Scott Patterson View Post
    Is that truss framing or did they just use the plates to attach the 2x4x12"s together?

    An unsupported span of 24' is more than twice the length for SYP of that dimension. No matter, it is wrong and with that much deflection I bet the teeth in those plates are pulling loose in several areas.
    Yes Scott, they are pulling out! Here is an additional photo for you.

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  4. #4
    Join Date
    Feb 2009
    Location
    Southern Vancouver Island
    Posts
    4,549

    Default Re: Joist inquiry

    Your last pic shows exposed rafters and joists, presumably above the garage area. It looks like the original structure may have been built correctly with manufactured trusses. Is it possible that webs or uprights were cut to make room for storage above the workshop area?

    It needs repair. You have done your job by pointing it out as wrong.
    It can be fixed in a variety of ways, depending on what the new owner's needs are.

    Google span tables.

    John Kogel, RHI, BC HI Lic #47455
    www.allsafehome.ca

  5. #5
    Join Date
    Nov 2011
    Location
    Oregon, USA
    Posts
    333

    Default Re: Joist inquiry

    An easy and effective repair would be to span the nailer-plate joints with 8' 2 x 4s, after the sag is first (gradually) removed. Through-bolted to the originals. The 8' length should be enough to carry the maximum positive bending moment applied to the members. I'd suggest to the buyer to not trust the seller doing something on his own, as the results could be worse than what's there now.


  6. #6
    Join Date
    Mar 2012
    Location
    Lansdale, PA
    Posts
    876

    Default Re: Joist inquiry

    Quote Originally Posted by Greg Subick View Post
    Saw this in a detached garage that was built in the early to mid-eighties. Garage depth is 24' and joists used were two 12' 2x4's attached at their ends. Sagging has occurred with the storage above. Seller says, "well, okay, it's been like this for almost 30 years-what's the big deal?" My question is, what would the requirements be the joist size requirements over this span? I've included a photo of the garage for roof pitch visual as well as the joists. Thanks in advance.
    Work on terminology and providing proper information. Trusses are not joists and 24' long 2x4s means nothing when referring to trusses. Whether 2x4s were proper would depend upon the design of the truss. However, properly designed trusses should not be sagging more than maybe 1 inch. When looking at trusses make sure you look for damaged members or joints, or missing members. As someone pointed out, maybe the owner cut out some web members to make room for storage. Typical trusses (especially with 2x4 bottom chords) are seldom designed for any storage.

    BTW, when a seller says that has been like that for xx years, ignore them.


  7. #7
    Join Date
    Mar 2007
    Location
    Washington State
    Posts
    579

    Default Re: Joist inquiry

    Not sure from the photos but I would guess that it was built properly with engineered trusses. The problem is that they installed storage above, the extra weight has caused bowing and separation to develop at splices in bottom cords. Most likely this can be easily repaired by jacking up and installing additional bracing such as sistering over splices in lower truss cords.


  8. #8
    Join Date
    Feb 2010
    Location
    Wenatchee Wa
    Posts
    301

    Default Re: Joist inquiry

    Since they are trusses and if there is any damage then you will need an engineer or the truss manufacturer provide a repair. We all could design a repair but only an engineer or truss manufacturer is allowed to.

    Don Hester
    NCW Home Inspections, LLC
    Wa. St. Licensed H I #647, WSDA #80050, http://www.ncwhomeinspections.com

  9. #9
    Join Date
    Aug 2011
    Location
    Hercules, CA
    Posts
    158

    Default Re: Joist inquiry

    Based on the location of the splice (midpoint of the span), these trusses were probably not designed for storage loading on the bottom cord. When storage loading is included in the truss design, the bc splice will occur next to a panel point (point where web members connect to the bottom cord) as the plates are not approved to resist bending moment. Either remove the storage loading or provide a repair by a registered engineer.

    Thom Huggett, PE, SE, CBO

  10. #10
    Join Date
    Sep 2013
    Location
    alabama
    Posts
    4

    Default Re: Joist inquiry

    Is it possible that this was built with an open ceiling and these members are really just rafter ties?

    The 2nd picture makes it look like the "rafters" are also 2x4 dimensional lumber which would not be properly sized for the span - suggesting a truss roof as others have suggested. In either case there should not be any bending loads applied to the bottom chords/ rafter ties. Would recommend removal of the flooring that has been installed above these members at the least. If it appears that these were engineered trusses that have been modified, then it's going to need more help than just unloading.


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