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Thread: Strengthening up ceiling rafters in garage

  1. #1
    DIY Junior Member 1320ms's Avatar
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    Oct 2009

    Default Strengthening up ceiling rafters in garage

    Doing some work in my detached 2car garage, the current ceiling construction is 2x4 rafters spaced 24" oc

    The garage is roughly 22ft x 26ft (wall with garage door is 22ft across)

    Previous owner put some 15/32 OSB up in the rafters for storage, I've got a few things up there but I'm hesitant to add much weight to it without strengthening up everything first.

    Here's a bad picture of the current ceiling structure..

    I do a lot of work on cars in this garage, and usually have a car in the garage sideways in order to get around to all the sides - so adding a support beam in the middle is not an option. What I'm debating on is custom ordering some 2x4's to go the entire 26ft span and sistering the rafter, or running a 4x6 beam across the 22ft span, and supporting that with a 6x6 beam up against each side wall. Also considering removing the current osb and sistering the 2x4 rafters with 2x6's or 2x8's, although I'd have to trim them at the top plate to fit with the angle of the roof

    Any suggestions? If at all possible id rather avoid having any beams as with all the tools its a tight fit in this garage as is.
    Last edited by 1320ms; 07-11-2012 at 08:35 PM.

  2. #2
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Yakima WA


    I would talk to a company that does custom trusses. Every city has these companies. I don't know what can be retrofitted, but these are the folks that can give you any options.

  3. #3
    DIY Senior Member TJanak's Avatar
    Join Date
    Sep 2009
    South TX


    Like Gary said, check into trusses or consider a glulam beam. Dimensional lumber, even sistered 2x12's does won't give you much support over a 22' span. When I took out a wall in my living room I originally had a 26' span. I could get a glulam beam for several hundred dollars that would go the full span. I also remember something about 3 2x12's glued and screwed but the glulam would have been easier. I used a local company but I believe even Lowes and HD can spec and order glulam beams.

    I ended up putting in two posts so my longest span was only 12'.

    When I need a precise measurement of something I often use the highly technical method of eyeballing it.

  4. #4
    In the Trades Gary Swart's Avatar
    Join Date
    Sep 2004
    Yakima WA


    I would just add this note. Even professional building contractors and carpenters do not build their own trusses. You can't just stick in some 2 by braces where it looks like it might help. Trusses are engineered using the building specs. Ideally of course, this is done before construction, but an engineer in a truss building company can tell you what, if anything, can be done to beef up what you have.

  5. #5
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona


    Those "nailing plates" indicate that this IS an engineered truss, however they were designed for a specific load but you do not know how much overdesign they used. You would have to know the characteristics of the wood actually used to compute their capacity. 24' 2x4s would add little to the strength.
    Licensed residential and commercial plumber

  6. #6
    DIY scratch-pad engineer leejosepho's Avatar
    Join Date
    Nov 2006
    200 miles south of Little Rock


    If I was convinced the roof structure was overloaded, wanted to not have to change that and could deal with a post in the door opening, I would likely make my own glulam beam with four 2x8s stacked flat, glued-and-nailed (with about 1" crown) and with a 2x6 on each side (centered overall, and with the 2x6 butt-joints staggered) ... then jack it into place and put a post at each end.

    Something else that can help is to be sure there is only one layer of shingling on the roof.
    Last edited by leejosepho; 07-19-2012 at 09:04 AM.
    "Great minds discuss ideas, average minds discuss events and small minds discuss people." --Eleanor Roosevelt

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