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Thread: Moving Attic’s Collar Ties Higher

  1. #1

    Moving Attic’s Collar Ties Higher

    https://postimg.cc/gallery/dZxQZ1L

    My attic has a finished floor and has collar ties located about 2/3 of the way up. It is my impression that I can relocate these collars ties all the way at the top to open up walking space in the attic. It’s my understanding that the ceiling ties below the finished floor are countering the forces of downward/outward pressure at the walls of the house, while the collar ties are countering upward lift, and they can be safely located all the way at the top of the attic instead. The house next door to mine (same design) has collar ties at the top as I describe, resulting in a walkable attic space.

  2. #2
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    Those collar ties are giving some support to the midspan of the rafters & removing them will probably require sistering the rafters. I think that would be well worth doing to gain the usable space. But I'm no authority.

  3. #3
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    Several points to make here.
    1. Those are not collar ties, they are rafter ties. Collar ties go near the top.
    2. You can’t omit those on many roofs but especially on that one. Looks like you have 2x4 rafters. That knee wall will just lean over without that rafter tie in high wind event or just the weight of the roof.
    3. Older building codes permitted rafter ties to be installed very high above the top wall plate, as much as two-thirds the distance between the top plate and the ridge. The 2012 IRC now limits this to one-third the distance between the plate and the ridge. For example, if an unfinished garage has a roof with a 4:12 slope and the roof span is 24 feet, the rafter ties should be located no more than 16 inches up from the plate, according to modern building standards.
    4. #3 is from this article:
    https://www.nachi.org/collar-rafter-ties.htm
    5. Houses with factory made trusses can’t be compared to stick built.

  4. #4
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    To me the rafters look like a mix of 2x4 an 2x6. Yes those are rafter ties not collar ties.
    George

    Making sawdust regularly, occasionally a project is completed.

  5. #5
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    For the types of changes you're talking about you want to contact a structural engineer. If this get this wrong it could mean nothing, or it could mean the collapse of the building's roof with damage to the occupants and anything stored inside. Structural engineers aren't cheap, but they don't cost the moon, and they will be able to give you the correct answer to this question.

  6. #6
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    snow load, wind loads, sesmic loads, (location) roof material type. Look into simpson ties to attach the rafters to the ridge beams,
    I am in California but I do not have to design for 200 pound/sq foot snow loads here like some parts of the state do
    Bill D.

  7. #7
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    This is very much an engineering problem and it's most likely that they are sized and placed where they are for structural reasons. You need an expert (engineer) to examine the situation...preferably with the original building plans if available...to determine if the change you want to make is possible and within both code and the laws of physics.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  8. #8
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    I helped a friend do it on a garage. They weren't prebuilt trusses so I doubt any engineering went into it. What we did was replace them one at a time with a scissor truss. Plenty of screws and glue. When finished he could walk down the center without ducking. He must have guessed correctly as it's still standing but like others have said, if you get it wrong you will wish you had left it alone.

  9. #9
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    Scissor trusses are designed to provide similar benefits to rafter/collar ties while providing additional headroom. I'm sure you'll agree, Alex, that doing the replacement wasn't "fun" however.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  10. #10
    Scissor trusses seem like a potential solution. I’m wondering what was done at the house next door, because it is the exact same plan as mine, but no rafter ties. It’s insulted and finished with paneling so would be hard to determine what was done with just a quick glance. I’m only assuming the previous owners of it followed code and didn’t just haphazardly remove the rafter ties to open up the space. FYI the house next door is owned by my family, so I have access to the attic if it would provide any help in regards to my situation in my attic?

  11. #11
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    Quote Originally Posted by Dexter McLaughlin View Post
    I’m only assuming the previous owners of it followed code and didn’t just haphazardly remove the rafter ties to open up the space.
    You know what "they" say about "assumptions"... There are a lot of folks who do modifications or get a "handyman" to do modifications that do not always follow code/requirements. I'm not say9ing that is the case here'; just that it's a possibility.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  12. #12
    Quote Originally Posted by Jim Becker View Post
    You know what "they" say about "assumptions"... There are a lot of folks who do modifications or get a "handyman" to do modifications that do not always follow code/requirements. I'm not say9ing that is the case here'; just that it's a possibility.
    Jim ,Jim,Jim ,you're changin' the story ...or you haven't listened to enough motivational speakers . It's " when you
    assume...."you make an 'ASS of U and ME"

  13. #13
    I really appreciate the opinions and advice offered so far, and I hate to question any of you, but it is possible you are mistaken about the necessity of these? I’ve visited 5 of my neighboring homes (with permission, lol) and none of them have these. The houses of this neighborhood were all built by the same company with identical plans. I’m not saying it’s impossible that all the neighboring houses simply made hazardous decisions to remove them without regard for physics, but I’m wondering if I took some more precise photos, or provided photos of the other attics, would that help at all?

  14. #14
    Put up some dimensions. Rafter size, spacing, rafter span, are the floor joists parallel or perpendicular? Everything. Is the knee wall staying? Could you put in a purlin with a kicker? Houses have accepted framing standards. I don't think rafter or collar ties are engineering dilemmas.

  15. #15
    Join Date
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    Again, we need an idea of local conditions. do you get snow loads? Do you have to clear snow off the roof. Any huricanes, tornadoes. is roof clay tile or slate. That roof, as is, will not support 200 pounds per square foot of snow so it would not be standing in parts of California. Metal ties at the ridge will reduce the need for collar ties. Or install a big ridge beam to reduce the span.
    Bill D

    https://www.mercurynews.com/2011/03/...nd-the-houses/

    https://www.tahoedailytribune.com/news/another-roof-collapses-near-lake-tahoe/
    Last edited by Bill Dufour; 01-24-2021 at 10:34 AM.

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