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  1. #31
    Join Date
    Apr 2008
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    SF Bay Area (East Bay)
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    2,177

    Default Re: Doubling rafter around skylight opening

    Quote Originally Posted by dgbldr View Post
    Same here. I can drill a hole in the middle of the rafter, but notching would raise eyebrows.
    And that's the catch- you're required (when required, see the exemption in post #24 above) to have 1" of clear space at the top, for the entire bay's width. By that definition, you'd need to cut, what, a 14 1/2" slot along the top of the double rafter? Maybe more since it's perpendicular to the flow up the bay?

    I think you could get it approved by an engineer, hey, maybe you'd triple the rafter. But it'd need a stamp. Again, I'm glad I work in an area where the delta T is so minimal...
    “It is difficult to get a man to understand something, when his salary depends on his not understanding it.” - Upton Sinclair

  2. #32
    Join Date
    Jun 2004
    Location
    Georgia
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    1,809

    Default Re: Doubling rafter around skylight opening

    Quote Originally Posted by dgbldr View Post
    Same here. I can drill a hole in the middle of the rafter, but notching would raise eyebrows.
    So you cut one rafter and replaced it with 2 shallowly notched ones. Why should this raise eyebrows?

  3. #33
    Join Date
    Dec 2005
    Location
    Michigan
    Posts
    7,472

    Default Re: Doubling rafter around skylight opening

    Quote Originally Posted by charles View Post
    So you cut one rafter and replaced it with 2 shallowly notched ones. Why should this raise eyebrows?
    If you notch a rafter, you need to prove the weakened rafter is sufficient, whether it's by itself, a doubler, or whatever function it serves. That requires engineering.

    You don't get to decide that 2 notched rafters are equivalent to one un-notched one. Only your engineer can decide that.

  4. #34
    Join Date
    Jun 2004
    Location
    Northwest lower MI
    Posts
    373

    Default Re: Doubling rafter around skylight opening

    As long as the notch doesn't exceed the prescriptive requirements no problem.

    R802.7.1 Sawn lumber. Notches in solid lumber joists, rafters, blocking and beams shall not exceed one-sixth of the depth of the member, shall not be longer than one-third of the depth of the member and shall not be located in the middle one-third of the span. Notches at the ends of the member shall not exceed one-fourth the depth of the member. The tension side of members 4 inches (102 mm) or greater in nominal thickness shall not be notched except at the ends of the members. The diameter of the holes bored or cut into members shall not exceed one-third the depth of the member. Holes shall not be closer than 2 inches (51 mm) to the top or bottom of the member, or to any other hole located in the member. Where the member is also notched, the hole shall not be closer than 2 inches (51 mm) to the notch.

    Exception: Notches on cantilevered portions of rafters are permitted provided the dimension of the remaining portion of the rafter is not less than 4-inch nominal (102 mm) and the length of the cantilever does not exceed 24 inches (610 mm).

  5. #35
    Join Date
    Apr 2008
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    SF Bay Area (East Bay)
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    2,177

    Default Re: Doubling rafter around skylight opening

    Quote Originally Posted by charles View Post
    So you cut one rafter and replaced it with 2 shallowly notched ones. Why should this raise eyebrows?
    Well, you cut one and replaced it with the two new notched sisters, but you also notched the two existing rafters on the edge of the opening.

    I'm not saying it couldn't work, but you'd need an engineer's stamp out here.
    “It is difficult to get a man to understand something, when his salary depends on his not understanding it.” - Upton Sinclair

  6. #36
    Join Date
    Apr 2008
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    SF Bay Area (East Bay)
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    2,177

    Default Re: Doubling rafter around skylight opening

    Quote Originally Posted by Roger P View Post
    As long as the notch doesn't exceed the prescriptive requirements no problem.

    ... shall not be longer than one-third of the depth of the member and shall not be located in the middle one-third of the span...
    I know in my particular case I'd be breaking that rule; I'd speculate that most skylight openings would have at least one end in the middle third of a rafter span, and I'd also think 1/3 the depth would be too short of a notch.
    Last edited by kfc510; 06-21-2014 at 09:50 AM.
    “It is difficult to get a man to understand something, when his salary depends on his not understanding it.” - Upton Sinclair

  7. #37
    Join Date
    Sep 2004
    Location
    down the shore
    Posts
    2,217

    Default Re: Doubling rafter around skylight opening

    I would think the only sure way notching would work in that situation is if you could demonstrate that the next size smaller rafter would be sufficient for the span - ie If you have 2x10 rafters where 2x8's would do, then you could notch 1 1/2" in the middle third.

    But to have a roof overbuilt like that likely isn't going to be the case in existing construction.

  8. #38
    Join Date
    Apr 2008
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    SF Bay Area (East Bay)
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    2,177

    Default Re: Doubling rafter around skylight opening

    It is a potential solution though, I appreciate it for that. So you need to get an engineer's letter or stamp on a detail, that's not the end of the world.

    Maybe you have to triple the edge rafters or use LVL's to satisfy your engineer, it'd still be worth it if it's the only way to vent the underside of the sheathing (and you needed to).

    You'd also have to integrate your baffles to that edge vent.
    “It is difficult to get a man to understand something, when his salary depends on his not understanding it.” - Upton Sinclair

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