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  1. #1
    Ravi Appan's Avatar
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    Default Ridges in roof line

    On a new house that is being constructed, I am able to see ridges in certain lighting conditions. Under other lighting conditions, the ridges are not as visible. Enclosing a picture here for reference. Could it be that the OSBs were not spaced properly underneath the shingles? Does this call for a re-do of the decking and the shingles?

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  2. #2
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    Default Re: Ridges in roof line

    This is most likely the result of the underlayment not being installed correctly or having gotten wet prior to the shingle installation. The wrinkles telegraph through the shingles with the resulting nice appearance.

    If underlayment has been exposed even just overnight, moisture from dew should be allowed to completely dry before shingling over. If this does not happen, the moisture will become trapped beneath the shingles. Wrinkling can telegraph through the shingle and make a good shingle job look terrible. The worse part is that the job can look good when you leave in the evening but the wrinkles can reappear the next morning for everyone to see.

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  3. #3
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    Default Re: Ridges in roof line


  4. #4
    Ravi Appan's Avatar
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    Default Re: Ridges in roof line

    If it is moisture trapped in the underlay would it not evaporate over time? Also the predictable pattern on how equidistant some of the ridge line is seems to make me suspicious of the decking expansion.


  5. #5
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    Default Re: Ridges in roof line

    The symmetrical pattern suggest improper spacing of the roof decking.
    Insufficient gap between and when heated bucking occurred.

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  6. #6
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    Default Re: Ridges in roof line

    I have to agree with Billy... Also if this is a truss system you will almost always see this type of pattern on a roof.

    At this stage not much can be done about it. You could ask the builder to remove the roof, decking and all and start over but it could look worse than what you have now..... Also the builder would most likely tell you to go and pound salt!

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  7. #7
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    Default Re: Ridges in roof line

    Quote Originally Posted by Billy Stephens View Post
    The symmetrical pattern suggest improper spacing of the roof decking.
    Insufficient gap between and when heated bucking occurred.
    I agree, but there is something which might be just as important - the roof sheathing panels are not staggered.

    Yes, they can be installed using a stack bond pattern (not staggered), but the trusses require more blocking and bracing.

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  8. #8
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    Default Re: Ridges in roof line

    Ravi,
    Get use to seeing this. It is a function of the truss system and the use of OSB..
    The engineering is there and the roof will work, just not look as you may want it to.
    The trusses will twist and move as temp and humidity changes as does the OSB (probably used).
    Blocking can make the trusses more rigid but that is more time and material that is not absolutely required.
    The divergence from 5/8 CDX to 1/2 OSB is another factor added to the equation.
    It is more than likely an appearance issue and not a defective construction issue.
    I still dislike the appearance even if it is done correctly (by code and engineered design).


  9. #9
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    Default Re: Ridges in roof line

    If this is a truss roof system then it is the trusses telegraphing through......hip trusses are hard to place correctly and sometimes they are not built exactly right. You would be amazed at how field conditions can effect mathematical truss or rafter calculations. See how the lines go all the way to the hip.....plywood is usually staggered so it is not the sheathing.


  10. #10
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    Default Re: Ridges in roof line

    I had seen the the same issue several years back and at that time researched it. I found a reference to a possible cause by, I believe, the wood products council or the APA (plywood association), I don't recall and don't have a copy of it today.

    In essence it said that if the installer of the plywood decking does not stand squarely on the truss member when fastening the plywood, it may flex and be fastened in a sagging position. Thus the visible rafter line as light glances across the roof field. Not visible in direct light.

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    Default Re: Ridges in roof line

    Quote Originally Posted by Ravi Appan View Post
    On a new house that is being constructed, I am able to see ridges in certain lighting conditions. Under other lighting conditions, the ridges are not as visible. Enclosing a picture here for reference. Could it be that the OSBs were not spaced properly underneath the shingles? Does this call for a re-do of the decking and the shingles?
    Ravi,

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  12. #12
    Dennis Webber's Avatar
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    Default Re: Ridges in roof line

    Quote Originally Posted by Ravi Appan View Post
    On a new house that is being constructed, I am able to see ridges in certain lighting conditions. Under other lighting conditions, the ridges are not as visible. Enclosing a picture here for reference. Could it be that the OSBs were not spaced properly underneath the shingles? Does this call for a re-do of the decking and the shingles?
    I'm going to disagree with the commenter's on this. I've seen this before many times, and I think I know exactly what's causing it.

    When a worker nails down a sheet of OSB to the trusses/rafters, he was standing on the OSB in mid-span (between the trusses). As he nailed it down, he nailed his body weight deflection into place, causing the OSB to permanently sag between the trusses while remaining higher at the trusses. Crates a "wavy" effect.

    The correct way to attach decking is to stand over the trusses when nailing down sheets of decking. The workers here were either lazy (as it does take more effort to straddle the spans) or stupid of what they were doing. Perhaps a combination of both.


  13. #13
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    Default Re: Ridges in roof line

    Quote Originally Posted by Dennis Webber View Post
    I'm going to disagree with the commenter's on this. I've seen this before many times, and I think I know exactly what's causing it.

    When a worker nails down a sheet of OSB to the trusses/rafters, he was standing on the OSB in mid-span (between the trusses). As he nailed it down, he nailed his body weight deflection into place, causing the OSB to permanently sag between the trusses while remaining higher at the trusses. Crates a "wavy" effect.

    The correct way to attach decking is to stand over the trusses when nailing down sheets of decking. The workers here were either lazy (as it does take more effort to straddle the spans) or stupid of what they were doing. Perhaps a combination of both.

    Maybe if the roofer is 400+lbs and jumping as he nails..


  14. #14
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    Default Re: Ridges in roof line

    Quote Originally Posted by Bob Knauff View Post
    I had seen the the same issue several years back and at that time researched it. I found a reference to a possible cause by, I believe, the wood products council or the APA (plywood association), I don't recall and don't have a copy of it today.

    In essence it said that if the installer of the plywood decking does not stand squarely on the truss member when fastening the plywood, it may flex and be fastened in a sagging position. Thus the visible rafter line as light glances across the roof field. Not visible in direct light.
    I agree with Bob. May have been installed while standing on the center of the board between the trusses...or perhaps they used warped boards that were sitting outside in the rain too long...

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  15. #15
    Dennis Webber's Avatar
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    Default Re: Ridges in roof line

    Quote Originally Posted by Garry Sorrells View Post
    Maybe if the roofer is 400+lbs and jumping as he nails..
    Not really. I've done hundreds of inspections in manufactured housing and industrialized construction and have seen these in almost every plant and state I've inspected in. It's very common to find it.

    It doesn't really seem to matter what a worker weighs, whenever he stands between the supports and staples or nails the deck in place, he nails the deflection in the deck caused by his body weight. Keep in mind that roof decking is only 3/8" or 7/16" thick and deflects quite easily. Obviously, the heavier the person doing the decking, the greater the deflection and the more waviness in the roof line.


  16. #16
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    Default Re: Ridges in roof line

    Quote Originally Posted by Dennis Webber View Post
    I'm going to disagree with the commenter's on this. I've seen this before many times, and I think I know exactly what's causing it.

    When a worker nails down a sheet of OSB to the trusses/rafters, he was standing on the OSB in mid-span (between the trusses). As he nailed it down, he nailed his body weight deflection into place, causing the OSB to permanently sag between the trusses while remaining higher at the trusses. Crates a "wavy" effect.

    The correct way to attach decking is to stand over the trusses when nailing down sheets of decking. The workers here were either lazy (as it does take more effort to straddle the spans) or stupid of what they were doing. Perhaps a combination of both.
    Isn't that what Bob said earlier?
    It would be easy enough to determine if this was the cause with a framing square and tape measure in the attic. It sounds likely.

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