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Old 12-20-2013, 09:17 PM   #16
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Drywall Cracking Under Snow Load

Gary or others - any input on the collar tie installation height to best help with these issues?


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Old 12-21-2013, 05:26 AM   #17
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Drywall Cracking Under Snow Load

You need an answer from a framer---I suggest you start a framing thread---the carpenters seldom look into this forum---Mike----
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Old 12-21-2013, 07:23 AM   #18
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Drywall Cracking Under Snow Load

Collar ties are normally installed 1/3 of the way down from the peak to the joist, as Oh Mike previously indicated. The purpose of collar ties is to equalize uplift pressure on the roof during high wind events, so they are not likely to improve your particular problem, but they are supposed to be installed, and they won't hurt anything.
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Old 12-21-2013, 10:46 PM   #19
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Drywall Cracking Under Snow Load

Sounds a lot like this, from David Utterback; "
Rafter ties do not have to be at ceiling height to be effective, but they must not be placed any higher than the lower third of the roof pitch. In other words: Measure vertically from the outside wall's top plate to the bottom of the ridge, and place the rafter ties within the lower third of that measurement. Once they get above that point, they lose their most effective leverage.
I've seen builders compound their mistakes when they try to use rafter ties as ceiling joists in semivaulted ceilings. For maximum headroom or aesthetic balance, they place the rafter ties halfway up the roof pitch, near the center of the rafter span where they're too high to be an effective tie. Applying the insulation and the drywall greatly increases the load on the rafters at their most critical point: midspan (what engineers call the maximum bending moment). This added load can cause the rafters to sag, pulling the ridge down and also pushing the exterior walls outward." From; http://myconco.com/ComEngProb.html

I doubt they used any bolts on the rafter/joist connection; pp.7; https://docs.google.com/viewer?a=v&q...WvZygC-vGi-JoA

As in Fig. 10A, but the joist are rafter ties; https://docs.google.com/viewer?a=v&q...RMyCq7zQ737mAg

They may have put them too high, measure the height of the ceiling to top of a window inside; go outside and measure the window to top of wall or soffit block- if soffit isn't dropped.

PS. My post 5 on collar ties....
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Old 12-22-2013, 01:06 PM   #20
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Drywall Cracking Under Snow Load

Retaping isn't going to help. The drywall should have been floated both sides of those cracks you're seeing to minimize cracking, but some framing issue is behind it all.


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