Bending/Warped roof rafters

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Old 09-06-16, 10:34 AM
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Bending/Warped roof rafters

Hello, new to this forum and hoping to grab some answers. I own a dutch colonial (gambrel style house) built in 1977. I've owned the house for 11 years. Maybe it's my old age and worrying about my kids but the roof has always had a low spot in the plane of the roof in the back. It's like the roof rafters in that area are warped or bending. I've had a home inspector and a carpenter look in the attic and no cracks or structural issues can be observed with the rafters. In fact, when in the attic, you can't even tell there's a low spot. I've had the roof re-shingled and the contractor said there were no issues. Both the carpenter and the home inspector said the rafters were most likely installed upside down causing the bowing. No other issues with the roof...no leaks, nothing. No issues with the foundation or any other portion of the house near that roof section. In that area where the rafters are warped, the soffit is being raised. Prior to reshingling, there were two layers of shingles. I also recently had insulation added to the attic as well as soffit baffles; the soffits were previously clogged. So, everything points to the history here as causing the sagging...two layers of shingles, poor ventilation as contributing factors to the sagging/warping. Since increasing the ventilation, the soffit appears to be have warped even more (bent upwards). I've called an engineer and they want $750 bucks to assess the problem (or tell me everything is fine). Again, 11 years, lots of snow, no problems. Should I be concerned or is there a reasonable explanation? Just want some opinions before pulling the trigger on an engineer. Thanks!
 
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Old 09-06-16, 10:39 AM
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Welcome to the forums!

Is this something that would show up in a pic? http://www.doityourself.com/forum/el...-pictures.html
With both the inspector and carpenter giving it an onsite thumbs up I'd be inclined to believe it's not a big issue.
 
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Old 09-06-16, 11:10 AM
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Yeah, i would probably agree. Just paranoid I guess. What would cause a dip like that? The roof is slightly wavy which makes sense given the age of the house...roofs get wavy, I get it. But why in that section would it be more pronounced? On that side of the roof, there was a different shingle than on the front and I think only the back had two layers of shingles...weird. Someone trying to save some money I guess. I'm wondering if taking the extra weight off and opening up the ventilation has cause some shifting. We even had about 2 feet of packed snow on the roof in 2015...the most snow ever on the roof...no issues. Anyway, here are some pics from the inspection report...Name:  Location of dip.jpg
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Size:  17.9 KBName:  Dip in roof.jpg
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Old 09-06-16, 11:15 AM
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A gambrel roof is a barn style roof. That is not a gambrel roof.

The roof is probably sagging from being overspanned, under built, overloaded, or a combination of all 3. Being underventilated wouldnt help. If you put a string line on the ridge from end to end and it is sagging, that is the problem... and thats something that can't be corrected without reframing the roof.
 
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Old 09-06-16, 11:41 AM
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The span between rafters is one foot. Look to be 2X6. In the front of the house, there are double rafters side by side. The section in the pictures is the only section with a dip aside from some minor waves in the sheathing...probably a four by four section and maybe three rafters. All other sections of the roof are straight. I wouldn't think 2X6s spanned one foot would be overspanned but I'm no builder. The ridge is perfectly straight by the way. If the ridge was sagging, I'd be very worried! The roof was severely under ventilated...I unplugged the soffit vents, added insulation, and added a ridge vent. Really my question is if the rafters in this section were installed with the crown facing down, is this a plausible explanation? It seems to me like it would be considering all the other facts.
 
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Old 09-06-16, 11:45 AM
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The span that X was referring to is the length of the rafter between supports, possibly the distance between the ridge and the exterior wall. It is plausible that some of the rafters were set with the crown down and that could result in a dip.
 
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Old 09-06-16, 11:54 AM
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If the span was too great then wouldn't the entire roof be sagging? So that's probably not the case...the crown being upside down is the only cause left that I can think of that makes sense.
 
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Old 09-06-16, 11:59 AM
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Each board doesn't necessarily have the same strength as the next and how the house is framed might put more stress on one joist/rafter than another. Having the crown down makes it more noticeable. Have you been on the roof to make sure the area in question feels solid? If it doesn't give or give more than the rest of the roof - there really isn't anything to be concerned about.
 
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Old 09-06-16, 12:08 PM
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Lots of people of been on the roof myself included...the roofing contractor walked up there, twice I've had snow shoveled off the roof, of course had the roofers up there and they found no issues. So I've had two carpenters stand in that spot to do just that...make sure it's solid. No rot or anything was found after the tear off of the old shingles. Solid as can be...guess it's just cosmetic at this point.
 
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Old 09-06-16, 12:53 PM
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Really my question is if the rafters in this section were installed with the crown facing down, is this a plausible explanation?
If it has ALWAYS been that way, and the ridge does not have a dip in it, that's a possibility. If you haven't got up there to eye the ridge, then....

It might be a coincidence but it's right over the window... one would assume they used a header there and that the top plate isn't dipping. From what I gather, you are saying it's straight across the rafters near the ridge and near the top plate but the sag is just a smallish 4x4 area in the center of the span.
 
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Old 09-06-16, 01:12 PM
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exactly...a smallish 4x4 area in the center of the span...everything else is straight...no other issues with the roof.
 
 

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