Thread: Truss causing these bumps?

The 'bumps' in this roof are over the porch of this 5 year old house. There were three which ran parallel to each other, ranging in length from about 14 - 30 inches, and starting about 8 inches up from the eaves. I have shown a picture of the front of the house, just for orientation, the two close-ups show the 'bumps' which are not exactly 16" (nor 24", nor multiples thereof) apart.

When I lifted the starter strip I saw the roofing paper was wrinkled in line with one bump but I couldn't see far enough under the shingles to tell whether that wrinkle got worse and could have caused the bump. Doesn't seem likely. The sheathing felt solid on either side of the bumps. Couldn't see the area from the attic hatch (attic picture isn't looking at the specific area).

I think its just aesthetic at this point. Any ideas?

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Is the sheathing PLY or OSB ? I have seen this is PLY sheathing where for some reason the layers of PLY delaminate and form a "bump".

I agree, also panels installed without proper spacing between them will many times buckle up or down. Sometimes a dip next to a hump will make the hump look even worse.

Originally Posted by Clint White

Is the sheathing PLY or OSB ? I have seen this is PLY sheathing where for some reason the layers of PLY delaminate and form a "bump".

Hi Clint,
The sheathing is OSB. The bump seems to be about the width of 2x lumber.

I agree with the decking theory. Even if the truss was elevated, it won't cause the dips between the trusses.
Either improper spacing for expansion (no edge clips) or possibly scrap pieces that don't span for a minimum of three trusses. Maybe even ply turned the wrong direction... but you said OSB.
I think the most likely is installation without the proper edge gaps.

I agree, probably decking, could be from not allowing for spacing or could also be from improper nailing allowing the ends to lift.

Too sharp of deformations for trusses.

I've seen water-soaked plywood do that, but not OSB. Could it be a heavy icedam-type of underlayment that was not laid flat? Or the starter shingles might have been shoved too tight together, nailed at the ends before the middle.

Originally Posted by Peter Wigle

The 'bumps' in this roof are over the porch of this 5 year old house. There were three which ran parallel to each other, ranging in length from about 14 - 30 inches, and starting about 8 inches up from the eaves. I have shown a picture of the front of the house, just for orientation, the two close-ups show the 'bumps' which are not exactly 16" (nor 24", nor multiples thereof) apart.

When I lifted the starter strip I saw the roofing paper was wrinkled in line with one bump but I couldn't see far enough under the shingles to tell whether that wrinkle got worse and could have caused the bump. Doesn't seem likely. The sheathing felt solid on either side of the bumps. Couldn't see the area from the attic hatch (attic picture isn't looking at the specific area).

I think its just aesthetic at this point. Any ideas?

Swelling from condensation (freezing) in air restricted eave space where the decking (and trusses) meets and extends beyond the inside to outside wall cavity - between the perforated eave vent and the wall and the performated eave venting and the closed portion of the eave, causing nail pops, etc. This sensitive transition can be more of a problem in a location with even more extended eave/porch roof extensions and darker roof coverings in Northern Climates such as the porch pictured and cold strong prevailing winds.

Seems to be present only in those areas which extend beyond the wall plate and at the wall plate but short of the vented area of the overhang that area not sufficiently separated (warm below and cold above). Perhaps less than sufficient thermal break and isolation and less than and seal for moisture/vapor barrier possibly allowing vapor and heat to migrate from the below brick faced wall.

See no evidence of insulation chutes (insulation dams) being present, let alone extending beyond the insulation blanket level, and ventillation openings not being large enough for the overhang to keep it sufficiently cool/cold. What direction is the front of the home and this porch overhang facing? Is this home Northern or Southern Ontario?

Regarding your mention of truss spacing being greater than 16" OC but less than 24" OC, if the trusses were about 19-3/16" OC (more exactly 19.2" OC) thats an alternative design spacing in construction (why those diamonds are on your tape measure) which the trusses in question may or may not have been engineered to use (comes out to 5 trusses per 8 foot sheet goods).

(P.S. You might want to invest in some gutter guards or ladder bumpers.)

Peter,
When you lifted up the shingles you said that you saw roofing felt. Do you know if there was any water and ice shield put done. I would expect this to be standard in your area. With that said, I'm thinking it looks like the bumps could be from sloppy overlap of the water and ice shield or perhaps the trusses did not line up correctly here (resulting in the roof bumps). In any case it doesn't look to bad or problematic.

Originally Posted by Robert Dalga

Peter,
When you lifted up the shingles you said that you saw roofing felt. Do you know if there was any water and ice shield put done. I would expect this to be standard in your area. With that said, I'm thinking it looks like the bumps could be from sloppy overlap of the water and ice shield or perhaps the trusses did not line up correctly here (resulting in the roof bumps). In any case it doesn't look to bad or problematic.

Robert I think your on the right track and everyone else is wrong. I would suspect the roof has ice and storm under the shingles. I actually had this happen on a brand new house I built. The ice and storm buckled, inturn causing the shingles to buckle. It's not from a sloppy overlap either, most ice and strom manufactures recommend cutting the material into no longer than... I think 12' pieces? Since this happened, I have noticed certain brands tend to expand more than others, and stay away from those. We also usually split up the long runs also. The manufacturer of the shingles actually paid us to replace the roof as they supplied both the ice and storm and shingles.

Randy
By the way how do I contact Brian? And who is he?

Originally Posted by Door Guy

By the way how do I contact Brian? And who is he?

Randy,

Brian is the owner of this site, the administrator, and can be contacted by clicking the 'Contact Us' link at the bottom of the page.

Simply ask Brian to change your user name to your real name, he is happy to do so.

No joint clips coupled with moisture.

If the trusses are not at proper spacing 16-24" and OSB is not fastend per specification or not correct thickness that will cause humps. I found this on a number of houses in Florida. OSB Board is not as ridged as ply.

The shingle are stacked and not stairstepped. This allows the joints to line every other row and the since more water is at the bottom rows moisture may be geting to the felt and when that happens the celluose swells and then wrinkles in the felt.