How would you report this dip / ridging

[Michael Thomas]

Suggestions as to how to report this roof:

1) Tear-off in 2003.

2) No ladder access at east eave as fence at lot line was too close.

3) South side of roof was observed from east and west rakes (roof was too wet to walk).

4) Two low-profile passive vents just below ridge per side, no soffit venting.

5) Entire underside of roof in attic finished with 3/4" wood paneling, no evidence of current water intrusion, no access behind knee walls. I didn't start stretching strings or anything, but I did not observe any distortion at the interior below the exterior defects.

Pictures:

A. East side of building, satellite dish serves as reference point in later pictures.

B. South side of roof looking east from west ridge.

C. Close up from same location showing dip to west of east rake.

D. Same roof, looking west from east rake, showing approximately 1-1/2 inch (at highest point) of "ridging" about 15 feet west of the east rake along what might be a rafter location or sheathing seam.

E. Finally, the one place where I could get a ladder to the eaves, at the front (west side) of the front porch, showing what appears to be 3/4 inch plywood used as sheathing and installed above the drip edge, with the result shown.

I'd like to say something more useful than "Get a roofer up there to determine what's happening" - after all, some roofer did the existing job in the first place - but don't know quite what that would be...

[Michael Greenwalt]

Looks like they forgot to use spacers when installing the sheathing.

[Jerry Peck]

1) Roof covering needs to be torn off.

2) Rood sheathing either needs to be properly re-nailed to the roof framing or deformed sheathing which will not properly re-nail flat needs to be replaced.

It looks to be like the rafters (assuming rafters, not trusses, but same would apply to trusses) were spaced too far apart, allowing the roof sheathing to be over-spanned ... or ... the roof sheathing was simply too thin and not strong enough to properly and adequately span from rafter to rafter.

[Billy Stephens]

It looks to be like the rafters (assuming rafters, not trusses, but same would apply to trusses) were spaced too far apart, allowing the roof sheathing to be over-spanned ... .
.
Or the crowns on the rafters were excessive, with some installed Crown Down, some installed Crown up.

[Gunnar Alquist]

One of your pics shows 3 ply and it looks like 1/2". That is more susceptible to sagging and deflection than a 5 ply. I see that periodically.

[Markus Keller]

The house probably has 2x4 rafters. The bows in pics 2&3 would be typical of old 2x4 rafters. If they did a tear off in 03 the roof probably had 3 layers on it for a long time.
Pics 4&5 however indicate a sheathing problem. Maybe the ply or felt got rained on during install, no spacing on ply, #30 felt instead of #15, trapped moisture.
They could open a few exploratory holes in the attic to take a look. Unfortunately without taking some shingles off it's all a guess.

[Jerry Peck]

#30 felt instead of #15,

Markus,

That part has me stumped ... 30# felt is better than 15# felt, just heavier, but I can't imagine that the difference would cause anything like that as the difference in relation to the total weight of the roof covering system (including shingles) is minimal. Besides, if old shingles were removed (210# per square) and replaced with new shingles (170# per square) the roof covering system would be lighter, overall.

[Bud Butczynski]

I started out as a roofer and have seen some pretty ugly stuff. Do you have any images from the crawlspace? The profile of the leading edge and curled seams of the plywood may be an indication that the sheathing was installed over the existing shingles. Don't laugh, I've seen it.

[Michael Thomas]

No part of the underside of the roof structure is visible from the interior, which is finished in knotty pine T&G planks - it's not going to be easy to start punching holes up there. Judging from what I can see at the rakes, it's unlikely the sheathing in on wood shingle or shake, but who knows?

The only other clue I've got is this this shingle on the opposite (north) side of the same (east) end of the roof, shot from the ground with my DMC-TZ1 from around 150' away - there is only a very limited sight-line to this side of the roof from the ground and not enough space at the north side of the building to get a ladder up unless you tie it off to the structure to prevent it going over backwards - you would be going almost straight up.

[Ron Bibler]

This looks like it has some movement going on. Q. how is the foundation doing, interior walls/ceilings and the windows and doors. is the structure racking. how is the siding and trim work doing. I understand a roof with a swayback. but buckling shingles.

A structure may fail to support its load when a connection snaps, or it bends until it is useless, or a member in tension either pulls apart or a crack forms that divides it, or a member in compression crushes and crumbles, or, finally, if a member in compression buckles, that is, moves laterally and shortens under a load it can no longer support. Of all of these modes of failure, buckling is probably the most common and most catastrophic.

Buckling (http://mysite.du.edu/~jcalvert/tech/machines/buckling.htm)

Best

Ron

[Eric Barker]

Holy cats are there a lot of assumptions flying on this one.

Michael, To answer your question. Why not state what you saw - significant deviations in the plane of the roof and warped decking. On a separate issue, and possibly related, poor ventilation details (assuming that since you could not see the underside of the roof it was finished off with vaulted ceilings).

I would be hesitant to lead a client towards a particular cause for the conditions. That I'd leave to a top drawer roofing contractor. But of course you and I know that that is likely to be the last person who is called to save the day. Standard operating procedure.