Roof Deck Seams Visible - What's Wrong?

Saw this yesterday (11/17) on the home I was inspecting, and several other homes around it. Brand new construction. I’ve seen this sort of thing before, but not this visible nor widespread. The decking is 7/16" OSB with rafters 24" OC. Location is central Texas. My guess is that it rained while the decking was exposed, and the edges all swelled up. OSB swells when it gets wet, but does not subsequently shrink back after it dries. Some of these ridges are 3/4" proud of the surface. Will this prematurely wear the shingles? What is your take on this, and what should be done?

Oh yeah … I forgot to mention that H-Clips were properly installed.

How was the attic ventilation and was the decking “bouncy” ?

Attic ventilation was fine (plenty of soffit & static vents). Deck was solid. This is a brand new home.

I wouldn’t buy it like that. I think you are likely correct that the shingles will wear. Also it looks like crap cosmetically. I’d write it up basically saying what you said and let the buyers make their own decisions. Bad move on the roofers part to leave exposed sheathing in a rain storm…

Do you have any photos of the swollen edges from inside the attic. A 3/4 inch deflection is pretty significant. I would be surprised if the shingle manufacture’s warranty would honor this if in the event the roof fails as it was installed improperly over degraded surface decking material. Also note that the swollen edges over the trusses are the nailing points which when the edges are already damaged (swollen from the water exposure) further weakens the integrity of the roofing structure. Water damaged OSB just comes apart / crumbles when anyone tries to used fasteners on it. Roofer (and the builder) ought to have their heads examined for going ahead and roofing over degraded decking. Just asking for a lawsuit.

I see this all the time. It is one of my pet peeves. Builders around here (SE MI & NW OH) refuse to cover roofs during construction. They tell homebuyers that this is “normal”. I tell my customers that it may be normal for the builder but it still isn’t right!

The problems are not only with roof decks. I see a lot of damaged sub-floors too. This is one of the reasons why home inspection is still a growing industry.

Those are definitely swollen edges on that OSB.

The builder should be forced to re-do their work.

Was those pics taken in the morning? If so go back in the afternoon…betcha can’t see them then :wink:

If this is new construction, it should point blank not be acceptable for sale until corrected.
No one should have to live with an obvious defect as such.
If the builder gets pinched on this one, next time he will protect the godarn thing properly. Makes all builders look bad. :slight_smile:

That’s caused by a significant amount of moisture being absorbed by the sheathing after the shingles were installed. Shingles have buckled at the panel edges as sheathing panels expanded.
It’s not really the roofer’s fault but the fault of the general contractor or whoever did the scheduling. OSB reacts pretty quickly once it gets rained on. I guess it’s possible that the roofer got up there on recently-rained-on sheathing that hadn’t yet expanded, but I think it’s more likely that the moisture was absorbed from the underside.
This has popped up in researching the roofing course and this photo a great example. In what I’ve read, they talked about moisture being absorbed for the underside. They never said… but they implied that sheathing panels reacted fairly quickly to being rained on. If it was rain on exposed panels which were then roofed over, it would have to be residual moisture on the surface of the sheathing that got locked in by the roofing materials that would cause enough swelling to buckle shingles 3/4", which is a lot of buckling and reflects a lot of sheathing expansion. That’s my 2 cents.

The source… man, it’s so dry here in CO that we seldom see this. Maybe closing the home up as drywall mud is drying, especially if the home has recessed lighting left on. That can create quite a bit of stack effect that pull moist air up into the attic. It could be made worse if there’d been recent rain and the air was humid and also if the sheathing was wet when the roofer climbed up there. It can be a combination of things.

Kenton…Honest question here…

What makes you say with such conviction, that the moisture was absorbed after the shingles were installed? And if so, what could introduce that much moisture to them?

I’m only asking, because the other explanations presented so far, seem more plausible to me on the surface. I’d like to know what you know on this. :smiley:

I added to my post below, Mark.


So it got rained on, shingled, then expanded/buckled…

May want to point out that it will come back to haunt the buyer when they decide to sell it.

Another problem in my opinion 7/16 OSB on 24" center.

With that much expansion, it’s hard to imagine that unabsorbed, residual surface moisture alone was enough be the cause. I’m guessing there were other moisture sources, maybe in addition to residual surface moisture.

Lots of guess work here. It would be easier to know if we knew the conditions the day of and the few days preceding shingle installation.

Yes, that condition will almost surely void the manufacturer’s warranty. Those shingles need to be removed and new shingles installed correctly… probably on the builder’s dime.

Thanks for all the replies. I spoke with an experienced construction manager yesterday, and he said that this will happen if they dry-in the home too quickly after rain that has soaked the roof deck. After it rains, the roof deck has a better chance of recovery if it is left to air dry. Applying the underlayment and shingles locks in the moisture and makes the swelling effect much worse than if given the chance to dry in the sun. However, if it continues to rain, there’s not much you can do regardless.

Here’s what I wrote in the report:

[size=2]Roof - Deck Seams are Visible & Raised:[/size] The inspector observed that the roof decking panel joinery seams are quite visible and are raised. This is best observed during the early morning because of the angle of the sun. This appears to be an issue on some other homes in this area as well. It appears that the edges of the roof decking are swelled up (in some cases the ridges caused by these raised seams are 3/4" proud of the surrounding surface). This could have been caused by the decking being exposed to rain before the underlayment was installed. OSB panels swell along the edges when they get wet, but do not return to their original thickness when they dry.
[size=2]The home buyer has 4 main concerns:[/size]
[size=2]1.[/size] How does this affect the shingles? Will this cause premature wear?
[size=2]2.[/size] How does this affect the manufacturer’s warranty on the shingles? Will this void the warranty?
[size=2]3.[/size] Will this get worse? How will this affect the future market value of the home?
[size=2]4.[/size] If the roof is not to be re-decked & re-covered, what assurances & guarantees can the builder provide that will protect the homeowner against future roof covering problems/expenses that may be caused by this issue.
Recommend a qualified roofing professional evaluate and determine a course of corrective action that addresses all of the issues above.

Thanks again for all your help.

Peter Sullivan
National Property Inspections
Round Rock, TX

This is even more reasons to use the right product, if you don’t want to protect it until the roofer arrives.


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