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Nail Gun Pressure Damage


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Found plywood roof sheathing damaged at three areas of a 1 year house, in one case a nail end was visible and in the other two cases the nail shot all the way through into the attic.

I'm I justified in being concern that there may be a number of shingles damaged by overdriven nails? This was a two story colonial steep pitched roof so I did climb the roof.

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Originally posted by DLRambo

How big is the hole - it looked awful big for a nail. We see damages that look like that several times a week around the passive roof vents in an attic. I've never written them up.

Dan,

The damaged areas were right where the nails were driven in. You know how plywood is, if you apply a strong force in a small area it will rip out like a shotgun load going through it.

Dennis

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Dennis,

I can't see a roofer doing that kind of damage especially with an air driven tool. This looks more like a 28 oz. type hole that usually belongs to a framer.

If we had to speculate on the reason for it, I'd go with Chris's explanation.

Did you find 'H' clips in the installation? I don't see much of a space between the sheathing.

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Dennis,

After shooting over 100,000 round head nails, I can tell you this did not happen from the nail gun. Chris' explaination is the "best guess" and I'd put money on it. Never did it personally, but have seen others do stuff like that all the time.

Ron

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Originally posted by RobC

Dennis,

I can't see a roofer doing that kind of damage especially with an air driven tool. This looks more like a 28 oz. type hole that usually belongs to a framer.

If we had to speculate on the reason for it, I'd go with Chris's explanation.

Did you find 'H' clips in the installation? I don't see much of a space between the sheathing.

H clips, are you kidding? I find the correct spacing between OSB and plywood sheathing in about one out of 20 new houses.

Dennis

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Hi Rob,

I see H climps or edge blocking intalled only occasionally here in the Seattle area and then only with thinner roof decking.

For all practical purposes, unless a municipality zeros in on H clips and end blocking as an issue, and specifically mandates their use, the code requirement is that the panels be installed in accordance with their APA panel span rating, which means that H-clips and edge support or T & G panels aren't required until that maximum allowable span for the decking is exceeded - usually over 4ft. Since most trusses or rafters here are no more than 24in. o.c., that means almost never.

As for spacing - sure, the 1/8in. edge spacing requirement is there and can be accomplished using a 10p nail. The reality though, is that once the home has been built, unless you have H clips present there is no way to know, unless you find a problem has developed, whether they builder even tried to maintain the 1/8in. edge spacing, since the panels will normally expand and close that gap before construction has been completed.

Then too, I've never understood how placing a metal spacer between two pieces of plywood is supposed to maintain spacing. Doesn't placing the edges of the plywood tight to the spacers have the exact same effect as butting two sheets of plywood directly together at the edges?

FWIW, yesterday's inspection was a good example of how to know for sure that no effort was made to maintain sufficient edge spacing. While walking the roof I found a ridge along a course of shingles at mid-span of about 3-4 adjacent trusses and pointed it out to my client. I theorized that the OSB decking was probably butted too tightly together and was being forced upward at the joints. Later on, when I examined conditions in the attic, I found that was indeed the case and was able to prove it beyond a doubt, because someone, probably the roofer, tried to 'adjust' the edges of the panels by stomping on them and striking them with a hammer to try and align the seams. This resulted in mashed edges and one sheet had clearly been stomped on between two joists and was splintered inward.

Looking at that, I couldn't help but wonder what kind of an idiot, seeing those panels, wouldn't have taken a saw and kerfed the joint between adjacent sheets. Now, here is this home, 8 years years old with a 25 year architectural-grade roof, that, with good care, won't need a new cover for about another 16 years. The roof has never leaked and probably will never leak, despite this little 'ridge'. And, although this probably has marginally compromised the structural integrity of the roof plane, the practicality is that it'll easily handle any of the snow loads or winds we encounter here. I'm confident of that. So, what it means to a home buyer is that, unless they have the roof stripped off, the joints kerfed, the damaged panels replaced and a new cover installed, when/if they buy the house, they end up living with a defect that might bite them when they go to sell. Like a dented fender on a used car, this won't affect the performance of the home, but a potential buyer may use it for leverage.

ONE TEAM - ONE FIGHT!!!

Mike

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Most of my training occured in Colorado, where 'H' clips were the standard at the time(60's). Calgary experiences the same kind of weather albeit a bit colder and edge support is a standard here too. 'H' clips are the cheapest method and the most common over T&G or lumber framing (2x3).

I can't technically argue how a little piece of aluminum can distribute a load to the adjacent sheathing but I guess it does. We have to remember the load is not a point load (shoe/boot) but rather a distributed load that make the design function as intended.

Anyway, if nothing else they should be used to seperate adjoining sheets to allow expansion and contraction. By their nature they seperate the sheets by their wall thinkness. Wall sheathing experiences the same forces and should also be seperated to allow for movement.

We're all in a big hurry these days and to ask a framer to kerf the plywood,.... I wouldn't want to be there for the conversation.

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Last week I did an expert witness case, where among 100 other defects the roofer, installer, home owners cousin Ernie, or somebody had done some unique roof repairs. Since "H-Clips" were not used and the 2x4 rafters were spaced at about 33" centers, and the cripple wall in the attic supporting the rafters were 2x2's spaced every 8' or so - there was a witty bit of a sag in the roof.

The unique roof repair was going into the attic and taking pieces of 1x4's and putting them under the plywood seams and nailing them in place - with the nails going STRAIGHT UP. Walking the roof was a delicate situation to keep from spiking my feet (I was wearing my soft soled climbing tennies).

How did I discover the unique roof repairs?? I wish I could say - from the attic, but that was not the case. Thankfully after the 1st nail and I became intimately acquainted, it was only 2 hours till I was done and could stop by the Med Clinic for a Tetnus Shot.

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