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Re-education in 3 tab nailing


fqp25
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What exactly happens when nails are in the tar strip? I know it's wrong and makes them prone to wind damage, but does it prevent them from sealing to one another?

Saw this 2 times this week. The first was on a low pitch roof (less than 3 in 12) and all shingles were nailed in the tar strip, and the exposure was >5inches. I felt like I was going to fall through the sheathing. Yesterday the roof was 5 years old (5 in 12 pitch) and the sheathing felt real spongy. Does water wick back under the shingles because of the nailing?

Frank

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I can't prove the mis-placed nails will cause the shingle to leak or not. My educuated guess is that mis-placed nails will not cause leakage. If the nails stand proud of the shingle, then the strips may not seal as well.

According to the NRCA Roofing manual, if the shingles seal, then nailing is actually secondary and mis-placed nails aren't critical to the shingles' performance.

Regardless, I still write things up that aren't instaled according to the spec's.

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If the nails are to high, like in the tar strip, that means that the nail is probably not going through the shingle on the lower coarse. If the shingle doesn't have the nail in the back if it, what could happen? Could a group of shingles somehow float, especially if the sheathing expands/contracts?

Another question:

When water wicks back up through the shingle, is this called capillary effect?

Thank for all your help.

Frank

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Personally, in areas that are not hurricane-prone, I don't think anything happens when you nail through the tar strip, -at least not at pitches under 6:12, which is most roofs I see. At pitches steeper than that, you might start to see shingles slide down toward the gutter.

And though I've never tested it under controlled laboratory conditions, I am willing to go on record saying that no measurable amount of water can be drawn up through an asphalt shingle through capillary action unless you leave one soaking in standing water for a day or more, and even then I seriously doubt it would be an appreciable amount. If the shingles are saturated, or the wood beneath them is wet, the water is coming from somewhere else.

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I would think that the first roof would leak, shingles of any kind should not be on a slope that low without a complete cover of IWS. The spongy sheathing is likely due to the leaking low slope roof or they used the wrong sheathing material or failed to install the proper clips.

Tom

Careful not to mix opinion with actual requirements.

R905.2.2 Slope. Asphalt shingles shall only be used on roof

slopes of two units vertical in 12 units horizontal (2:12) or

greater. For roof slopes from two units vertical in 12 units

horizontal (2:12) up to four units vertical in 12 units horizontal

(4:12), double underlayment application is required

in accordance with Section R905.2.7.

While I don't disagree that 2:12 is a very low slope where shingles are concerned, it is allowed and with just two layers of felt. Of course IWS would be better but we are not the guy''s making up the regulations...

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