A note to roofers

Wow, is that on the new place?

It's one of the houses we looked at this weekend. And no, we aren't buying that one.

From experience as a roofer and having worked on many houses in other capacities, that is normal. If the nails don't go all the way through, your shingles are much more likely to be torn off in a windstorm. It's supposed to by covered by soffit on the underside so you can't see it there.

Interesting! Does this hold true in regions like Seattle, where the water is far more prevalent than the wind?

A very rough cross section sketch:
http://www.clanspum.net/~jarrod/shingles.png
The black is shingles, the red is tar that comes pre-applied to the shingles and the yellow is where the nails go.

The shingles themselves are waterproof, but the seams are not, but for the stripes of tar. The heat of the sun melts the shingles together a bit, and particularly melts them together at the tar strips. If water is getting in through your shingles, wind/water/ice/etc has already compromised your shingles and some/all need to be replaced. The longer nails thing is only really important during the time it takes for the shingles to melt together or if the tar seals have already failed.

Also, when a roof begins to leak, it is almost always at the seams of the underlying plywood or boards. Leaks through the nail holes are rare.

I just realized I made a mistake on the sketch. The nails go through the middle of a shingle and the top edge of the one below it, meaning there are 2 layers of nailed-down shingle in all places and each shingle (assuming standard size/type) had at least 6 nails holding it down.

Ahh, makes sense—thanks for the info!