What can make shingles come up on a roof?

Q: I'm asking this for our church...the Sanctuary was built 15 years ago. It is a 9/12 roof, too steep for me at age 67 to get up on. Under the shingles is roofing paper, under that is 5/8" plywood, under that is V lock metal. The shingles are coming up in several places , and the shingles were put on with an air nailer. We also have a leak but it's difficult which part of the roof the leaf originated in. I don't fully understand what is making the shingles come up; is it that not-fully-in nails are allowing the shingles to come up with wind and then ride on top of the nail heads? Given the relatively narrow nailing material, 5/8", and the fact that the tips of the nails won't go through the plywood due to the metal underneath, how does one nail new or repair shingles securely to the plywood? Thank you for any help!

A: Your observation and assessment of the roof problem on your Sanctuary hits the nail on the head (Pun Intended).

The pneumatic nail driver you mentioned is adjusted to drive the nail to just the right depth for the greatest efficiency.  If it drives to hard it will damage the shingle and cause premature failure.  If it is adjusted to light, the nail head will be elevated above the shingle which will cause the shingle overlapping to be damaged.  The pocket caused by the nail will allow wind, weather, dirt etc to cause a malfunction.  Dirt and moisture will damage the Seal Tab portion of the shingle to dry out and weaken its ability to hold shingles down in a heavy wind.  Wind damage will occur.

You are faced with the problems of replacing missing or damaged shingles as necessary for appearance and weather functions.   When replacing shingles, nail properly.  In a high wind area, use 6 nails per shingle. (The package says 4, and in certain wind areas 6 are required.)  Use ½” or ¾” Gal Roofing nails.  This will keep nails from reaching the metal under plywood.  The shorter nails should hold the shingles in place satisfactory.  As you notice shingles that are loose caused by nail heads, use roofers chalking  (elastomeric or equal) to hold shingle down and not let wind under shingles.  Use very sparingly. It does not take a lot to hold shingle down.  Too much will trap water under the shingle.

Your additional problem is fixing the leak.  Usually, fixing a roof leak is fairly simple.  However FINDING the leak is more complex.   Your “V Lock Metal” roof is hiding the location of the leak.   I would start with the labor intensive chore of “water testing”.  With the roof dry, place water (garden hose) down slope of  the leak.  Check to see if the wet spot shows on ceiling (or walls or whatever) if no evidence of moisture, move the hose up and Check it again.  Keep this action of moving the hose up on the roof.  If the roof has a leak, it will show up.  This is admittedly a very crude way to find a leak in this age of technology. If this fails, go to the internet under roof leak finder (or some other cute term) and you will find a roofer that has a Moisture Sensor.  It is a basic non-destructive device that finds moisture by measuring Electrical Impedance.  I have never used one.  But I have looked into it.  They are a bit “pricey”.   If the water testing does not find the leak, you may find that someone in your congregation is familiar with the tool and may have access to it.

When you find the cause of the leak, contact ASK A ROOFER for hints on how to do the repair.   I hope this note has some information in it that will help you.

Ask A Roofer

P.S.   You never mentioned in your correspondence how in the world you got the plywood applied over the top of your “V Lock Metal Roof”.

- John Stout with Go Roof Tune Up