Roofer installing Cambridge Xpress

Most common mistakes made by roofers – part 2

A successful roofing project requires more than only the right shingles. The job has to be done properly, following the correct application methods. In our previous blogpost we covered the first 5 common mistakes by roofers. The list of mistakes doesn’t end there, let’s take a look at the following 5 topics:

  • Improper shingle nailing
  • Use of improper nails
  • Not aligning shingles correctly
  • Improper flashing installation
  • Reusing old flashings

6.Improper shingle nailing

Shingles can slide down or blow off if they aren’t nailed correctly or if less nails have been used. You should use at least four nails per shingle. When installing a roof with steep graded, that minimum should be raised up to six nails. The placement of the nails is as important as the number of nails. They should be completely covered and kept dry by the next row of shingles. All nails should be driven straight into the wooden deck. Crooked, over-driven or under-driven nails can cause roof leaks!

Unstick the shingles carefully and try to fix all under-driven and high nails. Secure these spots with an extra bituminous mastic. But be aware: an excessive amount of mastic can cause blistering! Cover exposed nails with a piece of shingle or apply a small dot of Shingle Stick and some granules over it.

Correct nailing roof shingles

Improper shingle nailing

7. Use of improper nails

The standard roofing nail has a barbed body and nominal shank diameter of 2.7 mm with a head from 9 mm in diameter. Roofing nails must be corrosion resistant and galvanized. Properly driven and applied roofing nails are the only preferred fixing system for asphalt shingles!

If shingles are applied with staples, refix every shingle with proper roofing nails and, if necessary, apply some Shingle Stick. If you experience leakages through the corroded nails, try to fix these leaks with Shingle Stick. If this doesn‘t help, you have to consider a new roof.

8. Not aligning shingles correctly

Shingle alignment - both vertical and horizontal - is required. The best way to ensure that the shingles are horizontally aligned in new applications is by the use of a chalk line. Especially for tab shingles, the use of chalk line is highly recommended. The bottom edge of laminated shingles must align with the tops of the saw teeth of the shingles in the underlying course. Too high alignments increase the chance of wind blow off and wind driven rain backing up under the shingles.

When the roof doesn’t leak this is only an aesthetical problem.

Incorrect overlapping of Cambridge Xpress

Horizontal chalkline will help you align

9. Improper flashing installation

Metal flashings need to be installed around chimneys, skylights and in valleys or close to wall. Chimney flashings prevent leaks around the chimney and must always be placed under the shingles. Side wall flashings or step flashings must be covered with appropriate counter flashings.

When flashings are poorly installed, pop up the nails and slide a new flashing under the shingles. Secure new flashing and shingles with Shingle Stick. Don’t forget about counter flashing!

10. Reusing old flashing

When replacing an existing roof, the old flashing may look serviceable, but there is always the possibility that it has been punctured or damaged. New flashings are a small component in the cost of a roof replacement. Always install new flashings.

If they are free of exposed holes and are not damaged, copper and aluminum flashings are not necessary to change. All others should be replaced.

Reused old flashing

Correct new flashing

Be sure to keep an eye on our blog space, a new blog post concerning the next 5 common mistakes will follow soon!

Meanwhile you can always check the correct application methods on our website. Good luck!