Page 145 - 2018 National Home Improvement

2018 National Home Improvement Estimator, All Rights Reserved Page 120

• Lack of a 45-degree cant strip where a roof joins the wall, leaving the flashing unsupported at the
base of the wall.
• Poorly sealed seams and end laps.
• Poorly fastened base flashing at walls or curbs.
• Decay of the sheathing below.

Both metallic and non-metallic flashing can be used on the roof surface (base) with most types of roof
cover. Built-up roofing is an exception. As the surface heats and cools during the day, metal flashing
expands and contracts much more than roll roofing. The result will be ripples, tearing and eventually
separation of the built-up roofing at the edges of the metal flashing. Use roll-roofing materials as flashing
under a built-up roof.

All penetrations in the roof surface need flashing. Plumbing stacks and small vents should be flashed
with a roof jack or flange placed directly on the last ply of roofing material and stripped in with felt and
mastic or felt and bitumen. Prefabricated vinyl or plastic seals for plumbing stacks are effective, and are
available in a wide variety of styles and sizes. Larger penetrations should be made through a
roof-mounted curb built from 2 x 6 or larger framing lumber. Bituminous base flashing should run up the
curb, and metal counterflashing should run down the curb from above.

Attaching an antenna, flagpole, sign or bracing directly to the roof membrane is asking for trouble.
Leaks are almost certain. The best repair is to remove the attachment. However, if it must be mounted
on top of the roof, mount it using a raised curb-type support. Then install flashing to keep the roof
watertight.

Leaks around a roof penetration are usually caused by:
• Open or broken seams in a metal curb due to expansion and contraction.
• Standing water behind a penetration.
• Sagging or separating base flashing.
• Missing or deteriorated counterflashing.
• Splitting or separation of felt stripping over the edge of metal flanges.
• Improper priming and stripping of metal surfaces.
• Fasteners working loose around the flashing.
• Movement between stack vents or pipes and flashing.

Can’t Find the Leak? If All Else Fails . . .
If you’re truly stumped about the source of a leak, or have been called back several times to make
unsuccessful repairs of the same leak, try this; take a garden hose up on the roof and direct a steady
stream of water at every source likely to leak. When the leak is active again, trace the path of the leak
from the building interior to the roof surface. Be sure to brief the owner before you test for leaks – and
get the owner’s help in reporting an active leak.