Mastering Roof Inspections: Asphalt Composition Shingles, Part 18
by Kenton Shepard and Nick Gromicko
purpose of the series “Mastering Roof Inspections” is to teach home
inspectors, as well as insurance and roofing professionals, how to
recognize proper and improper conditions while inspecting steep-slope,
residential roofs. This series covers roof framing, roofing materials,
the attic, and the conditions that affect the roofing materials and
components, including wind and hail.
FLASHING, Part 2
A sidewall is a junction between a wall and a sloped portion of roof.
Sidewalls on roofs covered with asphalt shingles should always be
flashed using step-flashing. A step-flashing is a short section of
flashing that overlaps each shingle in the course below and is
overlapped by each shingle in the course above.
Except where walls are brick, the vertical part of the sidewall
flashing should extend up behind the exterior wall-covering, just like
Although you may sometimes see counter-flashing installed, it’s
more common that the exterior wall covering acts as the
counter-flashing. The exception is brick.
If you see continuous, one-piece flashing used as sidewall flashing
with shingles, such as the one pictured above, it’s a defective
You’ll see it fairly often because it’s a common defect. It’s easier to see in some situations than others.
This is an example of a defective installation where an asphalt
shingle roof meets a stone sidewall. Instead of installing the
step-flashing between the shingles, the lower flange rests on top of the
You’ll see sealant substituted for flashing in many different areas on roofs.
Sealant will eventually dry, shrink and crack.
Correction is most easily accomplished when the roof is replaced, but
that can be expensive. These asphalt shingles are installed over wood
shingles. If the limit in this jurisdiction is two layers, then, before
re-roofing can take place, all roofing materials will have to be
Since many jurisdictions no longer allow wood roofs, and asphalt
shingles should not be installed over spaced sheathing the way wood
shingles are, then this roof would need solid sheathing installed over
the existing sheathing across the entire roof.
The new step-flashing will need to have the vertical flange inserted
behind the exterior wall covering. In this case, that’s wood shingles,
too. This might require cutting the wall shingles up a couple of inches
above the surface of the new sheathing. There will be nails in the way
when the roofer is inserting the vertical flange. It will not be a quick
process. It will be expensive to have done correctly.
Because this is something of a quality issue and a potentially large
expense, you might not want to be aggressive in insisting that this
condition be corrected. If you were inspecting this home, you’d want to
alert your client to the fact that this condition might involve
considerable future expense to correct. You should also recommend annual
inspection and re-application of an appropriate sealant, as necessary,
and let your client know that the sidewall joint should have had
Considering the age of this home, it may have been correctly flashed
when it was first built, but the original flashing may have failed due
Correction can be even more expensive with other types of wall-covering materials.
In both headwall and sidewall conditions, unless the exterior wall is
brick, you should see a gap of at least 1½ inches between the bottom of
the exterior wall-covering material and the top of the roof-covering
You’ll often see siding and stucco installed right down on top of
the shingles. Without a gap, the exterior wall-covering can wick up
moisture from the roof. This can lead to decay, delamination, peeling
paint, and other problems. This condition is especially common on roofs
with multiple layers of shingles.