STANDARDS OF PRACTICE
The International Standards of Practice for inspecting the roof system is located at www.nachi.org/sop.
MASTERING ROOF INSPECTIONS
To learn about inspecting roofs, please visit Mastering Roof Inspections.
WOOD SHAKES
The Cedar Shake and Shingle Bureau provides standards for wood shake and shingle installation.
Left side wrong/right side right.
Installed with interlay (correct).
Observation
This condition increases the chance of roof leakage.
Exposed interlay (flush with butt of shake).
Observation
Felt paper is not designed for permanent exposure to sunlight. It will fail -- often in less than 6 months -- significantly increasing the chance of leakage.
Excessive number of fasteners.
Observation
Although the fasteners are typically not visible during an inspection, an excessive number of fasteners will limit the ability of shakes to expand and contract with changes in moisture content. Resistance to expansion and contraction can lead to cracking/splitting of shakes and premature failure of the affected shakes, and an increased chance of roof leakage.
Exposed fasteners.
Exposure to weather accelerates corrosion).
Excessive exposure.
Exposing too much of the shake is sometimes done in an effort to save money by using fewer shingles. This condition results in inadequate overlap and increased chances of roof leakage.
Inadequate gap between shakes in the same course.
Gaps between shakes should be 3/8” to 5/8”. This provides shakes with plenty of room to expand as they absorb moisture from precipitation. Resistance to can lead to cracking/splitting of shakes and premature failure of the affected shakes, and an increased chance of roof leakage.
Head wall flashing installed under shakes.
Observation
Flashing should be installed in a manner that keeps runoff on the surface of the roof-covering materials.
Continuous sidewall flashing.
Wood shakes should have step-flashing installed at sidewalls unless continuous sidewall.
flashing is required by local building regulations.
Undersized sidewall flashing.
Sidewall flashing flanges should measure at least 4”.
Shake Misc.
- Curled shakes are common but seldom cause leakage. Even so, the typical recommendation is that shakes curled to the extent that a gap exceeding ¾” is visible should be replaced. What to say in the report is up to individual inspectors. Consider telling clients about the typical recommendation, but mention that curling seldom leads to leakage. This leaves it up to your client to decide whether they want to include shake replacement as part of the negotiations. . Mention in the report whether you saw any sign of roof leakage.
- Weather-caused cracks will eventually develop into splits. Splits that occur less than 1.5” from a joint should be replaced. The typical rule of thumb is that when 30% or more of shakes on the roof are split, it’s time to replace the roof
Less than 1 ½ “ sidelap.
Interlay installed (both exposed and hidden).
Wood SHINGLES should NEVER have interlay installed because it increases the amount of tie required for the shingles to dry. Elevated moisture levels in wood shingles increase fungal activity, including fungi that cause wood decay and microbial growth. High moisture levels can also encourage the growth of lichen and moss, which will retain moisture against the wood, also encouraging decay.
Faster drying is the reason that the Cedar Shake and Shingle Bureau recommends installation with no underlayment when shingles are installed over solid sheathing. Shingles installed over spaced sheathing may have underlayment installed, but under no circumstances should interlayment be installed.
Excessive number of fasteners.
Exposed fasteners.
Excessive exposure.
Inadequate gap between shingles in the same course.
Inadequate overhang at eave.
Improperly flashed penetration.
The penetration on the right side is correct.
Continuous sidewall flashing.
What you see installed here is actually drip edge, not sidewall flashing.
