Identify type, approximate thickness

  • Roof sheathing is typically either plywood or oriented strand board (OSB)
  • 3/8-inch plywood was acceptable in the past some jurisdictions. It's presence as roof sheathing may not be desirable, but its presence alone is typically not a defective condition. Check with your local building department before calling it a defect.

Discolored sheathing;

  1. Leakage:
    1. Bad penetration flashing;
    2. Damaged/failed roof-covering materials
    3. Ice dams
  2. Condensation (look for moisture source);
    1. Room exhaust fans (bathroom, laundry)
    2. Separated combustion exhaust vents
    3. Inadequate attic ventilation
  3. Decayed, damaged or otherwise deteriorated

H-Clips are NOT REQUIRED. They are an architect's or engineer's call. Their purpose is to support the sheathing at midspan of rafter bays. No expansion gap exists at the point of clip contact.

Buckled Shingles

Buckled shingles are caused by shingles being installed over sheathing that is at near mill moisture content. OSB wrapped in plastic leaves the mill at about 6% moisture content. The bunk of OSB will remain at near mill moisture content until it is installed at the jobsite and has had a chance to reach equilibrium moisture content (EMC) with the jobsite environment. The amount of time required to reach EMC varies according to the site humidity levels.

Once installed, the panels will absorb moisture from the air until they reach EMC. As they absorb moisture, they expand in width and length. This is why manufacturers recommend that an eighth-inch gap be left between panels during installation. If shingles are installed before panels have expanded, the shingles will buckle above panel edges as the gaps close.


RADIANT BARRIER SHEATHING (Potential fire danger)


Radiant barrier sheathing consists of panels that have had thin foil bonded to the underside. A study by a forensic engineering firm, McDowell-Owens, suggests that this sheathing increases the potential for fire due to:

  1. Heat created at joints if the foil should become energized.
  2. Increased chance of lightning strikes.
  • Whether to include this information in a report is a decision that must be made by individual inspectors.
  • Radiant barrier sheathing will not void the warranty of most shingles.
  • Read the report here: