Cantilevered
Areas
Cantilevered areas and “allowable spans” are always of
concern to home inspectors. For a couple reasons: 1 – many times we are unable
to view the structure where these cantilevered areas are. 2 – There seems to be
confusion on the requirements for cantilevered areas.
The distance your joists can
safely cantilever or overhang is determined by the size of the joists, the wood
type and grade of the lumber and the
spacing between joists. Many building departments limit joist cantilevers to
24" maximum. Cantilevered areas are also prone to damage at the area where
they exit the structure. The American Wood Council states that cantilevers
are limited to 1/4 the span of the joists, (refer to the chart above).
Specifically the joist must back space at least 3 times the distance of the
cantilever if the cantilevered area is supporting a wall or roof. The member
should back space at lease 2 times the distance of the cantilevered area if not
supporting a wall or roof structure. What should a home inspector be looking
for;
- A general home inspector rule of thumb in the field; cantilevered distance should be no more than 2 times the width of the joist. For example a 2x10 joist actually measures 9 ½”. Therefore the cantilevered distance should be no more than 19 inches.
- Examine both areas inside and outside of the house for damage or deflection
- Joists or members should be installed “crown up”
- Maximum allowable overhang cannot exceed 1/4 of the actual main span.
- Evidence of leaks / moisture at the house insertion, inside and outside
- Proper flashing and counter flashing should be visible
- An adequate drainage plane ensuring water is drained away from the structure
- If possible, check the basement structure to ensure the cantilevered section is properly installed
- A minimum of 5 framing nails should be used to attach the joists to the rim joist
