Many decks and balconies are cantilevered. These are usually a series of joists which have most of their length inside the house, and up to one-third of their length exposed outside. They support a deck or balcony with no vertical support below.
While cantilevering can be a dramatic architectural detail, it can be very troublesome, functionally. Many cantilevered joists are conventional framing lumber such as spruce, pine or fir. These species work well indoors but are more prone to rot than cedar and other rot-resistant woods normally used for decks.
Some builders use pressure treated lumber for cantilevered joists. Cedar is also rot- resistant, but is not a particularly strong wood and not normally a good choice for cantilevering.
Cantilever problems include
Many cantilevers are overextended, and the deck or balcony is springy.
The biggest single problem with cantilevered decks is the difficulty in maintaining a weathertight joint where the joists pass through the house wall. These joints typically move as a result of expansion and contraction caused by changes in moisture and temperature.
This area is hard to access since it is usually out of sight from above, and may be well above eye level when viewed from below. Caulking is usually the only protection of the joint between the cantilevered joists and the house wall. Caulking may be imperfect when installed, or may deteriorate over time. Rot in the cantilevered joists and water damage to the wall assembly are common problems.
Where the interior sections of the cantilevered joists are not well secured to other joists and framing members, the inboard ends of the joists can rise, causing bumps in the floor as the outboard ends are depressed.
Cantilever problems may be the result of
Springy decks or balconies are an inconvenience. Weakened framing creates a life safety hazard. Decks or balconies may collapse with people on or below them.
Cantilevered decks should be viewed with caution. If you are technically inclined, you can use a ladder if necessary to examine the cantilevered joists at their point of penetration through the wall. Probe the joists with a screwdriver or awl. Look for gaps. Note the location of the cantilever so you can check inside the home for evidence of water damage or a bump in the floor. If you are not comfortable doing this yourself, call a carpenter to inspect your deck for you.