ASHI Smart Inspector Science - Cantilevered Deck Issues

By Tom Feiza, Mr. Fix-It, Inc.,

A “cantilevered” deck or balcony is hung on the side of a building with no support posts. Typically, the home’s framing joists are extended beyond the envelope to support the deck.

Always take a careful and critical look at cantilevered decks and balconies. They’re subject to serious issues with flashing, water intrusion and structural elements.

Deck flashing done right

Here’s what to look for with deck flashing (Illustration X039). Deck boards must be spaced to allow drainage near the wall. Flashing above the deck must originate behind the siding and extend to allow drainage over or around the deck boards.

X039 - Cantilevered Deck Flashing

Also, two-part flashing must be placed around the joist and lapped over the moisture-resistant wall covering below.

Note that the structural deck joist is an extension of the home’s wood joist framing. This is common in residential construction.

A real-life example

From above, this deck looks fine (Photo 1) – or at least the fresh paint and caulk look good. But maybe the paint is a clue that someone’s trying to hide something.

Caltilevered Deck

As we look for deck flashing near the rule, we can’t see any flashing through the caulk (Photo 2), but we can see a deck board tucked into/under siding and pitched into siding (the ruler shows the pitch discrepancy). The deck board directs water into the wall and over the top of painted brick veneer.

Deck Flashing

Framing concerns

Sistered joists are visible beneath this deck (Photo 3), but the sisters are not supported at the ends and provide no structural support. Maybe they’re just a fresh nailing surface.

Sistered Joists

Viewing from the opposite direction confirms our suspicion: improperly sistered joists (Photo 4). There’s a new corner support post but no structural beam over the post.

Sisters, Flashing, Post

We can also see more clearly that the deck board actually extends over the top of brick veneer, allowing water to drain into the wall. Luckily, the deck is protected by a wide overhang, so water exposure is limited, but I would still check the brick veneer and the home’s interior for water intrusion damage.

The takeaway

Cantilevered decks and balconies always raise concerns regarding improper flashing and control of water. You must watch for serious rot, water intrusion and structural issues. Always identify these, and consider recommending further evaluation.

Tom Feiza has been a professional home inspector since 1992 and has a degree in engineering. Through (, he provides high-quality marketing materials that help professional home inspectors educate their customers. Copyright © 2020 by Tom Feiza, Mr. Fix-It, Inc. Reproduced with permission.

To learn more, attend Tom’s technical presentations at educational sessions for ASHI chapters and local groups. Tom can also provide his knowledge for your educational event; contact him at

Photos / Illustrations / Captions

Photo 1. Cantilevered Deck
Photo 2. Deck Flashing
Photo 3. Sistered Joists
Photo 4. Sisters, Flashing and Post
Illustration X039 Cantilevered Deck Flashing

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