How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manfuactured and modular homes
What are the warning signs of a dangerous deck?
Saturday, August 4, 2018
Building a wood deck off the back of a home is the classic weekend-warrior project. They look easy to build, so many homeowners feel comfortable putting together a backyard deck with some nails, lumber, and a little common sense. But the figure-it-out-as-you-go ingenuity that goes into a homeowner-built deck sometimes violates basic engineering principles—which can result in a catastrophic failure like the one in the picture above. It’s estimated that only half of the 40-million decks in America are building code-compliant, leaving 20-million with potential safety problems and in need of repair or rebuilding. Here’s ten places to look for warning signs of a substandard and potentially dangerous deck:
1) The number one safety priority in deck building is providing a continuous, securely connected load path. This means constructing a series of sturdy connections from the top of the deck structure to the bottom that transfers the load of the people and furniture on the deck, along with the weight of the deck itself, through each part of its frame safely to the ground or an adjacent structure (typically a wall of the the home). Because we have hurricanes to consider in Florida when designing a deck, the connections must also be able to resist uplift forces from strong winds roaring under the deck.
So, when you look at a deck from a safety standpoint, focus on the structural connections first. They should be clearly visible.* Nails alone are not acceptable structural connectors; especially nails set at an angle to tie together two structural components, such as a joist to a beam. This is called “toe nailing” in the construction industry and is a sign of inferior construction. Metal connector plates, straps, and bolts, like the ones shown in the drawing below, are what you should find. Every hole in the connectors should have a nail in it. Also, the connections should be snug. Any lumber that is pulling away from its connection point needs immediate repair.
2) The ledger connection, where the deck meets the house, is the most common location of failure in a poorly built deck. A ledger is a board secured to the wall of the house that the deck joists sit on top of or are connected to the side of. It’s absolutely necessary to use thru-bolts or structural lag screws to secure the ledger board to the wall of the house—and never nails. Nails can slowly work loose over time, causing the ledger to pull away from the wall and collapse the deck. Look for the zig-zag pattern of bolts or lag screws, both of which have large heads, across the length of the ledger board, like in the drawing below. 3) A good builder uses spacers to create a small gap between the ledger and the wall to allow rain flowing down the wall to pass behind the board, thereby avoiding what carpenters call a “water trap”— where water seeps into the crack created when a ledger is pressed against the wall and then cannot drain out, with the ensuing wood rot at the back of the board.
4) Deck boards should span across at least three joist bays, connected at four joists, to be safely secured. Short deck boards, like the one below that spans between only two joists, are dangerous and another indication of a non-professional deck.
5) Because their wood is directly exposed to sun and rain every day, decks do not have a long life. Wood rot is the culprit. It will show up first in areas where water puddles, such as a slightly cupped deck board, or where the end grain of the wood is exposed at the top of wood posts or end of joists or beams. Even with the regular application of a sealing/preservative coating, the life expectancy is 10 to 15 years. Also, the cracks that open naturally in wood as it ages invite water intrusion and rot.
Pressure-treated wood postpones wood rot but does not stop it. Weather also corrodes the metal connectors, especially in coastal locations exposed to ocean salt spray. An older deck may be safely constructed but still dangerous due to deterioration of its components.
Professional inspectors probe for rot with a long screwdriver, but you can also just use your finger. Look for stained, wrinkled areas and, If they collapse under finger pressure, the wood is no longer structurally sound.
6) Undersized beams and joists are another concern. Look for sagging beams, and feel for bounce in the floor—an indication of undersize joists or joists spaced too far apart—as you walk across the deck.
7) Another red flag is 2x4 lumber used for beams or joists. Their actual size is 1-1/2” by 3-1/2” and a 2x4 is not code-compliant for deck structural members, such as beams or joists. The minimum size allowed is 2x6.
8) The deck posts should sit on, and have a structural connection to, a concrete pad that is poured-in-place into the ground. Those little blocks with a hole for a 4x4 post sold at home improvement stores are not adequate, because they settle unevenly into the ground over time and do no provide uplift protection in a hurricane.
9) Decks built directly on the ground or within a couple of inches of it are doomed to a very short life due to ground moisture wicking into the wood. They are also difficult to inspect because the underside is mostly concealed. While no one will die from a collapse of one of these decks, it can still cause an injury. They will begin to fall apart within a few years of completion, as shown below, and should not be taken seriously as a home improvement.
10) Deck safety involves more than just structural integrity of the platform. The deck perimeter and steps to it should protect you or your guests from falling. Any deck that is over 30-inches above the ground requires a railing at least 36-inches high. Give it a good shake to see if the railing feels secure. The railing pickets should have no more than 4-inches of space between them for protection of small children, and any steps to the deck with four or more risers (vertical sections) should have a railing and a handgrip piece on at least one side, either integral with the top piece of the railing or offset from it.
One additional step you can take to verify that a deck meets safety standards is to ask for proof of a building permit and final inspection sign-off by a municipal building department inspector. But, even with a building permit in hand, any deck warrants a careful safety inspection.
Your home inspector will go into more detail than our eight points, and provide you with information about the overall condition of the deck. If it has any safety defects, you will also get a repair list. Because outdoor decks have a surprisingly high rate of injuries and loss of life annually due to faulty construction, we recommend a professional inspection of an outdoor deck for any prudent homebuyer.
To learn about the life expectancy of a wood deck and what you can do to extends its life, visit out blog post “What is the average lifespan of a wood deck?”
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To learn more about exterior walls and structures, see these other blog posts:
Note - While it is possible to have adequate concealed structural connections at some points in a deck using inset lag bolts, the work is time-consuming and difficult. It would only be found in a contractor-built deck—not a homeowner project. If you don’t see a connector between load-bearing parts of a professionally-built deck, ask for proof of concealed structural connectors.
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