Learn how to inspect a deck or balcony and look for problems that can cause the deck to fail. Deck and balcony failure injure and hundreds of people a year.
Decks are a great amenity for a home, townhouse, or condominium, but without proper maintenance, they will fall into disrepair and pose a safety hazard. According to North American Deck and Railing Association, from January 2000 to December 2006, there were 179 reported deck collapses. Of those, 1,122 people received injuries and 33 people died. According to the same source, reported deck collapses have increased at a rate of 21 percent per year over the same period. Most collapses occurred in the months between June and August when the decks are obviously in peak use and loading, while the other collapses that were reported over the winter months were typically due to excessive snow and ice loads. The failures occur when the structure can no longer resist the loading that is placed upon it.
If you belong to a Homeowners or Condo Association, check your bylaws to determine if your HOA has an inspection schedule in place. This is critical for any elevated decks or balconies located on higher floors. The current International Residential Code (IRC) is one of the primary references for both deck designers and code officials, but does not address inspection and maintenance for existing decks. The International Code Council does recommend that exterior wood structures be inspected twice per year. Since the outdoor season is winding down, this would be a good time to inspect the structure of your deck or balcony.
As wood ages, it becomes weaker due to the lumber drying out, cracking, or even rotting. Pressure treated wood will eventually rot, especially if the cuts on the end of posts were not treated. If the deck was not constructed properly or piers and beams were not sized correctly, but were based on rule-of-thumb criteria, the problem will only get worse with age. If the deck was not properly maintained, a poor design will also limit the structures ability to support the intended loads. This is why periodic inspections are essential to ensure that the decks are stable and safe.
Causes of Failures
The main causes for deck collapses are either post and railing failures, or the connection of the deck ledger board to the house’s rim joist. The ledger board is usually a 2 by 8 or 2 by 10 pressure treated board that is bolted or screwed to the house and holds the joists of the deck. It is estimated that 80 percent of the deck collapses occur at the ledger to rim joist connection.
Deck ledgers should be screwed or preferably bolted to the building rim joists not merely nailed. Properly installed, bolts and lag screws will withstand the expansion and contraction of the wood. They can loosen over time, but will not pull out as nails would. You will notice a gap between the deck and the house is the bolted or screwed connection is loosening. If the ledger board has been nailed to the house, any lateral movement may cause the deck shift to the point of collapse.
A problem with the connection between the ledger board of the deck and the rim joist of the house.
Lag bolts and screws must be spaced properly to maintain the deck’s connection to the house. If bolts are spaced too far apart, they can bend if the deck becomes overloaded or is loose. Thirteen people died in a deck collapse in Chicago due to improperly spaced lag bolts.
If the connection between the ledger board and rim joist is not flashed properly, or if flashing was not installed at all, water can get behind the ledger board and cause the rim joist on the house to rot. This is because rim joist are not pressure-treated and will be susceptible to rot if they remain wet over long periods of time Flashing can be installed in the form of either a metal coil cut to the length of the ledger board and bent to fit under the siding and cover the top edge of the board, or in pre-formed flashing that comes in various lengths. Aluminum flashing should not contact pressure treated wood due to a corrosive chemical reaction of these two materials causing the aluminum to dissolve completely over time. New pressure treated wood uses alkaline copper quaternary (ACQ) chemicals for preservation, which is even more corrosive then previous treatments that were applied to wood. You should make sure that the correct anchors were used for attaching the posts to the pier and that cast aluminum porch post supports are not being used. This change in chemical treating also does not allow for making repairs to existing decks. ACQ in new wood will corrode existing connectors within three years. Decks need to be replaced in their entirety once decay has been observed.
Railings are one of the most obviously safety issues with decks and balconies because it is readily apparent when they are loose. There are many guidelines for railing design and requirements for installation which include height, grasping ability, design loads in both vertical and horizontal direction, space between railings, and even spindle location. Railings also need to be securely fastened to the deck framing with bolts that go completely through the post into a beam or joist. It is unacceptable to notch posts, so make sure that the deck’s support posts are separate from the railing posts. It is important that you inspect the railings at least twice a year and even a sound deck may have problems with the railings that need to be corrected.
The wood used to construct decks should last 20 to 25 years if properly maintained, but decks that are shaded can degrade faster as the wood does not dry out. This process is made worse if the wood has not been stained or painted. In cases such as this the wood loses it structural integrity as well as the ability to hold a fastener.
As wood ages it will expand and contract, causing graying, splintering, and cupping. This is also a sign of the wood losing its structural capabilities and nearing the end of its life cycle. The older the wood is, the more nails and screws will be pulled out from the decking and joists.
See my article on Deck Sealing and Minor Repairs at https://knoji.com/how-to-repair-and-seal-your-deck/
Check any railings or handrails to be sure they are firmly held in place and check that the risers and stringers to be certain they are securely attached and not decayed.
If the area behind the stair treads is open, this opening should be no more than 4” high.
Pay special attention to any areas that tend to remain damp, are regularly exposed to water, or are in contact with fasteners. Use a tool like an ice pick or a screwdriver to penetrate the wood surface. -If you can easily penetrate ¼ to ½ inch, break off a sliver of wood without splinters, or the wood is soft and spongy, decay may be present.
Fasteners include nails, screws or anchors in the ledger board. Tighten any loose fasteners, and pound in any nails that have popped up. (Note: The ledger board should not be fastened with only nails.)
If a fastener appears rusted or corroded, consider replacing it. A corroded fastener can cause deterioration in surrounding wood.
The deck or stairs should appear even without sagging and should not sway or move when tested.
Railing should be secure. Push on them to be sure there is no give.
Verify that they are high enough (most codes require a 36” high railing and usually encourage 42” high railings) with rails no more than 4” inches apart (measured from the inside of the rails) to keep small children and pets from squeezing through, especially if the deck is elevated.
Inspect the flashing along the ledger board. Pay close attention to areas where water is present or runoff from downspouts and gutters may add to the problem.
If you have a grill or fire pit placed on the deck, be sure that you use a non-flammable pad beneath it. Prolonged exposure to high temperatures will cause the wood to become brittle and crack.
Remove leaves and other debris from the deck surface which can hold water. Trim back trees to prevent larger branches from falling and damaging the deck.
Wood decks are very susceptible to the elements and can change in condition at a very rapid rate. A separate detailed inspection and analysis should be made for decks that are over 10 years old. If you have aging deck structures or have a concern about their stability, reach out to a professional to ensure the safety of your family. Remember to inspect your deck twice a year, May and October at the very least.