Everyone thinks they can build a deck. Yet every year, hundreds of people are injured from deck failures. And the vast majority of those failures can be pegged to improper installation and lack of maintenance. Common mistakes include bolting beams to the sides of posts, over-spanning, spacing joists incorrectly and using improper wood, fasteners and brackets.
According to installation experts, there are a few particularly egregious construction errors that continue to pop up, mistakes that could eventually prevent decks from being able to handle loads from Mother Nature and the movements and weight of people standing on them.
Here’s a rundown of the most common— and hazardous—errors:
1. FAILURE TO CONNECT
Most deck collapses—90% by one estimate—occur because the deck separates from the house. Poor installation of the ledger board that connects the deck to the house “is central to those failures,” observes Kim Katwijk, who owns Deck Builders Inc. in Olympia, Wash., and is a regular contributor to Professional Deck Builder magazine.
Installers’ biggest mistake is when they nail decks to the ledger board instead of using galvanized lag screws or through-bolts to connect every deck joist through the ledger board to band joists within the house. Not only do lag screws and bolts provide stronger, longer-lasting connections, they also resist the deck wood’s expansion and contraction.
Because an attached deck requires flashing to prevent water intrusion, building a freestanding deck might be a better option, suggests Tim Reed, a Weyerhaeuser Distribution dealer sales rep Phoenix. “Depending on the size of the deck, all you need [for a freestanding deck] is three more 4x4s and three extra bags of cement.”
Katwijk cautions that connecting a deck to a house, even when flashed properly, can create “collection zones,” in which dirt and debris get trapped and comingle with water that, over time, will erode the wood. To prevent this, he uses a “stand off”—a piece of composite wood cut at a 15-degree angle that he coats with roofing construction sealant and attaches to the ledger board. The opening this creates allows litter to slip through.
2. ALLOWING FOR ROT
Rot is a deck’s worst enemy. And three things cause rot, says Katwijk: exposure to excess moisture, oxygen and temperatures over 37 degrees Fahrenheit. To prevent rot when he’s joining two pieces of deck wood, Katwijk slips a 1/2″ fascia between the boards to let in more air, and caulks the fascia to limit the collection zone.
3. IMPROPER FOOTINGS
Decks are likely to fail, and their posts likely to rot, when footings are improperly installed. Eric Kent, owner of Archadeck of Charlotte (N.C.), says his decks sit atop footings that incorporate twin 16×16 cinderblocks with concrete piers and 6×6 posts, dug into a hole 12″ to 18″ deep.
4. FAILING TO FOLLOW MANUFACTURER INSTRUCTIONS
Particularly for manmade materials, follow recommendations to ensure the performance and longevity of the deck. For example, Tamko’s installation instructions for its EverGrain decking recommend that a sister board be used at butt joints to provide adequate fastening areas. The supplier also advises that decks need to be fastened at every joist perpendicular—as opposed to toe-nailed—to the deck surface.
5. LACK OF MAINTENANCE
The integrity of a deck’s construction can be undermined if homeowners aren’t vigilant about maintenance. Even composite decking has some recommended upkeep, such as washing off debris.
Most decks need a thorough cleaning twice a year, says Stacey Baker, a Weyerhaeuser Distribution dealer sales rep in Tacoma, Wash.; consult with the manufacturer for exact recommendations. Educate homeowners about the importance of regular maintenance—and the consequences if those practices aren’t maintained.
6. IGNORING YOUR SURROUNDINGS
During the building process, installers should consider the surrounding environment. In the Pacific Northwest, for instance, Baker says pine needles will get caught in typical 1⁄8″ gaps between deck boards, so 1⁄4″ gaps would be more conducive to efficient deck maintenance. Consult with your local rep for special considerations for your area.
Pictured above: Attach decks through the ledger board to the band joists using lag screws or throughbolts. Image courtesy of Glenn Mathewson, buildingcodecollege.com.