Do It Yourself
Check Your Deck Once a Year
Part 1 of 2 – Underneath Your Deck
Did you know that 58% of people involved in deck failure either die or are injured? Between 2000 and 2006 of the 179 deck collapses reported, 33 people were killed and 1,122 people were injured.
Because we at the Reilly Group have seen so many poorly constructed, unsafe decks during home inspections, we’d like to offer a few tips for making sure your deck is soundly constructed and maintained.
Decks require a building permit, but many home owners negligently build theirs without one. Many older decks were also built before there were codes dealing with decks. Because of this, decks often pose a serious safety risk. Remember, the average wood deck is made to last about 15 years, but only with proper inspection and maintenance.
If you’re a homeowner who has a deck you can use these tips to check to make sure your existing deck is safe.
General Sight Exam
Take a general look at your deck. Look for areas that are cracked, loose, worn, warped, split or otherwise eroded. Take notes and make repairs.
Even if you don’t know why, if your deck just makes you feel like it looks unsafe, then get it checked out by a professional. Oftentimes, your visual sense will help you uncover a problem.
Here’s a photo of a deck that imparts that feeling:
Despite the well-maintained home and clean property, this deck is unsafe as it does not have the proper footings or lateral bracing. Also, it’s support posts are too small and at an angle, instead of directly below the deck.
Footings & Posts
All footings should be made of concrete and go to a depth that is below the frost line. Posts should not be buried in the concrete (as this causes moisture to get sucked into the wood which undermines the wood’s strength, causing it to split or decay) but should be bolted to the footing. Your wooden posts should never touch the soil as this will increase moisture and rapidly degrade the wood.
Replace any footings that are too shallow, cracked or misaligned with posts. Replace any posts that are visibly cracked or that are misaligned or warped. You can tell if your posts are misaligned by standing at the end of a row of posts and looking down the line – the posts should all line up in your line of sight. If they don’t line up, replace the posts that are misaligned.
If the posts are over-notched they should replaced. Overnotching is when too many cutouts have been made into the post so that they affect the structural integrity of it.
Post should be at least 4X4 and spaced between 4-5 feet, underneath the floor joists, for maximum strength. If your deck is over 4-6 feet high, a minimum of 4X6 posts should be used and 6X6 is recommended.
Posts with Lateral Bracing
Although not often required by law, all decks over 2 feet high should have lateral bracing to provide extra strength. You can easily see lateral bracing because it is most often at an angle and looks like a letter K or sometimes it crosses each other like the letter X.
Here is an example that shows good lateral bracing:
Lateral bracing ensures that your deck won’t “sway.” You can check that your deck doesn’t sway by standing on the deck at the center of the railing. Beware that if your deck is structurally unsound this can cause it to fall and/or for you to get hurt. Spread your feet apart to form an upside down V and grasp the railing then sway your body from left foot to right foot for at least 30 seconds. If you feel the deck move, then it is unsafe. Get off it immediately until it is fixed. We suggest using a professional contractor to fix your deck at this point.
The deck should be securely bolted to the home.
90% of all deck collapses occur due to failure of the deck ledger joist.* Where it meets the home, the deck should be attached to a “ledger” joist which is a long piece of lumber beneath the deck and against the house that all the floor joists are attached to. The ledger joist should be attached to the home with bolts that are staggered. Make sure all bolts have washers and are tight and that the joist is not cracked or warped. You should tighten the bolts at least once a year. If there are any bolts that have become detached from the joist, your deck is unstable. Don’t go on your deck until it is fixed.
Flashing on the joist will help preserve your deck. If your deck has flashing check to make sure it is underneath the house’s siding and formed over the edge of the ledger joist so that water is diverted away from where it is connected to the house. Water damage can erode the stability of the ledger joist over time.
Ledger joist connection to wooden structure:
Ledger Joist connection to brick structure:
Floor joists should be between 12 and 24 inches apart, depending on the building codes in your area. Spacing that exceeds that is dangerous.
Most decks over 25 years old were built before there were codes for building decks so make sure you check that there is a ledger joist and it is bolted, not nailed, to the home. Check that the bolts aren’t rusty or loose. If there is no ledger joist, don’t use the deck until it is inspected or fixed by a professional.
Look for Part 2 in our August newsletter.
Additional Resources:
North American Deck and Railing Association - Deck Safety Program
North American Deck and Railing Association - Deck Inspections
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