Deck Check: Beneath Your Deck

Posted on Posted in Deck Safety

May is Deck Safety Month. It’s the perfect time to do a Deck Check. Last week’s article provided you with the North American Deck and Railing Association’s (NADRA) 10-Point Deck Safety Consumer Checklist. This week, we’ll look into more detail on how to inspect beyond what you normally see on your deck – check beneath your deck.

Before we go to the how’s, let’s familiarize ourselves with the parts underneath a deck.

Raised deck construction falls in two categories: freestanding and attached. Freestanding decks are self-supporting, the posts and frame bears the deck’s entire weight. Attached decks are fastened to the house wall through a ledger board. The ledger is THE piece of wood that connects your deck to your house and supports one side of a deck. It’s a key point of support, so its importance can’t be overstated.

Flashing refers to thin pieces of impervious material installed to prevent the passage of water into places it doesn’t belong. Beams are horizontal members to which the floor boards are directly fastened or which support a system of joists. A joist is a framing lumber that decking is attached to. Decking is the floor surface of a deck. Posts are the vertical structural element that rests on the footing and supports the beam. They bear the load of the entire deck structure including family and friends. Footing is the below-ground support of a deck’s post, usually made from concrete.


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How to check beneath your deck:

Ledger board

Check the fastening method used to connect the ledger board to your house. Bolts are ideal. Nails or anything other than bolts are improper fasteners and may risk the safety of your deck. Given the potential for injury should the deck break apart from the house, it’s important to select the right type of bolt as well as the correct size and spacing of bolts to handle expected design loads. Make sure there are no loose or corroded fasteners. Finding these early can mean the difference between a collapse and a structurally sound deck.

Check the flashing if it’s worn or missing. Without flashing, there’s nothing to prevent water from seeping behind the ledger board that connects deck framing to the house. Over time, trapped water leads to decay, not only in wood building materials but even in metal fasteners that hold the deck together. The result is never good, and often expensive and time-consuming to repair.

Joists and Beams

Inspect each individual joist and beam for rot and termite damage. Poke the wood. If it feels spongy or breaks apart, it’s time to change that particular joist or beam. Make sure to also pay close attention to pieces surrounding a compromised beam.

A common point of failure is where connections are made. Checking the hardware in these areas for rust or corrosion is very important. Even if high-quality, corrosion-resistant hardware was used, water can collect in these areas and cause the wood to rot. Check again with a sharp object to ensure there aren’t any rotten pieces of wood.


Posts aren’t typically the place where a deck will fail, but if they aren’t checked and something goes wrong, it will almost certainly lead to a complete collapse of your deck. As with your joists, feel around for any rot or termite damage in the wood, paying close attention to areas where water could stand for long periods of time. Your hardware should also be checked for corrosion.


The footings, often made of concrete, are your deck’s foundation. They are as important as any other part of your deck and must be checked for cracks. If concrete is cracked or dry, it means your post is standing on very unstable ground. This can cause posts to sway, warping the deck and possibly leading to collapse. Again, checking the hardware that connects your posts to your footings for rust should be a priority.

As you may have gathered, decks are truly susceptible to water damage. Even if your decking is made of vinyl, ledger boards, beams, and joists are often made of wood. If wood is left unchecked, rot, rust, and termite damage may make your deck a safety risk and may lead to a tragic accident. For attached decks, the damage may even extend to your house and also leave your house vulnerable to structural damage.

Aside from regular deck checks, you may want to consider waterproofing your deck. Water can degrade your deck’s wood elements, may cause metal parts to rust or create a rich environment for mold or mildew to grow causing damage and health concerns. There are many options for waterproofing your decks depending on where the deck is located and how the deck was designed.

You may consider deck waterproofing as a DIY project and apply water sealants, waterproof membranes, and rubberized coatings yourself. It is vital to note that even before you start the waterproofing process, deck preparation is essential. Inspect your deck for loose, creaky or obviously warped boards, then repair or replace them. Sand the deck as well, especially if it is old or was treated with a sealer in the past. Having a smooth surface is essential and removing any sealer as much as possible is necessary for adding new waterproofing materials.

Wash away all dirt with a deck cleaner, power washer, or both in combination. You must remove all dirt, mold and mildew. Deck cleaner will help restore the appearance of the wood and remove mildew and stains, such as rust from nails, but is hazardous and should be used with caution. The deck should be dry before using any waterproofing method.

If you don’t have the time or the desire to do so, you may always decide to retain the services of a professional waterproofing contractor. A professional deck waterproofing contractor will inspect your deck and recommend the best waterproofing method for your deck.

Westside Company is a preeminent waterproofing company serving most of Southern California for over two decades. Whether the deck is made of wood, composite, stone or stucco, Westside Company has had experience in working with such.

Aside from waterproofing, Westside Company also provides inspections and deck maintenance services to ensure that your deck is in tiptop shape for many, many years of enjoyment for you and your family. Call us at 310 994 4626 or email at and set up an appointment today. We are serving clients with residential and commercial properties in the greater Los Angeles area, Santa Monica, Malibu, Anaheim among others.