How Long Do Treated Deck Joists Last?
The framing of a home is covered by siding, brick, caulk, and paint. However, the framing of a wood deck is exposed to rain, snow, sun, termites, and other natural elements. That’s why it’s important to understand the deck joists and beams that support your deck and how long they last.
Many times, people want to install new deck planks with old framing. Before making this choice, check the condition of the deck joists. If the joists, beams, or struts are rotting or decaying, they need to be replaced with new ones.
If you’re installing PVC or composite decking, you may also need a new frame. Most companies that manufacture composite decks specify that the boards should be spaced 12 inches apart. The joists in your old deck framing may be spaced 16 inches or even 24 inches apart.
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New vs. Treated Deck Joists
While all deck joists should be made of pressure-treated lumber, things are different now than they were 30 years ago. For example, because preservatives change over time, today’s wood decks are built with posts above grade and attached to concrete footings. This way, they don’t touch the ground and add excess moisture. This method of construction also makes wood rot less likely.
In the past, copper chromate arsenate (CCA) was used to protect pressure-treated wood from rotting. However, due to its arsenic content, the use of this preservative was discontinued as early as 2003. Now, copper alkali quaternary (ACQ) is used to treat wood for preservation. This is a water-based wood preservative containing a water-soluble copper (II) complex and alkyl or aryl quaternary ammonium substituents.
How Long Do Wood Joists Last?
On average, quality joists and decking structures last ten years or more. However, this depends on the weather conditions where you live and how well you maintain it.
Because ACQ-treated wood contains more copper, a barrier is needed between the joists and the metal studs. Corrosion occurs when the zinc in galvanised nails comes into contact with ACQ. Waterproof tape on the joists holds the metal studs and screws in place and protects the wood with a thin membrane. This keeps out preservatives that can be harmful to wood.
The type of lumber you choose for your deck framing is another important consideration. Which type of wood should you choose? Pine, redwood, Douglas fir sapwood or mahogany? Some woods are inherently impervious to decay. Tropical hardwoods such as old-growth teak and fir are some of the most durable woods. Some domestic wood species that are very resistant to decay are black locust, red mulberry, Pacific yew and Osage orange.
Ways to Extend the Life of Deck Joists
To make deck joists last longer, do the following:
- Use pressure-treated lumber for the deck substructure. Cover the tops of the joists with butyl waterproof tape when building a new deck.
- Apply a vapour barrier paint or sealant to the joists before installation; this stops water from entering the deck and joists, thus preventing conditions from worsening.
- Install metal joist hangers and leave at least 1/8 inch of space between the load-bearing joists and the ends of the transverse joists to allow for air circulation
- Use hidden fasteners when laying deck boards to prevent the deck boards from coming into contact with the joists. At the same time, you need to maintain an even 1/4-inch space between deck boards.
- Clean the deck frequently so that dust and other things don’t stick to the boards and cause them to get wet.
- Plan carefully how you will build your outdoor area. If the wrong joists are cut or drilled to install wiring, plumbing, or piping under the deck, the structure will be less stable.
- Inspect all parts of your deck at least once a year to find the problem before it spreads to other parts.
- Don’t put anything on the deck that will absorb or hold water. Don’t put plants on any wooden parts, and don’t put a hose on the deck that could make it too wet, create insects or grow fungus.
When to Replace Deck Joists
Even if the deck looks good on the outside, there may be a problem. Check the base to see if there are any other problems. Over time, deck joists will slowly break down with the weather and may no longer be able to support the deck.
Mould or disease on the old material can spread to the new material, which can accelerate the damage to the entire deck. If the deck joists are to be replaced, other parts of the deck will also need to be repaired. This will keep the deck in good condition and extend its life.
You should look for the following signs to determine if the deck joists need to be replaced:
Mold, Rot and Decay
If you see small holes of rot all over the deck. You should repair all joists immediately so that the rot does not spread to other parts of the deck. Check to see if other parts of the deck are also rotting, especially the underside of the deck. Dirt and water vapour from the ground can easily transfer to the wooden support structure and beams. This will lead to rotting of other parts, such as joists and beams.
Joists with Cracks
Fractured joists show up as cracked boards. If the temperature varies greatly, the wood will begin to splinter over time. If broken joists are found, it is best to replace them all immediately to avoid future problems.
Sinking Decks and Buckling Joists
If part of the deck is sinking and the foundation material is moving. Then it is easy to tell that the joists are flimsy and weak. Broken joists make the deck unstable and can lead to accidents if not replaced immediately.
Another thing you can do is to take a close look at each joist to see if any need to be replaced. The joists can be viewed from the crawl space or unfinished basement so that the deck does not have to be lifted.
Damaged Framing
It is a good idea to repair all major structural portions of a deck with foundation damage. This will maintain the integrity of the deck and extend its life.
Replacement of Deck Materials
The structure of the deck and its longevity is very important in keeping your outdoor furniture in place. If you want to change certain parts of the deck, you may need to replace the foundation and joists to carry the weight of the new part.
Termite Problems
Look for splintered wood and black spots on the framing where termites will feed on dying wood. If you don’t remove them immediately, they can form colonies on the deck and make matters worse.
Deck Structure
Look for pipes or wiring on the deck that are close to the joists. Even if the deck joists are in the right place. However, cuts made to the joists to make room for other structural components may reduce their strength.
Other Possible Solutions
You don’t have to spend a lot of money replacing all your joists because of a minor problem. You can also take the following steps to save your deck.
Repair or Replace Selected Joists
Instead of rebuilding all the deck joists, you can repair the broken ones. This will save you a lot of time and money. If you see a little movement in the deck planks, try replacing the planks and deck joists. For a longer life, replace the joists with redwood or composite materials. If you don’t have any major structural damage to your deck, you may want to take this step.
Remove and Install New Fasteners
Remove any rusted or broken nails or other metal fasteners from the deck so that the rust doesn’t spread to other parts. Then select matching fasteners and refasten the joists or other parts.
Deck Joist Replacement Guide
You may want to replace the material of the joists with a more durable one, such as composite decking material or other pressure-treated wood. If you don’t want to fix all the deck joists, you can have a professional take a closer look at the current deck structure. This way they can check the strength of the joists and give you a targeted plan. They can give you recommendations and other possible options so that you know how much the entire project will cost.
A professional should be the one to replace the floor joists, especially since the joists are hard to reach from the basement or tunnel. This is because you may need to cut through parts of the deck and sub-structure to get to the faulty joists. If you can easily access the joist from the basement and think you can remove and put it back on yourself. Then make sure you wear your safety gear and set up your work lights.
Summary
This is all the information you need to know about deck joists. This blog has the potential to help you choose whether to replace your deck joists or repair them. Keep in mind that if any of the major structural components are damaged, you should replace all parts of the deck.
Frequently Asked Questions
How long do treated deck joists typically last?
Quality pressure-treated deck joists can last 10 to 30 years or more. It depends on the type of treatment, local climate, and how well the deck is maintained. ACQ-treated lumber used in modern construction generally offers reliable longevity when properly installed and sealed. Regular inspection and maintenance are the most important factors in maximising their lifespan.
How do I know if my deck joists need to be replaced?
Look out for these warning signs during your annual inspection:
- Soft or spongy wood when pressed, indicating internal rot
- Visible mold, fungal growth, or dark staining
- Cracks or splits running along the grain
- Sagging or bouncing when you walk on the deck
- Termite damage, visible as hollow wood or mud tubes
- Corroded or missing fasteners connecting joists to the frame
If you notice any of these signs, consult a licensed deck builder before the damage spreads further.
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