If you built your deck without using the best-treated lumber, you may need to replace your deck boards and deck joists. Be aware that replacing decking and joists can be very difficult and take a long time. Unfortunately, if the rot is very severe, then repairing the rotted deck and joists may require extensive work.

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1. Why Do Decks Rot?

Deck rot is caused by the simple fact that any wood that is constantly exposed to moisture and cannot be dried will rot. To avoid deck and substructure rot, you should start with the best-treated lumber you can find. When building a new deck table, you may want to purchase treated lumber that can be put in direct contact with the ground or buried in the ground. Pressure-treated lumber contains the most copper preservative agents.

If a deck drainage system is not constructed correctly, the wood will often rot due to moisture. A deck drainage system below the joists can damage the deck in two ways:

First, this system absorbs moisture. Drainage systems attached to the underside of deck joists create high levels of moisture. The sewer system is like the bottom of an elevated swimming pool. A lot of stuff can build up on top of the sewer system. This debris decays and forms an organic substance that absorbs moisture. The only way for air to circulate is through the space between the top plates, which is about a quarter of an inch wide or less. This is where the system drains.

Secondly, the heat of the summer months further heats these trapped moist woods, which accelerates the decay process. Over time, the humidity, heat, and lack of air circulation lead to wood rot.

2. Factors that Make Decks Rot Faster

There are several other things that can accelerate the decay of a deck. The most important one is not installing deck joist tape on top of the deck joists before laying the lumber. The decision to make this tape was made when it was discovered that the fasteners used to hold the deck in place were causing the deck to rot. By simply applying this tape to the top of the joists, you can eliminate the need to replace rotted deck joists.

The problem is that deck screws can cause tiny cracks in the top of the deck joists. If water seeps under the deck into the cracks, it will cause the treated wood to swell. Over time, this action will make the cracks larger. If the cracks are larger, more water will enter.

The fact that there is a lack of tape can also easily lead to deck board rot. While decking keeps moisture out of the top of the joists, the tight space between two boards is more susceptible to moisture. Capillary attraction draws water under the deck boards, and it takes a long time for water to evaporate. When decking is exposed to sunlight, the temperature can rise above 120 degrees Fahrenheit, accelerating the rotting process.

3. How to Prevent Deck Rot

To prevent deck boards from rotting, you should first buy the best-treated lumber available. Again, use only treated lumber that is approved for direct contact with the ground or for burial in the ground.

If it is not possible to tape the joists because the deck is already built, try to keep the spaces between the boards as clean as possible. Each fall, inspect the deck and clean up any debris that has accumulated on top of the joists. A stiff brush and water spray will remove all dirt and dust from the wood.

If you find mold, mildew, or algae on the sides and bottom of your deck, clean it immediately. These organisms can cause deck planks to rot. Your goal is to have all treated wood sitting out in the open looking new at all times.

Do not paint or seal the underside of the deck joists. Paints and film-forming sealers make it more difficult for treated wood to expel moisture. If not handled properly, trapped moisture can cause treated wood to rot.

3.1 Install a Drainage System for the Deck

Installing a drainage system below the deck is one of the best ways to prevent deck rot. Installing a deck drainage system above the joists is most effective. All joists and beams will be completely protected from water ingress. The screws will stay in place longer with this type of installation.

If you’re building your deck yourself, choose an easy-to-install above-joist system. When you hire a builder, be sure to ask if the drainage system will be located above the joists.

If you want the bottom of the deck to look polished, you should cover the joists with waterproofing material. The deck drainage system above the joists will protect the waterproofing material. Add air to the ceiling below the deck with strip vents to make it safer, especially in areas with high humidity. These vents will exhaust hot air and prevent excessive high or low temperatures.

3.2 Selecting Pressure-treated Wood

Many things can cause pressure-treated wood to rot. Treated wood is known to rot. One reason for this problem is poor quality control at the treatment plant. Sometimes the treated lumber you buy may not have adequate protection. Unfortunately, you can’t test it before you install it to make sure it will work well.

If you think you might be at risk, or if you buy treated wood of a lower quality. You can also treat these woods with a liquid that you make yourself. A copper naphthenate solution can be brushed onto deck planks to help them last longer.

3.3 Ventilate the Deck in the Right Way

Keep all treated lumber at least 18 inches off the ground. This is the best way to allow air to flow through the deck. The next thing to do is not to install a decorative ceiling under the deck. Even with ventilation slots in the ceiling, deck joists can rot. This is because the deck may not get enough moving air. We expect that any standing water on the deck planks needs to dry out as soon as possible.

4. How to Fix a Rotted Deck

If you are handy, you may be able to repair or replace rotted framing yourself. In addition, you will need to remove the joists from all the deck boards above them. You’ll need to remove any joist hangers or tie rod connections and separate them from the end band planks. If you want to know when to replace decking or joists, you should know how to inspect them. This should be true regardless of the size of the project.

4.1 Step 1: Look at the Deck and Find Out What Needs to Be Fixed

The first thing you need to do is to take a thorough look at the deck and find any rotted deck planks that you think need to be repaired. To find rotted wood, use an ice pick or a pointed long-handled flathead screwdriver. Applying light to moderate pressure to wood that has rotted will allow the ice pick to pass through easily.

Try an ice pick on a piece of wood that is not rotted to see how much force you can use to insert it 1/4 inch into the wood. That way, when you come across rotted wood, you’ll know right away.

You should start by looking for rotted wood where the deck joists meet the deck above, at the top. Work your way along the entire length of the frame, inspecting from both ends.

4.2 Step 2: Remove the Deck Planks and Look at the Joists

You may be wondering how to replace the deck joists. The first step is to remove the deck fasteners. This may be difficult to do if the fasteners are nails sunk into the wood deck. No doubt the top of the wood will be damaged if you use a cat’s paw nail removal tool.

If the trim boards are laid with hidden screws and plastic tabs, and the tabs fit between each board. Then your job will be easy. To remove all the screws, use a drill or driver in reverse.

4.3 Step 3: Removing Rotten Wood

Use a tool or saw to see off the rotted wood. Cut and remove all rotten wood.

4.4 Step 4: Use Wood Filler with Care

Keep in mind that the filler you intend to use to replace rotten wood will not add any structural value to the deck framing. In addition, fillers usually do not adhere well to treated lumber.

In this way, you’ll find that it may be difficult to repair using filler or epoxy in a way that is both aesthetically pleasing and consistent with the appearance of the original floor joists. If you do want to use a filler, be sure to brush copper naphthenate over the newly cut or chiseled wood to make it last longer.

4.5 Step 5: Reinforcement on the Joists

Laying new treated lumber over deck joists that do not have severe wood rot is the best way to repair rotted deck joists. If the rot is only in the top inch of the joist, treated 2×4 can be screwed to the rest of the deck joist.

All areas secured with 2×4 screws must be at least 3 times higher than the depth of the rot. In other words, if only one inch of the floor joist is rotted, a 3.5-inch 2×4 will suffice.

Note that if the rot is bad enough, the deck boards must be replaced instead of patching it.

4.6 Step 6: Replace with New Deck Boards

If securing with nails has been sufficient, it is now time to lay down new deck boards and secure them to the 2x sister material. Cut the deck boards to the right length and width, then secure them together with nails or hidden fasteners.

5. When to Replace Rotten Deck Joists

If at least 20% of the width of the deck joists is rotted, it’s time for new ones. Now you need to know how to install the new deck joists. Because of all the rot, the joists aren’t as strong as they once were. It may no longer even meet the span requirements of the building code.

6. To Summarize

You want your deck to be safe for you, your family, and any friends who come to visit. Then it’s best to start inspecting your deck for rot as soon as possible. Perform a thorough inspection of the joists, deck boards, and railings. If you are unsure how to inspect your deck for rot, hire a professional.

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