Why Are My Deck Boards Rotting? 4 Common Problems and How to Fix Them

Rotting deck boards are no joke. Not only are they unsightly, but they also lead to serious damage. Over time, this could impact the structural integrity of the deck itself, leading to extensive repairs or even a full replacement. Board rot is attributed to several factors, including fungal growth, untreated wood, moisture, and, of course, wood-eating termites. So if you’re asking, “Why are my deck boards rotting?” continue reading. Let’s go over the major causes in order of how common they are. 

1. Moisture

Moisture and wood are mortal enemies, so it comes as no surprise that this is the leading cause of deck board rot. Everything here depends on the drainage system surrounding the deck. If this system isn't working properly or is poorly designed, even regular rainfall can pool up and start to deteriorate the boards. This is especially true near the foundation. Leaky gutters or downspouts also contribute to this issue. 

The Solution 

As with all wood rot, the solution involves replacing the impacted boards or patching up problem areas with epoxy. However, that won't actually fix the underlying issue. You have to find out why there's poor drainage to do that. Ensure gutters and downspouts are pointed away from the deck, and make sure that water is never allowed to pool up or stagnate anywhere near it. If you’re building a deck from scratch, build it on a slight incline. This will automatically direct water away from the deck. Contact a local water restoration company for severe issues with moisture damage on your deck.

2. Fungal Growth

Where there's moisture, there's also fungus. This includes mold, of course, but other wood-decaying fungal species like Serpula lacrymans and Armillaria. Given the proper conditions and time, these fungi will eat the wood from the inside out. Wood-eating fungus loves shaded areas, moisture, and decaying matter (like yard debris). Decks provide all three. Mold also presents unique health hazards, as toxic species can lead to health issues from allergies to respiratory conditions. 

The Solution 

As before, start by patching up rotted parts of the wood or replacing entire boards if necessary. However, that's only the beginning. If left unaddressed, the fungi will likely return to cause more trouble. The best way to handle mold causing deck boards to rot is to cut off all of the things that fungi need to survive. Eliminate stagnant or pooling water and try to introduce more sunshine. This can be as simple as moving deck furniture around at regular intervals. Remove debris from your deck (and around it) and stay on top of cleaning tasks. Consider laying down a protective deck sealer and, if there's an extreme amount of mold growth, contact a local remediation pro. 

3. Untreated Wood

Untreated wood is more susceptible to moisture damage and fungal growth than treated wood. Untreated wood is easily damaged, and a cracked or cupped board will trap moisture, which leads to fungal growth. Wood that hasn't been treated is also susceptible to galvanic corrosion, which is when nails corrode and allow moisture to seep in. Untreated wood can also be a haven for pests, including termites. So, over time, untreated wood can cause 

The Solution

As always, treat or replace the impacted boards. After that, things get a bit tricky. It's not as if you can go in and rebuild the entire deck with treated lumber. Instead, amp up your maintenance routine. Clean the deck regularly with a specialized cleaner and apply a dedicated wood sealant. Consider staining the deck for even more protection. You should also take extra steps to minimize exposure to moisture, which are outlined above. Contact a local deck refinishing pro to discuss specific steps relevant to your fixture. 

4. Termites

Termites are pesky little insects that feed on wood, weakening the boards and making them more prone to rot. Are you wondering, “Why are my deck boards rotting?” This could be the cause. Termites eat the cellulose from the inside out, creating tunnels throughout the interior. This weakens the structural integrity of the wood, though it doesn't cause rot by itself. These tunnels are a perfect repository for moisture and, as such, various types of fungi. That will open up the deck boards to significant rot. 

The Solution

The solution depends on how bad the infestation is, though most cases require a local exterminator who specializes in termites. They'll suss out how big the colony is and act accordingly.

Once the termites have been eliminated, repair the impacted boards with epoxy or wood putty. Replace the boards outright in severe cases. As for prevention, ask your pro about liquid soil treatments that will act as a barrier around the foundation to keep termites away from the deck. 

Signs That You Have Rotting Deck Boards 

There are a number of ways to figure out if your deck boards are rotting. Here are some signs worth considering. 

• Spongy texture: If you feel a soft or spongy texture when you press the board, or even when walking on it, it could indicate the presence of rot. 

• Crumbling or crackling: The same goes if the wood crumbles when touched or if it appears cracked in certain areas. 

• Peeling or bubbling paint: If the deck boards are painted and that paint is peeling or there are bubbles on the top, it likely indicates that the wood underneath is absorbing moisture. This, of course, causes rot. 

• Discolored wood: Rotted wood tends to be darker when compared to healthy wood. Look for dark patches or discoloration in your deck boards.

• Visible mold: If mold is visible on the surface of a board, it's likely infected the interior as well. The same goes if the boards have a damp, musty smell. 

How to Prevent Deck Board Rot 

Prevent deck board rot by following some common-sense guidelines. Keep the deck clean and well-maintained, pay special attention to debris and moisture, and remove both immediately. You should also seal the deck regularly and move furniture and fixtures around at regular intervals to allow sunlight into areas that are typically shaded.  

When to Call in a Pro

Consider calling in a pro whenever you have significant rot throughout a deck, as boards may have to be replaced. The same is true when encountering mold, particularly toxic mold. Contact a remediation pro unless you have plenty of experience with this foul fungus. The presence of termites also requires a professional, as extermination is a tricky process.