Wood Rot in Decks and Porches
Rotted structural members can go unnoticed. This ledger board was rotted up against the house but went undetected until the decking was removed.

Exposure to the elements and proximity to the moist ground can leave wooden decks and porches susceptible to rot. Compromised structural elements in a deck or porch can lead to serious injury, so it is vital that homeowners periodically check for rot-causing fungus.


Identifying Wood Rot
Wood rot is the result of fungus that feeds on moist wood. As the fungus sends tiny threads into the wood for food, the wood fibers are gradually broken down and the wood decomposes. The two main types of wood rot differ in appearance and effect. The first produces brown-colored spots, and the affected wood tends to break off in cubes, inspiring the name “cube rot” or “brown cubical rot.” The second type of rot leaves a white or yellow color on the wood and gives it a spongy or stringy feeling. A common mistake is to call rot “dry rot”—this phrase is often used to describe very old wood that has long-since rotted and dried out. Wood rot always requires moisture to feed on.

Sometimes homeowners confuse stains with rot. A stain might be caused by mold or mildew that affects the surface of the wood. These blemishes do not impact the integrity of the wood itself. Conversely, healthy-looking wood might hide rot-producing fungus. To determine if wood has been affected by rot, a homeowner should use a sharp, pointed object like a pick or a screwdriver and attempt to pierce the wood in question. If the suspected area breaks off in chunks, the wood is rotted. Soft or “punky” wood is a common sign of rot. Moist or wet areas in the wood also indicate potential rot.

Common Trouble Spots
Decks and porches are typically built to leave wood vulnerable to rot. In particular, porch or deck undersides often rest close to the ground, where moisture can take hold. If possible, a homeowner should use a flashlight and inspect the underside of the porch or deck for areas of rot. Rot tends to migrate from joists to the underside of deck planks —an important area for routine checking.

In a deck or porch that fastens directly to a house, there can be potential for rot. Inadequate flashing or water run-off problems can lead to pooling, which will inevitably lead to rot. Homeowners should check all the areas where the deck or porch contacts the home. Where the deck or porch comes into contact with house siding is another potential trouble spot, both for the structure and the siding.

Fight Back to End Rot

The presence of wood rot doesn’t necessarily mean all is lost. Do-it-yourself remediation options are available, providing the scope of rot infestation is not too great or seriously affecting structural members. Compromised wood should be removed, and up to two feet of additional wood in either direction of the decay should be removed and replaced. Other options include the use of penetrating epoxy sealers on decaying areas. These products harden the soft or “punky” rotting wood and are meant to halt the spread of rot.

If any structural member needs replacing, it is best to call a professional.



Any direct contact with the ground or masonry (such as concrete) can lead to wood rot. Portions of the deck or porch that contact masonry should be inspected regularly for signs of rot.

There are a number of steps a homeowner can take to prevent wood rot on decks and porches. Since rot requires moisture, it is essential to keep decks and porches as dry as possible. Downspouts and water run-off should be guided away from the structure—this means adequate flashing, gutters, etc. Potted plants resting on the deck or porch can cause moisture pooling; likewise, plants and shrubs planted nearby can contribute to moisture and water buildup on and around a wooden structure. Even the sprinkler can be a culprit—homeowners should take care that watering tools not spray the porch or deck.

Products like stains and sealers can treat the wood and keep moisture from leading to rot. Most of these products are meant to be reapplied. Homeowners should follow manufacturers’ guidelines for reapplication. The active chemicals in these agents vary as well. Sodium borate is one well-known fungicide. Penetrating epoxies are also useful as stabilizers for decaying wood.

There are also products on the market to protect the joists and underside of the deck boards from moisture. The use of specially treated wood will also ensure a longer-lasting deck or porch.

To ensure that the underside of the porch breathes properly, it is critical to maintain airflow. This space should not be completely enclosed. Any concrete used for a foundation should not come into direct contact with wooden support posts, because concrete absorbs water. The use of deck spacers is important in deck construction to help minimize areas where wood meets wood. Spacers are particularly vital where the deck meets the house or ledger board. Where the ends of deck boards might meet, a 1/4-inch space is advised to allow for ventilation.

Credit: Renovate Your World