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HOW ROTTED ROOF DECKING AFFECTS YOUR ROOF AND HOME
What is Roof Decking?
Roof decking or sheathing refers to the thin boards of wood that span the trusses and support the rest of the roof. If your roof decking gets wet, it can develop wood rot and impact the performance of your whole roof. This problem can go unnoticed, as damaged roof decking hides beneath shingles and above the attic insulation. Sheathing isn’t normally visible, so it can be challenging for homeowners to find this problem before it becomes serious. However, you can easily avoid this problem if you know when to look for wood rot on your roof decking, how to identify the problem and how to fix it.
What is the Best Option for Roof Decking?
Most roof decking is made from plywood or a plywood composite known as Oriented Strand Board (OSB). OSB is composed of intertwining wood strands bonded together by a waterproof resin and is a popular option due to its low price point. Plywood, while a bit more expensive than OSB, is much denser and provides greater protection against moisture.
What Causes Rotted Roof Decking?
Water is your roof’s number one enemy. Since roof decking is made from wood and wood composites, it is particularly susceptible to rotting and water damage when continuously exposed to sustained or excess moisture. Water seeps into your roofing system in many different ways. Old and worn out roofing shingles, overflowing roof gutters or spouts, torn flashing around chimneys, ice dams or snow accumulation during the winter season, excessive humidity and rising heat in the attic, and inadequate roof ventilation can all allow water and moisture to slowly make its way into your roofing system and lead to rotted roof decking. Not repairing a leak as soon as you notice it can lead to mold, damage to the structure of your home, water damage, and even fire if water comes in contact with electrical wiring.
What are the Signs of Rotted Roof Decking?
There are many signs of rotted roof decking:
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Roof leaks
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Wet spots on the ceiling
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Stains on interior walls
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Peeling wallpaper
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Water stains on rafters
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Mold and mildew in your attic
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Sagging ceiling or roofline
One of the most common signs that a roof’s decking is damaged is a roof leak. Water leakage can lead to ceiling spots or leaks, stains on interior walls, cracked paint, or peeling wallpaper. A quick inspection of the attic might uncover dark water stains on the rafters or in the insulation, or even light passing through holes in the roof. If left undetected, mold and mildew will develop in the walls, ceilings and insulation. A sagging ceiling or roofline is another clue that there are major problems with a roof’s decking and the roofing structure. Soaked or waterlogged decking can warp, which can lead to a bowed or wavy roofline and ceiling.
Since your roof is consistently exposed to various weather conditions, you should have your roof inspected twice a year – once in the fall, after hot weather has subsided, and once in the spring, after the danger of ice and snow is behind you. You should also have your roof inspected after a big storm, hurricane, or other potentially damaging weather event.
Why is Rotted Roof Decking a Problem?
Most roof decking, also called sheathing, is plywood or oriented strand board (OSB). These thin sheets of wood absorb moisture when exposed to it through excess condensation or a roof leak. When sheathing is exposed to moisture frequently, there is always a chance it will decay or develop wood rot. While a single exposure to moisture is unlikely to lead to rot, routine water exposure may.
How to Identify Wood Rot in a Roof Deck
If your decking is rotting, it may or may not have developed a fungal growth that can ruin its stability by eating away at it. Whether or not there is a fungus, or just normal decay of wood due to moisture, rotting roof decking can cause several problems for your roof and your home, including:
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Bowing or bulging: Moisture and wood rot may cause your decking to sink in or swell up. From the outside, this looks like you have a bulging or bowing spot on your roof. The shingles above this spot may not function properly. Further, the decking can eventually fall in.
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More fungal and mold growth: Unchecked wood rot and moisture can lead to the growth of other fungi and mold. These can reduce the air quality of your home and may make the symptoms of certain respiratory conditions worse. There are two main types of wood rot: dry rot and wet rot. There are also several subspecies of wood rot fungus. Therefore, every wood rot infestation may look different. Wet wood rot tends to look discolored or darker than the roof around it. Dry wood rot tends to look like a fungal growth, and it makes the wood cracked and dry.
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Damage to insulation: Wood rot and moisture can damage your attic insulation, which is beneath your decking. This damage can reduce the energy efficiency of your home and cause you to spend more money heating or cooling it.
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Damage to other wood: Dry wood rot (one type of wood rot) can spread to other wood in your home, potentially even to structural wood. Replacing structural wood can be expensive, so it is best to stop dry wood rot as soon as you find it.
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Damage to other home systems: If the moisture issue that caused the wood rot goes unresolved, it may damage many other parts of your home, including the electrical system. Wet rot may also spread to other wood if the moisture is left unchecked.
Below are more signs to help you identify wood rot in your roof:
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Wood is darker in spots.
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There are black, white, yellow, brown or grey growths and discoloration.
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The wood feels spongy and weak to the touch.
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The wood easily crumbles or cracks.
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There is a damp, musty smell.
An experienced roofer may suspect wood rot simply by stepping on the shingles above the rot and feeling it give more than normal.
Signs of dry wood rot include:
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There are grey, white or brown growths on the wood (may look like mushrooms or like pizza.)
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The wood has dried out and has long cracks in it.
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There is a musty smell.
When Should I Check My Roof for Wood Rot?
Tearing up a few shingles to look at the decking isn’t a normal home maintenance practice that you’d do on a monthly or yearly basis. You should look for wood rot either when you don’t know the condition of the deck (as in, you’re buying a new home) or when you suspect that moisture may have penetrated to the roof deck. You should ask a professional home inspector or roofer to check your decking for wood rot when:
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You’re about to sell your home and want to make sure your roof will boost your home value.
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You’re purchasing a new home and want to make sure its roof is in good condition.
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Your roof has had a leak, ice dam, tree damage or other potential damage.
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You’re doing a full roof replacement.
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Your attic has developed moisture issues.
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You are about to install new attic insulation or ventilation.
If your roofer has reason to suspect that your roof decking may not be in good condition, they may recommend you let them look at it. They may not have to remove shingles to do so. Instead, they may be able to spot the signs of decking rot from inside the attic.
Why is My Roof Decking Damaged?
Leaks and condensation are the two most common causes of a rotting wood deck. It makes sense to look for deck rot around notorious leak points, such as skylights, roof penetrations and anchor points for roof-mounted items. In order to fix the problem, you first need a professional roofer to resolve the underlying leak.
What if My Roofer Didn’t Replace My Roof Decking After a Leak?
Homeowners may be concerned if they discover that although decking is routinely replaced as part of roof repair, the decking on their roof wasn’t. This may be a cause for concern, or it may not. Not all wet decking needs to be replaced. If only a small area of the decking was exposed to water, and it wasn’t exposed long enough to damage it significantly, your roofer may choose to leave it in place. However, your roofers may have also made a mistake by leaving behind decking that did need to be replaced. To start, ask your roofer why they chose not to replace your decking. If you’re not satisfied with their answer, reach out to another roofer for a second opinion.
Ask a Professional About the Condition of Your Roof Decking