How To Recognize Rotten Roof Decking

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What is Roof Decking?

Your roof isn’t just decked out in shingles.  If it were, you would have many issues with leaks and storm damage.  Your roof is equipped with many layers that keep your home protected. Shingles protect all of the under layers.  The ice and water barrier helps to keep ice and water out.  Your roof decking serves a more important purpose.  It sets the foundation for the rest of the roof’s layers to lay upon.

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.

Here are some more signs to help you identify wood rot in your roof:

• Wood is darker in spots.
• There are black, white, yellow, brown or grey growths and discoloration.
• The wood feels spongy and weak to the touch.
• The wood easily crumbles or cracks.
• 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:

• There are grey, white or brown growths on the wood (may look like mushrooms or like pizza.)
• The wood has dried out and has long cracks in it.
• There is a musty smell.

The Top Signs You Have Rotten Decking

The most common sign you will see when there is rotten decking is roof leaks.  However, there are a few more things that should raise red flags as well.

Sagging Roof

When excess moisture seeps into the wooden roof decking, there are significant consequences.  You may notice the wood in your attic beginning to warp.  The boards will look wavy or bowed, like too much weight placed on them.   Additionally, as the issue worsens, you will be able to detect the sagging from the exterior of your home.   There may be an entire section of your roof that has begun to sink lower than the rest.  That is a sign that something is wrong with the decking or the rafters.

Water Stains in the Attic

Have you taken a peek into your attic space recently?  If you fear there may be an issue with your roof, that may be the first place to start looking.  When your roof decking has begun to rot, the wooden boards at the top of your attic will have water stains.  These stains typically appear as dark areas.  These stains will tell you that moisture has crept its way to your decking, and it may be time to address the excess moisture before it’s too late. 

Mold or Mildew in the Attic Space

Mold growing in the attic space.  One of the issues homeowners pray they never have to face is mold or mildew growth.  When there is excess moisture in the attic space, and there isn’t proper ventilation to dry it out, it can result in mold and mildew.  You will notice the dark stains popping up all over the attic, as well as the smell of mildew.  Mold and mildew can not only call for extensive repairs and treatment but can also negatively impact your family’s health.  When you notice mold or mildew, rotten decking may be to blame.

Roof Delamination

As mentioned, there are several layers of materials underneath the shingles that keep your roof water tight.  These materials can adhere to your roof because of materials like nails and the wooden decking’s natural texture.  Rotten decking and excess moisture causes the glue to separate and the wooden boards loose structural integrity.  As a result, materials will no longer stick to them (delamination).  When this occurs, you may notice missing shingles or visible flashing on your roof.

Roof Leaks

Decking is your roof’s last line of defense against water.  When it fails, the water will begin to come into your home.  Leaks can also be a cause of rotten decking.  When you notice a leak, it’s possible the rotting has already begun or it has already grown severe.

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. I f 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.