Plywood decking sits beneath the shingles on your roof. If moisture gets under the shingles, it can lead to wood rot in the decking. The shingles can remain in good condition for some time as the decking rots, which hides the damage until it is severe. Knowing some signs of rotting roof decking can help you catch the problem early when it's not as severe.

1. Sunken Deck

Rot causes the decking boards to soften, swell, and warp. This can be quite visible, even from the ground, as the roof will dip down between roof support trusses. If you notice that the roof seems to be sinking or bowing inward, prompt repair is needed. If the rotten decking gives out, you may be dealing with a roof collapse. Even a small collapsed section poses a danger and can be expensive to repair.

2. Excessive Moss

It's time to clean the roof and check the decking if there is a lot of moss growing on the shingles. The excess moisture causing the decking to rot can also create the perfect environment for lush moss growth on the roof. Further, moss can push up shingles and allow more moisture to penetrate through to the decking, thus increasing the moisture problems and worsening the rot. 

3. Spongy Roof

Although it's not a good idea to get up on the roof or walk around, as it is both dangerous and can damage shingles, there are still times when it may be necessary. If you are up on the roof and notice that the surface feels flexible, soft, or spongy, then get down immediately. A spongy roof means that the decking is beginning to swell and rot, which means it is more likely to collapse when you are walking on it. Prompt repair is needed.

4. Musty Attic

A visit to the attic can reveal possible decking rot issues. If your attic has the musty odor of mold and mildew, then it's time to look for moisture. The underside of the roof decking is the attic ceiling, which may be visible if it's not covered in wallboard or insulation. Dark, wet spots and visible mold growth on the attic ceiling also point toward roof decking rot as the problem. 

5. Curling Shingles

Eventually, the moisture affecting the decking will seep into the shingles. The edges of the shingles may begin to cup and curl upward due to moisture exposure from underneath. In some cases, the granules on the shingles loosen and begin to fall off the roof, also due to moisture exposure from the decking. 

Contact a residential roof repair service if you suspect water damage to the roof decking. 

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