The roof decking may also be referred to as the sheathing. It is the plywood underlayment that forms the base of the roof. Underlayment and shingles are attached to the decking, so it should never be exposed to the elements. Ideally, the decking will rarely require replacement and can be used under new shingles over and over again. Occasionally, though, damage can affect the decking. The following are types of damage that can necessitate the replacement of the decking.
Decking can develop rot because it is made of wood. Ignoring shingle damage and leaks is one cause of rot. Moisture that seeps beneath the shingles will dry slowly in the decking. The decking wood will swell and fibers will begin to break down. Rot can also affect decking from the underside. If your attic isn't properly ventilated, moisture can collect against the underside of the decking boards and rot may set in. Water damaged and rotting decking boards may look swollen, feel spongy, or have mildew and mold growth on them. Rot can't be stopped, so the decking must be replaced.
Punctures or holes through the decking are typically the results of storm or tree damage. Branches and other debris that lands on the roof can punch a hole right through the decking and into the attic. Animals, particularly larger ones like raccoons, may also cause punctures. The animals tear up shingles and chew through decking in an attempt to get into a warm, dry attic. Regardless of the cause, holes are difficult to repair. In some cases, a roofing contractor can patch a decking hole if it is fairly small, but larger damage will require the replacement of the affected decking sheets.
Warping, much like rot, is usually caused by moisture. Warping can occur along with rot, or it may occur without any rot at all. This is because the decking wood may warp if it becomes wet, even if it dries out quickly enough to avoid rot issues. This typically occurs when there is a leak that is repaired quickly but not fast enough to prevent the saturation of the decking. Rot can also be the result of sub-par decking materials that simply tend to warp as they age. Warped decking won't lay flat, which means there will be gaps on the roof that can lead to leaks.
Contact a local roofing company for more help if you suspect issues are plaguing your roof decking.