Most homeowners, when they consider roof replacement, think of the roof shingles, and the structural pieces beneath them. The roofing system starts with the roof decking, or plywood sheathing, to which the shingles, underlayment, flashing, and fasteners are attached. The roof replacement cost could increase if any of these layers begin to rot or deteriorate.
Roofers get the most common and expensive problem after completing a roof-topping job: rotted roof decking. When the contractors remove the original shingles from the roof and expose the rotted plywood, most homeowners aren’t aware of the problem. Most of the time, homeowners don’t know there is an issue until the contractor has removed the roof shingles and can see the underlying damaged plywood (soft, weak, moisture-damaged). From then on, repairs are inevitable, as new roofing materials cannot be fitted over damaged decking due to structural and safety issues.
Damage to roof decking is not the only factor that affects roofing costs. It significantly affects the amount of work, material costs, installation timelines, the structure’s stability, and the roof’s performance over its lifetime. Homeowners can also do a lot to be prepared for the cost of their deck repair if they understand what causes plywood to deteriorate and how contractors can address it.
What Roof Decking Actually Does
Roof decking, also known as roof sheathing, is a structural surface affixed to the roof framing. This is then overlaid with shingles and underlayment. Most houses are built on a plywood or oriented strand board (OSB) decking because it offers the following:
- Structural support
- Nail-holding strength
- Weather resistance
- Load distribution
If there is no solid decking, roofing materials can’t stay securely affixed to the home. Decking also helps to spread load from;
- Snow accumulation
- Roofing materials
- Wind pressure
- Maintenance foot traffic
However, if the plywood becomes weak due to moisture or age, it will cause the rest of the roof to break.
Why Roof Decking Starts Rotting
Typically, roof decking deterioration begins when water enters the roof. Small leaks can allow water to seep under shingles over time, causing water to seep through the plywood. The most common reasons for rotted roof decking are:
- Aging shingles
- Flashing failures
- Poor attic ventilation
- Ice dam formation
- Storm damage
Damage to roofing materials due to moisture is difficult to detect and may only be identified after a prolonged period, as it often occurs within the roof. Roof decking is especially vulnerable in wet climates and areas with heavy rainfall because ventilation systems cannot remove moisture from the attic. Exposure to water will diminish plywood’s strength, soften it, and cause it to warp over time.
Hidden Damage Often Becomes a Major Surprise
The problem with replacing roof decking is that damage to the roof deck usually is not identified until the roofing project is underway. Until the shingles and underlayment are removed, contractors will not have a clear view of the decking’s condition. Some of the following roof conditions seem to be fairly stable:
- Soft plywood sections
- Mold-contaminated decking
- Delaminated wood panels
- Structural moisture damage
- Sagging roof surfaces
Many roofing quotations do not include the cost of replacing the roof decking, but do provide an allowance for it. But there are a few additional costs one may not be aware of until the old roof is fully exposed.
Why Rotten Decking Increases Roofing Costs So Quickly
If the plywood is replaced with another roofing material, there is an additional cost to the roofing project beyond the cost of the roofing material. If damaged decking is discovered, it will be the contractor’s responsibility to:
- Sand damage out of the wood (rough edges)
- Remove and replace broken items; dispose of damaged materials.
- Replace some of the plywood boards.
- Add strength to the structure, if required.
- Re-secure roofing components
These repairs will require additional man-hours, tools, materials, and time. The costs of structural repairs may be even higher if damage extends beyond the rafters or roof framing. This can sometimes mean that the roof will have to be replaced before installing new shingles. The larger the damage and the more costly it will become as they continue to be ignored due to moisture.
Plywood Replacement Costs Depend on Damage Severity
The cost of replacing the roof decking can vary widely depending on the extent of deterioration. Minor repairs and changes to the roof are much more affordable than major repairs and restorations. The replacement pricing is influenced by a number of factors:
The quantity of broken pieces of plywood.The degree of broken plywood.
- Roof accessibility
- The pitch of the roof and the roof height.
- Local labor costs
- Structural repair requirements
If you’re looking for a roofing solution that requires more advanced safety equipment, it may be more expensive. These will usually be cheaper to repair, and in most cases, buildings with a pitch of up to moderate (2:1 or 4:1) and no more than one storey will be easier to repair. Some homes will only require replacing a few sheets of plywood, while others may need to replace their entire deck with plywood. The final cost could be related to the extent of moisture intrusion before repairs.
Water Damage Rarely Stays in One Place
Water can travel far and wide when it gets through glaring holes in your roof. Water will flow under underlayment and on decking surfaces without anyone ever knowing inside. If stains are seen on the ceiling, then moisture has impacted:
- Multiple plywood panels
- Roof framing
- Insulation
- Ventilation systems
- Fascia boards
This ‘secret’ type of spread is often one of the reasons why deck replacement work is much more extensive than it should be. Water also reduces the effectiveness of fasteners, as soft or decaying wood will not hold nails. If a roof is placed over a roof decking, it will not perform any better than the underlying decking.
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Mold and Moisture Make Repairs More Expensive
If the decking is rotting, it can create additional moisture issues that complicate the project. Molds grow best in damp wood in poorly ventilated areas of the attic. If it is found that mold growth has occurred, the Contractor may need to:
- Remove affected materials
- Improve attic ventilation
- Replace insulation
- Treat structural surfaces
- Correct airflow problems
The extra time required for mould remediation may also necessitate special cleaning processes to be carried out before the roof is installed. Decks will continue to take their toll on a house until all the root causes of its chronic moisture problems are corrected, either by ventilating the house or by repairing the leak. Without addressing the issues that can cause deterioration, it will persist under the new roof.
Roof Ventilation Plays a Major Role
One of the main culprits of long-term decking deterioration is poor ventilation. If there is inadequate airflow, moisture and heat are trapped under the roof year-round. This is because if there is poor ventilation, it can result in:
- Condensation buildup
- Wood rot
- Mold growth
- Premature shingle aging
- Structural moisture damage
The attic rooms of older homes are often hard to keep at a controlled temperature due to inadequate intake or exhaust ventilation. Some contractors will be called upon to add ventilation enhancements when replacing the roof to prevent future moisture problems. By keeping plywood dry through proper attic ventilation, the roofing system can last longer.
Click to find out about Roof Ventilation Upgrades: A Look at Modern Roofing Technology.
Older Homes Often Require More Decking Repairs
Old roofs often have many years of moisture issues, along with several layers of roofing material and outdated roofing techniques. As a roof ages over the years, it may make plywood more vulnerable to:
- Long-term condensation
- Repeated leak exposure
- Structural weakening
- Nail fatigue
- Warping and delamination
If your property is an old home, the decking may not meet current building code standards. The number of structural problems uncovered during re-roofing an old home is much greater than one would expect. The cost of these repairs is tied to the project, but they certainly strengthen the house and make the roof more reliable.
Why Quality Installation Matters So Much
The biggest culprit behind early decking degradation is improper roofing installation. Poor flashing, poor ventilation, and poor waterproofing allow moisture to seep in, causing slow deterioration of the plywood below the surface. Professional contractors make a detailed evaluation:
- Decking condition
- Moisture exposure
- Ventilation balance
- Structural stability
- Fastener integrity
Professional roofing contractors such as Northwest Roof Maintenance know that the risks are high if shingles are replaced without first repairing the decking. Roof repair companies in Vancouver, WA can assess the roof’s structure before installing new roofing materials. This can be shortened and lowered in time and cost, but usually creates significant future structural issues by replacing the decking.
Preventive Maintenance Helps Reduce Future Costs
It’s never too late to have a roof routinely inspected, and it’s one of the best ways to prevent major roof deck damage. If moisture is detected in structural wood parts, it will not spread because it will be detected early. Regular maintenance can be used to detect:
- Flashing weaknesses
- Ventilation issues
- Soft roof areas
- Moisture buildup
- Early wood deterioration
By resolving these issues in a timely fashion, future restructurings may be avoided. The cost of preventive maintenance is less than the cost of replacing large areas of rotting roof decking.
Frequently Asked Questions
What causes roof decking to rot?
The most likely causes of rotted roof decking are a leaky roof, poor attic ventilation, leaking roofing flashing, or moisture buildup in the attic.
Can new shingles be installed over rotten plywood?
Answer: Damaged decking must be replaced before installing new roofing materials to ensure structural stability and adequate fastening strength.
How do contractors know if roof decking is damaged?
Contractors will also be able to observe soft surfaces, sagging areas, areas that were moist, or any other visible area of deterioration when they remove the old roofing material.
Does homeowner insurance cover rotten roof decking?
Coverage depends on the cause of the damage. Sudden storm damage might be acceptable; long-term damage or maintenance issues are usually not.
Conclusion
These form the foundations of the roofing system and could be a substantial cost for a roof replacement if the roof decking has rotten areas or any plywood is damaged. Several factors can cause hidden moisture intrusion, poor ventilation, material degradation, and installation mistakes, all of which can be detrimental to a plywood product long before they are noticed on the backside.
After the roofing material is stripped off, the contractor should fill in any damaged sections of the decking to ensure the new roof is long-lasting, safe, and functional. Taking the time to conduct regular inspections, ensure proper ventilation, and promptly repair leaks is a key way for homeowners to avoid costly repairs from extensive roof deterioration. Visit your nearest area for the best roof replacement services.
