Roof Decking and Sheathing Reference
Why this matters
Roof decking is the structural surface that supports the roofing material. Customers usually don't see it (under the shingles), but the decking condition + specifications affect the roof's overall performance. Damaged or inadequate decking compromises any roofing material. Reroofing customers often need decking work.
Decking materials
| Material | Notes |
|---|---|
| Plywood | Standard residential; multiple grades; long-lasting |
| OSB (oriented strand board) | Modern equivalent; less water-resistant than plywood |
| Skip sheathing | Older homes; spaced boards |
| Solid sheathing (old) | Tongue + groove boards |
| Plywood with FireGuard | Specific applications |
Modern standard: plywood OR OSB.
Thickness
For different applications:
| Use | Typical thickness |
|---|---|
| Standard asphalt shingle | 7/16 to 5/8 inch |
| Tile / clay | 5/8 inch minimum often |
| Slate | Sometimes 3/4 inch |
| Specialty / commercial | Various |
Match to the customer's load + applicable code.
Why decking matters
The roofing material:
- Mounts on the deck
- Decking supports the material
- Decking must be adequate
- Decking damage = roofing failure
A reroof opportunity to verify decking.
When to replace decking
| Trigger | Action |
|---|---|
| Visible rot | Replace |
| Spongy / soft when probed | Replace |
| Damaged sections | Replace damaged areas |
| Worn / old (50+ years) | Consider replacement |
| Wrong material for current roofing | Replace |
Verify during reroof.
Common decking issues
For aging roofs:
| Issue | Cause |
|---|---|
| Rot at the eave | Water penetration; clogged gutters |
| Rot at penetrations | Failed flashing |
| Rot in valleys | Concentrated water |
| Bowing / cupping | Moisture cycles |
| Edge nail pullout | Aged nails |
| Layered deck (old skip) | Older construction |
Each is repairable.
Reroof procedure for decking
Step 1: Remove existing roofing
- Strip old shingles
- Remove old underlayment
- Reveal the deck
Step 2: Inspect decking
- Walk the entire deck
- Probe with awl or screwdriver
- Visual inspection
- Document any damage
Step 3: Repair damaged areas
- Cut out damaged sections
- Install matching replacement
- Secure with proper fasteners
- Verify smooth deck
Step 4: Verify the underlayment + new roofing
- Install ice + water shield (where required)
- Install underlayment
- Install new roofing material
The complete reroof includes decking work as needed.
Decking inspection process
For reroof inspection:
- Visual identification of damaged areas
- Probing for soft / rotted wood
- Customer documentation
- Quote for replacement scope
Customer's reroof quote should include decking scope.
When the customer balks at decking work
For customer pushback:
- Show the customer the damaged areas
- Explain why replacement is needed
- Customer's choice
- Document if customer refuses
A customer who refuses decking is settling for inferior install.
Decking spec for new construction
For new builds:
- Per IRC R803 (Decking)
- Engineering for the structural load
- Verify with framing inspection
Code-driven.
Decking spec for reroof
For replacement decking:
- Match the existing
- Code-compliant for the new roofing
- Customer's investment
Verify.
Plywood vs. OSB
For replacement:
| Aspect | Plywood | OSB |
|---|---|---|
| Water resistance | Moderate | Lower |
| Strength | Standard | Lower per same thickness |
| Cost | Higher | Lower |
| Service life | Long | Long if maintained |
Modern installations use either.
When to use plywood specifically
For:
- Hurricane areas
- High moisture areas
- Areas where decking is exposed sometimes
- Customer's premium choice
Plywood is more forgiving.
When OSB is acceptable
For:
- Standard residential
- Cost-conscious customer
- Standard installation
OSB is cost-effective.
Customer education
For decking discussion:
- "Your roof's deck supports the shingles"
- "Any damaged deck must be replaced"
- "Customer's investment in decking now prevents bigger problems"
- "Standard scope at reroof"
A trained customer understands.
When decking is significantly compromised
For severely damaged:
- Major reroof scope
- Customer's investment
- Sometimes entire deck replacement
- Customer's understanding
Significant work.
Specialty: structural decking
For unusual situations:
- Tongue + groove boards (old homes)
- Specialty thickness needed
- Engineering involvement
Specialty work.
When the customer's home has multiple layers
For old roofs:
- Multiple roofing layers stacked
- Each adds weight
- Reroof = strip + start fresh
Layering is generally not recommended.
Decking with skip sheathing
For older homes:
- Spaced boards instead of solid deck
- Common for wood shingle / shake roofs
- New asphalt requires solid deck
- Customer's reroof includes deck conversion
Customer's investment.
Code requirements
For decking:
| Code | Requirement |
|---|---|
| IRC R803 | Decking thickness + species |
| IBC Chapter 23 | Wood construction |
| Local code | Sometimes more stringent |
| Hurricane zones | Specific requirements |
Verify customer's specific area.
Hurricane zone requirements
For hurricane-prone:
- Thicker decking minimum
- More fasteners per square foot
- Specific fastener types
- Customer's specific code
Stricter requirements.
Insurance considerations
For decking:
- Some insurance requires inspection at reroof
- Customer's specific policy
- Documentation supports
Insurance may help.
Documentation
For each reroof:
- Decking condition assessment
- Repair scope
- Materials used
- Customer file note
When the customer can't see the issue
For hidden damage:
- Customer's understanding through photos
- Document the issue
- Quote the scope
- Customer's decision
A transparent approach.
When the customer attempts to skip decking
For customer cost concerns:
- Don't skip decking on a reroof
- Customer's quality + warranty depends
- Customer's choice with consequences
- Document any conversation
Decking is part of the work.
Fastener selection
For decking:
| Use | Fastener |
|---|---|
| Standard plywood / OSB | 8d nails |
| Hurricane zone | More + specific |
| Specialty | Per code |
Match to the application.
Common pitfalls
- Skipping decking inspection - missed damage
- Installing over damaged decking - short-term solution
- Wrong decking material - premature failure
- Inadequate fasteners - wind / impact damage
Customer's home value
For decking work:
- Premium reroofing includes
- Customer's investment in home
- Resale value supports
A quality reroof.
Specialty: structural insulated panels
For some modern construction:
References
- IRC R803 (Roof Sheathing)
- IBC Chapter 23 (Wood Construction)
- APA - The Engineered Wood Association
- NRCA installation standards
- Manufacturer documentation (Weyerhaeuser, Louisiana Pacific, etc.)
- Manuall internal: Asphalt Shingle Replacement SOP, Roof Slope and Measurements, Replace Damaged Shingles