Understanding the critical differences between roof decking and roof sheathing is key to assembling a durable and code-compliant roof. While these components work together in the overall roof system, they serve distinct purposes.
This comprehensive guide examines all considerations for choosing and installing roof decking vs sheathing so your project checks all the structural, weatherproofing, sustainability and aesthetic boxes.
We’ll compare the costs, benefits, and appropriate uses of various wood, plastic and metal roof decking and sheathing materials.
You’ll gain insights for pairing the right products with your specific climate conditions, load requirements, roof pitch and desired finishes.
Let’s dive into the specifics so you pick ideal materials and avoid potentially costly or dangerous missteps.
Roof Decking vs Sheathing
Simply put, roof decking forms the structural base layer installed atop roof trusses or rafters. While roof sheathing covers the decking to seal the interior from outside conditions.
But breaking it down further:
Roof Decking
Common Decking Materials: Plywood, OSB, engineered wood
Roof Sheathing
Common Sheathing Materials: Plywood, OSB, foam/fiber boards, metal panels
While sheathing protects the decking, both elements work together to create a sound, functional roof system. But mixing up their distinct purposes can undermine performance. We’ll clarify optimal usage moving forward.
Decking and Sheathing Options Comparison
You’ll choose from a variety of wood, plastic and metal alternatives for roof decking and sheathing based on structural specifications, weather factors, sustainability goals and costs.
Wood Roof Decking and Sheathing Products
Wood dominates the roof decking scene based on structural integrity, affordability and broad building code acceptance.
Plywood
Boasting cross-directional strength and stiffness, plywood roof decking resists sagging over years of snow, wind and foot traffic loads. The dimensional stability also minimizes swelling issues. Pressure treated and fire-retardant versions expand options.
Oriented Strand Board (OSB)
OSB roof decking provides cost savings over plywood but typically requires thinner 19/32 inch panels spaced closer together on rafters. The mat-formed panels handle roof loads well despite slightly less uniform performance.
Engineered Wood
Composite engineered lumber often exceeds solid wood for spanning capacity between roof supports. The manufactured boards reduce shrinking, twisting and variability concerns. Common for flat roof structures.
Downsides of wood:
Here is a brief comparison table of plywood, osb and engineering wood.
| Property | Plywood | OSB | Engineered Wood |
|---|---|---|---|
| Strength & Stiffness | Cross-directional strength, stiffness | Good roof load handling, slightly less uniform | Often exceeds solid wood for spans |
| Resistance to Sagging | Resists sagging over time, loads | Handles roof loads well | Common for flat roofs |
| Dimensional Stability | Minimizes swelling issues | Slightly less uniform performance | Reduces shrinking, twisting, variability |
| Cost | Moderate | Cost-effective, needs more panels | Cost-effective alternative to solid wood |
| Treatment Options | Pressure treated, fire-retardant options | Standard panels without special treatment | Varies based on specific type |
| Common Applications | Roof decking | Roof decking, sheathing | Flat roofs, various construction uses |
Plastic/Foam Roof Sheathing Alternatives
While unsuitable for roof decking directly, non-wood options provide affordable sheathing enhancements:
Plastic Lumber
Polyisocyanurate Rigid Foam
Extruded Polystyrene (XPS) Foam Board
Here are the pros and cons of plactic or foam roof sheating
Metal Roof Sheathing
Going beyond wood, fiber/plastic sheathing brings unique attributes:
Aluminum
Steel
Cementitious Wall Panels
Fiber-Cement
You can Also Read: What Is Metal Roof Decking: A Complete 7-Step Guide To Durable Material
Let’s explore what to watch for when selecting materials.
Key Factors When Picking Decking vs. Sheathing
You can’t approach roof decking and sheathing as “one size fits all” decisions. Carefully examine the following based on your house, climate and objectives:
Local Building Codes and Loads
Verify products satisfy structural standards for snow, wind uplift and occupancy intended loads per local codes. Stick with well-rated industry brands. Review rafter spacing to size decking appropriately.
Pitch and Span Considerations
Account for rafter type, angle, widths and spacing when specifying decking to safely support anticipated loads without sagging. Wider spans demand thicker, stiffer decking products.
Climate and Weather
Humidity/precipitation resistance, meeting uplift pressures for hurricane or high snow regions, fire ratings in wildfire zones, etc. Ensure decking and sheathing endure regional conditions.
Moisture Protection Properties
Preventing water intrusion extends roof lifespan significantly. Require warranted water resistance specs for decking and sheathing. Flashings further augment protections.
Eco-Friendly Materials
Minimize environmental impacts by requesting FSC high percentage recycled content certified decking/sheathing materials. Plastic lumber also diverts waste.
Weight Considerations
Factor in board size limitations if installing by hand vs crane. Many composite products offer strength plus easy handling.
Cost Comparisons
Balance your budget with the longevity benefits of durable decking and sheathing. Don’t cut corners that could undermine roof integrity.
| Feature | Roof Decking | Roof Sheathing |
|---|---|---|
| Material Cost | $0.50 – $2.00 per square foot | $0.30 – $1.50 per square foot |
| Labor Cost | $1.50 – $3.00 per square foot | $1.50 – $3.00 per square foot |
| Total Cost | $2.00 – $5.00 per square foot | $1.80 – $4.50 per square foot |
Install right and even premium grades pay dividends for decades.
Correct Installation Techniques
Proper design coordination and workmanship ensures roof decking and sheathing uniformly transfers loads, resists uplift, and seals inclement weather outside the building.
Follow manufacturer specifications for secure application:
For Roof Decking
For Roof Sheathing
Failing to anchor roof decking and sheathing correctly jeopardizes the entire roof system. Don’t risk thousands in repairs by skipping steps.
You Can Also Read:
Selecting The Best Roof Sheathing For Your Home: A Detailed Guide
What Is Roof Deck Construction: A Great Approach To Design Excellence
Protecting Roof Decking and Sheathing Long Term
Extending roof lifespan equates to better returns on decking and sheathing investments. We recommend:
- Ventilation and Air Flow
Ridge, gable and soffit vents prevent humidity buildup from condensing on the decking or sheathing underneath. - Temporary Tarps
If a gap occurs between roofing phases, use tarps rated for UV exposure to shield any exposed decking or sheathing. - Flashing Around Valleys and Protrusions
Properly integrating flashing forces water off the roof without permeating openings by vents, pipes etc. - Routine Inspections Periodically check beneath shingles for dark moisture spots, loose sheathing, cracking or warped decking requiring repair.
- Manufacturer Warranties Decking and sheathing products often come with helpful exposure life and workmanship warranties.
- Consulting a Professional Roofer
- Virtually any roof project goes smoother by engaging an experienced roofing contractor early on for:
- Roof Evaluation – A roofer can survey to pinpoint areas needing repair or reinforcement to support new decking/sheathing.
- Load Calculations – Improper structural planning invites failures. Have loads analyzed to size decking/sheathing appropriately.
- Complex Roof Structures – Vaults, steep pitches and intricate facets complicate installations and benefit from an expert.
- Historic Home Considerations – Preserving architectural aesthetics while upgrading decking and sheathing on classic homes preserves history.
- Permit Applications – Roofers know specific codes to ensure your plans pass critical town/county inspections for safety assurance.
While budget dictates DIY applicability, don’t risk safety or wasted expenses by overlooking technical specifications.
Conclusion
Selecting ideal roof decking and sheathing involves more than grabbing the first product spotted at the lumber yard. But methodically aligning materials with structural loads, weatherproofing needs, codes and costs sets up success.
Remember decking forms the structural foundation and sheathing seals the interior. Both elements mutually support roof functionality when integrated properly.
There are many material options; just consistently factor performance into the decision calculus beyond initial price.
And thinking lifecycle costs often reveals better grades pay future dividends despite mildly higher upfront pricing through decades of reliable service. Install correctly and your roof works dependably for years ahead.
FAQ’s
What thickness of plywood is best for roof sheathing?
While 5/8 inch plywood roof sheathing complies with most residential codes, enhancing to 3/4 inch boosts impact resistance, handles high snow loading and provides stiffer feel underfoot.
How much does it cost to sheath a roof?
With 4×8 plywood sheet prices fluctuating around $50 on average, the material cost to conventionally sheath a 28 square (3000 sq ft) shingle roof runs $1400-$2800 for 1/2 to 3/4 inch sheets. Add professional labor to install.
What screws should be used for roof sheathing?
Ring shanked nails or screws with 2 inch minimum lengths secure roof sheathing against standard 90+ mph wind uplifts. Use 2.5-3 inch screws to withstand 140+ mph hurricane force wind loads.
Should you nail or screw roof sheathing?
While sufficiently embedded nails work, screws with gasketed washers prove less likely to back out over decades of thermal expansion/contraction cycles. Screws also less prone to pull through sheathing under extreme wind uplifts.
What is the best sealant for roof sheathing?
Look for durable, water-based synthetic rubber sealants that retain flexibility after drying. These widely seal roof sheathing seams, gaps and joints through extreme temperature fluctuations.