How many sheets of plywood do I need for a roof?

Each 4x8 sheet of plywood or OSB covers 32 square feet. Divide your total roof area by 32, then add 10-15% for waste from cuts at edges, hips, and valleys. For example, a 2,000 sq ft roof needs 2,000 / 32 = 62.5 sheets, plus 10% waste = approximately 69 sheets. Always round up to the nearest full sheet.

Should I use OSB or plywood for roof decking?

Both OSB and plywood are code-compliant and widely used for roof decking. OSB (oriented strand board) is typically $5-15 per sheet less expensive than equivalent plywood and is the most common choice for new construction. Plywood is preferred in wet climates because it swells less when exposed to moisture and is easier to re-nail after swelling. For roof replacement where the decking will only be exposed briefly, OSB is a fine choice. For areas with high humidity or frequent rain delays during construction, CDX plywood offers better moisture resistance.

What thickness of roof decking do I need?

The required thickness depends on rafter or truss spacing. For 16-inch on-center framing, 7/16-inch OSB or 3/8-inch plywood is the minimum per code, but 1/2-inch is the practical minimum for nailing schedules. For 24-inch on-center framing, 5/8-inch OSB or 1/2-inch plywood is typically required. For tile roofs (which are very heavy), 3/4-inch plywood is often specified. Always verify with your local building code and roofing material manufacturer's requirements.

How much does roof decking replacement cost?

Roof decking replacement costs $1.50 to $4.00 per square foot installed, including material and labor. Material-only costs range from $0.78 to $2.80 per square foot depending on sheet type and thickness. Labor for professional installation typically adds $1.00 to $2.00 per square foot. Full replacement of 2,000 square feet of roof decking would cost $3,000 to $8,000 professionally installed.

Home › Roofing Calculators › Roof Decking Calculator

🪵 Roof Decking (Plywood/OSB) Calculator

Calculate sheets of OSB or plywood needed for roof decking, plus material cost, installation labor, and total project estimate with waste factored in.

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Who Should Use This

Homeowners replacing rotted decking, builders estimating new construction, contractors pricing partial or full roof deck replacement.

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What It Calculates

Sheet count with waste, material cost by decking type, professional installation labor, total deck weight, and total project cost.

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Example

A 1,800 sq ft roof needs about 62 sheets of 1/2" OSB. At $35/sheet plus professional install, expect $3,500–$5,500 total.

Enter Decking Details

Roof Area (square feet)

Decking Material

Installation

Waste Percentage

Pro Tip: When replacing only damaged sections, inspect surrounding boards carefully — water damage spreads. Replacing an extra 20% of borderline decking during a re-roof is far cheaper than reopening the roof later. OSB must be replaced when delaminated or excessively swelled.

Decking Estimate

Total Project Cost

Enter details above to calculate

Sheets Needed (with waste)

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Base sheets will appear here

Cost Breakdown

Roof Area—

Base Sheets (÷ 32 sqft)—

Sheets with Waste—

Material Cost (mid-range)—

Installation Labor—

Deck Weight (approx)—

Total Cost—

How It Works

4 Steps to Your Decking Estimate

Know exactly how many sheets to order before you start

Enter Roof Area

Input your total roof surface area. For sloped roofs, use the actual slope surface area — not the flat footprint. Each 4×8 sheet covers 32 square feet.

Choose Decking Type

Select OSB or plywood thickness based on your framing spacing and roofing material. Tile and slate roofs require thicker decking than shingles.

Select Installation

DIY installation saves $1–$2 per square foot in labor, but requires comfort working at height. Professional installation includes all fasteners and code-compliant nailing.

Set Waste Factor

Complex roofs with dormers, multiple hips, and valleys waste more material from cuts. Use 10% for simple roofs and 15% for complex designs.

OSB vs. Plywood for Roof Decking

Both OSB and CDX plywood are approved for roof sheathing under the International Residential Code (IRC) and virtually all local building codes. The choice comes down to budget, climate, and personal preference.

OSB (Oriented Strand Board) is manufactured by compressing and gluing wood strands in cross-oriented layers. It is typically $5–$15 cheaper per sheet than equivalent plywood, making it the dominant choice for new construction. Modern OSB with a water-resistant edge seal performs well in most conditions. The main concern with OSB is that it swells more than plywood when repeatedly wetted and dried — this can cause "nail pops" and surface waviness in the finished shingles over time.

CDX Plywood is made from cross-laminated veneer layers and has better dimensional stability in wet conditions. The "CDX" designation means: C-grade face, D-grade back, X (exterior) glue. It is the premium choice for wet climates, coastal areas, and anywhere the decking might be exposed to rain for extended periods during construction.

7/16" OSB: Minimum for 16" OC framing, budget-conscious projects
1/2" OSB or plywood: Standard residential, all framing spacings
5/8": Recommended for 24" OC framing, high-wind zones
3/4": Required for tile and slate roofs, premium construction

When to Replace vs. Repair Roof Decking

During a roof replacement, your roofer will inspect the decking and recommend repairs or replacement of damaged sections. Understanding when replacement is truly necessary helps you evaluate contractor recommendations.

Replace immediately if you see: Soft spots that compress when walked on, visible delamination or separation of layers, black mold growth through the decking, boards that crumble or flake when probed, or any area where fasteners no longer hold.

Repair is adequate if: The discoloration is surface staining only, the board is solid and rigid when tested, and there is no delamination. Light water stains without structural damage can be treated with a mold-inhibiting primer and left in place.

Cost implications: Decking replacement is typically charged per sheet at $50–$120 per sheet installed (material + labor) during a re-roof project. Identifying and budgeting for potential decking replacement before the project starts prevents surprise cost overruns. A roofer who inspects your attic before bidding can give you a more accurate preliminary estimate of decking replacement needs.

Nailing requirements: Roof decking must be fastened with 8d common nails at 6" spacing along panel edges and 12" in the field, or with ring-shank nails as specified by your local code. Hurricane clips and closer nailing patterns may be required in wind zones.

Key Insights

Roof Decking Facts

What contractors know — and homeowners should too

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32 Sqft Per Sheet

Every 4×8 sheet covers exactly 32 square feet. Dividing your roof area by 32 gives you the base sheet count before waste. Always add at least 10% for cuts and breakage.

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Decking Weight

7/16" OSB weighs approximately 70 lbs per sheet (2.2 lbs/sqft). 1/2" plywood weighs about 80 lbs per sheet. For a 2,000 sqft roof, that is roughly 4,400–5,000 lbs of decking — a significant structural load consideration.

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OSB Moisture Edge Sealing

Look for OSB panels with factory-applied edge sealer (often a green or blue coating on the edges). This dramatically reduces edge swelling during installation before the roof membrane is applied. Huber AdvanTech and LP TechShield are popular premium options.

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Leave a Gap

Panels must be installed with a 1/8" expansion gap at all edges and a 1/16" gap at end joints. This allows for thermal and moisture expansion and prevents buckling. Most panels have H-clips or panel clips built in or required between supports at 24" OC framing.

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Fastener Count

Each 4×8 sheet requires approximately 30–40 nails for standard nailing patterns (6" edges, 12" field). For a 2,000 sqft roof needing 69 sheets, that is roughly 2,000–2,800 nails. Use ring-shank or spiral-shank nails for better withdrawal resistance in high-wind areas.

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Code Compliance

Panel span ratings are stamped on each sheet (e.g., "24/16" means suitable for roof spans up to 24" and floor spans up to 16"). Always verify the panel's span rating matches your framing spacing. Using under-rated panels fails inspection and creates structural risks.

FAQ

Roof Decking Questions

A 2,000 sq ft roof requires 2,000 ÷ 32 = 62.5 base sheets. With a 12% waste factor, that increases to approximately 70 sheets (2,000 × 1.12 ÷ 32 = 70 sheets rounded up). At current OSB prices of $30–$45 per sheet for 1/2" panels, expect to pay $2,100–$3,150 for materials alone. Professional installation adds $1.25–$1.75 per square foot, bringing the total installed cost to approximately $4,600–$6,650.

In some cases, yes — installing new decking over structurally sound existing decking is allowed by code as a "re-deck." The new layer must use longer fasteners that penetrate through both layers into the rafters by at least 3/4". However, this approach adds weight and height to the roof, which can cause problems at flashings and drip edges. Most roofing contractors prefer full tear-off and replacement of failed decking for a cleaner, more durable result. If only a portion of decking has failed, spot replacement of those sheets is the standard approach.

CDX Plywood is made from cross-laminated wood veneer sheets bonded with exterior (X) grade adhesive. "C" and "D" refer to the face and back veneer grades. Plywood has better screw and nail holding power, more consistent thickness, and better moisture stability.

OSB (Oriented Strand Board) is made from compressed wood strands bonded with waterproof resin. It is less expensive, more uniform in density, and performs comparably to plywood in most roofing applications. Modern OSB is often stronger than CDX plywood in bending strength per dollar spent.

For most residential roofing, either material is acceptable. CDX is preferred in humid climates; OSB is the cost-effective choice in dry to moderate climates.

Partial decking repair (replacing a few sheets) during a re-roof typically does not require a separate permit beyond the general roofing permit. However, replacing all or most of the roof decking on a structure may require a structural permit in some jurisdictions, particularly if changes to the framing are made. Always check with your local building department. A licensed roofing contractor will typically pull the required permits as part of the project — verify this before work begins.

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