Roof Decking Replacement

What Lives Under Your Shingles

The roof deck is the structural surface that everything else attaches to. It is usually plywood or oriented strand board (OSB) nailed to the rafters, and it must be solid, flat, and dry for the roofing system to perform. When the deck is rotted, delaminated, or sagging, new shingles installed over it will follow the same contours and fail prematurely. A roof replacement that skips the deck inspection is a roof replacement that misses the problem.

We inspect and replace damaged roof deck during every tear-off. Our crews find and fix rot, delamination, sagging, and water damage before any new roofing goes down. This is the step that separates a roof replacement done right from one that looks fine on the surface but fails within years.

When Deck Replacement Is Needed

We check every section of the deck during tear-off. Replacement is needed when:

• Rot — the wood is soft, dark, or crumbly when probed; usually caused by chronic water intrusion through failed flashing or shingles
• Delamination — the layers of plywood separate, creating air pockets and weak spots; OSB swells and loses structural integrity when wet
• Sagging — visible dips or curves in the roof surface that indicate the deck has lost rigidity
• Water damage — stains, mold, or wet insulation on the underside of the deck that indicate moisture has been present for a long time
• Inadequate thickness — the original deck was installed with insufficient sheathing thickness for the roofing material
• Poor fastening — nails that have pulled through or backed out, leaving the deck loosely attached to the rafters
• Fire damage — heat or fire has weakened the structural integrity of the sheathing

Common Causes of Deck Rot

Deck rot does not happen overnight. It develops over months or years from:

• Chronic leaks — failed flashing, missing shingles, or deteriorated underlayment that lets water reach the deck repeatedly
• Poor attic ventilation — warm, moist air from the living space rises into the attic and condenses on the cold underside of the deck, causing rot from below
• Ice dams — trapped water under the shingles at the eaves freezes and thaws, breaking down the deck surface over multiple winters
• Plumbing vent leaks — pipe boots that have dried out and cracked allow water to run down the vent pipe and onto the deck
• Bathroom exhaust — vent fans that dump moist air into the attic instead of to the outside create chronic humidity that attacks the deck

How We Replace Roof Decking

1. Tear-off — we remove all roofing material down to the bare deck
2. Full inspection — every sheet is probed and checked for rot, delamination, and fastener pull-out; we mark damaged sections with chalk
3. Removal — damaged sheets are removed; rafters underneath are inspected for rot and treated or sistered if needed
4. New sheathing — matching plywood or OSB installed with proper fastener spacing and depth; edges are staggered across rafters for structural continuity
5. Underlayment — new underlayment installed over the entire deck, including the replacement sections
6. Roofing installation — new roofing material installed per manufacturer specifications

Deck Replacement Costs

Component	Typical range
Plywood sheathing (per sheet, 4x8)	$50 – $90 installed
OSB sheathing (per sheet, 4x8)	$35 – $65 installed
Labor per sheet	$50 – $80
Rafter repair or sistering (per tail)	$100 – $250
Full deck replacement (average roof)	$2,000 – $8,000
Partial deck replacement	$500 – $3,000
Moisture barrier installation (per sq ft)	$1 – $3

Deck replacement is always quoted as a separate line item because the extent is unknown until the old roofing is torn off. We identify and price all deck work before starting the replacement, so there are no surprises.

Plywood vs. OSB for Roof Decking

Material	Pros	Cons
Plywood	Stronger, more water-resistant, holds nails better	More expensive
OSB	Cheaper, consistent thickness	Swells when wet, weaker when saturated

We match the existing deck material when possible. If the entire deck is being replaced, we recommend plywood for superior moisture resistance and nail-holding power. The price difference between plywood and OSB is typically $15 to $25 per sheet — a small premium for significantly better long-term performance.

Why Deck Thickness Matters

The International Building Code specifies minimum sheathing thickness based on rafter spacing:

Rafter spacing	Minimum sheathing thickness
16 inches on center	7/16 inch (OSB) or 15/32 inch (plywood)
19.2 inches on center	15/32 inch
24 inches on center	19/32 inch (OSB) or 5/8 inch (plywood)

Undersized sheathing sags between rafters, creating visible dips in the roof surface and stress points where nails can pull through. If the original builder used minimum-thickness sheathing on wide rafter spans, upgrading to a thicker material during replacement improves the roof’s structural performance.

Preventing Deck Damage

• Fix flashing and shingle damage promptly — deck rot starts with water getting past the roofing surface
• Maintain proper attic ventilation — moisture in the attic condenses on the deck and causes rot from below
• Insulate and air-seal the attic floor — warm, moist air leaking into the attic is the leading cause of deck rot in cold climates
• Inspect the attic annually for water stains on the underside of the deck
• Address ice dam problems before they cause repeated freeze-thaw damage to the deck
• Ensure bathroom and kitchen exhaust fans vent to the outside, not into the attic
• Install proper soffit and ridge ventilation to keep the deck dry year-round

How We Replace Damaged Decking

1. Tear-off — existing roofing removed to expose the full deck surface
2. Inspection — every sheet probed for soft spots; areas with visible rot, delamination, or water staining are marked
3. Cutout — damaged sections cut along joist or rafter lines for clean, structural edges
4. Framing check — rafters or trusses under the damaged area are inspected for rot or insect damage before new sheathing goes down
5. New sheathing — correctly sized plywood or OSB cut to fit, nailed with 8d ring-shank nails at 6 inches on center along edges and 12 inches on center in the field
6. Seam alignment — sheets staggered so seams do not align across adjacent rafter bays
7. H-clips — installed between unsupported sheet edges on open-span sections
8. Final check — surface is flat, secure, and ready for underlayment and new roofing

Deck replacement adds time to a re-roofing project, but it is non-negotiable. New roofing installed over damaged sheathing will fail prematurely because nails cannot hold in rot and the structural integrity is compromised.

Deck Replacement Costs

Component	Typical range
Plywood sheathing (per sheet)	$35 – $65
OSB sheathing (per sheet)	$25 – $45
Removal and disposal of damaged sheets	$50 – $100 per sheet
Rafter repair (if needed)	$200 – $600 per rafter
Labor for deck replacement	$300 – $600 per 100 sq ft

Most re-roofing projects involve replacing 5 to 15 percent of the deck. Extensive rot from long-term leaks may require replacing 30 percent or more. We price deck replacement as a separate line item so you see exactly what it costs.

Worried about the condition of your roof deck? Call us or request an inspection — we will assess the deck during a tear-off and replace any damaged sections before installing new roofing.