Roof Deck Condition Assessment and Replacement

Purpose

This procedure guarantees that every square foot of deck left under a new covering will hold a fastener, and that anything that will not is found, priced and replaced while it is still visible. Without it the crew covers soft sheathing, the shingle nail has nothing to bite, and the roof leaves in a wind the shingle itself was rated for. The quieter failure comes first: someone steps through a rotted sheet at a valley.

The deck is also invisible by mid-morning and unarguable after that. Every argument about deck condition is really an argument about whether anyone photographed it.

Scope

Covers plywood, OSB and board decking on residential and small commercial steep-slope roofs, during a tear-off or any repair large enough to expose sheathing: identification, condemnation criteria, the approval gate, replacement panel installation and the verification before underlayment covers it.

Does not cover fall protection or access setup, owned by the fall protection and ladder SOPs. Does not cover the strip sequence or the open-deck cap, owned by the tear-off and dry-in SOP. Does not cover framing repair: a sagging rafter, a cracked truss chord or a spreading ridge leaves this procedure and goes to the estimator with a note that an engineer or the building official may be needed. Does not cover insulated low-slope assemblies, lightweight concrete or steel deck.

Roles and responsibilities

What "sound" means on a deck

Sound is a fastener criterion, not a cosmetic one. A sheet is sound when a shingle nail driven anywhere in it penetrates at least 3/4 in into the sheathing, or fully through it where the sheathing is thinner than 3/4 in, and stays there. That is what the shingle manufacturer's instructions and the adopted IRC both require, and it is the only thing the deck has to do.

So gray, weathered or stained is not by itself a condemnation. Delaminated is, because plies that have swelled and separated no longer hold a shank. Soft under a probe is. Springy underfoot between rafters is a span question rather than a rot question, answered with a tape and the panel stamp rather than an opinion.

Procedure

1. Set the fall-through control before anyone walks a stripped plane. Treat every exposed deck as suspect until sounded, establish the walk route along rafter lines, brief it, and keep the crew off anything a strip worker has flagged. Acceptance: every worker can state the walk route and the flagged areas before stepping on, and fall arrest is already connected per the fall protection SOP. Wrong looks like a lead who flags an area on the radio and never marks it on the deck. Stop rule: an unflagged spongy area found underfoot stops walking on that plane until it is marked and either cut out or covered. Hazard: treat a soft sheet as a hole and control it as one, because 29 CFR 1926.501(b)(4) requires holes covered or guarded, and a cover under 1926.502(i) is secured, marked and able to carry twice the load put on it.

2. Identify the deck at a known-good location and write it down. Read the panel stamp for thickness and span rating where the sheathing is dry, tape the actual thickness at a cut edge, and measure on-center rafter spacing over three bays rather than one. Acceptance: thickness, span rating or "unreadable", decking type and measured spacing on the ticket before any panel is condemned. Wrong looks like "3/8 plywood" written from across the roof when the deck is 7/16 OSB. Stop rule: a span rating that will not carry the measured spacing is not this crew's call to install over, and the job stops for an estimator decision on overlay or full replacement. Hazard: reading a stamp means kneeling with your weight on one panel, so do it over a rafter, not mid-bay.

3. Sound and probe each section as it is exposed, before anything covers it. Walk the section on a grid about a stride apart, feel for deflection, and drive an awl at every valley, penetration, eave course and any stain, sag or dark patch. Acceptance: the probe goes no deeper than about 1/8 in under hand pressure in sound material, and every suspect spot either meets that or gets a keel mark. Wrong looks like sounding only where the old roof leaked, when eaves and north valleys rot from condensation with no leak history at all. Stop rule: a probe past 1/4 in under hand pressure condemns that panel, marked rather than debated. Hazard: probing puts a hand on deck a knee is about to follow, so keep your weight on a rafter line while you probe between them.

4. Check span, edge support and how the old deck was fastened. Compare the step 2 spacing against the panel span rating, look for edge clips or blocking where the rating requires edge support, and confirm panel ends land on rafter centers with a gap rather than butted tight. Acceptance: spacing at or under the rated span, edge support present where required, ends bearing on framing, and roughly the 1/8 in end and edge spacing APA recommends. Wrong looks like panels butted tight, which buckle as they take up moisture and telegraph a ridge through new shingles. Stop rule: unsupported edges on a rating that requires them means clips or blocking go in before underlayment. Hazard: none added here beyond the walking control already set.

5. Cut out and remove the condemned panels. Snap to rafter centers, set blade depth to deck thickness plus about 1/8 in and no more, cut, and lift the piece up and out rather than dropping it. Acceptance: every cut lands on a rafter center leaving at least half the rafter width for the new panel to bear on, and the opening is covered the moment the piece is out. Wrong looks like a cut that splits the rafter so neither panel gets bearing. Stop rule: a blade that meets anything that is not wood stops immediately and the area is opened by hand. Hazard: wiring, cable and flex duct run on top of ceiling joists and stapled to rafter sides, which is what the depth stop is for; cutting sheathing releases wood dust, so cut upwind with eye protection and extraction, and where it builds a visible cloud the respirator comes with a written program under 29 CFR 1910.134 rather than on its own. Old mastic or felt from a pre-1980s tie-in gets identified before you make dust out of it.

6. Count, price and get written approval before anything is covered. Total the condemned panels, compare against the contract allowance, and send the count with photographs to the office for a written change at the contract's per-sheet rate. Acceptance: an approved or declined count returned in writing with a time on it, before underlayment reaches that area. Wrong looks like a lead who installs and invoices, which the customer refuses because the evidence is buried. Stop rule: no approval means no covering that area; dry-in stops at the section boundary, the opening stays covered under step 1, and the crew moves to another plane. Hazard: none at this step, it is a call made from the ground. The risk here is the pull to keep working over an open decision, which the stop rule removes.

7. Install replacement panels to bearing, gap and fastening schedule. Match thickness and rating to the surrounding deck or better, run the long dimension across the rafters, land ends on rafter centers, leave the gap, and fasten to the adopted IRC schedule plus any high-wind amendment your jurisdiction adds. Acceptance: 8d common or ring-shank at roughly 6 in on panel edges and 12 in in the field is the common schedule, counted on every replacement panel, heads flush, none blown through the face. Wrong looks like a panel fastened only at its ends because the installer could not find the middle rafter. Stop rule: a panel that will not land on framing at both ends gets recut, never shimmed. Hazard: the nailer is live here and a contact trip on a panel edge drives a fastener through the hand holding it, so hands stay a hand-width clear of the nose.

8. Photograph and re-verify before the underlayment covers it. Photograph each replacement with a tape in frame and a landmark that places it on the roof, then walk the plane once more sounding everything flagged as marginal. Acceptance: one photograph per replaced panel, no flagged area unresolved, no fastener standing proud, no opening still open. Wrong looks like a photo set showing seven new panels that cannot prove which roof or which slope. Stop rule: an opening still open here stops dry-in on that plane, because underlayment over a hole hides it from everyone who walks the roof afterward. Hazard: this is the step where a tech walks a plane they now trust, so the walk still runs the rafter lines until the underlayment is down.

The record this produces

One deck entry per job: date, address, deck type, measured thickness, span rating or unreadable, rafter spacing, total panels on the roof, panels condemned with location and reason, the contract allowance, chargeable count, who approved it and at what time, the fastening schedule used, and the photographs.

The lead writes it before dry-in reaches that plane. The office reads the approval time if the customer disputes the change. The warranty desk reads the fastening schedule and the deck thickness, which are the two facts a shingle manufacturer asks for on a wind claim.

Worked pass: 24-square gable reroof, 1970s build

The plane totals 24 squares, and a square is 100 sq ft, so 2,400 sq ft of deck. At 32 sq ft per 4 ft by 8 ft panel, 2,400 divided by 32 is 75 panels. Contract allowance included 3 sheets.

Step 2: the stamp on a dry ridge panel reads 24/16, a tape at a cut edge reads 7/16 in, and three bays measure 24 in, 24 in and 24-1/2 in on center. Step 4: edge clips present at the field joints, gaps present at the ends. Passes.

Step 3: the crew probes 19 locations on the north plane. Sixteen take the awl no deeper than about 1/8 in. Three at the valley take it past 1/4 in and one goes through. Four more along the east eave read soft at the lower course. Condemned: 3 at the valley plus 4 at the eave is 7 panels, and 7 of 75 is 9.3 percent of the deck.

Step 6 fails. Seven condemned against an allowance of 3 leaves 4 chargeable, which needs approval, and the office cannot reach the customer for 95 minutes. The stop rule fires: the openings are cut under step 5 and closed with screwed-down, marked 3/4 in plywood covers, dry-in stops two courses short of the valley, and the crew moves to the south plane. Written approval for 4 sheets returns at 11:20 am.

Step 7 then runs on all 7 panels in 7/16 OSB, long dimension across the rafters, 8d ring-shank counted at 6 in on edges and 12 in in the field on each. One panel's north end lands on about a quarter of the rafter width because the cut drifted, so it is recut to the adjacent rafter rather than shimmed. Step 8 produces 7 photographs with a tape and either the chimney or the ridge vent in frame.

The honest ticket note is not the 95 minutes, which the south plane absorbed. It is that the number on file was a work line and no mobile was collected at sale. That fix belongs to the office.

References

• International Residential Code, Section R803 and the adopted fastening schedule, in the edition your jurisdiction has adopted, for roof sheathing thickness, span and attachment
• APA - The Engineered Wood Association, on panel span ratings, edge support and the 1/8 in end and edge spacing recommendation
• The shingle manufacturer's installation instructions, which set required fastener penetration into the deck and are a condition of the material warranty
• 29 CFR 1926.501(b)(4) and 1926.502(i), holes in a construction walking-working surface; 29 CFR 1910.134 for the respirator program
• See related: the tear-off and dry-in SOP and the fall protection setup SOP, both of which run before step 1