Roof Replacement Code Requirements: Tear-Off, Decking & Recover

Which code basis should a roof replacement use?

For qualifying residential work, Washington adopts the 2021 IRC with state amendments under WAC 51-51-003.

The eight checkpoints identified here use the Washington incorporated baseline: ICC 2021 IRC Chapter 9 read with WAC adoption, implementation, the complete current WAC index and official amendment resources/second-printing insert. Reviewed 2026-10-18. This is section-specific: Washington replaces R903.4.1. Confirm the building, existing-building route, local amendments and project conditions before applying a requirement.

When must the existing covering come off?

Replacement normally removes existing roof coverings to the deck. An existing ice barrier adhered to the deck may remain only with an added compliant ice-barrier membrane; that exception does not retain general roof-covering layers. IRC R908.3.

• Record whether the proposal is replacement, conventional recover or a complete separate structural system.
• Document existing materials and layers; unknown adhesion does not establish the retained-membrane exception.
• Agree how newly exposed deck defects will be documented, measured and approved.

When is recover allowed, and what rules it out?

Recover requires an affirmative permitted route: approved manufacturer installation; a complete separate system transmitting loads directly to structure without relying on the existing roof; the specified metal/tile-over-wood-shake route with R908.4 treatment; or a permitted coating over listed substrates. A verified complete separate system expressly needs no removal of the existing covering. Conventional recover is prohibited over a water-soaked or deteriorated covering/base inadequate for the new roof, existing slate, clay, cement or asbestos-cement tile, or two or more existing applications. IRC R908.3.1, R908.3.1.1 and R908.4.

• Prove both an allowed route and the absence of a conventional-recover prohibition; a sound single layer alone is insufficient.
• An independent direct structural load path differs from a new roof supported on the existing covering. Existing tile does not erase the express independent-system path.
• Verify the complete design and supporting structure; no wet or decayed structural member is assumed adequate.

What do pitch, deck and underlayment change?

Asphalt shingles require a solidly sheathed deck. Identify deck condition and repair quantities before installing the specified system. Asphalt shingles have a 2:12 minimum; metal shingles have a separate 3:12 minimum. IRC R905.2.1, R905.2.2 and R905.4.2.

Keep 3.99:12, 4.00:12 and 4.01:12 distinct. In the ordinary asphalt/tile Table R905.1.1(2) route, below 4:12 uses two layers. The upper no-wind band explicitly includes exactly 4:12 and calls for one layer (tile at least one); the wind-required route uses two layers. Above 4:12 the selected no-wind/wind route still differs. The material clause also uses low-band wording ending at four: retain that wording when selecting the assembly rather than rounding the pitch or declaring every exact-4 installation unresolved. A conservative compliant two-layer assembly is not blocked by that overlap.

R905.1.1 names an ASTM D1970 self-adhered alternate and another using a D1970 joint strip at least 4 inches wide, manufacturer deck instructions and approved table underlayment. The official model page’s alternate paragraphs were truncated. Their remaining application and attachment terms need a fully readable official clause and actual product/approval terms; no blanket layer or fastening waiver is established.

• Specify measured pitch, wind requirements, complete underlayment assembly and product instructions.
• The state insert/index reconciliation is complete for this checkpoint; the narrow remaining evidence need concerns complete alternate text and the actual approved assembly.

Where does an ice barrier extend?

Where local Table R301.2 designates an ice-barrier trigger for the listed coverings, extend the barrier at least 24 inches inside the exterior wall line. At slopes of at least 8:12, also extend it at least 36 inches along the roof slope from the eave. A detached accessory structure with no conditioned floor area is excepted. IRC R905.1.2; Table R301.2 footnote h and Washington local design criteria.

• A local ice-table entry must be known; no statewide YES or NO is assigned here.
• At 7.99:12 the steep-slope extension is not triggered; at 8.00:12 both the 24-inch inside-wall and 36-inch along-slope extents apply when the local trigger is YES.
• The detached unconditioned accessory exception remains separate from the local climate trigger.

Does a lighter second layer prove the roof can carry it?

No. IRC R908.2 requires support for the new covering and installation material/equipment loads. Added dead load, roof live load and ground snow are distinct. Table R301.6 roof live loads use horizontal projection and depend on slope/tributary area; design uses that load or Table R301.2 ground snow, whichever is greater. Ground snow greater than 70 psf invokes the listed engineered-design route; exactly 70 does not cross that threshold. R908.2 and R301.6 and R301.2.3.

Washington R102.7.1 permits an existing-building Chapter 45 route. Under R4504.4.2.1, a second covering layer adding no more than 3 pounds per square foot over one existing layer has a conditional exception to the dead-load-increase requirement. It is not universal recover permission, roof-capacity certification or a permit exemption; it is not a statewide percentage allowance.

For unreinforced masonry in Seismic Design Categories D0/D1/D2, R4502.2.2 requires parapet bracing/wall anchors when a reroofing permit is issued, subject to an evaluation showing existing compliance. That is a conditional building-specific trigger.

Which flashing, cricket and reuse details belong in the scope?

Flash wall/roof junctions, slope or direction changes and openings, and divert water at a sloped eave meeting a vertical sidewall. Metal flashing must be corrosion resistant and at least 0.019 inch thick. A cricket or saddle is required on the ridge side of a penetration wider than 30 inches measured perpendicular to the slope; exactly 30 inches does not trigger that clause. A qualifying R308.6 unit skylight installed with manufacturer flashing is excepted. R903.2.1 and R903.2.2.

R908.5/.6 allows reinstallation of slate/clay/cement tile only if undamaged, uncracked and unbroken. Replace rusted, damaged or deteriorated flashing, edging, outlets, vents and similar devices; do not reinstall aggregate surfacing. Reconstruct flashing to approved manufacturer instructions and prime metal receiving bituminous material. Appearance alone does not approve every reuse detail.

Do fire distance and positive drainage change the decision?

IRC R902.1 calls for classified A/B/C covering when law designates it or the roof edge is less than 3 feet from the lot line. Exactly 3 feet does not meet that distance test; the test does not itself select Class A. Applicable law, listing and deemed-compliant assemblies determine the class. No parcel or WUI designation is assigned here. R902.1.

Where required roof drains and elevated perimeter construction can trap water, provide the specified secondary drain or scupper: a same-size secondary drain inlet 2 inches above the low point, or a scupper three times the drain size with an opening at least 4 inches high and inlet 2 inches above the low point. Overflow discharge must be approved; sizing and installation refer to state plumbing Sections 1101 and 1103. Washington R903.4.1. For an existing recover/replacement with positive roof drainage, R908.1 excepts its 0.25:12 design-slope floor and the need to add secondary overflow drains/scuppers. It does not waive material-specific minimum slopes, authorize ponding or settle unrelated plumbing duties. R908.1.

How do repairs and local requirements affect this advice?

IRC R105.1 provides a base permit screen; R105.2 has no named roof-covering reroof exemption. R105.2.2 permits an ordinary-repair screen subject to structural, egress, piping and general-safety exclusions. It does not mean every repair requires a permit or that an exemption waives substantive code. Read R105.1, R105.2 and R105.2.2.

Washington R4503.2.1 permits like materials for repairs while retaining the unsafe-condition limitation. New-construction assumptions are not the only existing-building path.

Local amendments remain bounded by RCW 19.27.040, RCW 19.27.060 and WAC 51-04-030. Residential construction amendments generally need Council and local approval; the procedure-only exception does not change construction requirements. Use the actual jurisdiction, building and work scope. Read local permit planning.