4.2 Tear-Off, Re-Roof Prep & Substrate Repair

4.2 Tear-Off, Re-Roof Prep & Substrate Repair

Quick Answer: Tear off when the existing roof is wet, poorly attached, over layer limits, or covering a damaged deck. Recover only when the substrate is dry, sound, and code-compliant. Repair every soft, corroded, or non-holding area before installing new insulation or membrane.

After you identify the deck, Domain 2 work turns to whether the existing roof stays or goes. NRCA and most manufacturer specifications treat this as an engineering and durability decision, not a schedule preference. Illinois licensing questions frequently test that judgment.

Tear-Off Versus Recover

When Tear-Off Is Required

Remove the existing roofing system down to a suitable deck when moisture surveys or cores show wet materials, when fasteners no longer hold, or when the assembly already exceeds the number of roofs allowed by code or specification. Tear-off also becomes necessary when you must inspect or repair the structural deck—recovering over unknown damage is a common exam “wrong answer.”

When Recover May Be Acceptable

Recover (installing a new roof over an existing one) can be appropriate if the existing membrane or built-up system is dry, well attached, smooth enough for the new system, and within layer limits. Confirm that added weight and thickness meet structural and flashing-height constraints. Even then, remove wet areas and repair the deck locally before recovering the dry portions.

Re-Roof Preparation Sequence

1. Protect the site — Fall protection, debris chutes, ground barriers, and HVAC/intake protection.
2. Stage tear-off — Work in weather windows; do not open more deck than you can make watertight the same day.
3. Remove materials — Strip to the deck or to the approved recover surface; bag and dispose of wet insulation separately when required.
4. Inspect the exposed substrate — Re-check moisture, deflection, corrosion, and fastener zones now that the cover is gone.
5. Repair the deck — Replace unsound wood panels/planks, steel sheets, gypsum boards, or LWIC fill as needed; sister framing if structural damage appears.
6. Clean and dry — Sweep, vacuum fines, and allow surfaces to dry before primers, adhesives, or fasteners.
7. Verify attachment method — Re-test fasteners or adhesion on the repaired substrate before full production.

Substrate Repair Details

Wood

Cut out rotten plywood, OSB, or plank to solid framing. Match thickness so insulation and membrane lay flat. Use exterior-grade panels appropriate to the specification. Stagger joints and fasten to structure—not only to adjacent damaged boards.

Steel

Replace panels with rust-through or lost section. Clean light surface rust where the base metal remains sound and the specification allows. Confirm that new screws engage solid flanges; do not “chase” fastening into paper-thin metal.

Concrete

Remove unsound laitance and patch spalls with compatible repair materials. Address active cracks per the membrane manufacturer. Confirm dryness before adhered systems.

Gypsum and LWIC

Replace soft gypsum formboard. For LWIC, remove saturated fill, dry or replace, and restore a nailable or pourable surface that meets the system requirements. Venting strategies, when specified, are not a substitute for removing obviously wet fill under a vapor-tight recover.

Selective Tear-Off and Transition Details

Not every square foot of a large Illinois roof fails the same way. Selective tear-off removes wet or damaged areas while leaving dry, well-attached field areas for recover—if the specification and manufacturer allow a mixed approach. Transitions between tear-off and recover zones need clean steps, matched insulation heights, and watertight temporary seals at the work face. Poor transitions create ponds and stress concentrations that show up as early leaks. When in doubt on a licensing scenario, full tear-off to a verified deck is the more defensible choice than blending wet and dry layers under one new membrane.

Flashings, Curbs, and Perimeter Prep

Tear-off is incomplete if perimeter wood nailers are rotten, curb heights will be too low after added insulation, or through-wall flashings are left bridging the old system. Raise curbs and parapet flashings as required so the new system maintains design base-flashing heights. Replace soft nailers and damaged edge metal substrates before insulation goes down. These preparation items are frequently tested because a perfect field membrane still fails when the edge detail was never brought up to the new thickness.

Illinois Field Realities

Sudden Midwest storms can soak an open tear-off in minutes. Temporary night seals, phased tear-off, and weather monitoring are part of competent preparation—not optional extras. Document repaired areas for the owner and for your own quality record; exam items often reward the contractor who stops and repairs rather than covering defects. Coordinate dumpster placement, recycling rules, and dust control with the owner—especially on occupied schools and healthcare buildings common across the state.

Common Exam Traps

• Assuming recover is always cheaper and therefore always correct
• Covering wet polyiso or wet LWIC because “it will dry under the new roof”
• Fastening new insulation into rotten wood without replacement
• Ignoring manufacturer layer limits or local code layer limits
• Leaving the deck open overnight without temporary waterproofing
• Forgetting to raise flashings after adding insulation thickness

Sound tear-off and repair decisions protect the insulation and cover-board work that follows and keep Illinois re-roofs within both NRCA best practice and licensing expectations.