Roof Deck and Substrate Preparation
Roof Deck and Substrate Preparation
This domain tests substrate acceptance: deck condition, slope and drainage, insulation and cover board, vapor retarder continuity, priming, moisture, and penetration framing. The exam expects you to know what must be corrected before membrane work starts.
Core rules
- The deck must be structurally sound, clean, dry, and free of sharp edges, oil, ice, and loose material. Correct ponding and provide positive drainage; a common design minimum is 1/4 in/ft (2%), but follow code and specification.
- Wood decks need proper thickness, span, fastening, and gap control. Steel decks need specified gauge, span, and fasteners. Concrete must be cured, sound, and primed as required.
- Insulation must be attached per the assembly and covered with an approved cover board where required. Never torch directly to unprotected combustible insulation.
- Vapor retarder laps and penetrations must be continuous and sealed. Interruptions at curbs, drains, and expansion joints need framing and reinforcement.
- Prime substrates when required and only in compatible weather. Moisture testing is required for concrete and some other decks before covering.
Worked example
A new concrete deck reads damp at the surface and the specification calls for a vapor retarder. Do not simply prime and install membrane. Let the concrete cure, document moisture tests, install a compatible vapor retarder with sealed laps, then place insulation and cover board. The reason is that trapped moisture can blister the membrane and void the warranty.
Traps
Torching over combustible insulation; covering wet concrete; skipping primer; forgetting nailers at edges and curbs; treating a minor deck deflection as cosmetic.