Roof Assembly and Substrate
Deck types for EPDM installations, insulation selection and R-value requirements, cover board materials, and minimum slope specifications for single-ply membrane systems.
- Identify compatible deck types for EPDM systems including steel, concrete, and wood
- Calculate insulation thickness needed to meet target R-values using polyiso, EPS, and XPS
- Explain the purpose of cover boards and when gypsum, HD polyiso, or wood fiber is required
- State the minimum slope requirement for EPDM roofs and describe how ponding water is addressed
Lección 1
Deck Types and Preparation
The Foundation of Every EPDM Roof
The roof deck is the structural surface that carries the entire roofing assembly. Before any insulation or membrane goes down, the deck must be inspected, approved, and properly prepared. An EPDM system is only as reliable as the deck beneath it.
Three deck types account for the vast majority of commercial EPDM installations:
Steel deck is the most common substrate in commercial construction. Corrugated steel panels (typically 22-gauge or 20-gauge) span between structural purlins or joists. The flutes run parallel to the slope. For EPDM systems, steel deck must be a minimum of 22 gauge (0.0295 inches thick). Thinner gauges may not hold mechanical fasteners adequately. Before installation begins, verify that the deck is free of oil, excessive rust, and sharp edges that could damage the membrane.
Structural concrete decks are found in older commercial buildings, hospitals, and parking structures. Concrete must be fully cured (minimum 28 days) and dry before applying insulation or membrane. Moisture testing with ASTM D4263 (plastic sheet method) or a calcium chloride test should confirm the surface moisture level is acceptable. Uneven concrete surfaces may need a leveling fill or lightweight insulating concrete overlay.
Wood deck (plywood or OSB) is common in re-roofing and light commercial applications. Minimum thickness is 15/32 inch for plywood and 7/16 inch for OSB. Wood decks must be dry, structurally sound, and free of warped, delaminated, or rotted panels. Any damaged panels must be replaced before the roof system is installed.
Steel Deck
Min gauge: 22 ga (0.0295 in)
Common in: New commercial construction
Prep: Remove oil, rust, sharp edges; verify gauge
Concrete Deck
Cure time: Minimum 28 days
Common in: Hospitals, older buildings, parking structures
Prep: Moisture test, level surface, prime if needed
Wood Deck
Min thickness: 15/32 in (plywood) or 7/16 in (OSB)
Common in: Re-roofing, light commercial
Prep: Replace damaged panels, verify structural soundness
Deck Inspection Checklist
Before insulation placement, walk the entire deck and verify:
- All penetrations (pipes, ducts, drains) are framed and supported
- Deck is sloped to drains or scuppers (no reverse slope areas)
- No standing water from recent rain
- Steel deck fasteners (puddle welds or screws) are secure - no loose or rocking panels
- Wood deck is nailed at 6 inches on center at panel edges and 12 inches on center at intermediate supports
Steel deck must be minimum 22 gauge, concrete must cure for 28 days before roofing, and wood deck must be minimum 15/32 inch plywood or 7/16 inch OSB. Always moisture-test concrete and replace damaged wood panels before proceeding.