Roofing Scope of Work: What GCs Need to Include When Buying Out a Roofing Sub

A commercial roofing scope of work that's missing key items doesn't just create cost disputes — it creates leaks, warranty voidances, and owner liability. Roofing is one of the highest-consequence scopes on any project because failures aren't visible until water is already inside the building. This guide covers what to include in a commercial roofing scope of work, organized by the trade-specific work, package items, and the coordination requirements that define the interface between roofing and every trade that penetrates or loads the roof.

Deck Preparation

• Deck type and condition: Identify the roof deck type — steel deck, concrete, wood board, or existing built-up roof — and specify required preparation for each. Steel deck must be free of mill scale, rust, and contamination. Concrete decks require surface profiling if receiving adhered membranes. Existing roofs receiving a re-cover require condition assessment and documentation before new roofing proceeds.
• Deck deflection: Specify maximum allowable deck deflection under live load before roofing begins. Excessive deflection in steel deck causes membrane cracking — confirm the structural sub has brought the deck to design tolerance before the roofing sub mobilizes.
• Substrate board: On steel deck, specify substrate board type (cover board or insulation board) installed directly on the deck before the primary insulation layer. This provides a smooth, stable surface for membrane attachment and is required by most membrane manufacturers for warranty compliance. Frequently omitted from roofing scopes.

Thermal Insulation and Vapor Retarder

• Insulation type and thickness: Specify insulation product (polyisocyanurate, EPS, or XPS), total thickness, and minimum R-value after age-related thermal drift (not nominal R-value). Polyiso R-value decreases over time — design R-values must account for this. Specify whether insulation is single-layer or tapered.
• Tapered insulation: If tapered insulation is used to create positive drainage, require the sub to submit a tapered insulation layout drawing showing thickness at every drain point and ridge before procurement. Tapered insulation installed without a layout drawing regularly produces ponding water.
• Vapor retarder: Specify whether a vapor retarder is required by the wall/roof assembly design. Vapor retarder location (above or below insulation) must be specified by the design engineer — it is assembly-specific and cannot be a field decision.
• Fastening pattern: For mechanically attached assemblies, specify fastener type, spacing pattern, and minimum pullout value. Fastener pullout values must meet the structural engineer's wind uplift calculations for the project's location and roof zone. This is the most important structural requirement in any roofing scope and the most commonly omitted.

Roofing Membrane System

Tip: Specify the membrane system by manufacturer and product line, not just by membrane type. "60-mil TPO" without a manufacturer specification allows a sub to supply the cheapest product on the market. Specify manufacturer, product name, and minimum thickness.

• Single-ply membrane (TPO, EPDM, PVC): Specify manufacturer, product line, membrane thickness (minimum 60-mil for commercial), attachment method (mechanically attached, fully adhered, or ballasted), and seam type (heat-welded for TPO/PVC; solvent- or tape-welded for EPDM). Minimum seam width — 40mm for heat-welded single-ply. Test cuts at proctor intervals.
• Modified bitumen (SBS or APP): Specify number of plies, interply product, cap sheet product, and application method (torch-applied, cold-applied, or self-adhering). Surface granule color and reflectance requirement (if cool-roof compliance required).
• Built-up roofing (BUR): Specify number of plies, ply type (organic felt, fiberglass), bitumen type (Type III or Type IV), and surfacing (gravel, mineral cap sheet, or aluminum coating). Rarely specified on new commercial construction but common on renovation and re-roof scopes.
• Green roof or protected membrane assembly (PMA): If a vegetated or protected membrane assembly is specified, confirm whether the membrane and protection board are in the roofing sub's scope or split with a landscaping or hardscaping sub.

Flashings, Terminations, and Penetrations

Tip: More roofing leaks start at flashings and penetrations than at field membrane. These details must be fully specified — not left to the sub's standard practice.

• Perimeter edge flashings: Specify metal edge type (fascia bar, coping, or gravel stop), material (aluminum, galvanized steel, or stainless), gauge, finish, and manufacturer. Metal edge flashings that are undersized or improperly fastened fail in wind uplift events — specify width and fastener spacing.
• Counterflashing and through-wall flashing: At all parapet walls, specify whether the counterflashing is embedded (reglet), surface-mounted, or integral. Surface-mounted counterflashings require caulking at the top lap — specify sealant type and warrant period. Embedded reglet counterflashings require coordination with the masonry sub.
• Penetration flashings: All roof penetrations — pipes, conduit, vents, equipment curbs — receive a prefabricated or field-fabricated pitch pocket or pipe boot flashing. Specify whether pitch pockets are acceptable (they require ongoing maintenance and re-caulking) or whether self-terminating flashing cones are required. Pitch pockets are the most common source of localized roof leaks on any rooftop.
• Equipment curbs: Specify whether rooftop equipment curbs are provided by the HVAC sub or the roofing sub. Curb flashing and membrane integration is typically the roofing sub's scope regardless of who supplies the curb. Confirm this split in both subcontracts.
• Roof drains: Specify drain type (interior, perimeter, or siphonic), drain body material, and dome strainer specification. Confirm whether roof drains are furnished by the plumbing sub and flashed by the roofing sub, or whether both supply and flash is in the roofing scope.

Drainage

• Primary drainage: All primary roof drains designed by the mechanical/plumbing engineer of record. The roofing sub confirms that the drain leader sizes and drain locations match the finished roof slope directions from the tapered insulation layout.
• Overflow drains or scuppers: Required by code where interior drains are used. Specify overflow drain rim elevation (typically 50mm above primary drain rim) and confirm overflow drain outlet discharges to a visible location to allow maintenance staff to identify when the primary drain is blocked.
• Ponding water: Specify maximum allowable ponding water depth at 48 hours after the cessation of rain (typically 12mm maximum). Require the sub to demonstrate positive drainage from every area of the roof before membrane installation is accepted.

• Manufacturer's system warranty: Specify minimum warranty term (typically 20-year NDL — No Dollar Limit — warranty on commercial projects), what it covers (labor and materials for both membrane and flashings, not just membrane), and whether a rooftop inspection by the manufacturer's representative is required to activate the warranty. Many roofing warranties require a field inspection before they are issued — confirm this process is in scope.
• Flood test or nuclear density test: Specify acceptance testing before roofing is covered by protection board or ballast. For adhered systems, a flood test (damming roof areas and holding water for 24 hours) or an electronic leak detection (ELD) scan is best practice. Require the sub to schedule testing with the GC present.
• Tear-off and disposal: On re-roofing projects, specify scope of existing roofing removal — confirm whether one or multiple existing roof layers are removed. Identify whether existing insulation is to be removed or left in place. Hazardous material assessment is required before tear-off if the existing roof predates 1990 — asbestos-containing roofing materials were common. Confirm hazmat scope is separate from roofing scope.
• Walkway pads: Specify walkway pads at all roof access points, along equipment maintenance routes, and around all rooftop equipment requiring regular service access. Walkway pads protect the membrane and are required by most warranty agreements. They are consistently omitted from roofing bids.
• Safety and fall protection: The roofing sub is responsible for all edge protection, safety cables, and fall arrest systems required for their work and for ongoing owner maintenance access. Confirm permanent anchor points for roof access are in scope and specify CSA or ANSI load rating requirements.
• Hoisting and debris removal: Roofing sub is responsible for all hoisting of roofing materials to the roof level and for removal and legal disposal of all tear-off debris. On occupied buildings, specify requirements for containing and removing debris without contaminating the occupied areas below.

• HVAC/mechanical: All rooftop equipment curb locations must be confirmed and curbs set before roofing membrane is installed. The roofing sub cannot install membrane and flashings around equipment that hasn't been set. Establish a firm milestone date for all curb setting — this is a leading cause of roofing schedule delays.
• Plumbing: Roof drain body installation — confirm whether the plumbing sub installs the drain body (in concrete deck or insulated deck) or whether the roofing sub sets the drain. Roofing sub installs the drain flashing clamp ring and membrane into the drain bowl regardless. Overflow drain installation scope must also be defined.
• Electrical: All rooftop electrical conduit penetrations must be sleeved and flashed before roofing membrane is installed. Coordinate conduit locations with the electrical sub before membrane installation. Cutting through finished roofing for conduit additions is expensive and frequently voids the membrane warranty.
• Solar (if applicable): Solar racking penetrations or ballasted system layout must be coordinated with the roofing sub before membrane installation. On penetrating solar systems, the roofing sub or the solar sub installs the penetration flashings — confirm this split in writing. Improper solar flashings on roofing membranes void the roofing warranty.
• Structural: Rooftop equipment loads, ballast loads, and pavers must be confirmed within the structural engineer's allowable roof live load. The roofing sub is responsible for flagging any rooftop loading that exceeds what the structural system can support — but this requires the structural engineer's input. Establish this review process before rooftop equipment is ordered.
• Masonry/cladding: Through-wall flashings at parapet intersections with exterior cladding must be coordinated between the roofing sub and the cladding sub before either trade installs their work. The lap sequence — which material laps over which — determines whether the assembly drains properly.