Siding Scope of Work: What GCs Need to Specify When Buying Out a Siding Sub

Siding looks simple on paper and gets complicated fast in the field — particularly on commercial projects with multiple cladding types, complex transitions, or demanding moisture control requirements. A well-written siding scope of work closes the gap between what the architect detailed and what the sub actually plans to install. This guide covers what to include in a siding scope of work, organized by the trade-specific work, package-specific items, and the coordination requirements that regularly create disputes between siding, roofing, framing, and window trades.

Substrate and Sheathing

• Substrate scope boundary: Confirm whether the siding sub carries the structural or exterior sheathing, or whether sheathing is in the framing sub's scope. On commercial wood-frame projects, framing subs often price sheathing but siding subs assume it's included in their scope. This creates a real gap — clarify it in both subcontracts.
• Weather-resistive barrier (WRB): Specify the WRB by manufacturer and product, minimum lap dimensions (typically 150mm horizontal, 300mm at vertical laps), fastening schedule, and whether it's in the siding sub's scope or applied by the framing sub. Best practice: specify WRB as the siding sub's responsibility — it integrates with their flashing work.
• Surface preparation (renovations): On existing buildings, specify scope of existing cladding removal, fastener removal, surface repairs, and leveling required before new siding installation. Confirm whether hazardous materials (asbestos-containing cladding) are a separate abatement scope.

Metal Panel and Composite Cladding

• Material specification: Specify panel system by manufacturer and series (e.g., Centria Formawall, Kingspan Optimo, Petersen PAC-CLAD). Include finish/color with manufacturer's reference number, panel thickness and gauge, and span rating. Substitutions must require written approval with re-engineering confirmation — do not allow "or equal" without review.
• Panel orientation and layout: Specify horizontal vs. vertical installation, reveal width, alignment requirements relative to window heads, sills, and structural grid, and corner condition details (shop-fabricated vs. field-mitered).
• Fasteners: Specify fastener type (concealed vs. exposed), material (stainless steel or hot-dipped galvanized), and spacing per manufacturer's structural requirements and local wind uplift design. Exposed fastener systems are commonly installed with incorrect spacing — require a pre-installation inspection checkpoint before full installation proceeds.
• Thermal spacers: On commercial metal panel systems, thermal spacers at girts are required to prevent thermal bridging at the cladding attachment. Thermal bridging causes condensation and energy code compliance failures. Frequently omitted from both the design and the sub's scope.

Fiber Cement and Wood-Based Cladding

• Product specification: Specify manufacturer, product line, profile, thickness, and factory finish (factory primed, factory painted, or field painted). Factory-finished products require field touch-up paint at all cuts — this must be explicitly in scope. Unpainted field cuts on factory-finished products void the manufacturer's warranty.
• Layout and starting course: Starting course elevation must be established relative to finished grade, slab edge, and foundation waterproofing system. This is frequently miscoordinated — the siding sub starts at the wrong elevation relative to the waterproofing membrane termination.
• Clearances: Specify minimum clearance from finished grade to bottom of siding (150mm minimum), from roof membrane to horizontal cladding surfaces (minimum 50mm), and from deck surfaces to adjacent siding panels. These clearances are required for both warranty compliance and drainage.

Flashings and Transitions

• Window and door flashings: Specify flashing material (aluminum, galvanized steel, or stainless steel), minimum dimensions, end dam requirements, and sealant type at all siding-to-flashing laps. Most siding water infiltration problems originate at window head and sill flashings — get explicit on each detail.
• Horizontal cladding transitions: Where two cladding types meet (e.g., metal panel above, fiber cement below), specify a continuous waterproof transition flashing and identify which sub is responsible. This is one of the most commonly disputed scope items on multi-material facades.
• Soffit integration: Specify whether soffit work is included in the siding sub's scope or by another trade. If by another trade, specify the exact interface point and who provides soffit ventilation integration with the WRB.

Installation Quality Controls

• Fastener pattern submission: Require the sub to submit manufacturer's fastener pattern for approval before installation begins. Incorrect fastener patterns are the most common cause of warranty claim rejection on metal panel and fiber cement systems.
• Flatness tolerance: Specify maximum allowable bow, warp, or offset at panel joints — typically 3mm in 3m for commercial metal panel. Require the sub to inspect substrate flatness before installation and report deficiencies.
• Expansion gaps: Specify expansion joint locations and gap dimensions per manufacturer's thermal movement requirements. Metal panel systems expand significantly — missed expansion gaps cause panel buckling in summer and oil-canning.

• Scaffolding and access equipment: Siding sub is responsible for all scaffolding, swing stages, or boom lifts required for installation. On multi-story projects, scaffold can represent 15–25% of the siding sub's total cost — confirm it's in the bid and not assumed to be GC-furnished.
• Field cuts and waste treatment: All field-cut edges of factory-finished or factory-primed products must be treated per manufacturer requirements (paint, primer, or sealer). Specify that waste factor allows for this and that the sub provides touch-up materials as a closeout deliverable.
• Caulking and sealants: Specify sealant type (low-modulus silicone or polyurethane by location), color, and application scope at all panel joints, penetrations, and transitions. Siding subs commonly exclude sealant at complex transitions or at trade interfaces — confirm all sealant is in scope.
• Mockup: Many commercial siding specifications require a full-size installation mockup (typically a 3m × 3m minimum panel area) for architect and owner review before full installation proceeds. Confirm this is in scope, including the cost of any required adjustments after mockup review.
• Installer certification: Many cladding system manufacturer warranties require installation by a certified applicator. Confirm the sub holds current certification and will provide certification documentation at closeout.
• Warranty documentation: Confirm what manufacturer's warranty is provided and what the installation requirement is to maintain it. Many siding system warranties require a registered installation — confirm the sub completes registration at project closeout.

• Framing/structure: Siding sub must confirm girt spacing, framing depth, and structural sheathing completion before ordering panel systems. Metal panel systems are engineered around specific girt spacings — ordering before framing is confirmed is a leading cause of fit-up problems on site.
• Windows and doors: Window subs typically install the window unit and provide rough flashing at the rough opening. The siding sub installs cladding to the window perimeter and provides the finish flashing at all four sides. Confirm this interface explicitly in both subcontracts — water infiltration at window perimeters is the most common siding callback and warranty claim.
• Roofing: Roof-to-wall transition flashing is frequently a disputed scope item. Confirm whether the roofing sub or siding sub provides the step flashing or transition membrane, and who provides the counter-flashing over it. Neither sub should assume it's the other's responsibility without written confirmation.
• Electrical: Exterior lighting fixtures, outlet boxes, and any conduit penetrating the siding system must be sleeved and located before panels are installed. Coordinate with the electrical sub on all penetration locations — cutting through installed metal panel is expensive and can void the warranty.
• HVAC/mechanical: Louver openings, exhaust fan thimbles, and mechanical penetrations must be established before siding panels are installed. Mechanical sub must provide confirmed opening sizes and locations before siding layout begins.