Siding Scope of Work: Cladding Systems, WRB Integration, and Flashing Sequencing
What belongs in a siding scope of work — cladding system specs (Hardie, LP, metal panel), weather-resistive barrier integration, drainage plane, flashing sequencing, and the trade interfaces that drive water-infiltration claims.
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.
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Substrate, Cladding Systems, and Flashing Specifications
The line items that govern a siding buy-out — substrate scope boundary, weather-resistive barrier and drainage plane, manufacturer-specific cladding systems (Hardie, LP, metal panel), fasteners, and flashing details must be explicit before mobilization.
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 and the broader waterproofing envelope.
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 painting 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.
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Common Siding Scope Gaps at Buy-Out
Items routinely left out of siding sub bids — scaffold and lift access, field-cut edge treatment, sealants at trade interfaces, installer certification, and manufacturer warranty registration — that drive change orders or void warranties if not nailed down.
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.
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Siding Coordination with Framing, Windows, and Roofing
Interface items between the siding sub and the framing, window, roofing, electrical, and mechanical trades — the trade interfaces that drive water-infiltration callbacks and warranty disputes if scope is unclear.
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. Coordinate the waterproofing sub's wall membrane termination with the siding sub's starting course so the drainage plane is continuous.
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.
Siding Scope of Work — FAQ
What is a siding scope of work and why does it matter?
A siding scope of work is the contract document that defines exactly what cladding system, accessories, flashings, and trade interfaces the siding subcontractor is responsible for — and what they're not. It matters because siding sits at the intersection of structural framing, weather-resistive barrier, windows, roofing, and waterproofing, and water infiltration claims (the costliest defect category in commercial construction) almost always trace back to an undefined transition or a sealant joint that nobody priced. A clear scope locks in WRB responsibility, flashing sequencing, fastener patterns, manufacturer warranties, scaffold cost, and the specific interfaces with adjacent trades.
Is the weather-resistive barrier (WRB) in the siding sub's scope or the framing sub's scope?
Either works, but the best practice is to assign WRB to the siding sub. The WRB integrates directly with the siding sub's flashings, window flashing laps, and termination details — when it's split between two trades, the laps and integration almost always get done wrong. If the framing sub does install the WRB (common on Type V wood-frame), require the siding sub to inspect and accept the WRB before installing cladding, and require photo documentation of all window opening flashing laps before the cladding goes on.
How do I avoid voiding a manufacturer cladding warranty (Hardie, LP, metal panel)?
Three things kill warranties: untreated field cuts (factory-primed product must be primed at every cut edge), wrong fastener spacing/type (read the manufacturer's installation manual, not the architect's spec), and missing clearances (Hardie requires 150mm to grade, 50mm to roofing). Require the sub to be a manufacturer-certified installer where applicable, submit the fastener pattern for approval before installation, and complete the warranty registration at closeout. Many fiber cement and metal panel warranties are voided 80% of the time by simple field cut treatment failures.
Who installs the flashing at the roof-to-wall transition — roofer or siding sub?
This is one of the most disputed scope items. The cleanest assignment is: roofer provides base flashing or step flashing tied into the roof membrane; siding sub provides counter-flashing over the base flashing, integrated with the WRB and cladding above. Spell out both pieces in both subcontracts so neither party can claim the other was supposed to do it. On masonry or brick veneer, the masonry sub installs through-wall flashing instead — confirm which condition applies on each elevation.
What's the most common cause of siding-related water infiltration claims?
Window perimeter flashing. The window sub installs the unit with rough flashing at the rough opening; the siding sub installs cladding around the window and provides finish flashing at head, jambs, and sill. The sill flashing in particular needs end dams turned up at both jambs — this is routinely omitted, and it's the primary failure point. Require sill flashing with sealed end dams, head flashing with kicker/drip edge, and a sealant joint at jambs (no sealant at the head — water needs an exit). Photo-document every window before cladding installation.
Should I expect scaffolding in the siding sub's bid or carry it as a GC cost?
Standard practice is for the siding sub to include scaffolding, swing stages, or boom lifts in their lump sum — but this is a frequent assumption gap. On multi-story commercial work, access equipment can be 15–25% of the siding contract value, so confirm it's priced in the bid and not assumed to be GC-furnished. If the GC is providing scaffolding for multiple trades (siding, masonry, painting), state that explicitly and net the cost out of the siding bid.
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