Most siding replacement projects in coastal BC fail before the first board goes up. Not because of poor craftsmanship or cheap materials, but because the quote never included the work that actually keeps water out. If you have received a proposal that lists cladding, labour, and little else, you are looking at an incomplete scope, and signing it could cost you far more than you saved.
In Northern BC’s wet climate, the layers behind your siding, including the water-resistive barrier, flashing, battens, and substrate, can represent a substantial portion of total project cost. BC Building Code Section 9.27 sets clear requirements for how exterior walls must be protected against moisture, and most standard quotes do not come close to meeting them.
This guide is written for property owners who are not contractors. It will show you exactly what a complete siding replacement scope looks like line by line, what gets quietly left out of most proposals, and what questions to ask any siding replacement contractor before you sign anything. By the end, you will know how to read a proposal with confidence and protect your building from the inside out.
Why Siding Quotes in Northern BC So Often Miss the Point
Most siding quotes follow a predictable structure: materials, labour, and removal of existing cladding. That’s it. The work behind the wall, the moisture barrier, the drainage layer, the flashing integration, rarely appears as a line item. For many climates, that gap is a problem. For Prince Rupert, Terrace, Kitimat, and Port Edward, it is a liability.
Coastal Northern BC carries one of the highest moisture loads on building exteriors in Canada. BC Building Code Section 9.27.2.2(5) triggers mandatory dual-plane protection where the moisture index exceeds 0.90 and degree-days fall below 3,400, conditions that apply to coastal Northern BC based on its climatic classification. A quote that omits those requirements is not a leaner price; it is an incomplete scope.
Most property owners accept these quotes without recognizing the gap, because they do not know that water-resistive barriers (WRBs), capillary breaks, and flashing integration are code-mandated components, not contractor discretion. The result is predictable: new cladding goes over an assembly that cannot manage moisture, and the wall begins to fail from the inside. Damage accumulates behind the cladding, invisible until it is structurally significant and expensive to repair. Understanding why building envelope failures start at the seams, not the surface explains exactly how this hidden deterioration progresses.
A cladding-only quote in this climate is not a starting point you negotiate from. It is a scope you reject.
What BC Building Code Section 9.27 Actually Requires
Here is what the code actually says, without interpretation.
BC Building Code 2018 Section 9.27 requires that all wood-frame exterior walls exposed to precipitation be protected by two distinct planes. The first plane is the cladding itself. The second plane is the water-resistive barrier (WRB) installed behind the cladding. This is a code mandate, not a best-practice recommendation. Both planes must be present and properly integrated before a wall assembly is considered compliant.
The Capillary Break Requirement
Beyond the two planes, the code requires a capillary break between the cladding and the WRB. Three methods are permitted:
- A drained and vented air space not less than 9.5 mm deep, running the full height and width of the wall
- A drainage material not less than 9.5 mm thick with 80% or more open cross-sectional area
- Masonry cavity construction per Section 9.20
The 9.5 mm rainscreen gap is the method most commonly used in residential work. For context on how the drainage plane integrates with the full wall assembly, see the details that make or break the assembly.
Vapour Barrier Position and Materials
The vapour barrier must be placed close enough to the warm side of the wall assembly to prevent condensation from forming within the assembly. The vapour barrier must be placed on the warm side of the assembly; acceptable materials are governed by BC Building Code Table 9.25.5.2.
Any siding replacement contractor quoting work in Prince Rupert or Terrace should reference these requirements directly in the scope document. If the quote contains no mention of Section 9.27, that gap is worth questioning before you sign.
What a Complete Siding Replacement Scope Should Include Line by Line
Now that you know what the code requires, here is what that translates to in a written scope. Read your quote line by line against this list before you sign anything.
1. Substrate inspection and preparation. The scope must state that existing sheathing will be assessed for rot, delamination, and structural damage before any new material is installed. Any damaged sections must be replaced and the work documented. “Minor repairs as required” is not an acceptable scope line.
2. WRB installation. The quote must name the specific product, state the overlap dimensions, and describe the method of attachment. A line reading “house wrap supplied and installed” tells you nothing about code compliance. You need the product, the seam treatment, and the fastener schedule written out.
3. Capillary break system. The scope must state whether the assembly uses a drained and vented air space of at least 9.5 mm, a drainage mat of at least 9.5 mm with 80% or more open cross-sectional area, or another compliant method. If the method is not named, it has not been priced. Learning how to protect the siding and the wall behind it starts with confirming this line exists in the document.
4. Metal flashing. Every penetration, window head, door head, sill pan, roof-to-wall intersection, and base of wall must be listed. The scope must also describe how the flashing integrates with the WRB layer: which edge laps over which, and what sealant is used. Integration is not assumed; it is written.
5. Cladding selection and installation. The actual product must be named: fibre cement, metal siding, stucco, or other. The scope should include the installation method, the fastener schedule (corrosion-resistant fasteners meeting Section 9.27.5.5, confirm the specific specification in the scope document), and any manufacturer requirements that affect the warranty.
6. Trim, corner detailing, and finishing. These are frequently absent from base quotes. They are required for a weathertight result, especially at windows and doors.
7. System-specific drainage integration. For metal siding or stucco installations, the scope must explain how the drainage plane is maintained behind that specific system, since the approach differs from standard lap siding.
8. Staged payment and inspection schedule. Each phase, substrate, WRB, flashing, cladding, should be a distinct milestone. Payment for each stage is released only after that stage is verified. This is how you confirm the hidden layers were installed correctly before they are covered.
What Gets Left Out of Most Quotes and Why It Matters
Knowing what a complete scope looks like is useful. Knowing what typically gets stripped out before a quote reaches you is more useful.
The WRB is the most common omission. Some quotes list it as an allowance or flag it as an optional upgrade. It is neither. Labelling it optional obscures a code requirement and shifts the cost risk onto you.
Metal flashing disappears from base scope just as frequently. When it does appear, it is typically a single line: “flashing as required.” That language tells you nothing about which locations are covered, how head flashing integrates with the WRB, or whether sub-sill drainage is addressed. Unspecified flashing is effectively unpriced flashing.
Substrate work presented as “minor repairs as required” is an undefined cost. In coastal Northern BC, substrate damage behind failing cladding is the norm, not an exception. Vague language becomes a change order the moment demo reveals rot. Understanding how exclusions and assumptions prevent misunderstandings on a project like this can save you significant money before you sign.
The mandatory 9.5 mm capillary break drainage layer rarely appears in residential quotes at all. Its absence is not always deliberate. Many contractors simply are not pricing to the code standard, and the gap does not surface until the work begins or an inspector flags it.
Vapor management is almost never addressed. The position and permeability of the vapor barrier determines whether the wall assembly functions through a Northern BC winter. A siding-only quote will not mention it.
The combined cost of substrate preparation, WRB, flashing, and capillary break installation can be comparable to the cost of the visible cladding. A quote showing only cladding cost is showing you roughly half the project.
Red Flags to Look for Before You Sign a Siding Proposal
Knowing what gets left out is useful. Knowing how to spot it in a specific proposal is what protects you before you sign. Read the document line by line and look for each of the following.
“Supply and install siding” with nothing else. If the scope description stops there, you have a cladding price, not a building envelope scope. No WRB, no flashing, no substrate work means those items are either not included or will appear as change orders after demo begins.
Flashing as a single line item. One line that says “flashing included” tells you nothing. Ask which locations are covered: window heads, door heads, sill pans, roof-to-wall transitions, and base of wall. Ask how it integrates with the WRB layer. If the contractor cannot answer specifically, the flashing has not been scoped, it has been acknowledged.
Substrate listed as an allowance or “TBD after demo.” In coastal Northern BC, unknown substrate cost means unknown project cost. Require a written inspection protocol and a defined change order process for additional substrate work discovered during demolition.
No reference to BC Building Code Section 9.27. Any siding replacement contractor working in a high-moisture zone should reference moisture management requirements without being asked. Its absence from the document suggests the contractor is not pricing to code standard. This pattern, vague scope and unrealistic certainty about final cost, appears across renovation work types and is worth treating as a consistent warning sign.
Generic WRB language. “House wrap as required” does not name a product, confirm drainage layer compliance, or give you a basis for comparing bids. The proposal should specify the WRB product and drainage method.
No staged inspection schedule. Once cladding goes on, the layers behind it cannot be verified. A single deliverable with payment on completion gives you no checkpoint. Require sign-off stages tied to substrate, WRB, and flashing before cladding begins.
A price significantly lower than other bids with no explanation. A lower number rarely means a more efficient contractor. It typically means the hidden scope items are absent. As outlined earlier, these scope elements together represent a significant cost that a cladding-only price does not capture.
Questions to Ask Any Siding Replacement Contractor Before Signing
Once you have identified the red flags in a proposal, the next step is direct: ask the questions that separate a contractor who understands building envelope work from one who is pricing cladding only.
1. Ask which protective plane each line item corresponds to under BC Building Code Section 9.27. Every cost item in the quote should map to either the first plane of protection (cladding) or the second plane (WRB, flashing, capillary break). A siding replacement contractor with legitimate Northern BC experience answers this without pausing. Vague answers mean the scope is not built to code.
2. Ask specifically how flashing integrates with the WRB at window heads, door heads, and roof-to-wall transitions. The correct answer describes a lapped, tied-in system where each layer sheds water to the one below it. “We caulk around it” is not an acceptable response; caulk fails and is not a substitute for a continuous second plane of protection.
3. Ask for a written process covering hidden substrate damage. Require the contractor to define in writing who assesses damage found during demo, how additional work is priced, and what triggers a formal change order. In coastal Northern BC, substrate rot is common. An undefined process becomes a dispute after demolition begins. This is also worth reviewing alongside guidance on how to budget a commercial construction project when material prices are unstable, since the same scoping discipline applies.
4. For metal siding or stucco siding bids, ask how the drainage plane is maintained behind that specific system. These materials have different installation requirements than fibre cement. Expect a concrete answer, not a generic one.
5. Ask for a marked-up elevation showing WRB coverage, flashing locations, and capillary break placement. A sketch on a printed photo is sufficient. Verbal descriptions are not.
6. Ask who is responsible for pulling the permit. Siding replacement involving WRB and substrate work may require a permit, confirm requirements directly with the building department in your municipality before work begins, and confirm in writing which party is responsible.
A Complete Scope Protects More Than the Wall
Once you have asked the right questions, the decision is straightforward: a quote that addresses every layer of the assembly is a building envelope scope; one that does not is a cladding price, and those are not the same project.
Before signing any proposal, run it against this checklist:
- WRB specified by product and installation method, not just listed as “house wrap”
- Flashing detailed at every penetration, head, sill, and roof-to-wall transition
- Substrate work defined, not deferred to an open allowance after demo
- Capillary break method stated, confirming the code-required 9.5 mm drainage system
- Staged inspections included, with payment milestones tied to verifiable work
If a line item is missing, ask the contractor to explain it. A contractor who cannot describe the hidden scope clearly has not planned how to build it. The same discipline that keeps a home addition on budget and on schedule applies here: scope clarity before work starts prevents costly surprises after demo.
J & J Construction delivers building envelope work in Prince Rupert, Port Edward, Terrace, and Kitimat, with written documentation at every stage. If you are reviewing a siding proposal and want a second opinion on the scope, contact us before you sign.
Conclusion
Review every proposal against the checklist above before you sign. If a line item is missing or vague, ask for a written explanation.
J & J Construction provides building envelope work across Prince Rupert, Port Edward, Terrace, and Kitimat. Contact us today for a scope review you can actually build from.