Methodology

Roof area = (floor area ÷ storeys) × pitch multiplier × overhang factor (1.1). Pitch multipliers: low 1.03, moderate 1.09, steep 1.25. A 2,000 sq ft two-storey home at moderate pitch is about 1,199 sq ft of roof (12 squares). A roofer's measurement always overrides this.

Every estimate is shown as three separate lines so the same inputs never produce two unexplained numbers:

Material compatibility: torch-on (SBS) and single-ply membranes are low-slope systems. They are never priced as the whole roof of a pitched (moderate or steep) home; the calculator blocks that combination and instead prices any flat section (addition, carport, porch) separately as a mixed roof.

Every input can be answered “Not sure”; unknowns are replaced by listed assumptions and lower the confidence (three or more unknowns = “not enough is known”). Horizon views compare intervals strictly: repair wins only if its high end is below the replacement low end, replacement wins only if its high end is below the repair low end, otherwise the view says “uncertain”. Remaining life = material lifespan minus age, reduced for widespread damage, repeated repairs and recent leaks. Signals toward a replacement evaluation: at or past lifespan (2 points), inside the end-of-life window (1), repair over 35% of replacement (1), two or more leaks in two years (1), several prior repairs (1), widespread damage (1). Two or more points = “replacement evaluation may be economically reasonable”. Horizon views add typical follow-up repair allowances and include a replacement when even the optimistic remaining life runs out inside the window.

Active water, timing, roof age and repair history are asked on every assessment and must be answered explicitly or as “Not sure”; unanswered questions block the result. Without photos the result is labelled rule-based; it is called AI-assisted only when photos were actually analysed. Each problem has a default urgency and a fixed set of follow-up questions. Active water entry or a sudden change raises urgency one step; widespread extent raises low to moderate. Repair-vs-replace evaluation follows the problem's typical outcome, adjusted by age band and extent. Photo observations, when enabled, come from a vision model instructed to use only hedged language and to flag hazards; they never change the price and never override the rules downward.

We compare 17 stated fields. Completeness = fields stated ÷ 17. Critical fields (price, area, material, product line, tear-off, underlayment, ice-and-water, flashing, ventilation, decking allowance, disposal, both warranties, payment terms) that are missing generate a question to ask. We never rank contractors; scope differences and gaps are shown as facts.

Rates are re-checked quarterly against published Greater Victoria and BC ranges and, as the anonymized quote database grows, against real quotes submitted through the comparison tool. Change one factor here and every page and calculator changes together. See Sources for the calibration references.