Methodology

How we work out your numbers.

Every cost, saving and priority BlockSun shows for a home is computed from that home's own measurements and public records — not a city average and not a contractor's pitch. Here is the whole method, including what it cannot tell you.

What we measure about your home

Every estimate starts from the building and parcel themselves, not a city average. Roof footprint comes from building outlines; lot area and perimeter come from county parcel polygons. Year built, living area, bedroom and bathroom counts, assessed land and improvement values and use type come from county assessor public records. Where our computer-vision pass has run on recent aerial imagery, we also record roof material, apparent roof condition, and whether the home already has solar or a pool.

How cost is calculated

Projects priced by area (solar, roofing, turf) multiply the measured area by a current regional rate per square foot, adjusted for roof pitch and — for re-roofing — the detected roof material, since tile and slate cost several times what asphalt does. Projects priced by perimeter (fencing) use the measured lot perimeter and a rate per linear foot. Projects that do not scale cleanly with the building (HVAC, windows, batteries, pools) use a cost band for the local market, narrowed by home size. Published public rebates and credits are subtracted to show a net cost, with the program named and its expiry shown.

How a solar system is sized

We size an array to what the household is likely to use, not to how much roof there is. Expected annual consumption is estimated from living area, bedroom count and whether there is a pool, with a small allowance for future electrification; the result is then capped by what the roof can physically hold. This matters under NEM 3.0, where exported power earns a fraction of what avoided power is worth — so an oversized array sells its surplus cheaply instead of saving you money.

How savings are calculated

Solar savings model the system's expected annual production against the home's utility tariff under California's NEM 3.0 rules, which pay far less for exported power than for power you avoid buying — so the figure reflects self-consumption rather than a flat retail credit. Where a project's saving is primarily comfort or condition rather than a measurable bill reduction, we show no annual saving instead of inventing one.

How priority is decided

Priority is an estimate of urgency, not of profit. It is driven by observed condition where computer vision has assessed the roof, and otherwise by the age of the relevant system inferred from year built. Discretionary projects stay low-priority by design. When nothing scores as pressing, the plan says the home is in good shape — we would rather say that than manufacture a project.

Financing figures

Any monthly figure shown is illustrative: the project cost amortized at a benchmark rate for that project type, refreshed from published rate data. It is not an offer of credit, not an underwriting decision, and not a quote. Actual terms come from a lender after an application.

Property value context

Where a third-party estimate of a home's value is shown, it is an automated valuation model (a Zestimate) and is labelled as such — it is an algorithm's opinion, not an appraisal. Sale prices shown are arms-length recorded sales; we filter out non-market transfers such as family quitclaims, which would otherwise drag a comparison down. Assessed values are acquisition-based under California's Proposition 13 and are routinely far below market value; we present them as public record, never as worth.

What we do not do

We do not sell homeowner information. Nothing is passed to a provider until you ask for a quote, and then only to providers who do the specific project you picked. Providers do not pay to change a home's ranking or its numbers — the ranking is computed from the property, and no provider can buy their way up it.

Accuracy and corrections

These are planning estimates. A real bid depends on access, condition, permitting and choices no aerial dataset can see, and a licensed local contractor confirms the real number for free. If a figure looks wrong for your home, tell us — corrections improve the model for the whole block.

Typical cost by project

Project	Typical cost	What it scales with
Solar	Installed cost runs about $3.05 per watt — roughly $12,000–$27,500 for the 4–9 kW system most homes need.	Sized to the measured roof; savings under NEM 3.0
New roof	Installed cost runs about $3.50–$30.00 per square foot depending on the material.	Scales with measured area
Pool	Most projects run $45,000–$85,000.	Cost band for the local market
HVAC	Most projects run $8,000–$18,000.	Cost band for the local market
Battery	Most projects run $12,000–$22,000.	Cost band for the local market
Windows	Most projects run $9,000–$22,000.	Cost band for the local market
Turf	Typically about $12.00 per square foot installed.	Scales with measured area
Fencing	Typically about $45 per linear foot installed.	Scales with measured lot perimeter

Questions

Are BlockSun's cost estimates accurate?

They are planning estimates built from your home's own measurements and current regional pricing, not contractor bids. Expect them to be in the right range for budgeting and to be confirmed — up or down — by a site visit, which is free.

Does BlockSun charge homeowners?

No. Looking up any home, seeing its ranked plan and comparing costs and savings is free and requires no signup.

Can a contractor pay to rank higher on a home's plan?

No. The project ranking is computed from the property's own measurements, condition and age. Providers cannot buy position in it.

Where does the property data come from?

County assessor and parcel records (public record), building outlines, and our own computer-vision analysis of recent aerial imagery. Third-party listing data, where shown, is labelled with its source.