Methodology

This page explains how the SidingCalcs calculators and the reference datasets are derived and verified — and why they need no ongoing maintenance to stay correct. It is the method behind the siding coverage-by-material reference and its waste-factor-by-layout companion, our signature data assets.

1. Timeless wall/gable-area geometry, stable conventions

Every tool computes from a closed-form identity: wall area = perimeter × wall height; gable area = ½ × base × height; net siding area = gross − openings; squares = ceil(area × (1 + waste) ÷ 100); boxes = ceil(area × (1 + waste) ÷ coverage per unit); house-wrap rolls = ceil(area × (1 + overlap) ÷ roll coverage); and cost = (net area × your $/sq ft [or squares × your $/square] + labor + add-ons − discount) ×(1 + contingency). The only baked-in numbers are stable identities and labeled published typicals. These do not drift, so the statements stay true over time.

2. Siding quantity as plane geometry; siding cost as a quantity × unit-price sum

Siding quantity is plane geometry — the net area is the wall perimeter times the height, plus the gable triangles, minus the openings, and a box or bundle covers a stated number of square feet at a stated exposure, so units = ceil(area × (1 + waste) ÷ coverage). Siding cost is a quantity × unit-price sum — the area (or the squares) times the price you enter, plus labor and add-ons, with a contingency. Round siding UP to whole squares/boxes/bundles so you don’t run short mid-wall.

3. The signature coverage & waste references

The coverage-by-material reference tabulates the LABELED exposure and coverage per box/bundle/square for each common material (vinyl double-4″ ~200 sq ft/box, cedar shingle ~25 sq ft/bundle at ~5″ exposure), and the companion gives the LABELED waste factor by house layout. Both are dated snapshots (currently 2026-07-13), not live feeds: they hold only stable identities and clearly labeled published planning ranges, so they never need maintenance. Assumptions and limits are stated on the page.

4. Where the conventions come from

The 1 square = 100 sq ft is a definition. The coverage / exposure ranges are the manufacturers’ published planning ranges by material; the waste factors (~10–15%), the standard door/window/garage deductions (door ~21 sq ft, window ~15, patio door ~40, single garage ~63, double garage ~112), the story/access multipliers and the cost bands are LABELED published planning typicals, cited in Sources and user-adjustable.

5. No prices, no feeds

There is deliberately no live material or labor price, no regional cost index, no product catalog, no contractor directory and no live rate. Every cost tool works on the prices you enter from your own quotes and bills ($/sq ft, $/square, labor $, add-on $, $/lf). Labeled cost bands are shown only as a sanity guide. That is why the site is correct regardless of what siding or labor prices do.

6. Numeric self-check

Every formula is asserted against a worked example with known numbers (for instance: a house with a 140 ft perimeter, 10 ft walls and two 30 × 8 ft gables is 1,640 sq ft gross, 1,336 sq ft net of two doors, ten windows and a double garage, and about 15 squares at a 10% waste factor — roughly 8 boxes of double-4 vinyl; sided at $7.00/sq ft with a 10% contingency, about $10,287; in fiber cement at $9/sq ft about $13,226; 500 sq ft of cedar shakes at 15% waste is about 23 bundles). A release gate runs all of these and fails on any mismatch, so “verification” here is mathematical correctness plus accurate conventions — not a time-based check.

7. Estimate or quantity guide, not a design

The contingency %, waste %, coverage per box, exposure, door/window/garage deductions, story/access multipliers and cost bands are labeled planning typicals — a starting point, not a spec. Every result is a planning estimate or a siding quantity / material guide: get itemized written quotes from licensed, insured siding contractors, measure your actual walls and gables and follow the manufacturer’s exposure and installation instructions, and allow extra for waste, trim and complex layouts. Moisture/flashing, structural sheathing, pre-1978 lead-paint abatement and code certification are set by the EPA RRP rule, a certified pro and local code; they are out of scope. Nothing here is an installation procedure, a moisture/flashing verdict, or a certified design.