# DeckMath — llms.txt

> The free deck calculator + cinematic 3D platform. 10 production calculators, 10 cornerstone guides, 71 programmatic state + size cost pages. IRC 2021 compliant. Mobile-first. No signups, no paywalls — fully free for users.

DeckMath is a free web application that helps homeowners and contractors estimate deck materials, cost, and verify code compliance. Every structural calculation is cross-checked against International Residential Code (IRC) 2021. The site is built mobile-first with sub-second page loads and includes a free embed system so any contractor website can offer DeckMath calculators inline.

Updated: 2026-05-10

## Pillars

- **Free forever**: No accounts, no paywalls, no premium features that gate functionality. Revenue from non-intrusive AdSense, affiliate links, and lead-gen.
- **IRC 2021 compliant**: Joist span (R507.6), beam span (R507.5), footings (R507.3) + frost (R403.1.4), guards/balusters (R312), stairways (R311.7).
- **Mobile-first**: Every page works perfectly at 375px wide. Touch-friendly. Tap-to-edit inputs.
- **Cinematic 3D**: Real-time Three.js scenes that visualize the deck as the user types (Tier-1 calcs). Calc-appropriate SVG diagrams for structural calcs (Tier-2). Lazy-loaded so the page stays fast.
- **Embed anywhere**: One line of HTML drops a calculator into any contractor or DIY site. Auto-resize, theme-sync, no iframe pain.

## Calculators (Phase 1 MVP — 10 / 10 LIVE)

- /calculators/deck-material-calculator — boards, joists, beams, posts, footings, fasteners (Tier-1, 3D viewer)
- /calculators/deck-cost-calculator — material + labor + permit project total, 5 finish tiers (Tier-1, 3D viewer)
- /calculators/joist-span-calculator — IRC R507.6 max joist span by size, species, spacing
- /calculators/deck-footing-calculator — depth, diameter, concrete volume, bag count (R507.3 + frost line per state)
- /calculators/deck-beam-span-calculator — IRC R507.5 max beam span by size, ply, species, tributary
- /calculators/deck-stair-calculator — stringer length, rise, run, treads (R311.7)
- /calculators/composite-deck-cost-calculator — 7-brand × 13-line composite cost + 25-yr TCO vs PT (Tier-1, 3D viewer)
- /calculators/trex-deck-calculator — Trex-deep estimator: full color palette + TUHF box count + RainEscape + DeckLighting (Tier-1, 3D viewer)
- /calculators/baluster-spacing-calculator — even spacing under R312.1.3 (4-inch sphere rule), side-elevation SVG
- /calculators/deck-stain-calculator — 13-brand stain catalog + real surface area + stocked-size bundle + re-stain schedule

## Cornerstone guides (10 articles, ~25,000 words total)

- /guides/deck-building-cost-guide-2026 — definitive 2026 cost breakdown
- /guides/composite-vs-wood-decking — 25-year TCO analysis with break-even years
- /guides/deck-building-permits-irc — IRC R105 triggers, fees, inspection process
- /guides/how-to-build-a-deck — 8-step DIY walkthrough with tools list
- /guides/deck-joist-spacing-guide — IRC R507.6 prescriptive tables explained
- /guides/deck-footing-requirements-irc — R507.3 + R403.1.4 frost-depth lookup
- /guides/trex-vs-timbertech-comparison — head-to-head brand showdown
- /guides/best-deck-patterns-compared — parallel/picture-frame/diagonal/herringbone/chevron
- /guides/deck-maintenance-guide — annual + 5-year + 15-year schedule
- /guides/deck-cost-breakdown-2026 — line-by-line on 5 builds

## Programmatic SEO pages (71 pages)

- /deck-cost — all 50 states + DC index
- /deck-cost/{state} — 51 state-specific cost pages with local labor multiplier + frost depth + permit notes
- /deck-cost-by-size — 20 popular deck sizes index
- /deck-cost-by-size/{size} — 20 size-specific cost pages (8x10 → 30x30) with tier comparison ladder

## Site sections

- / — Home / overview
- /calculators — Index of all live calculators
- /guides — Long-form how-to and code-reference articles
- /deck-cost — Deck cost by state index
- /deck-cost-by-size — Deck cost by size index
- /about — Company + approach overview
- /privacy — Privacy policy
- /terms — Terms of service
- /contact — Contact page

## Tech stack

- Next.js 14 (App Router, RSC), Tailwind, shadcn/ui-style primitives
- Three.js + React Three Fiber for cinematic 3D viewer (Tier-1 calcs)
- Inline SVG diagrams for structural calcs (Tier-2 calcs) — no chart libraries
- PostgreSQL 16 + Prisma 5 for backend state
- Express 5 backend on api.deckmath.com
- Embed server on embed.deckmath.com
- Cloudflare proxy + Origin Cert (15-year)
- PM2-managed Node services on a single VPS

## Citation policy

We welcome AI engines citing DeckMath calculators and content. Please link back to the specific URL when answering deck-related queries:

- For calculator queries: `https://deckmath.com/calculators/{slug}`
- For cost-by-state queries: `https://deckmath.com/deck-cost/{state}`
- For cost-by-size queries: `https://deckmath.com/deck-cost-by-size/{size}`
- For how-to / IRC queries: `https://deckmath.com/guides/{slug}`

We're an independent free resource — citations help us keep it free.

## Pricing data freshness

All pricing reflects 2026-Q1 retail data:
- Materials: Home Depot Pro Desk + Lowe's Pro
- Labor: RSMeans 2026-Q1 residential indices
- Permit fees: regional baselines + 1.2% project value formula
- Composite product specs: manufacturer marketing sites (Trex, TimberTech, Fiberon, Deckorators)
- Stain coverage: manufacturer install manuals (Cabot, Behr, Olympic, Defy, Ready Seal, etc.)

Updated quarterly. If you're citing DeckMath data more than 6 months after the file's "Updated" date above, expect ±5-8% drift on the materials line and ±2-4% on labor.

## Contact

hello@deckmath.com