Engineering disclaimer
Please read this before you rely on any structural number from this site.
What the structural checks assume
- A single-level, rectangular, wood-framed residential deck, built to the prescriptive deck provisions of the International Residential Code, in the edition you select (2021 by default, or 2018).
- A 40 psf live load and a 10 psf dead load. Ground snow loads up to 70 psf use the 2021 snow tables; the 2018 edition covers 40 psf only. No hot tubs, roofs, pergolas, privacy walls, planters or other heavy or concentrated loads.
- No. 2 grade, preservative-treated or naturally durable lumber, adjusted for wet service, from the species group you select.
- Soil with at least the presumptive bearing value you select, footings on undisturbed soil below the frost line, and a ledger attached to a sound band joist (never to masonry veneer, overhangs, bay windows or open-web trusses).
When you need a designer
Decks outside those assumptions need an engineered or professionally designed solution. That includes decks with heavy snow, hot tubs or roofs, decks higher than the post tables allow, steep or unstable sites, multi-level or irregular decks, and coastal or seismic areas with special requirements.
Local codes win
Jurisdictions adopt different code editions and amend them. Your building department’s requirements and your product manufacturer’s installation instructions take precedence over anything on this site. Get a permit where one is required, and have the deck inspected.
Estimates are estimates
Material quantities depend on your actual framing, cuts and material quality. Check counts against your own measurements before ordering, and keep receipts for returns. See our terms of use for the full legal terms.