Sources & Method
Every number on this site traces to a published standard. Here is the list, and how each page is checked.
The standards used
| Subject | Standard |
|---|---|
| Deck framing | IRC Section R507 — beams R507.5, joists R507.6, posts R507.4 |
| Guards & railings | IRC Section R312; loads from IRC Table R301.5 |
| Stairs | IRC Section R311.7 |
| Floor & roof framing | IRC Tables R502.3.1, R802.4, R802.5 |
| Wood design values | AWC National Design Specification (NDS) and its Supplement |
| Prescriptive deck guidance | AWC DCA 6, Prescriptive Residential Wood Deck Construction Guide |
| Steel shapes | AISC Steel Construction Manual shape tables |
| Pipe flow | Darcy-Weisbach, Hazen-Williams, Colebrook-White |
| Sheet metal & gutters | SMACNA Architectural Sheet Metal Manual |
How values are verified
A figure does not go on a page until it has been read from the code text or the standard itself. Secondary sources — other calculator sites, summaries, aggregators — are not treated as sources, because they have repeatedly been found wrong. Two of the best-ranking deck calculators on the web currently disagree with IRC Table R507.5(1) and with each other.
Two specific traps are worth naming, because they caught us:
- State documents are not the base code. A Pennsylvania stair guide reproduces IRC R311.7 accurately except for the riser and tread dimensions, which Pennsylvania amends — exactly the values a reader would come for.
- Code databases silently substitute jurisdictions. A query for residential guard requirements returned Illinois commercial code. Any source used here has to state which code, which edition and which jurisdiction it is showing.
The build check
Every figure quoted in a worked example is declared as an assertion and executed against the same data the calculator uses, each time the site is rebuilt. If a table is edited and the paragraph beneath it no longer matches, the build fails and the page does not publish. The visible table and the calculator's own lookup are generated from a single source, so the two cannot drift apart.
Editions and amendments
Values here are drawn from the 2018 and 2021 IRC unless a page says otherwise. Adoption is state and county specific, and local amendments are common — some jurisdictions rewrite stair dimensions outright. Confirm against the edition your building department enforces.