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Methodology

Calculator pages show the formula, the code section it comes from, and a worked example produced by the same function the page uses. The article, the screen, and the tests share that result.

Each cited clause lives in one registry. The code-check panel, the code table on a tool page, and the list below all read that registry, so a section number is not retyped by hand.

Sources in use

2021 International Residential Code

  • IRC R311.7.5.1 (2024: R318.7.5.1)
  • IRC R311.7.5.2
  • IRC R311.7.5.3 (2024: R318.7.5.3)
  • IRC R311.7.2
  • IRC R311.7.1
  • IRC R311.7.3
  • IRC R311.7.8 (2024: R320)
  • IRC R311.7.8.1 (2024: R320)
  • IRC R311.7.6, R311.7.7 (2024: R318.7.6)
  • IRC R312.1.1
  • IRC R312.1.2
  • IRC R312.1.3 (2024: R321)
  • IRC R802.7.1
  • IRC R802.6
  • IRC R802.7.1.1
  • IRC R905.2.2

The 2024 section numbers in parentheses are listed for reference and have not been checked against the published code.

American Wood Council DCA 6

  • AWC DCA 6 Figure 28
  • AWC DCA 6 Figure 29
  • AWC DCA 6 Figure 30
  • AWC DCA 6

Journal of Light Construction

  • JLC

Manufacturer literature

  • Trex
  • Trex

Rule of thumb

  • Rule of thumb
  • Rule of thumb

States and cities adopt different editions and often amend them. A passing check means the model-code limit on the page, not a permit.