Sources & methodology

Data sources

• Products: manufacturer product pages and technical documents. Each product lists its evidence links.
• Prices: seller pages, recorded with the date and tax status.
• Suppliers: each company’s own website.
• Rules: GOV.UK and the Planning Portal (UK); the National Construction Code (ABCB) for Australia.
• Keyword research: Semrush estimates, used only to decide which questions to answer. We do not use them as traffic forecasts.

Calculators

Every calculator prints its formula under “How this was calculated”. The board engine is unit-tested TypeScript:

• rows = ceil((across + gap) ÷ (board width + gap))
• linear metres = rows × run
• boards = ceil(linear metres × (1 + waste) ÷ board length)
• joists = ceil(run ÷ centres) + 1

Cost totals never count a missing price as zero; incomplete totals are labelled Partial.