How to space fire hydrants around a building
US hydrant layout is driven by required fire flow rather than a single fixed radius. IFC Appendix C and NFPA 1 set an average spacing and a maximum distance from any point on the street frontage to the nearest hydrant, and both tighten as the fire flow goes up. This tool takes the building footprint, works out the perimeter to be covered, divides it by the spacing for the selected tier and compares the result with the minimum hydrant count for that tier.
The tiers prefill representative values: roughly 500 ft spacing with a 250 ft maximum distance for one- and two-family dwellings, about 450 ft and 225 ft for moderate commercial fire flow, about 350 ft and 210 ft in the 4,000 gpm range, and about 300 ft and 180 ft for very high fire flow. A dead-end street or single point of access reduces the allowed spacing, which the selector applies. Every value is editable because the adopted edition of IFC Table C102.1 and local amendments govern.
Required fire flow itself comes from IFC Appendix B, based on building area and construction type with reductions for automatic sprinklers, and can exceed what a single hydrant delivers. Treat the output as a layout starting point, then confirm flow test data, main sizing, apparatus access and hydrant placement with the fire protection engineer and the fire code official having jurisdiction.
Frequently asked questions
Each fire flow tier carries a minimum number of hydrants regardless of site size, so a small site with a high fire flow is governed by that minimum rather than by perimeter divided by spacing.
Perimeter hydrants alone will not cover it. The usual answers are additional on-site hydrants fed by a looped private main, or interior protection such as standpipes and sprinklers, coordinated with the fire department.