Water-Based Systems Layout
This domain tests whether you can turn an occupancy description into an installable sprinkler layout that satisfies NFPA 13 and its companion standards, then prove the layout with a water supply analysis. Level I centers on light and ordinary hazard occupancies, standard spray sprinklers, pipe-schedule and simple hydraulic layouts, hanger basics, and the working-plan content a plan reviewer expects to see. ESFR and complex storage design sit above this level.
Codes, plans, and drawing content
The layout begins with the occupancy classification, because light, ordinary group 1 or 2, and extra hazard each set the density, remote area, and maximum sprinkler coverage. Working plans must show scale, north arrow, occupancy class, ceiling and roof construction, sprinkler type and temperature rating, pipe sizes and materials, hanger locations, riser and test connections, water supply data (static, residual, flow, date), and hydraulic reference points.
Spacing rules
- Standard spray, light hazard: 15 ft maximum between sprinklers, 225 sq ft maximum per sprinkler.
- Ordinary hazard: 15 ft spacing and 130 sq ft per sprinkler.
- Generally not less than 6 ft apart; the last sprinkler no more than half the spacing from a wall.
- Deflectors 1 in. to 12 in. below the ceiling for standard pendent and upright sprinklers.
- Larger coverage from hydraulic calculation applies only where the standard's specific allowances are met; do not default to it.
Water supply
A flow test gives static and residual pressure at a measured flow. Available flow at 20 psi residual is estimated from those two points, which is the reference pressure used to compare supply against demand.
Worked example
Static 70 psi, residual 50 psi at 900 gpm. Available flow at 20 psi = 900 × √((70 − 20)/(70 − 50)) = 900 × 1.58 ≈ 1,420 gpm. Skipping the 20 psi offset and using √(70/20) = 1.87 gives about 1,680 gpm, an unsafe overstatement of the supply.
Traps that cost marks
- Applying 225 sq ft coverage to an ordinary hazard occupancy.
- Measuring the wall distance from the next sprinkler instead of keeping it at half the spacing.
- Forgetting the hose allowance when comparing demand to available supply.
- Submitting a flow test without static, residual, flow, and date.
- Mixing units in Hazen-Williams work; black steel uses C = 120.