Irrigation System Design and Installation Reference

Why this reference exists

Irrigation install + service is the highest-margin lawn-care service line. Customer pays a substantial one-time fee for a typical residential install, plus a much smaller recurring annual service + winterization revenue. Done wrong (poor coverage, weak pressure, frozen pipes), the system frustrates customer + drives 1-star reviews. This is the working design + install framework.

System fundamentals

Water source:

• Municipal tap from house supply (most common residential)
• Well (rural; requires pump sizing match)
• Pond + lake (some rural; permits required, filter)

Backflow prevention:

• RPZ or DCVA at supply (REQUIRED per most jurisdictions for irrigation)
• Protects potable water from contamination
• Annual testing required (see Backflow Preventer Test reference)

Controller:

• Timer + zone-by-zone scheduling
• 6-12 zones residential typical
• Smart controllers (Rachio, Hunter Hydrawise, Rain Bird ESP-Me): weather-responsive + app-controlled
• Standard controller priced well below a smart-upgrade unit

Zone valves:

• Solenoid-controlled valves; one per zone
• Buried in valve boxes
• 1" or 3/4" typical
• Hunter PGV, Rain Bird DV, Toro 252 common

Mainline + laterals:

• Mainline: from supply to zones (always pressurized)
• Laterals: from zone valves to sprinkler heads (pressurized only during zone run)
• PVC SCH 40 or poly tubing depending on climate

Sprinkler heads:

• Spray heads (fixed pattern): 4-15 ft radius, low precipitation
• Rotor heads (Hunter PGP, Rain Bird 5000): 20-50 ft radius
• Drip emitters: for shrubs + beds + small areas

Sizing flow + pressure

Step 1: Water meter test

Bucket-fill test:

1. Open one outdoor hose bib full open
2. Time how long to fill a 5-gallon bucket
3. 5 gal ÷ time = gallons per minute (GPM)
4. Most residential: 8-15 GPM available

Step 2: Pressure test

Pressure gauge at hose bib:

• Static: 50-80 psi typical
• Working (with hose running): may drop 10-20 psi

Step 3: Zone sizing

Sprinkler heads listed with their GPM at specific psi:

• 8 ft radius spray head: ~1 GPM
• 12 ft radius spray head: ~2 GPM
• 30 ft rotor: 2.5-4 GPM
• 40 ft rotor: 4-7 GPM

Zone GPM ≤ supply GPM (with safety margin).

Example: 10 GPM supply, want 12 ft spray heads at 2 GPM each → 5 heads per zone maximum.

Layout design

Coverage rule: head-to-head spacing.

Each head should reach the next head with its full radius. Coverage from one head overlaps the next, ensuring even watering.

Example: 30 ft rotors → space 30 ft apart in a triangular pattern. Square spacing leaves dry corners.

Common mistakes:

• Underdistance spacing (waste of water)
• Overdistance spacing (dry spots)
• Mixed precipitation rates per zone (some areas overwater, others dry)
• Wrong sprinkler type per area (rotors in narrow strips waste; sprays at long distances inadequate)

Zoning principles:

• Same plant type per zone (turf, beds, drip emitters)
• Same sun exposure per zone (south-facing vs north-facing)
• Same precipitation rate per zone
• Same root depth per zone
• Practical zone size: 5-15 heads typical, runtime 10-45 minutes

Installation procedure

Step 1: Permit + utility locate

• Call 811 (free; 48-72 hour notice)
• Locate gas, water, electric, sewer
• Permit pulled (typically a modest fee)
• Customer signs scope

Step 2: Trench + supply

• Trench depth: 6-12" (below frost line in winter regions; some 18-24")
• 1" PVC SCH 40 mainline OR poly tubing
• Tap supply at house main OR dedicated meter

Step 3: Install backflow + manifold

• RPZ or DCVA at supply (typically 12" above grade)
• Manifold with zone valves in box near home
• Wiring run from manifold to controller

Step 4: Run laterals + install heads

• Trenches per zone layout
• Risers + heads at planned positions
• Adjust heads to grade
• Use barbed fittings for poly tubing

Step 5: Drip + low-flow

• Beds, shrubs, hedges
• Drip line OR emitters at each plant
• Lower pressure (10-30 psi) via pressure regulator
• Manifold filter recommended

Step 6: Wire controller

• 24V DC wiring from controller to valves
• Multi-conductor wire (1 common + 1 per zone)
• Bonded to ground per NEC
• Controller wired to dedicated 120V outlet

Step 7: Backfill + restore

• Replace soil + seed lawn
• Mulch over disturbed beds
• Photograph valve box locations + zone layout

Step 8: Commission

• Pressure test mainline
• Energize each zone individually
• Test coverage of each zone
• Adjust heads as needed
• Program controller per customer preference
• Walk customer through setup

Winterization

Critical in cold climates:

1. Shut water supply
2. Drain mainline at low point OR blow out with compressed air
3. Open zone valves to drain laterals
4. Drain backflow preventer
5. Disconnect controller from power OR set "off"
6. Document for customer

Spring activation: reverse procedure + leak-check + adjust heads.

Recurring revenue: a modest per-visit fee, 2x/year per customer. 200 customers adds up to meaningful annual recurring revenue.

Smart controller features

Smart controllers (Rachio, Hunter, Rain Bird):

• Weather forecast integration (skip rain days)
• Soil moisture sensor optional
• ET-based scheduling (evapotranspiration)
• App control + monitoring
• Watering log + history
• Saves 20-40% water vs traditional timer

Customer benefit: lower water bill, no manual programming.

Code + permitting

• IPC + IAPMO Uniform Plumbing Code (irrigation provisions)
• ASSE 5012 / 5013 (backflow testing)
• Local water authority (some require permits, others not)
• Some jurisdictions require licensed irrigation contractor (separate from plumbing)

Common pitfalls

• Wrong head spacing: dry spots OR wasted water
• Mixed precipitation per zone: same zone runtime overwaters some + underwaters others
• Skipping backflow: code violation
• Bad zoning (large + small heads same zone): pressure imbalance
• Insufficient mainline size: pressure drop at far zones
• No winterization: pipes freeze + burst
• Forgetting filter on drip: emitters clog
• No drainage check at low points: pipes don't drain
• Customer not trained on controller: runs wrong schedule

Customer talking points

For install bid:

1. "Standard install: $X. Includes [zones, heads, controller, backflow, install]."
2. "Smart controller saves 20-40% water + handles weather automatically."
3. "Annual winterization + spring activation: $Y each, important to prevent freeze damage."
4. "10-year warranty on parts + labor on initial install."

For repair customer:

1. "Issue: [diagnosis]. Repair $X."
2. "While we're here: I noticed [other issue]. Want to address now or schedule?"
3. "Recommend annual service contract: $Z/year covers winterization + spring + minor repairs."

References

• IA (Irrigation Association) certifications + standards
• ASIC (American Society of Irrigation Consultants)
• EPA WaterSense Specification for Irrigation Controllers
• ASSE 5013 (backflow testing)
• Manufacturer manuals (Hunter, Rain Bird, Toro, Rachio)
• Manuall internal: How to Test a Backflow Preventer, Annual Whole-Home Plumbing Inspection