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Building Code Reference

Got a CALGreen 4.304.1 correction?

Water-efficient landscape MWELO

For builders in California, Greater Seattle, the Las Vegas area, the Denver area and Kansas City · CrossBeam Permits

What this code requires, how to fix it, and how cities and counties review it

What this code requires

CALGreen 4.304.1 requires new residential construction projects with 500 square feet or more of landscaped area to comply with the Model Water Efficient Landscape Ordinance (MWELO). To comply, you need a landscape plan that includes a water budget calculation, an irrigation system design, and a plant palette that stays within the Maximum Applied Water Allowance (MAWA) for the site. Under MWELO, new construction triggers it at 500 sq ft of landscape area and rehabilitated landscapes at 2,500 sq ft.

How to fix it

  1. Confirm whether your project triggers MWELO

    Measure all landscaped areas on the project site, including any existing landscaping that will be altered by the permit scope. MWELO applies to new construction with 500 sq ft or more of landscape area, and to rehabilitated landscapes of 2,500 sq ft or more. Hardscape doesn't count, but planted and turf areas do, and pools and spas count as water features. If you're right at the line, document your area takeoff on the plans so the checker can verify the calculation. Show the square footage breakdown by area type on the title sheet or landscape plan.

  2. Calculate the Maximum Applied Water Allowance (MAWA)

    For residential landscapes the MAWA formula is: MAWA = (ETo - Eppt) x (0.62) x [(0.55 x RLA) + (1.0 x SLA)], where ETo is the reference evapotranspiration for your city, Eppt is effective precipitation (used only where the local agency allows it), RLA is the regular landscape area in square feet, and SLA is the special landscape area (edible plants, recreational turf, etc.). Include this calculation in a landscape water use table on your plan sheets. Take the ETo for your city from the MWELO Appendix C table or CIMIS, and confirm it with the city before finalizing the number.

  3. Prepare the MWELO landscape documentation package

    Under the performance option, MWELO's Landscape Documentation Package has six elements: a project information sheet, a soil management report, landscape, grading and irrigation design plans, and the water efficient landscape worksheet. The core of it is: (1) a planting plan with a plant palette that lists each species, its water use factor (WUCOLS classification: VL, L, M, H), and the area it covers; (2) an irrigation plan showing zone layout, head types, flow rates, and precipitation rates; (3) a water budget table showing that the Estimated Total Water Use (ETWU) stays at or below the MAWA. Many designers use free MWELO water budget worksheets published by MWDOC or DWR to generate the table. Include all of them in your submittal.

  4. Add zone-level irrigation data to each irrigation zone

    Each irrigation zone on your plan must show: the zone type (drip, spray, or rotor), the precipitation rate in inches per hour, the scheduled run time, and the calculated applied water in gallons per year. If you're using a smart controller, note the manufacturer, model, and that it's SWAT-certified. Generic notes like 'drip irrigation per manufacturer specs' are not enough. The checker needs zone-level numbers to verify compliance with the water budget, so list them in a zone schedule table on the irrigation plan.

  5. Include soil and mulch specifications

    Add a planting note specifying a minimum 3-inch layer of mulch in all planting areas (rock mulch is acceptable in low-water zones). Include a soil preparation note if the soil will be amended. Compacted clay soils that haven't been tilled won't support water-efficient planting, and some checkers require evidence of soil health improvement. MWELO requires compost at a minimum of four cubic yards per 1,000 sq ft of pervious area, incorporated to a depth of six inches, so a note such as 'Compost at 4 cu yd per 1,000 sq ft incorporated to 6 inches, per soil test and MWELO' typically satisfies this requirement and keeps the correction from coming back.

  6. Submit the Landscape Documentation Package as a separate plan sheet

    Put all MWELO elements on a dedicated sheet labeled something like 'L-1: Landscape and Irrigation Plan — MWELO Compliance.' Keep the water budget table, planting legend, and irrigation schedule on the same sheet where possible. Some cities require a signed Certificate of Completion at final inspection confirming the landscape was installed per the approved plan. Ask the building department at permit issuance whether they require this form, and get the blank template early so it doesn't hold up your certificate of occupancy.

  7. Verify landscape inspection requirements before closing the permit

    Many jurisdictions require a landscape inspection before the certificate of occupancy is issued. Find out whether the city's planning or building department handles landscape inspections, since in some cities they're split between departments. At inspection, the inspector will check mulch depth, plant installation, and that the irrigation controller is programmed per the approved schedule. Have a copy of the approved L-1 sheet on site. If you changed any plants or moved irrigation zones during installation, get the plan updated and re-approved before scheduling the inspection.

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Why you got flagged

Plan-checkers flag CALGreen 4.304.1 most often because the landscape plan is submitted without the MWELO water budget calculation. The Maximum Applied Water Allowance is a formula based on site area, the evapotranspiration adjustment factor (ETAF), and the local reference evapotranspiration rate. When a designer leaves that calculation off the submittal, the checker has no way to confirm the irrigation design meets the cap, so the correction goes out.

A second common flag: the irrigation design shows a drip or spray system but doesn't call out flow rates, precipitation rates, or controller settings by zone. MWELO requires the irrigation design to demonstrate compliance with the water budget by zone, not just show pipe runs and head locations. If your plans read like a standard irrigation layout without zone-level water data, expect a 4.304.1 correction.

Plans sometimes include a landscape plan and an irrigation plan but skip the soil and mulch requirements. MWELO also requires a minimum 3-inch mulch layer in planting areas and a soil health measure. If those notes are missing from the landscape plan, 4.304.1 is often cited alongside the water budget correction.

A fourth pattern shows up on addition and ADU projects where the applicant believes the existing front yard landscaping doesn't count toward the 500 sq ft threshold. If the permit scope touches the existing landscape area (regrading, new irrigation, replanting), plan-checkers typically count that area, pushing the total over 500 sq ft and triggering MWELO even when the new construction footprint alone is small.

The official code

California Green Building Standards Code 2025, Section 4.304.1 — MWELO compliance

Read the source →

Common questions

Does CALGreen 4.304.1 apply to ADU projects?
Yes, if the project adds 500 sq ft or more of new landscape area, or rehabilitates 2,500 sq ft or more of existing landscape. Plan-checkers may count existing landscaping that's regraded, replanted, or re-irrigated as part of the project. A detached ADU with a small footprint can still trigger MWELO if the contractor is resodding the backyard or installing new irrigation as part of the scope. Check your project area takeoff before assuming you're under the threshold.
What is the MAWA formula for CALGreen landscape compliance?
For residential landscapes, MAWA = (ETo - Eppt) x (0.62) x [(0.55 x RLA) + (1.0 x SLA)]. ETo is the annual reference evapotranspiration for your city, and Eppt is effective precipitation where the local agency allows it. RLA is the regular landscape area in square feet. SLA is special landscape area (edible gardens, recreational turf, water features) that gets a higher water allocation. The 0.62 factor converts ETo from inches to gallons per square foot. Run the numbers in the MWDOC or DWR MWELO worksheet tool and paste the resulting table onto your plan sheet so the checker can verify it directly.
Can I use artificial turf to avoid the MWELO water budget?
Artificial turf doesn't require irrigation, so it shows zero applied water in the water budget calculation. That can help you stay under the MAWA. However, the landscape plan still needs to be submitted with the full MWELO documentation package if the total landscape area (including the turf area) exceeds 500 sq ft. The plan-checker still needs to see the planting plan, irrigation plan for any planted areas, and confirmation that artificial turf is the specified material.
Does MWELO apply to commercial projects or just residential?
CALGreen 4.304.1 is in the residential mandatory measures chapter, so it applies to residential projects. Commercial projects have their own MWELO requirements under a different part of CALGreen (the nonresidential chapter, Division 5.304). Many cities also adopt MWELO through their own local ordinance, which can apply stricter thresholds or lower square footage triggers than the state minimum. Check your city's adopted version to confirm the threshold and documentation requirements for your specific project type.
Who prepares the MWELO landscape documentation — the contractor or the designer?
The landscape plan and water budget documentation are typically prepared by a landscape designer, licensed landscape architect, or the project designer of record. The contractor isn't expected to run the MAWA calculations, but you should confirm that the designer has included all three MWELO components (planting plan, irrigation plan, water budget table) before you submit for plan check. Missing any one of the three is a common cause of a 4.304.1 correction on the first submission.
What happens at the landscape inspection for MWELO projects?
The inspector will verify that the installed landscape matches the approved plan: correct plant species, mulch depth of at least 3 inches, irrigation heads and zones installed per the approved layout, and the controller programmed per the approved schedule. Some cities require a post-installation Certification of Completion signed by the landscape designer. If you changed any plants or moved irrigation zones during installation, you may need to get the plan updated and re-approved before the inspection. Bring the approved L-1 sheet on site.

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