MEP Plans in Humboldt County, CA

Humboldt County project facts we design around

County seat	Eureka
Population	132,380 (Census 2024 estimate)
Incorporated cities	7
Unincorporated residents	About 70,006 (53% of the county)
Permits in unincorporated areas	Humboldt County Planning and Building Department – Building Division
Title 24 climate zones	CZ 1 (about 91% of residents), CZ 2 (about 9% of residents). Confirmed by ZIP for every project
ADU approval timeline	Approve or deny within 60 days of a complete application (state law)

HVAC design across Humboldt County

Climate Zone 1: coastal, marine-influenced climate (about 91% of residents)

Ocean air keeps summers mild and winters cool rather than cold, so heating and cooling loads are small. The common mistake here is oversizing: a rule-of-thumb unit short-cycles, controls humidity poorly, and wastes panel capacity. A room-by-room Manual J usually supports a compact ducted or ductless heat pump, and in many small units a single well-placed mini-split head does the job.

• Right-size the heat pump from a real Manual J instead of a tonnage guess
• Bath and kitchen exhaust plus whole-unit ventilation sized to ASHRAE 62.2 — tight coastal units trap moisture
• Corrosion-resistant outdoor equipment placement near the ocean

Climate Zone 2: North Coast inland climate — warm dry summers, cool winters (about 9% of residents)

Summers are warm and dry while winters are cool and wet, so the heat pump has to cover both seasons well. Many projects here are rebuilds or additions on older lots, so confirming the existing service, panel and sewer before design avoids redesign later.

• Heat pump sized for both heating and cooling seasons
• Existing service and panel capacity confirmed before layout
• Ventilation and moisture control for wet winters

Unincorporated Humboldt County

Unincorporated communities are permitted by the county, not by a city. County plan check reviews MEP drawings against the same California Mechanical, Electrical and Plumbing Codes and the Title 24 Energy Code as any city, but the submittal checklist, forms and fees are the county's own, so we prepare the set to match. In rural areas, parcels outside a sewer district often rely on a private septic system; adding an ADU can require the county's environmental health division to confirm the system has capacity, and the plumbing plan then shows the connection to the septic tank instead of a sewer lateral.

What's in a Humboldt County MEP set

• Mechanical: HVAC layout, Manual J load calculation, equipment schedule, exhaust and whole-unit ventilation
• Electrical: power and lighting plan, panel schedule, NEC 220 load calculation, single-line diagram
• Plumbing: supply and DWV layout, fixture units, water heater, gas (if any), sewer or septic connection
• Title 24 (add-on): energy compliance for your address's climate zone, coordinated with the MEP design so the two documents agree

Pricing is flat statewide: ADU plans from $995, full ADU MEP package from $2,295, Title 24 add-on $240. Standard turnaround is 5 business days with two revisions and corrections included.

Humboldt County cities and communities

Place	Climate zone	Electric utility
Arcata	CZ 1	Pacific Gas and Electric (PG&E)
Blue Lake	CZ 1	Pacific Gas and Electric (PG&E)
Eureka	CZ 1	Pacific Gas and Electric (PG&E)
Ferndale	CZ 1	Pacific Gas and Electric (PG&E)
Fortuna	CZ 1	Pacific Gas and Electric (PG&E)
McKinleyville (unincorporated)	CZ 1	Pacific Gas and Electric (PG&E)
Rio Dell	CZ 1	Pacific Gas and Electric (PG&E)

Shown for most addresses in each city. We also serve Humboldt County's other 1 city and every unincorporated community.

Humboldt County ADU MEP questions

Who issues building permits for an ADU in unincorporated Humboldt County?

In unincorporated areas, home to about 70,006 residents (53% of the county), ADU and residential permits go through Humboldt County Planning and Building Department – Building Division. Inside the county's 7 incorporated cities, that city's own building department reviews the plans instead. We prepare the MEP set for whichever office has jurisdiction over your address.

What Title 24 climate zones are in Humboldt County?

Humboldt County spans 2 Title 24 climate zones: CZ 1 (about 91% of residents), CZ 2 (about 9% of residents). Zones follow ZIP-code boundaries, so we confirm the zone from your project address before sizing the HVAC or running the Title 24 report.

Who provides electric service in Humboldt County?

It depends on the address. In the Humboldt County places listed on this page, most addresses are served by Pacific Gas and Electric (PG&E). We confirm the serving utility for every project, because service upgrades and new meters are requested from the utility, separately from the building permit.

How much do ADU MEP plans cost in Humboldt County?

Our pricing is flat across California: single-discipline ADU plans start at $995, a full MEP package for an ADU up to 600 SF is $2,295, and a Title 24 report can be added for $240. Residential (single-family) full MEP packages start at $3,495. Standard turnaround is 5 business days, and corrections are included.

How long does ADU approval take in Humboldt County?

California law requires local agencies, counties included, to approve or deny a complete ADU permit application within 60 days. Incomplete or inconsistent drawings are the most common reason the clock restarts, which is why MEP plans that match the architectural set, and a Title 24 report that matches the MEP design, matter.