How much do ADU permits cost? It depends first on jurisdiction: the City of Bellingham and unincorporated Whatcom County use different codes and fee schedules. On a Bellingham lot, the fixed City charges — land-use fee, park impact fee, and water, sewer and stormwater system development charges — total about $12,677 before the valuation-based building permit, plan review and transportation impact fee. On a rural lot in unincorporated Whatcom County, a septic system alone typically runs $15,000–$40,000. The building permit itself is just one piece; utility hookups and site-specific studies often cost more than the permit fees.
Below is the fee-by-fee breakdown so you can budget accurately before breaking ground. If you want us to handle the entire permit process, our Full Permit Package covers all submissions, coordination, and approvals — and your investment is applied as a build deposit when you sign the Letter of Intent.
Impact fees do apply in the City of Bellingham. Earlier versions of this page said ADUs pay no impact fees. That was wrong. Per the City Building Permit Fee Worksheet BSD#064 (dated 2026-08-27), each ADU pays a park impact fee of $1,470.93 (exemptions possible under BMC 19.04), and the transportation impact fee receives a 50% ADU credit — reduced, not waived. No school impact fee applies.
City of Bellingham ADU Permit Fees & Government Charges
| Fee Type | Amount | Notes |
|---|---|---|
| Land use — ADU Type I | $294 | Effective 2026-10-01 (was $214). |
| Land use — ADU Type II | $728 | Effective 2026-10-01 (was $531). |
| Building permit | Valuation-based | The fee is calculated from project valuation. City valuation rates: $177.63/sf new living space · $105.84/sf garage-to-living conversion · $146.13/sf basement conversion. |
| Plan review | 65% of permit fee | Charged in addition to the building permit fee. |
| Park impact fee | $1,470.93 per ADU | Exemptions possible under BMC 19.04. |
| Transportation impact fee | 50% ADU credit | Reduced, not waived. An update to this fee is pending at the City. |
| School impact fee | N/A | Listed as not applicable on the City fee worksheet. |
| Water system development charge | $2,911 | 5/8″ × 3/4″ meter. |
| Sewer system development charge | $7,637 | Single-family residential (SFR) rate. |
| Stormwater system development charge | $364 | CPI-adjusted. |
| Fixed-dollar charges (Type I path) | $12,676.93 | Land use Type I + park impact fee + water, sewer and stormwater SDCs. Add the building permit, 65% plan review and the reduced transportation impact fee. |
Source: City of Bellingham Building Permit Fee Worksheet BSD#064, dated 2026-08-27; land-use fees reflect the increase effective 2026-10-01. Last verified 2026-10-05.
Unincorporated Whatcom County charges ADU fees under its own schedule: the 2025–2026 Unified Fee Schedule (Ordinance 2024-063), in force through 2026-12-31. A rural ADU (outside a UGA) goes through an Administrative Approval Use (ADM), a Type II process under WCC 22.05.028, before the building permit. In a UGA (excluding LWWO, GC, AG, R and RF districts), the ADU is a permitted use and goes straight to a building permit. We confirm your county fees in the feasibility study.
Utility Connection Costs
| Utility | City of Bellingham (Sewer) | Rural County (Septic/Well) |
|---|---|---|
| Sewer/Septic | $3,000–$8,000 (sewer hookup) | $15,000–$40,000 (septic system) |
| Water | Water SDC listed in fees above; service line priced per site | Well work priced per site; a new permit-exempt well triggers a WRIA 1 fee |
| Electrical service | $2,500–$4,000 (200A upgrade, if needed) | $2,500–$4,000 (200A upgrade, if needed) |
| Trenching | $15–$45 per linear ft | $15–$45 per linear ft |
| Sewer/septic + electrical | $3,000–$12,000 + trenching | $15,000–$44,000 + trenching & well |
Rural utility costs are the single biggest differentiator between city and county ADU projects. City SDCs are counted in the fee table above, not here. Cost ranges as of 2026-10-05.
No gas line to budget for: the 2021 Washington State Energy Code (effective 2024-03-15) requires heat-pump space and water heating in new residential construction, and the Washington Supreme Court struck down Initiative 2066 in full on 2026-09-17, reinstating that requirement. All-electric is the code baseline.
Professional Service Costs
| Service | Typical Cost | When Needed |
|---|---|---|
| Architectural design | Quoted per project | Always; scope and level of customization drive cost |
| Site survey | Quoted per project | When property boundaries are unclear or required by jurisdiction |
| Structural engineering | Quoted per project | Required for most new construction and major remodels |
| Geotechnical report | $8,000–$20,000 | Required for sites with slope, fill, or questionable soil |
| Critical areas consultant | Quoted per project | Required when critical areas are present on or near the property |
| Energy code consultant | Quoted per project | Often included in architectural services |
| Permit expediting / management | Varies | Our Full Permit Package investment is applied as a build deposit |
| Total professional services | Varies | Highly variable by project; we scope it in your feasibility study |
Total Pre-Construction Budget
How much does it cost to permit an ADU in total? Here is what is fixed and what depends on your project, before construction begins:
City of Bellingham (City Sewer)
Before construction begins. Fees per City Fee Worksheet BSD#064 (2026-08-27).
Rural Unincorporated County (Septic/Well)
Before construction begins. Septic alone is $15,000–$40,000.
What About Construction Costs?
The fees on this page are real line items, but they are not an extra bill on top of our pricing — they sit inside the all-in figure we quote. A full ADU runs $450–$650/sq ft as of 2026-10-05, including design, permitting, construction, and standard utility connections. Finish level is what moves you within that band. For the complete picture, see our full ADU cost breakdown or our pricing packages.
Not sure what your specific property will require? Book a free 30-minute consultation -- we'll talk through your jurisdiction, utility access, and the cost factors to plan for before you commit.
Ways to Reduce Permit Costs
Choose a simple, repeatable design — fewer custom details mean less design and engineering time. See our ADU design services.
Skip the parking pad in the City of Bellingham — no off-street parking is required for an ADU (BMC 20.10.036, as amended by Ord. 2025-12-035, effective 2025-12-23; citywide parking reform made permanent August 2026). In unincorporated Whatcom County, ADU parking is set by WCC 20.80.580(63).
Convert an existing structure — in the City of Bellingham, the valuation rate for a garage-to-living conversion is $105.84/sf and for a basement conversion $146.13/sf, versus $177.63/sf for new living space (Fee Worksheet BSD#064, 2026-08-27), so the valuation-based permit fee is lower. BMC 20.10.036(B)(15) also lets an existing detached garage convert even where it does not meet current setback or lot-coverage standards, with no parking replacement. Current building, egress, fire-separation and energy code still apply.
Submit a complete application the first time — resubmission fees and delays add up. See our Bellingham permit guide.
Bundle permit work with construction — our Full Permit Package investment is applied as a build deposit when you sign the LOI.
Check your eligibility for the Washington HEAR rebate (up to $1,750). The federal 25C energy-efficiency tax credit ended 2025-12-31 and is no longer available (as of 2026-10-05).
Last verified: 2026-10-05. City of Bellingham fees per Building Permit Fee Worksheet BSD#064 (dated 2026-08-27); unincorporated Whatcom County fees per the 2025–2026 Unified Fee Schedule (Ord. 2024-063). Cost ranges are estimates; actual costs vary by project scope, jurisdiction, and site conditions.
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