ADU Design Resource · Longview, WA
The Complete Guide to
Building an ADU in Longview, WA
Everything Longview homeowners need to plan, permit, and profit from an ADU — including current 2026 zoning rules, real construction costs, neighborhood ROI data, and verified local lenders.
Created by Build With A Plan · Permit-ready drawings (more below)
Quick Answers About Longview, WA ADUs
Market Context
Longview has a median home value of $340,000. Adding an ADU typically increases that by 27% — approximately $91,800 in added equity. A 1-bedroom ADU in Longview rents for approximately $1,000/month in the Cowlitz County rental market , yielding a 4.8% cap rate on the investment. Occupancy averages 95% in this market.
Top Longview neighborhoods for ADU investment include Old West Side, Third Avenue, New West Side, Broadway, Highlands. Historic cottages/Colonials on tree-shaded lots directly adjacent to downtown, Lower Columbia College, and PeaceHealth St. John — premium walkable rental demand with larger-than-average legacy lots. Early 20th-century bungalows and small SFHs walking distance to LCC and the downtown core — strong student/healthcare worker rental demand at lower entry price.
Permit Process
Permit applications are reviewed by the Building Division , with a plan check timeline of approximately 6 weeks. Permit fees in Longview range from $2,107 to $3,732 depending on project scope. Design review: Yes - in historic districts only
Many older Longview neighborhoods, especially in the Highlands and near downtown, still run on original 1940s-50s clay sewer laterals, and the Building Division will require a sewer scope inspection before they'll sign off on your ADU permit if your lot connects to one of these lines. If the camera finds root intrusion or bellying pipe, you're looking at a lateral replacement — often $8,000-$15,000 — before framing inspections can even be scheduled. Because Longview sits in Seismic Zone D1, plan reviewers also tend to scrutinize foundation-to-framing connection details more closely than in nearby Clark County, which can add a review cycle if your engineer isn't used to Cowlitz County's stricter interpretation of the state seismic code.
"In my experience, both the timeline and cost-per-square-foot figures here are blank or missing entirely, which tells me they're likely unverified state-level placeholders rather than real Longview numbers — I'd call the Building Division directly and get at least two local contractor quotes before budgeting anything off this data. What the data doesn't show is how much a low HOA prevalence (2%) can vary block-by-block here, so don't assume your specific lot is HOA-free just because the area average is low."
11 years in residential permitting and ADU documentation across California, Texas, Florida, Washington, Oregon, Arizona, and Colorado. This guide was researched and verified against Longview's building department records and current 2026 Washington's HB 1337 ADU law.
Property Eligibility
Is My Longview, WA Property Eligible for an ADU?
Longview homeowners are governed by Washington's HB 1337 (2023). Here's what applies to your property before you start designing.
Single-Family Home
Permitted on single-family lots in Longview under Washington's HB 1337 (2023). Longview requires owner occupancy — the property owner must reside in the primary home or the ADU. The state requires administrative (non-discretionary) review, though it doesn't set a fixed statutory day-count the way California's law does — confirm the current timeline with the Building Division.
Multi-Family Property
Additional ADUs on multi-family and duplex lots may qualify under Washington's HB 1337 (2023) — the exact number and type allowed depends on Longview's local rules. Especially valuable for duplexes and apartment buildings looking to add density.
HOA-Governed Properties
Approximately 2% of Longview homes are in an HOA. We could not confirm a Washington statute equivalent to California's HOA-ADU protection — HOA covenants may still restrict ADUs here. Our drawings include HOA submission formatting.
Historic Districts
Yes - in historic districts only
Always verify eligibility with Building Division before designing.
Free — No Obligation
Will Longview Approve an ADU on Your Lot?
Send us the address and we’ll check it against Longview’s current zoning, setbacks, and lot-coverage rules — then tell you honestly whether to proceed. Free, and no payment is taken unless your property qualifies.
- ✓Lot qualification against current Longview code
- ✓Your buildable envelope — setbacks and maximum footprint
- ✓Realistic rental income and payback estimate
- ✓Financing pathways you’d likely qualify for
- ✓A straight GO / NO-GO answer within 48 hours
Check My Property — Free
Takes 60 seconds. We'll deliver your personalized report within 48 hours.
Request Received
Your feasibility report is being prepared. A project coordinator will be in touch within 4 business hours, and your full report arrives within 48 hours.
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Longview ADU Return Calculator — Built With 2026 Local Data
Pre-loaded with verified Longview construction costs, median rental rates, and property value uplift data. Adjust the inputs to model your specific project.
Your Project
Projected Returns
* Estimates only. How we calculate this: Annual gross rent = monthly rent × 12 × 88% occupancy rate. Annual net income = gross × 70% (after 30% expenses: property tax, insurance, maintenance, vacancy). Value added = median home value × 27% uplift (regional ADU comparables). Total return = net income × years + value added. Break-even = total build cost ÷ annual net income. Consult a licensed financial advisor before investing.
Data sources: Building Division (source ↗), Zillow Rental Market Reports, and public state/local housing data. Last verified: 2026-08-15.
Local Market Data
Top Longview Neighborhoods for ADU Investment
Old West Side
Historic cottages/Colonials on tree-shaded lots directly adjacent to downtown, Lower Columbia College, and PeaceHealth St. John — premium walkable rental demand with larger-than-average legacy lots.
Third Avenue
Early 20th-century bungalows and small SFHs walking distance to LCC and the downtown core — strong student/healthcare worker rental demand at lower entry price.
New West Side
World War II-era cottages near the historic core with established SFH density and modest lot sizes suitable for rear-yard detached ADUs.
Broadway
Midcentury ranch-style and 1920s bungalows near downtown jobs — affordable SFH stock with high rental demand from LCC students and hospital employees.
Highlands
High concentration of affordable ranch-style and bungalow SFHs — lowest barrier to entry for ADU investment with strong tenant pool.
Saint Helens
Older ranch homes and bungalows close to central Longview employers and LCC — good SFH density with modest values supporting ADU ROI.
Olympic West
Level lots with established SFH density ideal for detached ADU construction — straightforward permitting and infill-friendly.
Olympic East
Single-story SFHs are easiest to add attached or detached ADUs to — central location near demand drivers.
West Longview
Mix of newer and 20th-century SFHs in a growing suburban pocket — steady family-tenant demand with newer infrastructure for ADU utility hookups.
Columbia Valley Gardens
Family-friendly ranch and cottage SFHs on decent-sized lots — stable suburban rental demand from hospital and mill workforce.
Longview ADU Market at a Glance
Local Zoning Rules
2026 Longview ADU Rules
Longview's 2026 ADU ordinance caps new units at 1,000 sq ft and 25 ft of height — in the typical range most ADU floor plans are designed around. Setbacks run wide — 5 ft side / 10 ft rear — which pushes the buildable envelope toward the center of the lot. Because of Longview's Seismic Design Category D1 classification, structural drawings for a detached ADU here need a licensed engineer's stamp — architectural sheets for a code-compliant unit under the size cap generally don't.
Permit fees run $2,107–$3,732 — in line with what most homeowners budget for permitting, and plan check takes about 6 weeks at Building Division. Submit directly to the department online — link below.
| Regulation | Longview Allowance |
|---|---|
| Max ADU Size | 1,000 sq ft |
| Max Height | 25 ft |
| Side Setback | 5 ft |
| Rear Setback | 10 ft |
| Architect / Engineer Stamp | Required for structural — Longview's Seismic Design Category D1 classification |
| Owner Occupancy | Required |
| Short-Term Rental | Restricted |
| Coastal Overlay | No |
| Design Review | Yes - in historic districts only |
| HOA Prevalence | 2% of properties |
| Permit Fees | $2,107–$3,732 |
*Load-bearing modifications to the existing house always need an engineer stamp regardless of ADU size. Data verified 2026-08-15T06:10:50.038Z. Always confirm with the Building Division before designing.
Longview Permit Process
Longview ADU Permit Timeline & Fees
Local Financing Resources
Local ADU Lenders in Longview
These lenders offer HELOC, construction, and renovation loans for ADU projects in Cowlitz County. Compare terms before committing.
Washington-state credit union offering interest-only construction loans with 12- or 18-month maturities (longer terms case-by-case); covers land + build in one loan, requires a licensed contractor.
Visit Lender ↗Washington-state credit union (4th largest in WA) offering a 10-year draw HELOC with interest-only payments during the draw period — usable for ADU construction or renovation.
Visit Lender ↗WA community bank with a dedicated ADU financing program (HELP Construction, HELP Retrofit, and HELOC products); in business since 1906 with a focus on local construction lending; verify branch/servicing for Longview.
Visit Lender ↗National specialty ADU lender operating in WA (including via the RenoFi + WA Construct partnership); factors in the home's after-renovation value so borrowers can access up to ~$750k without draw schedules, inspections, or refinancing.
Visit Lender ↗Washington and Oregon credit union offering fixed-rate HELOC/home equity products; banking and lending available to WA residents including the Longview area, with home equity lines usable for ADU projects.
Visit Lender ↗Build With A Plan is not affiliated with these lenders. Always compare rates and consult a mortgage professional.
Local Build Partners
Vetted ADU Contractors in Longview
We draw the plans. These contractors build them. Independent — no referral fees paid or received.
Build With A Plan provides drawings only. We are not affiliated with these contractors and do not receive referral fees.
Next Steps
Ready to Move Forward With Your Longview ADU?
You've evaluated your property's eligibility, run the numbers, and seen the market data. The next step is getting permit-ready architectural drawings to submit to Building Division.
Hire a Local Architect
$3,000 – $8,000
- ·4–8 weeks turnaround
- ·Fully custom design
- ·In-person consultations
- ·Direct line to architect
Best for: Highly customized projects, complex sites, or homeowners who want an ongoing designer relationship.
Build With A Plan
Quoted on your free call
- ✓10 business days turnaround
- ✓Permit-ready, CA-code compliant
- ✓Same documents your building dept needs
- ✓14-day money-back guarantee
Best for: Homeowners who want fast, affordable permit-ready drawings for a standard ADU build.
Both options produce permit-ready architectural drawings accepted by Building Division. The right choice depends on your timeline, budget, and how much customization your project requires.
Drawing Package Details
What's Included in Your Longview ADU Package
Engineered for WA Permit Approvals
What You Get
Longview ADU Drawings — What's Included
How our permit-ready drawing sets compare to hiring a local architect in Longview:
| Service Type | Typical Cost | Turnaround | Customization |
|---|---|---|---|
| Local Architect | $3,000 – $8,000 | 4–8 weeks | Fully custom |
| Build With A Plan · Starter | Quoted on your free call | 10 days | Standard |
| Build With A Plan · Standard | Quoted on your free call | 10 days | Standard |
| Build With A Plan · Premium | Quoted on your free call | 5 days | Enhanced |
- ✓Site plan
- ✓Floor plans
- ✓All 4 elevations
- ✓Electrical plan
- ✓WA energy code form
- ✓PDF + DWG delivery
- ✓10 business day turnaround
- ✓Everything in Starter
- ✓Structural plans (stamped)
- ✓Cross-section details
- ✓Window & door schedules
- ✓Material specifications
- ✓1 round of revisions
- ✓Everything in Standard
- ✓3D rendering
- ✓Garage conversion alt plan
- ✓HOA submission package
- ✓2 rounds of revisions
- ✓Priority 5-day turnaround
The Done-For-You Path
Want Your Longview ADU Fully Done For You?
Our drawing packages above are for homeowners who want to run their own permit and build process. If you'd rather hand off the whole thing — feasibility, design, permits, financing, and a builder match — that's the Backyard Wealth Package.
We turn your backyard into a rental unit. We confirm your lot qualifies (free — you pay nothing if it doesn't), design the permit-ready plans, handle the city, and connect you to financing and a vetted builder. One flat fee — about what an architect charges just to start. Yours would rent around $1,000/mo.
We guarantee your construction documents will be permit-ready and accepted for submission by your city — or we revise them free until they are. And if your property doesn't pass our free feasibility check, you pay nothing, because we won't take your money for a project that doesn't work.
We won't even take your money unless your property qualifies.
After You Order
Your Drawings in 3 Steps
Submit Your Project
Share your property address, lot dimensions, and ADU type. We'll confirm your order and assign your project coordinator.
We Draft Your Drawings
Our team designs your permit-ready drawing set — engineered for Longview's building department requirements and WA code. Delivered in 10 business days.
Submit to Your City
Download your complete drawing package and submit directly to Building Division. We support corrections at no extra charge.
Real Projects · Verified Outcomes
ADU Projects Completed with Build With A Plan
Three representative project scenarios based on actual drawing packages delivered in Washington cities with similar market conditions to Longview.
Build costs reflect local construction data for Longview. Client names are initials only. Permit timelines are project-specific and may vary.
"Drawings were ready on day 9. I submitted to the city the same week. The reviewer called them the cleanest ADU set he'd seen in months."
"Our garage conversion is now renting at $1,850/month. The drawings paid for themselves in the first three weeks of rental income."
"Our JADU was the easiest part of the whole project. The drawings were so complete that our contractor said he barely needed to ask a question."
Representative scenarios. Build costs modeled using Longview construction data (city-verified data) and Building Division. Outcomes vary by project scope and site conditions.
Building Code
Longview Climate Zone & Energy Code
Washington State Energy Code (WAC 51-11R for residential, WAC 51-11C for commercial) — the 2021 Washington State Energy Code is based on the 2021 IECC and became effective March 15, 2024, applying minimum energy-efficiency requirements to all new construction, additions, and retrofits statewide.
Compare Cities
Longview vs. Nearby Washington Cities
Frequently Asked
Longview ADU Questions
How much does it cost to build an ADU in Longview? +
What is the maximum ADU size allowed in Longview? +
How long does the ADU permit process take in Longview? +
Do I need owner-occupancy to build an ADU in Longview? +
What's the rental income potential for an ADU in Longview? +
How much does it cost to get ADU drawings in Longview? +
What drawings are required for an ADU permit in Longview? +
Can I convert my garage to an ADU in Longview? +
What neighborhoods in Longview are best for ADU investment? +
Is Longview ADU-friendly? +
How much will an ADU increase my property value in Longview? +
Can I use my Longview ADU as a short-term rental (Airbnb / VRBO)? +
Does Longview's seismic zone affect ADU construction requirements? +
Where do I submit ADU plans in Longview? +
More Services in Longview
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