The $150K Opportunity Hiding in Your Backyard

Washington just changed the game for homeowners

In 2023, Washington passed House Bill 1337 — one of the most aggressive ADU (Accessory Dwelling Unit) laws in the country. As of 2024, every city in Washington must allow at least two ADUs on any residential lot.

That means if you own a house in Washington, you almost certainly have the right to build a detached ADU (DADU) in your backyard, convert your garage into a living unit, or add an attached apartment to your home.

And the value? A well-built 400–600 sqft ADU adds $150K–$300K to your property value and can generate $1,500–$2,500/month in rental income.

What HB 1337 actually says

The key provisions:

• Two ADUs allowed on any lot zoned for residential use
• No owner-occupancy requirement for most cities (you don't have to live on the property)
• Reduced parking requirements — no additional parking needed for ADUs within a half-mile of transit
• Streamlined permitting — cities can't impose unreasonable barriers
• Size limits: Up to 1,000 sqft or proportional to the primary dwelling

The math on ADU construction

Let's break down a typical 400 sqft detached ADU (DADU) in the Seattle metro area:

• Site prep and foundation: $15K–$25K
• Framing and structure: $30K–$45K
• Electrical, plumbing, HVAC: $25K–$35K
• Interior finishes: $20K–$30K
• Permits and design: $10K–$15K
• Total: $120K–$170K

• Property value increase: $200K–$300K (based on comparable sales with ADUs)
• Rental income potential: $1,800–$2,500/month ($21K–$30K/year)
• Net value creation: $80K–$180K (immediate equity)

Three ADU strategies with FLYP

Strategy 1: Build and sell

Add an ADU before listing your home. The ADU adds $200K+ to your sale price, and FLYP funds the construction. You pay nothing until closing.

Strategy 2: Build and rent

Build an ADU for rental income. Use a HELOC to fund construction through FLYP's contractor network. The rental income covers the HELOC payment from month one.

Strategy 3: Build and house family

Build an ADU for aging parents, adult children, or as a home office. The unit adds property value whether or not you rent it.

What makes a good ADU lot?

Not every lot is equally suited for an ADU. Here's what we look at:

• Lot size 5,000+ sqft
• Rear or side yard access for construction
• Existing utility connections nearby
• Zoning allows detached structures
• Flat or gently sloped terrain

• Lots under 5,000 sqft (attached ADU or garage conversion)
• Sloped lots (may need retaining walls)
• Lots with existing outbuildings (conversion opportunity)

The garage conversion shortcut

Don't have room for a detached unit? You might have a garage that's worth more as living space.

A garage conversion to a permitted ADU typically costs $60K–$100K and adds $100K–$150K in property value. It's faster than new construction (8–12 weeks vs. 16–24 weeks) and avoids many of the site prep costs.

Requirements:

• Existing garage in reasonable structural condition
• Ability to add a bathroom and kitchen/kitchenette
• Adequate electrical panel capacity (or upgrade)
• Proper egress windows and ventilation

Why FLYP for ADU construction?

Building an ADU is the most complex renovation project most homeowners will ever undertake. It involves architecture, engineering, permits, utility connections, inspections, and 6+ months of construction management.

FLYP handles all of it:

• Design and permitting — we work with architects who specialize in ADUs
• Contractor management — our builders have completed hundreds of ADU projects
• Budget control — fixed-price contracts, no surprise change orders
• Timeline management — realistic schedules with accountability

Check your lot

Enter your address on our site and we'll run a parcel analysis showing your lot size, building footprint, available space, zoning, and ADU feasibility. It takes 60 seconds and it's free.

You might be surprised what's hiding in your backyard.

Ready to see what your home is really worth?

Get a free, no-obligation renovation plan from FLYP. Zero out-of-pocket costs.