Inside a Real DADU Deal: How to Analyze Numbers Before You Break Ground
Most investors love the idea of building a DADU - a detached home in the backyard that prints rent, creates equity, and adds long-term value. But here’s the harsh truth: most DADU projects fail on paper before they ever fail in construction.
Why? Because the investor didn’t analyze the deal like a builder - they analyzed it like a dreamer.
Let’s walk through a real, data-driven look at how to break down a DADU deal - step by step - so you know exactly what you’re getting into before you spend a dime.
You can’t build profitably on bad dirt. Let’s say you find a home in North Seattle listed for $900,000. It’s on a 5,000 sq. ft. lot, zoned SF-5000, and has alley access (a huge plus for DADU builds).
Right away, that’s a potential 3-unit property:
Main home (existing)
Basement ADU (convertible)
DADU (new build)
Quick Check:
Use Seattle’s GIS zoning map and verify:
Setbacks (typically 5’ sides, 20’ rear)
Lot coverage (limit ~35%)
Existing trees or easements
Utility access (sewer + power)
If those boxes check out, you’re holding a lot that can multiply in value without needing to buy another property.
Before you even touch a shovel, you’ll spend on soft costs: design, permits, consultants, and fees.
Typical DADU soft costs:
Survey + site plan: $4,000
Architect + structural: $25,000
Permit + city fees: $12,000
Utility trenching estimates: $10,000
Engineering + reports: $6,000
Legal (condo or LLC setup): $3,000
Total Soft Costs: $60,000
These costs don’t add square footage - but they make your square footage legal, profitable and financeable.
Now, the construction phase. Let’s assume a 750 sq. ft. 2-bed, 1-bath DADU built at $500 per sq. ft. all-in (materials, labor, contingencies).
Build cost:
750 sq. ft. × $500 = $375,000
Add a 10% contingency buffer ($37,500) for delays, price hikes, or upgrades.
Total Hard Costs: $412,500
Category Cost
Acquisition (Home) $900,000
Soft Costs $60,000
Hard Costs (Build) $412,500
All-In Cost $1,372,500
Now you’ve transformed a single-family home into a 2-unit property with a high-quality rental.
Based on Seattle comps, homes with a detached DADU appraise significantly higher due to multi-unit potential.
Comparable sales:
Main home + DADU pairs in this area sell for $1.75M–$1.85M depending on finishes and lot appeal.
Let’s take the conservative midpoint: $1.8M ARV
Built-in equity: $1.8M - $1.372M = $428,000 forced equity
That’s before any rent or refinance.
Here’s where your cash flow engine kicks in.
Unit Rent Estimate Notes
Main Home (3-bed) $4,000 / mo Mid-range single-family rental
DADU (2-bed) $3,000 / mo Modern new build w/ parking
Total Monthly Rent $7,000
Even after property management, taxes, and insurance, your net cash flow could hover around $2,000–$2,500/month once stabilized.
Cap Rate: Based on all-in cost ($1.37M) and NOI ($30K/year), your cap rate is ~2.2%, but once refinanced and cash-out is taken, the ROI multiplies.
Here’s where smart investors think like developers, not landlords. After the build, you refinance at the new appraised value.
New appraised value: $1.8M
Refinance (70% LTV): $1.26M
If your total invested cash was $1.37M, your refinance gives you back ~$1.26M - meaning you’ve recovered most of your capital while keeping a cash-flowing, appreciating, two-unit property.
You now control a $1.8M asset for roughly $100K out of pocket - and $7,000 a month in rent covering your holding cost.
That’s how real developers build wealth - not by flipping, but by forcing appreciation and recycling capital.
Once the DADU is stabilized, you’ve got choices:
Rent both units long-term for consistent income.
Sell one unit via condo conversion and hold the other.
Refi again to fund your next DADU project.
Each move leverages what you built - not what the market handed you. Always design your DADU with future condo conversion in mind (separate utilities, access, and parking). It’s your equity exit ticket.
You don’t need to be a developer to build like one. You just need to understand the math - and play the long game.
The DADU strategy works because it’s repeatable, scalable, and aligned with Seattle’s zoning evolution. One property at a time, you’re not just investing - you’re creating inventory and engineering equity.
