House Hacking in Saint Louis County, MO: Strategies and Numbers

Saint Louis County is a good fit for house hacking, and the math is more accessible here than in most comparable metros. The median home price sits at $293,458, median rent runs $1,477 per month, and the gross yield on rental properties clocks in at 6.04%. That combination means a renter-offset payment is achievable across multiple strategies without requiring a six-figure income. The county also explicitly permits ADUs on lots as small as 5,000 square feet with 50-foot minimum width, no business license required to rent one. Missouri state law bans local rent control, so once you set a rent at market rate, no ordinance caps future increases. These are real advantages for a first-time house hacker.

The main risks to hold in your head before buying: Boeing's 692-worker layoff in early 2025 and ongoing union contract rejection create blue-collar renter instability in north county. Property taxes vary from $835 per year in Berkeley to $18,955 in Clayton, which reshapes the math by submarket. And the recently shelved Green Line rail extension means transit-proximity uplifts in north corridor areas are years away at best.

Strategy 1: Duplex or Small Multifamily

This is the cleanest house-hack structure in St. Louis County. You occupy one unit, rent the other, and the rental income offsets your mortgage payment.

The numbers: At the county median price of $293,458, a duplex is likely priced somewhere in the $220,000–$320,000 range depending on submarket. With an FHA loan at 3.5% down on a $270,000 purchase (a realistic duplex entry point in mid-county), your down payment is about $9,450. On a 30-year note at roughly 6.75%, principal and interest runs about $1,680 per month. Add property taxes at the Kirkwood rate of 1.19%, insurance, and you are looking at total PITI in the range of $2,100–$2,300 per month.

If the rental unit fetches $1,300–$1,477 per month (in line with the county median rent), your net out-of-pocket to live runs $625–$1,000 per month. That is below market rent for most of these same submarkets.

Where to look:

• Maplewood and Webster Groves sit in the mid-county band that produced about one-third of multifamily completions in 2024, with occupancy stabilizing near 94%. Walkable, young-professional demand, and rents that support the offset math without the tax burden of Clayton.
• Kirkwood has a 1.19% effective tax rate, one of the lower intra-county rates, which keeps PITI manageable. It attracts stable, longer-term tenants.
• Richmond Heights offers similar mid-county proximity to MetroLink stations. Properties near existing stations in Brentwood, Clayton, and Maplewood carry a transit premium and attract car-free renters who prioritize walkability.

Avoid north-county duplexes in Berkeley or Hazelwood as a first house hack. Gross yields are higher, but Boeing's employment concentration there means vacancy and delinquency risk rises sharply if layoffs deepen or a strike materializes.

Strategy 2: ADU (Accessory Dwelling Unit) Add-On

If you buy a single-family home on a qualifying lot (minimum 5,000 square feet, 50-foot width), you can add an ADU without rezoning and rent it without a business license. This is a slower-build strategy: you live in the main home, then add the ADU either at purchase (if one exists) or as a value-add project.

The numbers: A single-family home in the $250,000–$310,000 range in mid-county will have the lot dimensions to qualify on many parcels. A detached or attached ADU rented at $900–$1,200 per month (a conservative discount to the $1,477 county median for a smaller unit) reduces your effective housing cost. On a $280,000 purchase with PITI around $2,200, a $1,000 ADU rent brings your net to $1,200 per month.

The construction cost of a new ADU is not covered in the brief, so do not let anyone quote you a price without local contractor bids. What the county's own code does confirm: you do not need to go back for a rezoning approval, which removes a common first-timer obstacle.

Where to look: Maplewood, Webster Groves, and Kirkwood all have established single-family stock on standard lots with the footprint to support ADU additions. These neighborhoods also have the renter demand (young professionals, Washington University and BJC employees) to keep an ADU occupied.

Strategy 3: Room Rental in a Larger Single-Family Home

St. Louis County has two anchor institutions generating consistent room-rental demand: BJC HealthCare with 30,000+ employees and Washington University with 13,000+ employees. Travel nurses, residents, and university staff frequently prefer furnished or short-stay rooms over traditional leases.

The numbers: A three-or-four-bedroom single-family home near the BJC or Washington University corridor in mid-county trades in the $280,000–$350,000 range. Renting two rooms at $700–$900 per month each generates $1,400–$1,800 per month in gross rental income. On a $310,000 purchase with PITI around $2,350, two occupied rooms push your net housing cost to $550–$950 per month.

Missouri has no statewide rent control, and the county has no STR licensing regime at the county level (individual municipalities may, so verify the specific municipality before closing). This gives you pricing flexibility for short-term arrangements common in healthcare worker housing.

Regulatory Gotchas

Property tax and homestead exemption: Missouri's homestead exemption applies only to your primary residence. If you own a duplex, the exemption covers your unit's assessed value share, not the rental unit. Run the municipality-specific tax rate, not the county average. Clayton's $18,955 median annual tax bill makes any house hack there cash-flow negative in most scenarios. The spread between Berkeley ($835) and Clayton is so wide that submarket selection has more impact on your monthly number than an interest rate move of 0.5%.

ADU rental rules: The county permits ADU rentals without a business license, but standard landlord-tenant and eviction statutes apply from day one. Missouri's eviction process is relatively landlord-friendly, but budget for at least 30–45 days if you need to remove a non-paying tenant.

STR and municipal variation: The county itself does not impose a short-term rental licensing regime, but individual municipalities within the county do. If you plan to use Airbnb or VRBO for your rented rooms or ADU, confirm the specific municipality's rules before purchasing.

HOAs: Many single-family homes in west and mid-county sit inside HOA-governed communities that restrict rentals, ADU construction, or room-by-room rentals. Pull the CC&Rs before making an offer, not after.

How Flood Risk Affects the House-Hack Math

South county properties near the Meramec River (Valley Park, Fenton, Eureka) carry recurring flood exposure. In November 2024, the Meramec was forecast to reach 32.5 feet against a major flood stage of 25 feet. FEMA's flood map updates are ongoing, and properties near tributary streams may face new mandatory flood insurance requirements. A flood insurance premium that was previously zero can add $1,500–$3,000 per year to holding costs. Stick to higher-elevation parcels in mid-county for your first house hack.

Getting Started: A 6-Step Checklist

1. Pull the municipality-specific tax rate for every property you underwrite. Use the 1.19% Kirkwood rate as a mid-county baseline; adjust up or down based on actual parcel data from St. Louis County's tax records.

2. Confirm lot dimensions before writing an ADU offer. The county's 5,000-square-foot minimum and 50-foot width requirement are objective; request the survey or check GIS parcel data before assuming the lot qualifies.

3. Check the municipality's STR or rental licensing rules. The county has no regime, but the city or village may. A five-minute call to the local building department saves a compliance headache.

4. Pull the CC&Rs on any HOA property. Ask your agent to pull and review before the inspection period closes, not after.

5. Run the FEMA flood map for south county targets. Check the FEMA Flood Map Service Center with the property's address. If preliminary updated maps show a zone change, price in mandatory flood insurance before closing.

6. Model Boeing exposure in north county. If a property is in Berkeley or Hazelwood, stress-test your vacancy assumption at 15–20% to account for blue-collar renter softness if Boeing's labor situation worsens.

Run your specific scenario through our House Hack calculator to see how submarket tax rates, ADU rent assumptions, and down payment size interact on your actual net monthly cost.