Example of a backyard cottage (ADU)
Image by prefabADU

Kennesaw’s draft allows backyard cottages (commonly referred to as ADUs) by land-use permit (LUP) in R-15, R-20, R-30, and R-40 districts and includes thoughtful design and safety provisions. This is a welcome move toward incremental infill and housing variety. Yet without trimming hidden obstacles, most homeowners will never take the plunge to build a backyard cottage.

Homeowners often add a backyard cottage to create flexible living space—for aging parents, adult children, or long-term guests—while keeping privacy and independence for all. Renting out a backyard cottage can generate steady income to offset mortgage or maintenance costs and boost overall property value. By making efficient use of existing developed land and infrastructure, backyard cottages/ADUs also support incremental, walkable development that strengthens neighborhood vitality and financial solvency.

Commendations

  • Broad district coverage
    Allowing backyard cottages across multiple residential zones opens options on diverse lot sizes and price points.
  • Manufactured homes permitted
    Factory-built units—often far cheaper and faster to install than stick-built homes—are expressly allowed.
  • Context-sensitive design controls
    Matching materials to the principal dwelling, hydrant proximity, and clear emergency access preserve neighborhood character and safety.

Key Critiques

  1. Parking mandates
    • Current rule: One dedicated off-street space for the ADU, plus existing parking for the main house.
    • Why it hurts: Parking minimums inflate construction & infrastructure costs, induce more car dependency, and consume valuable land with pavement–even though studies find no link between ADUs and parking shortages. Most homeowners already have driveway or on-street parking; removing this requirement would reduce long-term maintenance liabilities and encourage walkable, multimodal neighborhoods. (Strong Towns).
  2. Over-generous setbacks
    • Current rule: ADUs must sit behind the home with 10 ft side/rear setbacks .
    • Why it hurts: Oversized setbacks force units into the center of yards, breaking up shared green space between the primary dwelling and backyard cottage. A 5–6 ft setback meets safety codes while enabling cozier, less intrusive infill (Strong Towns).
  3. HOA approval requirement
    • Current rule: Written sign-off by any HOA or design committee before construction (Strong Towns).
    • Why it hurts: Deferring to private covenants embeds exclusionary rules into public policy. ADU permitting should remain an objective, ministerial process administered by the city—unmixed with private HOA agendas (Strong Towns).
  4. ADU-to-ADU buffers
    • Current rule: Undetermined buffer of 250, 500, or 1,000 ft between units.
    • Why it hurts: Any spacing mandate throttles gentle infill and creates underutilized land pockets. Incremental development happens in a naturally distributed pattern, codifying this puts unnecessary choke-points on this pattern and creates a false scarcity and potential competition amongst community members.
  5. Permit complexity & fees
    • Current rule: ADUs treated as a “privilege” permit with discretionary review, HOA sign-off, normal impact fees, and System Development Charges (SDCs) .
    • Why it hurts: Conditional-use hearings, discretionary waivers, and steep system development charges turn an already expensive backyard project into a high-risk, even-higher-cost venture. When ADUs aren’t by-right and SDCs are applied, permit counts remain in the dozens, not the hundreds .

Case Studies & Strong Towns Insights

  • Vancouver’s success
    By allowing ADUs nearly citywide—with no parking, no hearings, and no extra design mandates—Vancouver now adds over 1,000 legal ADUs per year, with 35% of single-family lots hosting one.
  • Portland’s turnaround
    Although ADUs were by-right since 1997, permit volumes stayed low until 2010, when Portland waived SDCs. Permits then jumped from fewer than 100 to over 600 annually—and design and size rules were relaxed.
  • Hidden hurdles
    Beyond zoning, financing costs, design fees, and permit uncertainty all discourage homeowners. Pre-approved plans and novel business models (e.g., turnkey builders like Dweller) can demystify the process and share risk.

Recommended Reforms

  1. By-right permitting
    Reclassify ADUs as an as-of-right use with clear, objective standards—no hearings or discretionary waivers.
  2. Eliminate parking & buffers
    Remove off-street parking and buffer mandates to lower cost and maximize lot utilization.
  3. Contextual size & height
    Allow ADU size up to a percentage of lot buildable envelope or match the principal dwelling’s ridge height +5-20% – rather than an arbitrary cap.
  4. Fee waivers & streamlined process
    Waive or drastically reduce System Development Charges (SDCs), impact fees, and permit costs for ADUs. Provide checklists or a library of pre-approved ADU plans to slash architectural expenses.
  5. Simplify owner-occupancy verification
    Replace annual notarized statements with a simple digital affidavit or in-person check-in.

Conclusion

Kennesaw’s draft ADU code is a strong first step toward housing diversity and incremental development. To turn permission into production, the City must strip out unnecessary barriers—parking, setbacks, HOA sign-offs, arbitrary caps, discretionary reviews, and steep fees—and adopt by-right, context-sensitive, low-cost pathways. Only then will ADUs fulfill their promise as a scalable, neighbor-friendly tool for resilient growth.

About Strong Towns

Strong Towns is a 501c3 nonprofit organization dedicated to transforming how cities and towns grow by advocating for financially resilient, incremental development. Through research, education, and grassroots engagement, Strong Towns promotes policies that prioritize human-scale streets, diverse housing, and fiscally responsible infrastructure over car-centric expansion.

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