ADU Site Planning: Where to Place It (And Where NOT To)

Couple discussing architect designing ADU

The single most important decision in your ADU project happens before you even think about floor plans.

Planning an Accessory Dwelling Unit? The biggest mistake homeowners make is falling in love with a design before considering where it will actually sit on their property. Your ADU's placement determines everything from construction costs to daily living comfort—and once it's built, you can't exactly pick it up and move it.

After designing dozens of ADUs, I've learned that the perfect location is rarely obvious. Here's what you need to consider before breaking ground:

The Golden Rules of ADU Placement

1. Follow the Sun (But Not Too Closely) Best practice: Orient your ADU to capture morning and afternoon light while avoiding harsh midday sun.

Why it matters: Natural light makes small spaces feel larger and reduces energy costs. But too much direct sun creates uncomfortable heat and glare.

Red flag locations:

·       Directly facing west with large windows (afternoon heat will be unbearable)

·       Tucked into corners where trees or buildings block all natural light

·       Positioned where the main house casts permanent shadows

Sweet spot: Southeast orientation captures gentle morning light, while strategic overhangs and landscaping control harsh afternoon sun.

2. Consider Your Neighbors (And Your Neighborhood) The reality: Your neighbors will have opinions about your ADU. Smart placement can turn potential opposition into support.

Avoid these neighbor relation disasters:

·       Placing windows directly facing neighbor's bedroom or living areas

·       Positioning the entrance where it creates a "fishbowl effect"

·       Building so close to property lines that it feels imposing

Diplomatic positioning:

·       Set back from shared fence lines where possible

·       Angle the ADU to face your own yard rather than theirs

·       Use landscaping and strategic window placement to create natural privacy barriers

3. Utilities: The Expensive Reality Connecting to utilities can be costly. Be sure to take this into consideration.

Placement mistakes that drain budgets:

·       Positioning the ADU far from existing electrical and water lines

·       Ignoring septic system locations (if you're not on city sewer)

·       Placing it where you'll need to tunnel under driveways or landscape

Cost-smart positioning:

·       Within 100 feet of existing utilities when possible

·       Along clear paths for utility trenching

·       Close enough to share systems with existing house like septic or electrical panels (where code allows)

Know Your Purpose Before You Position

The Rental Income ADU Primary goal: Maximum privacy and independence for tenants

Placement priorities:

·       Separate entrance that doesn't require walking past main house windows

·       Distance from main house bedrooms (noise buffer)

·       Street visibility for safety and easy identification

·       Dedicated parking that doesn't block main house access

The Aging Parent ADU Primary goal: Independence with support nearby

Placement priorities:

·       Close enough for easy check-ins and assistance

·       Ground-level access (avoid stairs where possible)

·       Visual connection to main house for peace of mind

·       Protected from street noise and activity

The Young Adult "Launch Pad" ADU Primary goal: Semi-independent living with family support

Placement priorities:

·       Some separation for privacy and independence

·       Easy access for coming and going (especially late nights)

·       Buffer zone from family activities during study time

·       Room for friends to visit without disturbing the main house

The Home Office/Studio ADU Primary goal: Professional space separate from home life

Placement priorities:

·       Professional entrance for client meetings

·       Quiet location away from household activity

·       Good natural light and views for productivity

·       Separate utilities for business tax deductions

The "Zones" of Your Property

Zone 1: Close to the Main House (Within 20 feet) Pros: Shared utilities keep costs down, easy to monitor and maintain, creates a "compound" feeling Cons: Can feel cramped for both households, noise carries between buildings, less privacy Best for: Parent units, home offices, or situations where interaction is desired.

Zone 2: Mid-Property (20-50 feet from main house) Pros: Good balance of privacy and connection, usually optimal for utilities, maintains property flow Cons: May require longer utility runs, can divide backyard awkwardly if not planned well Best for: Most ADU situations—rental units, teen spaces, guest houses.

Zone 3: Back of Property (50+ feet from main house) Pros: Maximum privacy for both units, can feel like separate homes, often the quietest location Cons: Expensive utility connections, may feel isolated or unsafe, harder to maintain and monitor Best for: Large lots, rental properties, or when maximum privacy is the goal.

Bottom Line Consult with an experienced architect who has ADUs in their portfolio. Whether as an investment, living space, or office, architectural design is critical. Once you break ground, the best way to a good night's rest is knowing your ADU's design is sound and sensible.