Rules vary by city—always check your local zoning code and consult professionals. This is not legal advice.

Thinking about building an ADU, backyard cottage, or small home?

You’ve probably run into a flood of confusing terms — setbacks, permitting, impact fees, owner occupancy, conditional use, floor area limits.

City planners speak code language. Contractors speak construction language. Most homeowners just want straight answers.

This guide breaks down the most common ADU and small housing terms in plain English, so you can understand what’s possible on your property and avoid costly surprises.

Bookmark this page — it’s designed to be a simple reference.

A

Accessory Dwelling Unit (ADU)

A smaller, secondary home located on the same lot as a primary residence. It can be detached, attached, or inside the existing home.

Attached ADU

An ADU physically connected to the main house, such as an addition or garage conversion.

Alley Access

Rear access to a property via an alley. Some cities reduce parking or driveway requirements when alley access exists.

B

Building Permit

Official approval from your city allowing construction to begin. Nearly all ADUs require one.

Buildable Area

The portion of your lot where you’re legally allowed to place structures after accounting for setbacks, easements, and utilities.

C

Conditional Use Permit (CUP)

A discretionary approval process that may require hearings or neighbor input.
It adds time, cost, and uncertainty.

Many Utah cities are eliminating CUPs for ADUs to make them easier to build.

Conversion

Turning an existing space — like a garage or basement — into a legal dwelling unit.

CC&Rs (Covenants, Conditions & Restrictions)

Legal rules enforced by a homeowners association (HOA). They can prohibit or limit ADUs entirely, overriding city zoning. Always review your HOA docs first—a common barrier for 20-30% of properties.

D

Detached ADU

A standalone structure separate from the main home. Often called a backyard cottage or carriage house.

Drainage Systems

Grading, gutters, and stormwater controls that direct water away from structures.
Cities often require drainage plans to prevent flooding or runoff issues between neighbors.

Poor drainage can delay permits or add unexpected site costs.

Density

How many housing units are allowed per lot or acre. ADUs gently increase density without changing neighborhood character.

E

Easment

A legal restriction that limits where you can build (utilities, drainage, access paths). Always verify easements before designing an ADU.

Egress Requirements

Legal mandates for safe emergency exits, like windows (min 5.7 sq ft opening) or doors in bedrooms. Critical for habitability and passing inspections.

F

Floor Area Ratio (FAR)

A rule that limits total building square footage compared to lot size.

Foundation Types

Slab-on-grade, crawl space, piers, or trailers. Each affects cost, permitting, and flexibility.

Fire Sprinklers

Automatic systems required in some areas (e.g., attached ADUs or wildfire zones). Adds $5K-$15K but can be mandatory per IRC or local fire codes.

H

Habitability Requirements

Minimum standards a space must meet to be legally lived in.

Typically includes:

• ceiling height minimums
• egress windows/doors
• heating
• insulation
• ventilation
• plumbing and electrical
• safe exits

Not every finished basement or shed automatically qualifies as legal living space.

Height Limits

Maximum vertical size for structures (e.g., 16-25 ft for ADUs). Restricts multi-story designs in sloped or historic areas.

I

Impact Fees

Fees charged by cities to help pay for infrastructure like roads and sewer systems. Some municipalities reduce or waive these for ADUs.

Internal ADU

A unit created within the existing home, commonly a basement apartment with a separate entrance.

Independent Entrance

A private exterior door for the ADU, required in most codes to ensure privacy and fire separation from the main house.

Insurance Implications

ADUs often require separate landlord or flood policies. Expect 10-20% premium hikes; notify your insurer early to avoid claim denials.

J

Jurisdiction

The city or county that controls your zoning and building permits. Rules can vary dramatically between neighboring cities.

Junior ADU (JADU)

A compact internal ADU (typically <500 sq ft) allowed in some states like California. Easier permitting for tiny units.

L

Lot Coverage

The percentage of your lot that can be covered by structures. Can limit ADU size or placement.

M

Maximum Floor Area

The largest size an ADU is allowed to be.

Many Utah cities cap detached ADUs around:

• 800–1,000 sq ft
• or a percentage of the primary home

This rule often determines whether you build a studio, one-bedroom, or two-bedroom layout.

Ministerial Permit

A streamlined approval (no hearings) for code-compliant projects. Opposite of CUP—faster and cheaper when your ADU qualifies as "by right."

O

Owner Occupancy Requirement

A rule requiring the property owner to live on-site (either in the primary home or the ADU). Common in many residential zones.

Off-Street Parking

Dedicated spaces not on public streets. ADUs may need 0-1 space, often waivable.

Occupancy Certificate (Final)

The last permit stamp allowing legal move-in after all inspections. Without it, no renting or living.

P

Parking Requirement

How many off-street spaces must be provided. Some cities waive this near transit or bike corridors.

Permitting

The overall approval process for building your ADU, including plan review, inspections, and compliance checks.

Typical steps:

1. Zoning approval
2. Building permit
3. Utility connections
4. Inspections
5. Final occupancy

Permitting timelines vary widely by city and can significantly affect project schedules.

Prefab / Modular

Homes built in a factory and delivered to your site. Often faster and more predictable in cost than traditional stick-built construction.

R

Residential Zone

A zoning category primarily intended for housing (R-1, R-2, etc.). ADU rules depend on the specific zone.

Right (Allowed by Right)

When something is automatically permitted under zoning rules without special hearings.

This usually means:

• faster approval
• lower costs
• less risk

“Allowed by right” is one of the best signs your ADU project will be straightforward.

S

Setbacks

Minimum required distances between structures and property lines. One of the biggest design constraints for ADUs.

Short-Term Rental (STR)

Rentals under 30 days (Airbnb-style). Many cities prohibit STR use for ADUs.

Skirting

Material used to enclose the underside of homes on piers or trailers for insulation and aesthetics.

Survey

A professional property measurement that confirms boundaries, easements, and buildable space.

Many cities require a survey before issuing permits. It can prevent costly placement mistakes.

U

Utilities Tie-In

Connecting water, sewer, gas, and power to the ADU. Distance from existing lines heavily impacts cost.

Utility Easement

A specific easement for public lines (e.g., sewer under your yard). Can't build over it—often requires relocation ($10K+).

Upcodes / Variances

Minor code tweaks for unique sites (e.g., small lot). Adds time but can unlock buildable area.

Zoning

The city's map dividing land into use categories (e.g., residential, commercial). ADUs are usually allowed "by right" in single-family zones (R-1) but check overlays like historic or flood zones.

Final Thoughts

Building an ADU or small home doesn’t have to be complicated — but understanding the terminology makes everything easier.

If you want help navigating zoning, design options, or choosing the right type of small home, we share practical guides and updates every week through Small Home Nation and The Small Housing Report.

You can also explore available homes, ADUs, and small housing solutions at:

👉 Build-Small.com

It’s a good starting place to see what’s possible and get a clearer picture of costs and timelines.