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Guest house and ADU plans: what to decide first

An accessory dwelling unit (ADU) is a second, smaller home on the same lot. Before comparing plans, decide who will live in it and where it can go. Those two answers rule out most options.

ADUGUEST HOUSELAND

Guest houses and ADUs are planned backwards. The plan is the last decision, not the first. Local rules decide whether you can build one, how large it can be and where it can sit. Your household decides what it needs to do.

Decide these first

  1. 01

    Who it is for

    A parent who will live there full time needs a different plan from occasional guests or a home office. Write the person down before the plan.

  2. 02

    What your local rules allow

    Zoning decides whether an ADU is allowed, its maximum size, its height and its setbacks. Ask your local planning office before you shortlist anything.

  3. 03

    Where it sits on the lot

    Placement sets the utility runs, the path from the main house, privacy and what each house sees from its windows.

  4. 04

    Detached or attached

    A detached unit gives privacy; an attached suite is closer for care and shares walls and systems.

  5. 05

    Utilities

    Ask whether the unit can share water, sewer or septic and power with the main house, or needs its own.

Three placements for a second unit on a lot: detached behind the main house, detached beside it, and attached to its side as a suite.

Detached, behind

Detached, beside

Attached suite

Three placements for a second unit.Diagram, not to scale

Three placements

Detached, behind the house

What it does

A separate small house in the rear yard.

The trade-off

Longest utility runs and a longer walk; most privacy for both households.

Suits

Adult children, long-stay guests, a quiet office.

Detached, beside the house

What it does

A separate unit set to one side, often with its own approach.

The trade-off

Needs lot width; both houses face the street.

Suits

Wide or rural lots, a unit with its own entry.

Attached suite

What it does

A self-contained suite sharing a wall with the main house.

The trade-off

Shared walls carry sound; less independence for both sides.

Suits

A parent who may need help nearby.

Trade-offs to expect

  • Small units are compact by necessity: storage and the bathroom are usually what gets squeezed.
  • A unit built for a parent today may house guests or a renter later. Rules on renting it are local, so check them before counting on it.

Ask before you buy the plan

  1. Does your zoning allow an ADU on this lot, and what size limit applies?
  2. Can the unit share utilities with the main house?
  3. Is there a step-free entry and a bathroom drawn for someone with limited mobility?
  4. Does the plan set include the foundation you need for that part of the lot?

Plans worth comparing

No verified plans are published for this brief yet. The table appears here once each spec has been checked against the seller's listing.

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