The ADU dictionary

A living unit built over an attached or detached garage. A space-efficient way to add a unit without giving up yard, where zoning permits.

A unit designed for easy use by people with limited mobility, using aging-in-place features. We describe designs as accessible or ADA-informed rather than certified ADA-compliant unless formally reviewed.

A common zoning term for a secondary dwelling — kitchen, bath, and sleeping area — subordinate to the primary home on a lot. Many Connecticut town codes use this phrase for an ADU.

A self-contained, smaller second home on the same lot as a primary residence, with its own kitchen, bathroom, and entrance. Can be detached, attached, or interior.

A building subordinate to the main home — a garage, shed, or ADU. Zoning often regulates its size, height, and placement separately.

What a home is expected to appraise for once the ADU is built. ADU-aware lenders may size a loan against this future value rather than today’s.

Staying in your own home safely as you get older. An ADU can support this by providing a step-free, single-level home for a parent or the homeowners themselves.

A licensed appraiser’s opinion of value. For an ADU, an as-completed or after-renovation appraisal can support future-value lending.

A use a town allows without a discretionary hearing, as long as it meets the written rules. Some Connecticut ADUs may be permitted as-of-right where local rules allow.

A unit that shares at least one wall with the main house — an addition, converted wing, or bump-out — with its own entrance and full facilities.

An informal name for a detached ADU — a small, standalone home in the rear yard, often used for family or rental.

The footprint of buildings as a percentage of lot area. Related to lot coverage but usually limited to roofed structures.

Authorization from the building department to construct, confirming plans meet the state building code. Required before ADU construction begins.

Net operating income divided by project cost or value, expressed as a percentage. A quick way to compare a rental’s return.

An ADU set up so a caregiver can live close by, balancing help with privacy and independence for both households.

Historically a building for carriages or cars; today it usually refers to a detached structure with living space, often above a garage.

What’s left after rent covers operating expenses and loan payments. Positive cash flow means the unit pays for itself and more.

Annual pre-tax cash flow divided by the cash you actually invested — a quick read on how hard your out-of-pocket money is working.

Replacing your existing mortgage with a larger one and taking the difference in cash. Simple, but you give up your current mortgage rate.

The town document confirming a finished unit meets building code and is legal to occupy. Issued after final inspections.

Local confirmation that a completed project matches its approved zoning terms. Sometimes issued alongside the certificate of occupancy.

Connecticut’s coastal review for projects within the coastal boundary. Shoreline-town ADUs may need a coastal site plan review.

All loans against a home — first mortgage plus any second — as a percentage of value. Most banks cap CLTV around 80%; some ADU lenders allow more for qualified borrowers.

A toilet set slightly higher than standard, making it easier to sit and stand for many older adults.

A loan sized to the completed project and released in draws tied to milestones, then converting to a standard mortgage when the ADU is done.

A short foundation wall that raises the unit above grade, leaving access for utilities underneath.

A shower with no lip or threshold, so a wheelchair or walker can roll straight in. A core accessible-design feature.

The total loan payments (principal and interest) on the financing used to build the ADU.

Net operating income divided by loan payments. Lenders often look for 1.25 or higher; some will underwrite an investment loan largely on this number.

Your monthly debt payments divided by gross monthly income. A key qualifying figure; projected ADU rent may help in some programs, subject to underwriting.

A fully separate structure from the main house, with its own walls, roof, and entrance. Often chosen for privacy and rental value where a lot allows it.

A code-required way to exit safely, such as an egress window or door in a sleeping room. Central to legalizing basement or interior ADUs.

A government-backed renovation mortgage that folds improvement costs into one loan based on the improved value. Program rules and eligibility apply.

On-site completion after the unit is set — flooring, trim, paint, fixtures, and connecting mechanicals — before final inspection.

Rated wall, ceiling, or floor assemblies that slow fire spread between an ADU and the main dwelling. Often required for attached and interior units.

FEMA-mapped areas with flood risk. Building in one adds elevation and construction requirements that affect ADU feasibility and cost.

Total building floor area divided by lot area. Some towns use FAR to cap how much total structure — including an ADU — a lot can hold.

The permanent base — slab, crawlspace, or piers — that anchors an ADU. Required for a unit to be a permanent, code-compliant dwelling.

Turning an existing garage into a living unit. Can be cost-effective, but structure, ceiling height, and parking rules all factor in.

Solid backing built into bathroom walls during construction so grab bars can be added securely later, exactly where needed.

A casual term for an ADU used to house a family member, often an aging parent. Interchangeable with in-law suite.

The total measured floor area of a structure, used to check size limits. How a town measures it (e.g. including or excluding garages) varies.

Areas intended for living — sleeping, cooking, eating — meeting code for light, ventilation, and ceiling height. Utility and storage areas usually don’t count.

A revolving credit line secured by your home’s equity that you draw from as needed. Flexible for staged construction spending; usually a variable rate.

An arrangement where an investor gives you cash now for a share of your home’s future value — typically not a traditional loan, and usually with no monthly payments.

A lump-sum second mortgage against your equity, usually at a fixed rate and fixed payment. Predictable, but less flexible than a line of credit.

A conventional renovation mortgage that finances improvements based on the home’s completed value, subject to lender and program guidelines.

Surfaces that don’t absorb water — roofs, driveways, patios. Towns cap it to manage stormwater, which can affect ADU and driveway plans.

A secondary living space intended for a relative. When it has its own kitchen, bath, and entrance, it can function as an ADU.

A unit created inside the existing footprint of the main house — a basement, attic, or walled-off portion — with independent access and facilities.

A small unit (often under ~500 sq ft) created within an existing home, sometimes sharing a bath with the main house.

Door and faucet handles operated with a push rather than a grip and twist — easier for arthritic or weak hands.

A loan amount as a percentage of the home’s value. Lenders cap LTV to manage risk; the cap helps determine how much you can borrow.

Leasing the unit to a tenant on a lease of a month or longer. Generally the most broadly permitted rental use for a CT ADU where local rules allow.

The share of a lot that structures may cover under zoning. A key limit on whether, and how big, an ADU can be.

A layout with the essentials — bedroom, full bath, kitchen, laundry — all on one floor, so daily life needs no stairs.

A home built entirely in a factory to the federal HUD code and transported on a permanent chassis. Distinct from modular, which is built to state and local building codes.

An ADU built in climate-controlled factory sections (modules), then delivered and assembled on a permanent foundation to the same building codes as site-built homes.

The day the factory modules are lifted by crane onto the foundation and joined. A milestone that typically takes hours to a day.

An arrangement where two or more adult generations share a property in separate spaces — a common driver for ADUs.

Annual rental income minus operating expenses, before loan payments. The starting point for cap rate and DSCR.

A lot that predates current zoning and doesn’t meet today’s minimums. It may still support an ADU, but the path can be more involved.

Building all or part of a home in a factory rather than on the lot. Factory work and site prep can overlap, which may shorten the overall schedule.

The ongoing costs of running a rental — taxes, insurance, utilities, maintenance, repairs, and management — subtracted from rent to find real return.

A requirement in some towns that the owner live on-site — in the main house or the ADU — to have or rent the unit.

A method where walls and components are built flat in a factory, then shipped and stood up on site. A middle ground between modular and fully site-built.

Concrete piers or footings supporting the structure at points, sometimes used on sloped or sensitive sites.

An umbrella term for units built off-site — including modular and panelized — then finished on your property. Often faster and less weather-exposed than fully site-built.

The main home on a lot, to which an ADU is secondary. Some towns tie ADU rules — like size or owner occupancy — to the principal dwelling.

Estimated rent a finished ADU could earn, often from an appraiser’s rent schedule. Some lenders may consider it, subject to product, appraisal, and legal rental status.

The final list of small items to correct or complete before a project is considered done and closed out.

A credit line structured around your home’s after-renovation value, which can unlock more than a standard HELOC while keeping your first mortgage in place.

An appraiser’s estimate of market rent for a unit, used by some lenders to credit projected income when qualifying a borrower.

A loan for homeowners 62+ that converts equity into funds with no required monthly payment. It carries estate, tax, and occupancy implications worth reviewing with a counselor.

Any loan secured by your home behind the first mortgage — including HELOCs and home equity loans. Lets you borrow without touching your first mortgage.

An independent utility meter for the ADU, which can simplify billing a tenant. Whether it’s required or possible varies by utility and town.

Whether an on-site septic system can handle the added bedrooms and flow from an ADU. Often a make-or-break item for lots without sewer.

The minimum required distance between a structure and your property lines. Setbacks often determine where — and whether — a detached ADU can sit.

Tying the ADU into a public sewer main. Availability, capacity, and connection fees vary by town.

Renting the unit for brief stays, such as nightly or weekly. Availability depends heavily on local rules.

A town’s review of how a project sits on the lot — access, drainage, parking, landscaping — before approval.

A poured concrete pad the ADU sits on. Often economical on level sites without a basement.

A discretionary approval a commission may grant for a use allowed only under specific conditions. Some towns route certain ADUs through this process.

Rainwater runoff a project must manage on-site. New roof and paved area from an ADU can trigger drainage requirements.

A very small dwelling, usually 100–400 sq ft. On a permanent foundation and built to code it may qualify as an ADU; the label alone does not make it legal.

A tiny house built on a trailer chassis. Because it is mobile and not on a permanent foundation, it is usually treated differently from a permanent ADU.

The all-in cost of a finished ADU — factory unit plus site work, foundation, utilities, delivery, finish work, and permits — not just the factory price.

Designing spaces usable by people of all ages and abilities without special adaptation — wider doorways, lever handles, good lighting, and step-free access.

Connecting the ADU to water, sewer or septic, electric, and sometimes gas — usually via trenching from the main house or street.

The share of the year you assume the unit sits empty. Building it into your math keeps projections realistic rather than best-case.

Permission to deviate from a specific zoning requirement, granted by the Zoning Board of Appeals when strict rules cause a hardship. Not guaranteed.

Review by a local inland-wetlands agency when work is near regulated wetlands or watercourses. It can affect where an ADU may be sited.

The clear floor space (commonly about a 5-foot circle) a wheelchair needs to turn around — a key dimension in accessible bathrooms and kitchens.

An entrance with no stairs or threshold to cross, so a walker or wheelchair can enter without a ramp workaround.

The local body that hears variance and appeal requests. You may encounter it if an ADU can’t meet a dimensional rule as-of-right.

Local sign-off that a project meets zoning rules — use, setbacks, coverage, height — often needed before or alongside a building permit.