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Addition Scope · Glossary
Home addition terms, and how to use them when you read a proposal
This glossary defines the terms that come up when planning a room addition, second story or ADU, from setback and lot coverage to load path, underpinning, roof tie-in and concealed-conditions clause. Knowing them helps you read drawings and bids, ask sharper questions and spot where a proposal is vague about the parts of the job most likely to change the price.
12 terms you will see in home additions proposals
- Accessory dwelling unit (ADU)
- A second, self-contained living space on a single-family lot with its own entrance, kitchen and bathroom, created by converting a garage or basement, adding on, or building a detached unit. Rules on size, parking, occupancy and rental vary by state and city.
- Bump-out
- A small extension of one room by a few feet, often cantilevered from the existing floor joists without its own foundation. HomeAdvisor notes about 24 inches is the usual limit before footings are needed.
- Concealed-conditions clause
- Contract language that says how hidden problems found during construction, such as rock, bad soil or rot in the existing wall, are documented and priced before work continues. It should carry unit prices.
- Design-build
- A delivery model in which one firm provides design, engineering (in-house or under contract) and construction, keeping responsibility in one place. The alternative is an architect who designs and bids the job to general contractors.
- Frost depth
- The depth to which soil freezes in winter, which sets how deep footings must go so the foundation is not heaved. It ranges from near zero in the South to four feet or more in the northern tier.
- Joy Score
- NAR's Remodeling Impact Report measure of homeowner happiness with a completed project on a 10-point scale. A primary suite addition scored a perfect 10 in the 2025 report despite modest cost recovery.
- Load path
- The continuous route that roof, floor and wind or seismic loads follow through walls, headers, foundation and footings to the soil. An engineer traces it before approving a second story.
- Lot coverage
- The maximum share of a lot that buildings may occupy under zoning. A large ground-floor addition can exceed it, which is one reason households on full lots build up instead.
- Plan review
- The building department's check of permit drawings against code and zoning before a permit is issued. CADTRI's 2026 guide reports two to eight weeks in most jurisdictions, with fees per correction cycle.
- Roof tie-in
- The junction where an addition's roof meets the existing roof or wall, as a shed, a perpendicular gable with a valley, or an extended ridge. It is the detail most likely to leak and should be drawn in section.
- Setback
- The minimum distance a structure must keep from a lot line, set by the zoning code and usually different for front, side and rear yards. Setbacks and lot coverage limits decide where and whether an addition can be built out.
- Underpinning
- Deepening or widening existing footings, usually in sections, so they can carry more load. It is the costly outcome of a structural review and often tips the decision from a second story to a room addition or ADU.
Addition proposals use a working vocabulary that builders, designers and building officials share and homeowners often do not. That gap matters, because the terms tend to cluster around the most expensive and uncertain parts of the job. A bid that mentions the roof tie-in but does not describe it, or that has no concealed-conditions clause, is telling you something about how the price was built.
The definitions below are short by design, and each one is written for a homeowner rather than a tradesperson. The sections that follow explain how to use them when reading drawings and bids, which terms are easily confused, and which questions each one should prompt before you sign anything. The planning guide shows where each term enters the project.
How do these terms help when reading a proposal?
Use them as a checklist. For a ground-floor addition, a complete proposal should say something specific about the foundation relative to frost depth, the roof tie-in, the opening into the existing house and how concealed conditions will be priced. For a second story, it should reference the engineer's findings on the load path and any underpinning. For an ADU, it should address setbacks, fire separation and utility connections.
Where a term is missing, ask about it. Where it appears only as a word with no detail, ask for the detail. A builder who can explain how the roof tie-in will be flashed, or how the load path runs from the new floor to the footings, has usually priced the work. One who cannot may be guessing, and guesses become change orders once the wall is open.
Which addition terms are most often confused?
Setback and lot coverage are often mixed up. A setback is a distance from a lot line; lot coverage is a share of the lot's area. An addition can satisfy one and fail the other, which is why both must be checked on the survey. Similarly, plan review and inspection are distinct: plan review checks the drawings before a permit is issued, commonly taking 2–8 weeks per CADTRI's 2026 guide, while inspections check the work as it is built.
Load path and underpinning are related but not the same. The load path is the route forces take through the structure to the soil; underpinning is one possible fix when the footings at the end of that path are too small. Design-build and general contracting also get blurred. A design-build firm handles design and construction under one contract, while a general contractor usually builds from someone else's drawings.
What questions should each key term prompt?
Each term points to a question worth asking before you sign. The answers reveal whether the price reflects your house or a generic version of the project, and they give you something concrete to compare between bidders. Ask the same questions of every bidder, in writing if possible, so the answers can be laid side by side.
- Setback and lot coverage: where exactly can the addition go, and how much area remains?
- Frost depth: how deep will the footings be, and is that priced as a separate line?
- Load path: has an engineer traced it, and what reinforcement did they specify?
- Underpinning: is it needed, how many footings are involved and how is it priced?
- Roof tie-in: which type is proposed, and can I see it drawn in section?
- Concealed-conditions clause: how are hidden problems documented, and at what unit rates?
- Plan review: who responds to corrections, and how many cycles are assumed?
How do the terms apply differently to each addition route?
Ground-floor additions lean on setbacks, lot coverage, frost depth and the roof tie-in; deep frost is one reason our analysis of EIA's 2024 survey puts 57.7% of Midwest homes over a basement, against 29.5% nationally. Second stories lean on load path, underpinning and plan review, since structural calculations draw more scrutiny. ADUs and conversions add their own vocabulary, including the ADU definition itself, which decides whether a space qualifies for the zoning allowances that apply to second units.
Bump-outs sit between these, using cantilevers where joists allow and footings where they do not. Conversions start from unfinished space, which by our EIA analysis includes 85.6% of attics and 41.1% of basements. For each route, the relevant terms are the ones that decide feasibility and cost. The room additions, second-story and ADU conversion pages explain how each term plays out, and the permits guide covers plan review in detail.
Why does the Joy Score appear in an addition glossary?
Because it measures something cost figures miss. The National Association of Realtors' 2025 Remodeling Impact Report gave an added primary suite a 10 / 10 Joy Score, even though Zonda's 2025 report found a midrange suite recoups only 32.3% of its cost at resale. The two numbers together describe what additions usually are: expensive, only partly recovered at sale and highly valued by the people who live with them.
Keeping both measures in mind helps with the hardest budget decisions. If a feature adds little resale value but would make daily life markedly better for years, it may still be worth including. If it adds neither, it belongs at the top of the list of things to cut; NAR's 2025 report, by contrast, gives added primary suites a perfect 10 / 10 Joy Score, a sign that satisfaction counts too.
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Glossary questions
What is the difference between a setback and an easement?
A setback is a zoning rule that keeps buildings a minimum distance from lot lines. An easement is a legal right for someone else, such as a utility, to use part of your land, which usually prohibits building over it. Both appear on a survey, and both can block an addition, so check each before design.
What does it mean when a bid says work is by others?
It means the item is excluded from that bid and someone else, often you, must arrange and pay for it. Common examples are permits, engineering, landscaping and utility company work. Each by-others item should be listed so you can budget for it and compare bids fairly.
What is an allowance in an addition contract?
An allowance is a placeholder amount for items not yet selected, such as flooring, tile or light fixtures. If your final choice costs more, you pay the difference. Check that allowances are realistic for your taste, since low allowances make a bid look cheaper than it will end up being.
What is a change order?
A written amendment to the contract that changes the scope, price or schedule. Change orders arise from your requests and from concealed conditions. Each should be priced and signed before the extra work starts, and the contract should say how they are calculated.
What is a certificate of occupancy for an addition?
The building department's confirmation, after final inspection, that the new space meets code and may be used as intended. Some jurisdictions issue a certificate of completion instead for additions to existing homes. Keep it with your records, since lenders and buyers may ask for it.
What is a stamped drawing?
A drawing sealed by a licensed engineer or architect, certifying that it was prepared under their responsibility and meets applicable codes. Building departments often require stamped structural drawings for second stories and other additions that change how loads reach the foundation. HomeAdvisor puts architect fees at 5–20% of project cost.
Where can I test what I have learned about addition terms?
The site's addition planning quiz covers many of these terms in the context of real decisions, such as choosing a route or reading a bid. It takes a few minutes and explains each answer, which makes it a useful check before meeting a designer or builder.
See the terms in context
Service guideRoom AdditionsA room addition builds new ground-floor space on its own foundation, tied into the existing walls and roof, to add a bedroom, family room, kitchen extension, bathroom or primary suite.
Service guideSecond Story AdditionsA second-story addition builds a new floor on top of an existing house, either over the whole footprint or over part of it, after an engineer confirms the foundation and walls can carry the load.
Service guideADU & Garage ConversionsAn accessory dwelling unit is a second, self-contained living space on a single-family lot, built by converting a garage or basement, adding onto the house, or constructing a detached unit.
Free planning tools
Free toolHome addition cost calculatorSize, material tier and complexity in, a realistic budget range out.
Free toolAddition comparisons: out versus up, conversion versus new buildSide-by-side tables for the decisions that change the price most.
Free toolAddition feasibility quiz: do you know what decides your project?9 questions that show what you already know and what to check next.
Free toolAddition polls: what other planners chose, feared and cutSee what other planners chose and add your vote.
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