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About Addition Scope
About Addition Scope: sourced planning for additions, and a way to get estimates
Addition Scope is an independent planning resource for homeowners considering a room addition, a second story, or an ADU or garage conversion. It publishes sourced cost, resale, structural and permitting information, explains the trade-offs an estimator would raise, and connects readers with independent local professionals who provide free written estimates. It does not design, build, or rate contractors.
Additions are the remodeling project with the widest gap between the drawing and the buildable thing. A concept sketch can show a second story on a house whose footings cannot carry it, or a garage apartment on a lot where the city prohibits one. Addition Scope exists to put the feasibility questions first, attach a real source to every number, and help homeowners arrive at a site visit with the right questions rather than the wrong drawing.
It is also a matching service. A project submitted through the estimate request goes to independent professionals who work in your area and take addition projects. They provide written estimates; you decide whether to hire anyone. There is no fee to you and no obligation, and the pro you hire is the one responsible for the design, the permits and the work.
Where do the cost and resale figures come from?
Every statistic carries a publisher, a year and a link. Cost figures come from published national guides: HomeAdvisor's addition, bump-out and sunroom guides updated June 2026, Angi's addition and garage-ADU guides, HomeGuide's build-out versus build-up comparison, and a 2026 permitting guide from CADTRI. Resale figures come from Zonda's 2025 Cost vs. Value Report, which prices 28 projects in 119 markets and finds a midrange primary suite addition recouping 32.3%, and from the National Association of Realtors' 2025 Remodeling Impact Report.
Where a figure comes from a search snippet rather than a verified page, such as HomeGuide's second-story range or the Mortgage Bankers Association's equity study as reported by a trade publication, the page labels its year and uses it as a second data point beside a verified figure. Nothing here comes from a survey this site conducted, because it has not conducted one, and no number is presented without the scope it describes.
How is survey and government data used without overstating it?
Housing stock figures come from our own weighted analysis of EIA's 2024 Residential Energy Consumption Survey microdata: 47.6% of homes have an attic, only 14.4% of those attics are finished, and 38.6% of homes have one full bathroom, and the one-bathroom share runs 29.7 pts higher in owner-occupied houses built before 1990 than in newer ones. Those describe installed stock, not projects. Demographic figures come from Pew Research and AARP, each with its survey year and sample. Market figures come from NAHB, AIA and Harvard's Joint Center for Housing Studies, which reports that owners 65 and over now account for 27% of improvement spending.
ADU figures are treated with particular care because they are regional. California's permit counts come from the state housing department and describe California. FHFA's appraisal comparison describes California properties. Freddie Mac's listing analysis is national but concentrated in four states. When Houzz reports that 10% of renovating homeowners built an addition, or that secured loans fund 18% of large renovations, that describes Houzz's sample. The distinction between a platform sample and the population is kept on every page.
What does Addition Scope not do?
It does not design, engineer or build. It does not hold a contractor's license or an architect's registration, carry construction insurance, or employ crews. It does not rank contractors, publish star ratings, collect testimonials or promise outcomes. It does not accept payment to recommend one professional over another. When a page says the pro you hire is responsible for the stamped drawings, the permit and the warranty, that is a description of how the arrangement works.
What it does is prepare you. The service pages explain the three routes, the calculator gives a first budget by route, the comparisons weigh build-out against build-up and conversion against new build, the quiz tests planning readiness, and the polls show what other homeowners weighed. If the reading persuades you that an attic conversion beats the second story you had in mind, the site has done its job.
How does the professional matching work?
You describe the project: the space need, the route you are considering, the parts of the house you want to keep, documents such as a survey or plans, and your location. That description goes to independent professionals in your area who take addition work, which may include design-build firms, general contractors and, for structural questions, engineers. They contact you to schedule a visit and provide a written estimate. You compare, using the checklists on this site, and hire one, none or someone else.
The homeowners who get the most from it arrive with a packet: the survey or plat, any original plans, photos of the foundation, the panel and the roof, a sketch of the room list, and a written statement of the everyday problem the addition solves. That packet lets each pro price the same scope and raise the same feasibility questions. The contact page lists everything to include; the reviews page explains how to check who responds.
How are trade-offs decided when sources disagree?
By scope first and date second. When HomeAdvisor and HomeGuide disagree on second-story cost per square foot, the pages show both and explain that structural outcome and regional labor account for the gap. When Zonda's resale figures and NAR's Realtor estimates differ for a primary suite, both appear with their methods named. Verified pages outrank snippets, government sources outrank cost guides on anything about rules, and every code or zoning statement ends with a reminder that the local jurisdiction decides.
Where evidence is thin, the pages say so. There is no national cost guide for temporary housing during a second story or for utility connection fees on a detached ADU, so those lines give a range. Survey behavior is reported as measured: TD Bank found 74% of recent buyers plan to stay at least two more years, which describes that group, not everyone. Showing the limit of what is known is what separates a planning resource from a sales page, and it is the standard every page here is held to.
How is the content kept current?
Cost guides revise several times a year, and the pages record each guide's update date so you can judge whether a figure is current. ADU rules change quickly at the state level; the pages describe the pattern and point you to the planning department for the rule in force. Survey data is used only for the period it covers. When a source is revised, the number and its date are revised together rather than leaving an old figure under a new year, and snippets are replaced with verified pages as they become available.
Services we match
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.
Homeowner polls
What other planners are choosing
About Addition Scope: common questions
Is Addition Scope a contractor, an architect or a lead-generation site?
It is a planning resource that also matches homeowners with independent local professionals. It does not design or build. The matching is free and carries no obligation; professionals receive your description and provide written estimates. Every page is written to be useful whether or not you request an estimate, which is why the cost, resale and feasibility content is sourced and dated rather than written as a pitch.
Are the matched professionals licensed and vetted?
They are independent businesses that have asked to receive addition projects in their service area. Addition Scope does not license, insure, rank or rate them and publishes no ratings or testimonials. You are responsible for checking licensing, insurance, references and, for structural work, the engineer's registration; the reviews page explains how. Treat each estimate as one bid among several and compare on scope using the service-page checklists.
Why do the cost figures on this site differ from what my neighbor paid?
Because national guides describe a mix of projects and your neighbor built one specific one, in one market, with one structural outcome. HomeAdvisor's $51,000 average covers bump-outs and suites alike; Zonda's $170,517 primary suite is a defined specification. Regional labor, the foundation verdict, the extent of existing-house changes and finish level can move a project by a factor of two. The pages name the scope beside each number so you can match it to yours.
Does Addition Scope earn money if I hire someone?
The matching service supports the site and is free to homeowners. That does not change what the pages say: costs come from published guides, resale figures from Zonda and NAR, demographics from Pew and AARP, all linked. No professional pays to be recommended ahead of another and no page tells you whom to hire. The advice to get the engineer's verdict before the concept drawing is the same whether you hire through the site or not.
Can I use this site if I plan to act as my own general contractor?
Yes. The feasibility sequence, structural questions, permitting steps and proposal checklists apply regardless of who manages the trades. Owner-builders still need stamped drawings, an engineer for structural work and every inspection. The pages note which tasks require licensed trades in most jurisdictions. If you later want a professional for one phase, such as the foundation or the roof tie-in, the estimate request can be limited to that phase.
How should I report an error in a statistic?
Use the contact page and name the page, the figure and the source you believe is correct. Every number links to its publisher, so the check is quick. Corrections update both the figure and its date. Figures from search snippets are labeled and are the first to be replaced when a verified page is available.
Does the site cover additions outside the United States?
No. Costs, codes, zoning patterns and survey data are U.S. sources, and the ADU discussion reflects U.S. state and local rules; the term itself varies elsewhere. Readers outside the U.S. may find the sequencing and structural sections useful, but the numbers should not be converted or assumed to apply, and planning routes differ by country.
Keep exploring
LocationsRegional planning notesHow climate, codes and prices change a project across U.S. regions.
ArticlesPlanning articlesCost guides, checklists and mistakes to avoid before you sign.
ReviewsHow to read reviewsWhat genuine contractor reviews look like and what they leave out.
Ready to price your home additions?
Tell us the size, the condition of what is there now, and what you want to change. Addition Scope passes your request to independent local professionals, who reply with written, no-obligation estimates. The service is free to use.