For the first time, three projects investors ask about constantly were priced in 2025 (a basement remodel, an accessory dwelling unit, and rooftop solar), according to the Remodeling 2025 Cost vs. Value Report (www.costvsvalue.com), which added all three that year. All three have a story, and the story is different for each.
The numbers
National averages, with job costs from Verisk XactRemodel and resale estimates from real estate professionals in 119 markets: a basement remodel costs $52,012 and adds an estimated $36,905 at resale, 71.0% of the cost recouped, 14th of the 28 projects in the report. An accessory dwelling unit costs $166,406 and adds $68,656, or 41.3%, 23rd of 28. A solar power installation costs $55,937 and adds $16,625, or 29.7%, 27th of 28. The complete tables are free at www.costvsvalue.com.
Solar is the second-lowest project in the entire report. Only an upscale primary-suite addition ($351,613 in, $63,136 back) ranks below it.
The basement: the one number two reports agree on
The Cost vs. Value Report's real estate professionals put a basement remodel at 71.0%. NAR's 2025 Remodeling Impact Report, using a different cost source and a survey of 4,005 Realtors, puts a basement conversion to living area at 71%. Two methods, same answer, which is unusual enough to trust.
Whether a basement is expected at all is regional, and the trend is away from it. Full or partial basements were under 36% of new single-family homes completed in 1971 and 16% in 2025, while slab foundations went from 38% to 75%, according to the Census Bureau's Survey of Construction. Our reading: a finished basement is worth most where basements are normal, because that is where buyers price the square footage, and it is a rarity buyers may not price at all where new homes sit on slabs.
Chart: type of foundation, new single-family houses completed, share of all completions, 1971 to 2025. Source: U.S. Census Bureau, Characteristics of New Housing, Survey of Construction, retrieved October 2026.
For a rental owner, though, 71% is the wrong number to stop at. The Cost vs. Value Report measures what a buyer pays for the finished space. A landlord's return on a basement is rent, and neither report measures rent.
That means the honest way to evaluate a basement on a rental is your own math, not a national ratio:
Payback in years = project cost ÷ annual net rent the space adds.
The report's national cost is a fair starting point: $52,012. The rent side has to be local: your market, your unit, and whether the space can legally be rented as a separate unit at all. As an illustration only: if a finished basement adds $900 a month net, that is $10,800 a year and a 4.8-year payback before any resale value is counted. At $500 a month, it is 8.7 years. Neither figure is a forecast; they are the formula with two hypothetical rents plugged in.
One more thing the ratio cannot see: a basement rented as a separate unit generally needs egress, ceiling height and permits that a family-room finish does not. Those requirements vary by jurisdiction and change the cost. Check them before the quote, not after.
The ADU: 41% at resale, and resale is not the point
An accessory dwelling unit is the most expensive of the three at $166,406 and recovers 41.3% of that at sale in the Cost vs. Value Report's estimate. On resale alone, it is a losing project.
Nobody builds an ADU for resale alone. The case is rent, and the same payback formula applies with a larger numerator: $166,406 divided by the unit's annual net rent. At a hypothetical $1,500 a month net, that is $18,000 a year and 9.2 years to payback, again an illustration, not a projection. Whether that is a good decision depends on numbers this article cannot know: your land, your zoning, your construction quotes, and your local rents.
What the data does settle: if you are counting on the ADU's resale value to carry the decision, the report's professionals say it carries less than half.
Solar: two datasets, two answers
This is the one that confuses people, so it is worth slowing down.
The Cost vs. Value Report asks real estate professionals how much a newly installed solar system adds to resale value. Their answer: $16,625 on a $55,937 system, or 29.7%. The Journal of Light Construction's review of the regional data puts the range at 24.6% to 40.7%.
Zillow 2019 asked a different question. It compared the sale prices of homes that already had solar to similar homes without it, controlling for bedrooms, bathrooms, square footage, age and location, over March 2018 through February 2019. Homes with solar sold for 4.1% more: $9,274 on the median home at the time, and as much as 5.4% ($23,989) in the New York metro. Zillow's own caveat: solar homes "may benefit from other features that are hard to measure yet valuable," so some of that premium may not be the panels.
Both can be true. A buyer may pay a few percent more for a house that has solar and still not pay anything close to the cost of installing it. On a $334,141 home, Zillow's typical value in 2022, a 4.1% premium is about $13,700, which is in the same neighborhood as the Cost vs. Value Report's $16,625. The two studies are measuring the same modest premium from two directions; neither one comes near the $55,937 installed cost.
For a landlord the resale premium is close to irrelevant anyway. The return on solar is the electricity bill, and it only accrues to the owner if the owner pays that bill. On a rental where tenants pay utilities, the owner funds the system and the tenant collects the savings unless the lease is written otherwise. No dataset here measures that; it is arithmetic on your own utility structure.
What to do with this, by situation
Buy-and-hold owner, considering a basement unit. Run the payback formula with your local rent and a permitted-unit quote, not the report's national figure. The 71% resale recovery is a floor under the decision, not the reason for it.
Considering an ADU. Same formula, bigger numbers, longer payback. Treat the 41% resale figure as what you get back if you have to sell before the rent has paid it off.
Considering solar. On a primary home you occupy, the case is the bill, not the resale, and the resale is a modest premium in both datasets. On a rental where the tenant pays utilities, the case has to be made in the lease, or there is no case.
The rule
The three newest projects in the report are all bets on income or savings, not on resale. The Cost vs. Value Report tells you what a buyer pays for them. Only your own rent roll and utility bill can tell you the rest.
How the exterior affects vacancy is in Curb Appeal and Vacancy. The pattern across the full 2025 ranking is in The 2025 Renovation ROI Rankings, and the complete ranking is free at www.costvsvalue.com.