Same lot, two options: $96k garage conversion or $178k detached cottage

Studying for the license exam right now and one thing that stuck: in a neighborhood where every house has a garage, taking yours away shows up in the adjustment grid. How much depends on your market. Ask an appraiser directly, some will do a consult for a few hundred dollars.

Nine to eleven weeks on a garage conversion means fourteen to twenty. I've never seen one come in on the quoted timeline once they open the slab and find the grade is wrong for a habitable floor. Attached garages usually sit a step below the house floor and getting drainage and moisture right under a new slab is where the change orders live. Ask what happens if the slab has to be replaced instead of topped.

Your third unknown isn't an unknown, it's a document you haven't finished reading, and it's the only one of the three that can void the project.

Go to the ordinance and find the definitions section first. Most ADU ordinances define separate categories, something like "internal", "attached", and "detached", and then apply different rules to each. Size caps, setbacks, parking, and owner occupancy are frequently written per category. A converted attached garage may fall under "internal" or "attached" depending on whether the garage is inside the building envelope, and that single classification can change your maximum size and whether you must live on site. If the owner occupancy language appears in a section about something else, check whether it's a general condition of the permit rather than a rule about one category. How the ordinance applies to your specific lot is a land use question for an attorney in your state if the language is genuinely ambiguous, but the zoning administrator will usually give you a written interpretation for free if you cite the section numbers.

Then check three documents the ordinance won't mention. Your deed for restrictive covenants, any HOA declaration, and your title policy exceptions. Private covenants can prohibit a second dwelling even where zoning allows it, and the city won't tell you that when they issue the permit. I've read plenty of 1950s and 60s subdivision covenants with a one dwelling per lot clause still on the books.

Also pull your homeowners policy and read how it treats a rental unit on the premises. That's a call to your carrier, in writing, before you spend $96,000 or $178,000.

Warrant, the covenant point is the thing I'd never have thought to check. Anchor, is your neighborhood a platted subdivision or older infill? Makes a difference to whether there's a declaration at all.

Mostly out of my depth here but I'll ask the obvious one: does either number include the utility work? Separate meter, sewer connection fee, tap fees? Those are city fees and they can be five figures on their own.

Vellum asked the right thing. Tap and impact fees are the line item that shows up after the contract is signed, because the contractor's quote is for construction and the fees are yours. In some jurisdictions a detached unit triggers a full sewer connection fee and an internal conversion doesn't, since you're on the existing lateral. That could be $8,000 to $20,000 of swing between your two options and it isn't in either number as posted.

On construction: the garage conversion at $96,000 for 440 feet is $218 a foot, and the cottage at $178,000 for 700 feet is $254 a foot. Those are both credible. Conversions look cheap per foot until you price the floor, the insulation in an uninsulated shell, and a fire separation wall between the unit and your house, which many codes require on an attached unit. Ask specifically whether the quote includes rated assemblies.

Scope creep on garage conversions is a genre. My worst one: opened the wall to run plumbing and found the header over the garage door was carrying more than it should have been, and we were into a structural fix that nobody bid. Anchor, whatever you pick, hold 15% back in your own budget that the contractor never sees.

Parking is what decides it for most of my clients, and I've watched that play out for five years running a service business next to this stuff. If your street has no overnight parking and you take away the garage, you now have a tenant with a car and nowhere to put it, and that shows up as complaints and turnover, not as a line in your spreadsheet.

Who's managing it? A detached unit with its own entrance and its own meters is close to a normal rental. An attached one bedroom sharing a wall with your bedroom means you're the maintenance person and the noise complaint department at the same time.

Read the insurance angle warrant raised more carefully than the rest of this thread. Most standard homeowners forms have limits on rental activity on the premises, and some carriers will move you to a different form entirely once there's a separate dwelling unit. Get the premium change quoted before you choose, in writing. I've seen a $1,400 annual increase turn a marginal spread into nothing.

Anchor, your per-dollar comparison is comparing gross rent to construction cost, which isn't a return. Option A: $1,325 times 12 is $15,900 on $96,000, or 16.6% gross. Option B: $21,900 on $178,000, or 12.3%. Now take out the fees girder mentioned, fathom's insurance, the property tax reassessment your county will do on new construction, and 8% for vacancy and turns. The gap narrows and both drop a lot. Neither is bad. But the numbers you posted are not returns and you'll make a worse decision if you treat them as such.

Canton beat me to it. I'll add the one nobody's put in yet: your time to income. Option A produces rent in maybe four months if quarry's timeline correction is right. Option B in eight to ten. That's six months of difference, roughly $11,000 of foregone rent on the B side, plus interest if you're borrowing during construction. Add it to B's cost and B goes to about $189,000 effective. Does that change your answer? For me it wouldn't, because B's rent advantage compounds for thirty years and the six months is once. But it should be in the model.

Ledger's framing is the one I'd use. Run both to a ten year hold with a 3% rent growth assumption and a terminal value that reflects what an appraiser will actually credit, which is halyard's question. If your appraiser tells you a detached permitted unit adds $120,000 of value in your market and an internal conversion adds $40,000, the whole thing is decided and you can stop building spreadsheets. The value add is the variable with the widest range and the least data, so it's worth paying to narrow it.

Reading this whole thread as somebody still figuring out where I fit, and what strikes me is that eleven months of care produced a good post. Anchor, you're not indecisive, you're missing three inputs. Fees, insurance, appraised value.

Trades side. Check your electrical service before anything. A 440 foot unit off a subpanel is usually fine, a 700 foot two bedroom detached with its own meter often means the utility sets a new service, and that's a queue you don't control. I've watched jobs sit six weeks waiting on a meter set.

Solder, does that apply if he keeps it on one meter and bills utilities as part of rent? Or does the code force separate service on a detached unit?

Management perspective: a 440 square foot one bedroom attached to the owner's house rents to a different tenant pool than a 700 foot two bedroom cottage. The small attached unit gets singles on short horizons and turns more often. The two bedroom detached gets couples and small families who stay two or three years. Turnover cost is real money, call it a month of rent plus $800 every time. Over ten years that difference alone is worth thousands and it never shows up in the initial spread.

Trellis, that's the most useful thing in here for me personally, thanks. Anchor, sorry for the drift.

$178,000 for a permitted 700 foot two bedroom that rents at $1,850 is a number I'd take in my market and can't find. If your ordinance permits it and the covenants don't block it, I don't understand the hesitation on B other than the cash.

How are you funding it? That's still not in the post. A HELOC at a variable rate on $178,000 during an eight month build is a very different project than $178,000 of cash. If you're borrowing, price the construction period interest and put it in canton's math. There's also a Fannie Mae policy effective March 2026 that lets projected ADU income count toward qualifying on an owner-occupied purchase, capped at 30% of qualifying income, which doesn't apply to a house you already own but does matter to your resale story since a future buyer may be able to qualify partly on the unit's rent. Confirm the current terms with a lender directly rather than taking my summary of it.

Tender's resale point is the one I'd underline. If buyers can finance partly on the unit's income, the pool of buyers for a house with a permitted detached unit gets wider than it is today. That's an argument for the permitted detached build over the conversion, assuming permits and appraisal both land.

Coming back to say I'd flipped to B after reading trellis and sable. Turnover and buyer pool both point the same way, and the parking issue I raised only exists in option A.

Anchor, one last practical thing. Whichever you build, get it permitted and get the final inspection card. I own a small multifamily where a previous owner did an unpermitted basement unit and I've spent two years and about $19,000 legalizing it, and the appraiser gave me nothing for it until the certificate was issued. Unpermitted space rents fine and appraises at zero.