Fixed-Price or Cost-Plus? The Orlando ADU Contract Choice That Decides Who Eats the Overruns

What those two words actually cost you

Strip out the jargon and it's simple. A fixed-price contract is one number for the finished ADU. If the job runs long, if lumber jumps, if the crew hits that pipe, the builder absorbs it. You already agreed on the price, so the surprises are theirs to swallow.

Cost-plus flips it. You pay whatever the job actually costs — materials, labor, subs — and then a fee on top for the builder. The good part is you see every receipt. The catch is that every one of those surprises lands on your side of the ledger, not theirs.

Here's the part that trips people up. You get two quotes for the same backyard unit, one clearly lower, and you lean toward the cheaper one. But the lower quote is very often the cost-plus one — and it's the only one of the two where the final number can still move on you. The higher fixed-price quote already has the builder's what-if cushion baked in. You're not paying more. You're paying to stop guessing.

Why cost-plus starts cheap and doesn't always stay that way

The builder's fee on cost-plus is usually a slice of the total — call it something like a quarter of every dollar the job spends. Sit with that for a second. The tile order that runs three grand over doesn't just cost you the three grand. It nudges the builder's cut up too. The more the whole thing costs, the more they earn. Nobody's twirling a mustache. It's just what the math quietly rewards.

Then there are allowances — placeholder numbers your contract drops in for things you haven't picked yet, like flooring or fixtures. Homeowners always ask the same thing: if I come in under, do I get the difference? Generally, yes. Go over, and you cover the gap. The real trouble is timing. The change order for that gap tends to show up after the floor's already down — when saying no isn't really a choice anymore.

That's the whole risk in one sentence. A lean cost-plus bid can win the job on paper and then rebuild its margin one change order at a time, each carrying the fee. None of that means cost-plus is a trap. It means the low number on the page isn't a promise. It's a starting line.

The third box nobody points to, and the lines worth reading

There's a middle option most people never hear pitched: a guaranteed maximum price. It's cost-plus with a ceiling. You still see every receipt and still pay real costs plus the fee — but the builder names a number the total can't cross. Go over the cap, and that overage is theirs, not yours. Come in under, and a lot of these deals split the savings with you. It's the closest thing to having both the open books and the guardrail.

Whichever way you go, a few contract lines carry more weight than the big number on the front page. On cost-plus, who picks the subcontractors — you, or only the builder's usual crew? How does a change order get priced, and does it need your signature before the work happens or after? How thin are the allowances — are they realistic guesses, or lowball placeholders designed to make the total look smaller than it'll ever be?

Ask those before you sign, not when the crew's already standing in your yard. The contract type sets the rules of the game. Those lines decide whether the rules are actually fair.

First figure out if the backyard even says yes

Here's the thing, though. The contract question only matters once you know an ADU fits your lot at all — and in Central Florida that's not a given. A parcel in unincorporated Orange County, out toward Rio Pinar or Meadow Woods, plays by county rules. A lot inside a city like Winter Garden follows that city's code instead. Setbacks, septic, lot coverage, and whether the place is your homesteaded primary residence all decide the shape of what you can build before a single dollar figure enters the conversation.

The county's Ready Set Orange program is worth knowing here: for owner-occupied lots in unincorporated Orange County, it offers a handful of pre-drawn ADU plans and step-by-step permitting help, no plan fee. It smooths the paperwork. It doesn't tell you whether your Azalea Park or Pine Hills backyard has room, or which contract keeps the surprises off your tab.

That's what the ADU Fit Check is for. Answer a few questions about your lot and what you're picturing, and you'll see whether a backyard unit actually pencils out on your property before you're deep in quotes and contract fine print. Start with the fit, then argue about fixed-price versus cost-plus. Not the other way around.

Common questions

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