Can you build a guest house or accessory dwelling on a Flower Mound lot?

Only on a few of them. Flower Mound treats a detached guest house with its own sleeping, cooking, and bathroom space as an accessory dwelling, and the Town's zoning code allows one only by Specific Use Permit, only on a lot of at least two acres, and only in the Agricultural, SF-E estate, or a Planned Development district that names it. It cannot be rented, short-term or long-term (a rule the Town added March 3, 2025), it must share the main house's utility meter, and it is capped at 50 percent of the primary home's habitable floor area or 2,000 square feet, whichever is smaller. On a standard subdivision lot, what you can build is an accessory building without living quarters, and a deed restriction or HOA can say no to either one.

That is a lot of "only." Here is how each layer works, and how to verify a specific lot before you write an offer on it.

What Flower Mound actually allows, and where

The Town draws a hard line between two things most people lump together as "a casita out back."

An accessory building is a detached structure with no permanent provisions for sleeping, cooking, and sanitation. A workshop, a pool house with a half bath, a studio, a detached garage. Those are permitted by right in every residential district, subject to the size, height, and setback rules in Sec. 98-1032 of the Town code. We covered those caps in detail in the post on what a 3-car garage or shop is worth in Flower Mound: a combined 750 square feet or 25 percent of the main house's floor area on a standard lot, 1,500 square feet in SF-E estate zoning, no more than two accessory buildings per lot.

An accessory dwelling is different. Sec. 98-2 of the code defines it as a dwelling unit accessory to the primary single-family use, "with permanent provisions for sleeping, cooking, and sanitation, located in a separate building on the same lot as the primary structure." The moment a detached structure has a bedroom, a kitchen, and a bathroom, it is an accessory dwelling, whatever you call it on the plans.

And the Town's schedule of use regulations (Sec. 98-952) lists accessory dwellings with an "S" in exactly three columns: A (Agricultural), SF-E (Single-Family Estate), and PD (Planned Development). An "S" means the use is allowed only after the Town Council approves a Specific Use Permit. Every other single-family district on that table, SF-30, SF-15, SF-10, and SF-5, is blank. Blank means not permitted at all.

The nine conditions in Sec. 98-983

Even with the right zoning, an accessory dwelling has to meet all of the conditions in Sec. 98-983 of the Town code. The ones that decide most projects:

• Two acres minimum. "An accessory dwelling shall not be located on any lot/tract of less than two acres." SF-E zoning only requires a one-acre lot, so plenty of estate lots on the west side qualify for the district and still fail this test.
• One per lot, in a separate structure from the main house.
• No rentals, including short-term rentals. This condition was added by Ordinance 11-25, adopted March 3, 2025. If the plan was to build a guest house and list it on Airbnb, or lease it to cover the construction loan, Flower Mound closed that door last year.
• Same utility meter as the primary dwelling, and building materials and architecture "similar to or in concert with" the main house.
• Size cap: habitable floor area no more than 50 percent of the primary home's habitable floor area, and never more than 2,000 square feet.
• Placement: same side and rear setbacks as the main house, and the front wall of the accessory dwelling has to sit at least ten feet behind the rear wall of the primary home.
• Lot coverage: main house plus accessory dwelling plus any other accessory buildings cannot exceed the district's maximum lot coverage, which is 25 percent in both A and SF-E.

Notice what that list does to the math on a two-acre estate lot with a 4,500-square-foot home. The accessory dwelling is capped at 2,000 square feet (50 percent would be 2,250, so the hard cap governs). A two-acre lot is 87,120 square feet, and 25 percent coverage is 21,780 square feet, so coverage is rarely the binding constraint out west. The two-acre floor and the rental ban are.

Why the rules are this tight, and why they are not changing soon

If you have read that Texas was about to legalize ADUs statewide, that was Senate Bill 673 in the 2025 session. It passed the Senate 31 to 0 in April 2025 and would have forced cities to allow an accessory dwelling of at least 800 square feet on every single-family lot. Flower Mound's leadership testified against it, telling lawmakers that roughly 7,000 potential ADUs would strain the Town's water, sewer, roads, police, and fire capacity. The bill reached the House calendar in late May and died there when the session ended.

Two things matter for a buyer in that story. First, even the state bill would not have overridden HOA covenants or deed restrictions that prohibit accessory dwellings. Second, the Legislature does not meet again in regular session until January 2027, so the rules above are the rules you are buying under for at least the next year and a half.

The three layers a buyer has to clear

I walk clients through this in a specific order, because each layer can kill the project on its own and the cheapest checks come first.

Layer 1: Zoning, and it costs $25 to be sure

Start with the Town's GIS zoning map at flowermound.gov. If the lot is anything other than A, SF-E, or a PD, stop. There is no variance path around a use that is not on the table for that district.

If the lot is in a Planned Development, which covers a large share of Flower Mound subdivisions built since the 1990s, the PD ordinance itself governs. Some PDs adopt SF-E standards and inherit the SUP path; many adopt SF-10 or SF-15 standards and never mention accessory dwellings at all. Do not guess. The Town issues a zoning verification letter for $25 (Appendix A of the Code), and for a purchase this size that is the best twenty-five dollars you will spend.

Layer 2: The Specific Use Permit is a public hearing, not a form

Right zoning and two-plus acres gets you the right to apply. It does not get you the permit. An SUP is a rezoning action:

• Application fee: $625 for an accessory dwelling SUP, plus legal notification fees (on-site signs at $200 each, $2.50 per mailed notice, $40 per newspaper notice), plus a $500 plan review deposit applied toward the total.
• Submittal: survey, zoning exhibit, conceptual site plan, landscape plan, color elevations, metes and bounds, a letter of intent, a property owner consent letter, and a current tax certificate showing taxes paid.
• Notice: every property owner within 200 feet gets a mailed notice, signs go up on the frontage, and the hearing is published in the newspaper.
• Hearings: the Planning and Zoning Commission hears it first, then Town Council votes. Both are public, and your neighbors can speak.

Council can approve, deny, or approve with conditions. Nothing in the code obligates a yes. If you are buying a property specifically to add a guest house, the honest way to write that into a contract is with an option period long enough to pull the zoning letter and talk to Planning Services (972-874-6350) about the lot's fit, not by assuming the SUP is a formality. Our post on how the option period works when buying in Flower Mound covers how to size that window.

Layer 3: Deed restrictions and the HOA, which the Town will not check for you

This is the layer that catches people who did everything else right. The Town's own accessory building packet says it plainly: approval by the Town "does not constitute approval to violate any deed restriction," and the Town does not enforce HOA requirements. A subdivision's covenants can prohibit any second dwelling, cap outbuildings below the Town's limits, require architectural review, or ban the very materials you planned on.

You find those rules in two places. The title commitment's Schedule B lists the recorded restrictions and easements that will survive closing, and the HOA resale certificate package includes the current covenants and any architectural guidelines. Read both before the option period ends. And if avoiding an HOA entirely is the point, the Flower Mound neighborhoods with no HOA still carry recorded deed restrictions in many cases, so "no HOA" is not the same as "no rules."

Three more practical checks belong in the same window:

• Easements. Accessory buildings cannot sit inside any easement, and drainage or utility easements on estate lots are often wider than buyers expect. That is one of the reasons we argue for a fresh survey when buying in Flower Mound rather than relying on a T-47.
• Septic. Many two-acre-plus lots on the west side are on an on-site sewage facility, and any accessory building on a septic lot needs approval from the Town's Environmental Health Division. A second dwelling may mean a larger system.
• Trees. Flower Mound's tree preservation rules apply to the footprint, and mitigation on a wooded estate lot can be a real line item.

What it costs, and what it does to value and financing

A detached guest house is a small custom home. National 2026 cost surveys put a custom-built structure at roughly $150 to $250 per square foot, or about $90,000 to $150,000 for a 600-square-foot unit and $150,000 to $250,000 at 1,000 square feet, before the Flower Mound-specific items: an engineered foundation and engineered grading and drainage plan for anything over 500 square feet, masonry that matches the main house on anything over 300 square feet, and the SUP costs above. A full kitchen alone runs $25,000 to $45,000 in those same surveys. Treat all of that as a starting range and get local bids; costs in the estate areas of 75022 run above national averages.

On the value side, be clear-eyed about what you are buying:

• It will not pay for itself in rent, because it cannot be rented. Any online calculator that adds rental income to justify the build does not apply here.
• Financing treats it as one extra unit, and only one. Fannie Mae allows a single ADU on a one-unit property; a lot with two is ineligible for conventional financing. Because Flower Mound bars rental use, the rental-income underwriting some lenders offer for ADUs does not help you qualify either.
• Appraisers value it on comparable sales, and there are few closed sales of two-acre Flower Mound homes with permitted accessory dwellings in any given year. Expect the contributory value to land below cost. That is normal for this kind of improvement; it is a lifestyle purchase that also adds some value, not an investment with a payback period.
• Unpermitted is worse than none. A guest house built without the SUP, or a "workshop" that quietly acquired a kitchen, is a disclosure problem, an insurance problem, and a resale problem. We covered how buyers should handle an unpermitted addition in Flower Mound, and the same logic applies with more force to a whole second structure.

Where it does make sense is exactly the buyer this blog is written for: a family planning to be in the house for a long time, on an estate lot that already clears two acres, who wants a separate living space for guests, a relative, or a home office and is willing to pay for it as part of how they live. For that buyer, buying the right lot is the whole game, and the checks above are how you confirm it before you are committed.

Frequently Asked Questions

Can I build a casita or guest house on a regular Flower Mound subdivision lot?

Not one with a kitchen, bedroom, and bath. Flower Mound's use schedule permits accessory dwellings only by Specific Use Permit in the A, SF-E, and PD districts, and Sec. 98-983 requires a lot of at least two acres. A standard SF-10, SF-15, or SF-30 lot can have a detached accessory building without living quarters, subject to the 750-square-foot combined cap and HOA rules.

Can I rent out an accessory dwelling in Flower Mound?

No. Ordinance 11-25, adopted March 3, 2025, added a condition to Sec. 98-983 that accessory dwellings "shall not be used as rental units, including short-term rentals." The unit also has to run on the same utility meter as the main house, which reinforces that it is part of one household, not a separate tenancy.

How big can an accessory dwelling be in Flower Mound?

Habitable floor area is limited to 50 percent of the primary home's habitable floor area, with a hard maximum of 2,000 square feet, whichever is smaller. The combined footprint of the main house, the accessory dwelling, and any other outbuildings also cannot exceed the district's 25 percent lot coverage limit.

What does the Specific Use Permit cost and how long does it take?

The application fee is $625 plus legal notification costs (signs, mailed notices to owners within 200 feet, and newspaper notices) and a $500 plan review deposit that applies toward the total. The request goes through a Planning and Zoning Commission hearing and then a Town Council vote, so plan on a multi-month process with no guaranteed outcome.

Does an HOA or deed restriction override the Town's rules?

Yes, in practice. The Town does not enforce HOA covenants and states that its approvals do not authorize violating a deed restriction. Recorded restrictions on the title commitment's Schedule B and the HOA's governing documents can prohibit a second dwelling entirely, even on a lot the Town would permit.

The lot decides the answer

In Flower Mound, whether you can build a guest house is settled by the lot before it is settled by the budget: zoning district, acreage, the Specific Use Permit, and the deed restrictions all have to line up, and any one of them can be a no. The good news is that every one of those checks can be run during an option period for a few hundred dollars, which is a small price against a six-figure build.

If a separate living space is part of the plan for your next home, that belongs in the search criteria from day one, not as a surprise after closing. Schedule a free Move-Up Strategy Call ... thirty minutes, no pitch, just a clear-headed look at where you are and what your best next move looks like.

This article is general information, not legal, tax, insurance, or lending advice. Zoning and fee figures are from the Town of Flower Mound Code of Ordinances as codified through May 2026; verify the current text and your specific lot with the Town's Planning Services, your title company, your lender, and where appropriate a licensed Texas attorney.

About Brian White

Brian White helps families in Northwest DFW make their move-up cleanly, selling and buying in one synchronized step. He built BlueFuse Group on a simple standard: other-first service, proactive at every turn, faith and excellence in equal measure. Brian has been married to Tisha for 27 years and is dad to three adult sons. When he's not protecting a family's equity or untangling a tight closing timeline, you'll find him chasing a round of golf or at Valley Creek Church.

Schedule a Move-Up Strategy Call ... no pitch, just a clear-headed look at your next move.