Kaufman County 1-Acre Septic Rule: Usable Space, Not Deed Acreage

What is the Kaufman County 1-acre rule?

The Kaufman County 1-acre rule says a lot that uses a septic system needs at least one acre of usable space. It's not one rule in one place. It shows up in four county documents, and they all point the same direction.^source

The TCEQ-approved OSSF order, Section 10(B), requires lots in platted or unplatted subdivisions served by public water but using septic, created after January 1, 1988, to have a USEABLE surface area of at least one acre (the order capitalizes the word). Section 10(C) raises that to two usable acres for new single-family lots served by individual water systems, which in practice means a private well.^source

The county's Subdivision and Land Development Regulations, Section 9.04, go further: lots served by septic shall have a minimum of one acre of usable open space, and a septic system on a lot smaller than one acre shall not be allowed, with one narrow exception for old plats covered below. The county FAQ puts it in a single line: Kaufman County requires 1 acre of usable space.^source

Kaufman County vs. Texas minimum lot size for septic

Kaufman County's minimums are double the state's. The state rule, 30 TAC 285.4(a)(1), sets 1/2 acre for new subdivision lots on a public water supply and one acre for lots without public water. Kaufman County, as a TCEQ authorized agent, adopted stricter numbers and its order says the stricter local rule takes precedence.^source

The county also added the word usable. The state rule talks about lot size. The county talks about the part of the lot that can actually hold a septic system. That one word is where most land deals go sideways.

What counts as usable space for a septic system?

Usable space is open ground that could legally hold part of a septic system. The county's subdivision rules say usable open space for septic does not include right-of-way, ponds, drainage easements, or utility easements, and a separate section adds that all ponds are excluded whether or not they sit in a drainage easement.^source

The county's definition of useable open space in the same document also leaves out rooftops, buildings, driveways, turnarounds, parking, and street right-of-way. So the house, the shop slab, and the concrete drive all come off the top.

Floodplain is the tricky one. The county definition allows floodplain areas in usable open space, but a septic site in the 100-year floodplain faces extra planning under 30 TAC 285.31(c)(2), including a plan to keep tanks from floating. Don't count on floodplain ground until your site evaluator says it works.

Worked example: when 1.5 acres isn't enough

One acre is 43,560 square feet. Here's how a lot listed at 1.5 acres off a county road can come up short once you subtract what doesn't count.^source

Say the survey shows 1.50 acres. The road right-of-way strip along the front takes 0.12 acre. A small stock pond in the back corner is 0.20 acre. A utility easement along one side is 0.10 acre. The planned 2,600 square foot house is about 0.06 acre, and the driveway and turnaround are another 0.05 acre.

That's 1.50 minus 0.53, which leaves 0.97 usable acres. Under the county's rule, that lot is short by about 1,300 square feet, and nobody noticed because the listing said 1.5 acres.

Even when a lot clears the acre, setbacks from wells, the pond, property lines, and the house still decide where the tank and spray or drain field can sit. Clearing the minimum makes a permit possible. It doesn't guarantee a clean layout.^source

Does the 1-acre rule apply to my lot?

It applies to any lot in unincorporated Kaufman County that will be served by a septic system, plus cities with an intergovernmental contract with the county. Inside cities that run their own septic program, the city decides. The county FAQ sends Terrell and Oak Ridge residents to their cities.

Timing matters. The 1-acre public water rule covers land platted or subdivided after the county's original order took effect on January 1, 1988. A lot on a plat recorded before that date is the one case where the county's subdivision rules allow a septic system on less than an acre, and only with a professional showing it's safe.^source

Adding a second system counts too. The county's OSSF application says that for parcels with an existing septic, an additional septic needs its own new address from Kaufman County 911/GIS and each septic must have one acre of usable space. That hits barndominiums, guest houses, and a second home for a parent. Our guide to septic rules for barndominiums, shops, and guest houses covers those setups.^source

• New lot, public water, created after 1/1/1988: 1 usable acre
• New single-family lot on a private well: 2 usable acres
• Old lot on a plat recorded before 1/1/1988: under 1 acre possible with a PE or RS study^source
• Second septic on the same parcel: another usable acre plus a separate address
• Inside Terrell, Oak Ridge, or another city with its own program: ask the city

How the 1-acre rule affects platting and splitting land

Splitting land to sell or give away usually counts as creating a subdivision, even without a formal plat. The state rule defines a subdivision as any division of a tract, including a metes-and-bounds deed or a contract for deed, and the county's platting rules say the same.

So carving a 1.2-acre homesite off grandpa's 20 acres with a deed doesn't get around the usable-acre rule. If that homesite will use septic and has public water, it needs a usable acre. If it will be on a well, it needs two.

The county subdivision rules state that every lot in any new subdivision using septic must be at least one net acre of usable open space. They also prohibit flag lots under two acres unless the Commissioners Court grants a variance, and they require a manufactured home rental community with more than one house per acre to use a TCEQ-approved package plant instead of individual septic systems.^source

Developers have one more step. Under 30 TAC 285.4(c), anyone proposing a subdivision that will use septic must submit planning materials prepared by a professional engineer or sanitarian, including a soil survey, floodplain map, and drainage plan, and get approval before any OSSF application. The permitting authority has 45 days to approve or deny them.^source

What to do if your lot is under one usable acre

If your lot falls short, you have a few real options and a couple of fake ones. Talk to Development Services and a site evaluator before you spend money on any of them.

The fake options are the ones that skip the permit: a system installed without approval, or a second house tied into the first system. Both surface at resale, and both can bring enforcement.^source

Before you buy a small tract in Kaufman County

Ask for the survey and plat before you fall in love with the lot. Then ask the seller and the county a short list of questions, and get a site evaluator's opinion if the numbers are close.

A soil and site evaluation usually runs $350-$700, which is cheap insurance on a lot purchase. If you're looking at acreage, our septic questions to ask before buying acreage go deeper.

• When was this lot platted or deeded off, and is the plat recorded before or after January 1, 1988?
• Is the lot on public water or will it need a well? That decides one acre or two.^source
• Where are the road right-of-way, easements, ponds, and floodplain on the survey?
• Is there already a septic on the parcel, and is it permitted?^source
• Is the parcel inside a city, or in unincorporated Kaufman County?
• Can a site evaluator confirm the usable area and a workable system location?^source

Who confirms usable area and issues the permit

In unincorporated Kaufman County, Development Services issues the OSSF permit and applies the usable-acre rules. The office is at 101 N. Houston Street in Kaufman, (469) 376-4127, and septic questions go to publicworks@kaufmancounty.net.^source

Your site evaluator and installer build the design around the usable area, and the application goes in with the soil evaluation. Our Kaufman County septic permit process page covers the full sequence, and if the lot checks out, our guide to septic system installation in Kaufman County covers cost and timing.^source