ADU Construction in Katy, TX

On a Katy master-planned lot, the yard behind a two-story house usually has room for one of these but not all three, and the fence line decides which. A detached casita wants a corner of the yard with a clear path from a gate or the side yard, its own small slab, and enough separation from the house to satisfy fire spacing and the HOA's sense of a single-family street. An apartment over a detached garage uses no additional footprint, which is why it clears review more often in Cinco Ranch and Firethorne. An attached wing shares the house's roof and utilities but gives the least independence of the three.

Garage conversion is the fourth option and the one we raise early. Most Katy homes have an attached two-car garage on a slab that already has power and is already inside the building envelope. Converting it adds no footprint, involves no new roof, and rarely triggers the setback or lot coverage questions a detached structure does. The trade is losing covered parking and the garage door, which some HOAs will not allow to be removed from the street face. If the family needs real separation, a detached unit is worth the harder review. If the goal is a livable suite for a parent within a few years, the conversion usually wins.

Katy's master-planned sections each carry their own deed restrictions, and the committee reading your ADU submittal is checking it against those, not against a general idea of what is reasonable. The things they generally weigh are how much of the lot is already covered by roof and concrete, the distance from the new structure to each property line, the height and whether it can see into a neighbor's yard, the materials and roof pitch relative to the main house, and whether the unit could be rented separately. We never quote a rule from memory because each section's numbers differ, and some have been amended. We pull the current guidelines for your address first.

Underneath the HOA sits the permitting body. City of Katy permits apply only inside city limits, and most of the greater Katy area is unincorporated, so the permit usually runs through Harris, Fort Bend, or Waller County with MUD review on top. That layer looks at the structure, the plumbing and electrical, and often at whether a separate utility connection is required for a unit with its own kitchen. The MUD may treat a second dwelling as a second tap. Knowing whether separate metering will be required changes the design and the cost, so we ask that question of the district before the plans are finished, not when the inspector shows up.

A detached ADU on a Katy lot sits on the same expansive clay the main house does, and it needs a foundation designed for it rather than a thickened patio pad. For a single-story casita that usually means a post-tensioned or conventionally reinforced slab with grade beams, sized by an engineer from a soil report or from the geotechnical data used for the subdivision. Over-garage apartments change the structure more than the foundation: the garage slab and footings have to carry a second floor, and if the existing garage was built for a single story it often makes more sense to rebuild the garage than to reinforce it piece by piece.

Framing follows the same wind and moisture logic as the main house. Gulf Coast wind loads shape how roofs are strapped and how sheathing is nailed, and a small building gets no exemption from that. The envelope matters more on a small structure because there is less mass to buffer heat: a well-insulated attic, a real vapor strategy on the walls, and windows placed for cross-ventilation make a casita comfortable on its own small air conditioner. Roof pitch and brick or siding get matched to the house not only for the HOA but because a mismatched outbuilding lowers the value of the whole property when it is time to sell.

The main house in a Katy subdivision was built with its sewer tap, water line, and electrical service sized for one dwelling. Adding a full kitchen and bath fifty feet away means trenching from the house or the street, and the choice between them is partly cost and partly policy. Extending from the house is simpler when the district allows it and the main panel has capacity, and many panels do not have much spare after a pool and an outdoor kitchen. A separate service and meter is required in some districts for a rentable unit and is worth having for a family member who wants their own bill. We confirm before trenching.

Sewer is the line that dictates placement. Gravity drain needs fall, and on Katy's flat lots a casita at the back corner may sit lower than the house's sewer connection, which means a small ejector pump or a different location. Gas is optional in a small unit and often skipped in favor of an electric range and a heat pump, which also removes a review item. Inside, the kitchen and bath are compact versions of the same work we do in the main house: waterproofing behind the tile, a properly vented bath fan, a range hood that exhausts outside, and a water heater sized for one or two people rather than a family.

The floor plan changes with the answer. A unit for aging parents wants a zero-step entry, a curbless shower, a bedroom on the same level as everything else, wider doorways, and a path to the main house that works at night and in rain. It may not need a full kitchen if meals happen in the main house, and dropping the range can simplify the utility and review side. A unit for an adult child home for a while wants a real kitchen, a door that closes, and enough sound separation that two households can keep different hours. Both are common reasons Katy families build these, and both fit on a master-planned lot.

A rental unit has to satisfy people you have not met yet, and it has to satisfy the HOA's position on leasing, which in many Katy sections is the first question to settle. Design for a tenant means a separate entrance that does not pass through the family's yard, its own parking space that does not block the driveway, separate metering, and finishes that hold up to turnover. Privacy runs both directions: the family does not want a stranger's windows facing the pool, and the tenant does not want to feel watched. Fence lines, a dedicated gate, and window placement handle most of it. We draw the site plan with those sightlines marked.