Septic System Plumbing
Capacity and permits before anything is designed.
About this serviceGreater Austin
Guest casitas and small second dwellings go up all over this part of Hays County, and the plumbing decisions get made late, usually after the slab is poured. Three of them determine what the whole project costs.
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Out here the limiting factor is almost never the water. It is what the on-site sewage system was permitted to handle, and adding a dwelling adds bedrooms to a system designed around the main house.
Sometimes there is capacity and the existing system can take the connection. Sometimes the answer is an expanded field, a second system, or a different location entirely because of setbacks from wells, boundaries and the existing field. All of that is a county permitting question and it has a lead time.
Establish it first. A casita designed and priced without that answer is a design that may need moving, and moving the building is more expensive than moving the drawing.
The simple route is a branch off the existing service with an isolating valve at the new building, so the casita can be worked on without shutting the main house down. That valve is not optional in practice: without it every future repair affects both dwellings.
Check the existing service will carry it. A line sized for one house feeding two, with a long run out to the second, can leave the casita with poor pressure whenever the main house is busy. Measuring what the service actually delivers before committing is a short job.
A separate meter is a different decision and it is mostly about renting. If the unit will be let, a submeter lets usage be attributed without arguments, though whether a second utility meter is available depends on the supplier and on whether the property can be served that way at all. Ask before assuming, since it affects where the plumbing goes.
The building also needs its own hot water, and a small unit near the fixtures nearly always beats running hot water from the main house across a garden.
A unit on wheels is plumbed like an RV: flexible connections, a hose-fed supply and a sewer connection that has to be sealed and fall continuously. It is also freeze-vulnerable in a way a permanent building is not, because everything runs under the floor in open air.
A unit on a slab is plumbed like a house: buried supply, a drain tied into the system at a proper depth, and rough-in that has to be right before the concrete goes down. That costs more at the start and is far less trouble afterwards.
Whichever it is, the decision belongs early. Converting a wheeled unit to permanent connections later means excavation that could have been done in one pass while the ground was already open.
We plan and plumb second dwellings around Driftwood, Wimberley, Dripping Springs and Buda, and we would much rather be involved before the pad is set than after.
FAQ
That depends on what it was permitted for and what capacity it has left. It is a county question with a lead time, and it should be answered before the building is designed rather than after.
Only if you want usage attributed separately, which mostly matters if the unit will be rented. Whether a second meter is even available depends on the supplier, so ask before planning around it.
Measure the existing service before committing. A line sized for one house can leave a second building weak whenever the main house is drawing water, and the fix is much cheaper before the trench is closed.
Nearly always. A small unit at the fixtures beats running hot water underground from the main house, which loses heat, wastes water and gives a long wait at the tap.
Simpler on the day and more trouble afterwards. It is plumbed like an RV, with flexible connections and real freeze exposure under the floor. A permanent connection costs more up front and behaves like a house.
Find out what the sewage permit allows, then measure the water service, then design. Those two answers shape the location, the cost and sometimes whether the project works at all.
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Capacity and permits before anything is designed.
About this serviceExtending a service that was sized for one house.
About this serviceA small unit at the fixtures rather than a long run.
About this serviceConnections under a wheeled unit in open air.
About this serviceTwo dwellings drawing on one service.
About this serviceHays County call outs at any hour.
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Septic capacity first, water service second, drawings third. That order saves the most money.
Talk through a second dwelling