Minimum setback requirements established by The Texas Commission on Environmental Equality (TCEQ) usually prevent initial house construction from occurring over any point of a septic system. These setback requirements include distances from the septic tank and the drainfield from foundations, pools, property lines, water wells, etc.
Some homeowners, whether accidentally or deliberately, build items like patio decks or home extensions over their systems. This can lead to greater expenses when finding and servicing the system.
It is never recommended to build a structure over any portion of your septic system. The most common problem we see is when someone wants to pump out their septic tank but doesn’t know where their tank is located.
It is not uncommon for us to find tanks located under a wooden deck, pool patio, driveways, or even room additions. Most of the time, this happens because the homeowner is unaware of the tank location and/or does not plan for future maintenance on their tank.
Sometimes a homeowner may make removable boards or trap doors that lead under a deck to their septic tank lid for access to pump the tank. No permanent structures should be built over any portion of the system, but at least in this case the homeowner can pump out their septic tank.
The drainfield works by absorbing water in the solids and some evapotranspiration. The soil beneath the drainfield needs oxygen so that the microbes in the soil can treat the effluent from the drainfield. However, if a permanent structure is built over a drainfield it can restrict the oxygen flow into the soil and restrict the evapotranspiration process.
A big risk to building over the drainfield is causing the lines to collapse. Also, the soil can compact around the trenches, which may not allow for percolation. Repairing the drainfield or moving it may require an entirely new system depending on your system age and the regulations for your local authority.