The decision to repair or reroute the sanitary piping under a home’s foundation should be based upon the following factors: whether the piping leaks under normal use or only during a hydrostatic test; whether or not the leak poses a hazard to the performance of the foundation, and to what degree; whether or not the repair of the leak poses a hazard to the performance of the foundation, and to what degree; whether or not the leak affects the performance of the piping system, for example by allowing roots to enter the system and cause back-ups; whether or not the leak will present an obstacle to the sale of the property; and whether or not the repair or reroute is affordable.
A thorough understanding of repair methods is an important prerequisite to making an informed decision to repair or replace the pipes under a residence. The three most common methods to repair underslab sanitary piping are: tunneling under the foundation, breaking through the concrete slab, and rerouting through the exterior wall and installing a new line buried around the perimeter of the structure. The type of existing piping under the foundation plays an important role in choosing a repair method. Cast-iron and concrete pipe will deteriorate over their useful life, lasting anywhere from twenty years to one-hundred and twenty years. ABS and PVC plastic pipe, when protected from fire and the harmful effects of the sun as buried piping is, will outlast virtually all the other materials used in the construction of modern homes including the concrete slab. The structural engineers and master plumbers at Vortex are uniquely qualified to give our customers, and potential customers, the knowledge needed to weigh the above factors and make informed choices.
Tunneling under the slab
In the mid 1990’s, tunneling became the most popular method to repair or replace leaking sanitary piping under Texas residences. Prior to that time, underslab sanitary piping was only replaced as part of a remodel or when it stopped draining the fixture or fixtures it serviced and could not be cleared by sewer augering (roto-rooting). Tunneling became an accepted repair procedure after underslab plumbing leaks jumped to the number one blamed cause of foundation damage and it became common to replace entire piping systems simply because they failed a hydro test.
Repairing or replacing underslab sanitary piping by tunneling starts with the excavation of an access hole adjacent to the foundation. After digging the access hole well below the bottom of the perimeter concrete gradebeam, the excavation then turns horizontal and proceeds under the foundation. The path and size of the tunnel is configured to allow plumbers to enter and replace the sanitary piping, either leaving it in the original location or rerouting it out from under the footprint of the residence and trenching a new line to connect to the city sewer main or building sewer.
The original sanitary piping is usually cut several inches beneath the bottom of the concrete slab and the new sanitary piping is connected using heavy duty couplers. The connection between the original piping and the new piping is a critical component of the new drain system and must be completed using the proper materials and techniques. The new piping must then be hung from the slab to prevent future displacement. After the new piping is installed and properly supported, a hydrostatic test is performed to insure that all of the leaks have been repaired. Finally, the tunnel is ready to be backfilled.
Backfilling the tunnel must be done in such a way as to prevent damaging the new piping. In addition, backfilling of the tunnel should be done in a way that limits the potential for the causing future foundation movement. Backfilling methods vary but commonly consist of one of the following: putting back the same soil excavated from beneath the foundation and from within the access hole; hauling off the soil excavated from beneath the foundation and backfilling with select fill or banksand, then filling the access hole with the excavated material; either of the above methods along with pumping a slurry to fill any voids left in the tunnel. Many cities, including Houston, require that the method of backfilling be specified in writing by a licensed Professional Engineer before the job passes final inspection.
The primary advantages of making underslab piping repairs by tunneling are avoiding the indoor mess associated with construction activities and the opportunity to replace large sections of older, less desirable cast-iron piping. Another advantage of making underslab plumbing repairs by tunneling is that the exact location of the leak or leaks does not need to be accurately pin-pointed because all of the piping is exposed in the tunnel. A third advantage sometimes realized in choosing to tunnel instead of break through the floor is saving the expense of replacing damaged floor coverings. The main disadvantage of making underslab piping repairs by tunneling is the high cost. The high costs are a direct result of the intense labor associated with the hand excavating, transporting and backfilling large amounts of soil.
Breaking through the slab
Breaking through concrete slabs to modify, repair or replace sanitary piping has been an accepted practice in the construction industry for as long as there’s been indoor plumbing. Many residential bathroom remodels involve the removal and replacement of concrete. Most commercial structures intended for varied retail use are constructed with the understanding that the individual lease spaces will have their slabs partially demolished and replaced almost as often as the number of times the tenant changes.
Repairing or replacing underslab sanitary piping by removing and replacing concrete begins by accurately locating the piping and the leaks. If possible, carpeting or other flooring is removed for later re-installation and attempts are made to control the mess associated with indoor residential construction activities. After the plumbing repairs are completed, a hydro test is performed before covering the work and patching the slab.
The primary advantage of making repairs to the underslab sanitary piping by breaking through the floor instead of tunneling is the enormous cost saving that can be realized in some instances. The cost savings are directly related to the amount of expensive tunneling avoided. The disadvantages of this repair method include the high level of accuracy required in pin-pointing the leaks, the indoor mess associated with construction activities, and the inability to replace large sections of piping as a preventative measure as can be done with tunneling. Oftentimes, the cost savings associated with breaking through the floor instead of tunneling are best realized on homes having ABS or PVC sanitary systems instead of the older cast-iron systems where replacing a majority of the piping has long-term preventative benefits.
Rerouting through the exterior wall
A third method of eliminating leaks on the sanitary piping under residences if to reroute the drain through an exterior wall and install a new sewer line by trenching around the perimeter of the structure. This procedure abandons the original drain by disconnecting it from the active piping. However, through wall reroutes can only be utilized with fixtures located on or very near an exterior wall. Kitchen and clothes washing machine (CWM) drains often are good candidates for through wall reroutes due to the physical layout of many homes built during the 1950’s and 1960’s.
The main advantage of rerouting a fixture’s drain through the exterior wall is the cost savings realized by avoiding tunneling or breaking through the slab. Another advantage of the through wall reroute is the location of the rerouted drain outside the footprint of the foundation allows for easy future maintenance or repair. A disadvantage of through wall reroutes is having the pipe visible penetrating the exterior of a structure, although objections can often be minimized by using copper pipe, painting the PVC pipe, or hiding the pipe behind landscaping. Another disadvantage associated with through wall reroutes is the frequent requirement of removing and replacing concrete paving in order to install a new drain by trenching around the perimeter of the structure.
Most jobs repairing or replacing the sanitary piping serving the typical Texas residence involve a combination of the methods described above. Let the engineers and plumbers at Vortex use their common sense and uncommon knowledge to your advantage. Contact Vortex and get a second opinion first!