Cast-iron was the pipe material used for underslab sanitary piping until the early 1970’s, at which time the use of cast-iron was replaced by black (ABS) plastic first and then white (PVC) plastic toward the end of the decade. Cast-iron will deteriorate over time, lasting anywhere from twenty years to one-hundred- and-twenty years or more. If you believe that the cast-iron from the sixties and prior is on the verge of failing then why test it? Does it matter whether it passes or fails a hydrostatic test if failure is eminent? Why not tunnel under the foundation and replace it? I can think of one reason…. how about if the tunnel to replace the piping allowed more water under the foundation than ever leaked from the system? Would you still tunnel under the foundation in the name of preventing foundation problems? It’s a good thing the leak or the tunnel are more of a hazard to the wallet than the foundation!
Leaking underslab sanitary piping didn’t always cause foundation damage. It started in the mid 90’s after a jury of our peers concluded that the exclusion of coverage for differential foundation movement under the standard Texas homeowner’s insurance policy would have one exception: if the differential foundation movement was caused by a plumbing leak under the slab. Subsequently, underslab leaks went from seldom being blamed to the number one blamed cause virtually overnight. Foundation contractors started plumbing divisions and began blaming foundation movement on plumbing leaks almost to the exclusion of all previously blamed causes, and insurance companies began hiring plumbers and engineers to inspect the multitude of houses filing foundation damage claims.
Standards of testing, as well as engineering theories about differential foundation movement and soil mechanics, were battle-tested in courtrooms across the state from the mid 1990’s to the early 2000’s. “That ounce of water leaking from a crack in the sanitary piping every time we flush is causing this part of my house to settle.” By the way, expansive soils swell when wet and shrink when dry. How about that oak tree over there removing two- or three-hundred gallons a day from the soil? That might make this area settle, you think? Give me a break!
We are often asked whether we do a camera test or a hydrostatic test. We reply that the camera is not a test. The camera is analogous to the visual part of a physical without any blood work, x-rays, urinalysis, electro-cardio gram, or any other test the doctor feels is indicated. If you want to know if a sanitary system is leaking, you must do a hydrostatic test. If you are using a sewer camera and looking at cast- iron, then every joint is a potential crack and there is no way to tell the joints from the cracks without hydrostatic testing and isolation testing. Hydrostatic testing water level drop and fill rates, scaled on an arbitrary 5-point system, mean absolutely nothing when it comes to judging the performance or condition of the system. All insurance companies require a “flow” test as part of the plumbing inspection on foundation claims. The flow test is simply pouring water into a leaking drain and comparing how much comes out the other end. It’s really simple and has absolutely no relationship to how fast or slow the system dropped or filled under hydrostatic testing conditions. Give me another break!
Plumbing reports which state It is always better to replace cast-iron before structurally damaging leaks develop should be viewed with skepticism. If you are a homeowner, a homebuyer, or a realtor, and you have been told that a leak on the sewer pipe can damage your foundation, have you considered whether or not a tunnel dug to replace the sanitary piping is also a hazard to the foundation? After all, the tunnel will almost always be a path for more water to migrate under the foundation during rain events than ever leaked from the sanitary piping whose replacement required the tunnel. Again, good thing the threat here is more to the wallet and not to the foundation. I might just have to say something on behalf of the house! Oops, too late!
Case Study – Hydrostatic Testing vs. Video Inspection
We were recently asked to test the sanitary piping under a foundation by a seller after an inspector for a buyer ran a sewer camera through the three systems and reported that he observed hairline cracks and minor leakage and stated that it is always better to replace cast-iron before structurally damaging leaks occur. No hydrostatic testing was performed, no video was forwarded to the seller showing the hairline cracks, and the buyer demanded that the seller replace the underslab sanitary system in its entirety. We tested the system for the seller and discovered that two of the three systems did not leak, and the third dropped very slowly. We suggested to both the
buyer and the seller that the tunnel to repair the one leaking system would allow more water to migrate under the house during rain events than was currently escaping the piping under normal service conditions, and suggested that to tunnel under the foundation and replace the other two systems that were not leaking was not in the best interest of the foundation. We suggested to both the buyer and the seller that a financial arrangement would likely have to be made considering the cost of repairing the one leaking system, regardless of whether or not it was actually repaired.
Lessons learned: A video inspection is seldom enough to determine whether or not a sanitary system is leaking beneath a residence. Only about half of the cast iron sanitary systems installed beneath residences constructed prior to the early seventies fail a hydrostatic test. Of course, the percentage of failures increases dramatically on residences which have had prior foundation repair. If you have been told that underslab cast iron sanitary piping which fails a hydrostatic test should be repaired because it can cause foundation damage, then how do you feel about the tunnels to replace the piping? Can these tunnels cause foundation damage? Are the leaks or the tunnels a
greater hazard to the foundation? And the big question that can’t be answered by the Russian judge’s 3.5/5 scoring, does the pipe even leak under normal conditions or just during a hydrostatic test? Remind me again, which one of us is PLUMB CRAZY?
Mike Williams, P.E.
TX MPL 37244
Vortex Plumbing, Inc