Plumbing in the Home/Roots in sewer lines


QUESTION: Hello: I am in the midst of very expensive repairs in the sewer lines in my basement.The trouble started when water stopped flowing from the basement floor catch basin into the main sewer line,and Roto-Rooter could not clear the blockage.To make a long story short,yesterday a plumber dug up the sewer line near the catch basin,and found roots packed in the cast iron pipes which had caused them to become corroded and brittle.The plumber was in the basement all day yesterday,and had to leave the job uncompleted at the end of his shift,as more concrete has to be broken up to find sound pipe to attach new PVC sewer replacement pipe.
My question is: Would it make sense to fill in the cavity above the repairs with loose gravel,and then pour fresh concrete over that?
My thinking is most of the labor and expense was because of heavy clay that had to be removed to expose the pipes,and if future repairs were required,it would be much easier to get to the pipes that needed replacement.Thanks!

ANSWER: 2/15/2014 10:39:17 AM

It is unfortunate when clay has been used as backfill and some areas will not allow it because it is difficult to get proper compaction. Of course the cost goes up considerably when the native soil has to be totally removed and replaced with suitable soil. Code requires that the pipe be laid on a solid compacted bed of fine grain material such as sand and the pipe should be encased in similar products absent any foreign materials or stones even small pebbles should not be in the first foot of the pipe bed.

Often though these guidelines are not closely followed and the native soil is used to backfill. It would certainly be good practice to not use any of the native soil if it is possible and practical. Regardless the pipe trench must/should be compacted to 100% if you are going to have concrete slab over it.

Roots will seek water and cast-iron will deteriorate in time. Your systems is likely over fifty years old to have cast-iron; ABS and PVC have been almost exclusively used in the past fifty years or so. If you are replacing all the cast-iron your concern is certainly lessened as the plastic will certainly be root proof excepting any faulty installation.

You should know or find out where the roots came from and how they entered the system and be comfortable that the roots will not invade the new system is my thoughts. I would not be anticipating ever having to dig the pipe up again. Still you should properly backfill and compact the trench and it would follow that a much better repair would result by eliminating the clay. I would use sand as opposed to gravel but that too is selective depending on availability and cost and inclination. By all means get 100% compaction and you should also reinforce and seal the patch work concrete if this is to be a finished floor or be in an inhabitable area.

Search the web for “trench backfill residential ABS DWV” will give you a lot of information. Each city will have their own rules but they will all be at least similar….

You have all the right ideas; just visualize what caused the problem and what you want to achieve and maybe you will want to eliminate some of the root source if possible…. Good Luck

---------- FOLLOW-UP ----------

QUESTION: Hi Cortez: Thanks for your prompt answer! I should have said I am in Canada,and the soil where I live consists of heavy clay,so the the builder likely just used native soil.The house IS old,built in 1950.My home is surrounded by mature elms,so the roots could have come from any of them.In your opinion,would regular application of Roto-Rooter's anti-root treatment prevent further root trouble? Thanks again.

It will help, but you can also use rock salt just like you use in water-softeners and it is much cheaper…pour a coffee can full of rock salt in the toilet and let it about half dissolve then flush it down…if you suspect roots have infiltrated ( forget to treat the line) then you would do this a couple times a day for a week or so. Regular application of once or twice a week in normal conditions will help keep roots out. But if you get all new underground and it is plastic you should never have a root problem “under normal circumstances”….the roots can come from any direction and nothing is absolute all the time so a little treatment is just insurance….

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Cortez (cort) Cate


PLEASE read this entire introduction. I have been doing this for a long time and I have come to the conclusion that if you are not willing to take the time to write a detailed question then don't expect a detailed solution! I am getting far to many questions that do not give enough detail to warrant a good solution. I realize it is a little difficult to formulate a good question but if you want a good answer you have to give me good this entire introduction please....remember this website is world wide I have no clue where you live if you don't tell give more detail on the fixture you are having problems with...a one piece eljer 3.5 gallon flush will be totally different than a one-gallon flush toto.....details are important. I can answer most questions related to residential and commercial plumbing for many buildings. I have sufficient knowledge of the UPC and UMC. I will speculate for you if necessary. In those cases I will try to give you some guidance and you should use that to refine the question further and we, together, can seek the answer via a follow up. Plumbing codes and practices vary around the world--If you don't tell me where you live the answer I give may not fit your locality. I am giving my time to you as a way of fulfilling my perceived obligation to share. I am here to try to help you find a solution to your problem. REMEMBER, If you want a good answer you need to ask a detailed question and include where you live, type of pipes, type of building, water pressure if it is a water problem, type of heater, age of appliance & building all these and many more are variables that have an effect on various situations. Detailed information will help produce a better answer.


Since 1972 a California licensed B-1 General Building Contractor, C-36 Plumbing and C-16 Fire Sprinkler Contractor; also installing and servicing Heating, Air Conditioning and Sheet Metal operating as C and C Building and Plumbing, California State License 279516. In 1995 I downsized the company to become semi-retired. Still I remain active in the construction industry. As head of a company I placed personnel and job safety as the number one objective followed closely by training and continuing education. Always seeking to stay informed of leading edge technology in the industry. Also I have spent several years as an Apprenticeship Instructor in the Pipe Trades Unions. Additionally I am a certified OSHA instructor.

United Association of Plumbers and Steamfitters Instruction Training, Ann Arbor, MI Bakersfield College, Bakersfield CA Cal Poly San Luis Obispo, San Luis Obispo, CA Foothill College, Los Altos, CA California Licensed Contractor from 1971

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