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Sump pumps not the whole story in sewer backups

Position of backwater valve in catch basin system is crucial

QUESTION -- My neighbour and I have had discussions about the subject of backup valves and sump pits for two years now. We live in Brandon and we were flooded in July 2005. Ours is an older neighbourhood, about 30 years old. Neither of us had the mainline sewer check valves or sump pit and pumps and we were flooded because the sewer lines were overloaded and black water backed up into our basements.

I installed a main check valve, a sump pit and pump and a floor drain check valve. My neighbour only installed a main check valve. He refuses to put in a floor drain check valve. His reasoning is that the weeping tile cannot be blocked. He says if the weeping tile is blocked it will cause the basement walls to crack and floors to heave from the resulting pressure built up in the weeping tiles. I say, the weeping tiles are only blocked for a relatively short time and the pressure he's talking about would not happen that fast. He says he would rather have a flooded basement than a cracked wall or heaved floor. Remember, he does not have a sump pit and pump.

My neighbour says a sump pump is useless because in a storm, often the power is out and then the pump doesn't work. That is what happened at his brother-in-law's place in Winnipeg and his basement got flooded from weeping tile water. A floor drain check valve would have prevented that and a water-tight sump pit.

With all the precautions I've taken, most say, it will never be flooded again. That's theoretically. Nothing is ever fail-safe.

Getting back to the question: When the main line check valve is closed by sewer backup, will having a floor drain check valve cause the floor to heave and the walls to crack because it has blocked the weeping tiles from draining?

-- Nathan T. Larry, e-mail

ANSWER -- I think you and your neighbour have a relatively good grasp of the concepts of the function of the backwater valve operations, but you are confused about the function of the weeping tiles relative to the floor drain in your older home. Your backup prevention measures are much more reliable than the home next door, but that is because of the sump pump, not the floor drain valve. I will explain the functions of those items in your homes and answer your question about damage due to blocked weeping tiles.

You are quite correct about the fact that the pump in your sump pit may not function until the next big storm that causes the sewers to exceed their capacity and force your main backwater valve to shut. In that situation, the rainwater flowing into the catch basin below your basement floor drain should drain into the sump pit through an overflow pipe connecting the two. Once enough water flows into the sump pit, the pump should engage and pump that water to the exterior of the home, through pipes attached to the sump pump. In some retrofit situations, one or more of the weeping tiles may have been cut to empty into the sump pit, rather than the old catch basin. In that situation, the sump pump may come on periodically. In my opinion, that is a better arrangement because it forces the sump pit to work, occasionally, which may prevent seizing from lack of use.

What your neighbour does not fully understand is the function and location of the back-flow prevention devices in your home. You state in your submission that you both have installed main "check valves" in your home. I assume these to be backwater valves located in the main house drain, located near the entrance of this sewer pipe into the home, below the basement floor slab. If that is indeed the case, the drain of the catch basin is located upstream of that valve. This means that once closed, wastewater can neither enter nor leave the catch basin from the main sewer. In other words, the small backup valve you put in the bottom of your floor drain catch basin is redundant. It will not be required, because water and sewage from the main drain cannot back up once the backwater valve is closed. If this one-way valve was installed at the top of the floor drain, that is a different situation that will be addressed later.

While preventing from sewage intrusion in the above scenario, this may open the door for a second issue to be dealt with. Since no water can now enter or leave through the blocked main sewer line, where does the rainwater go that is collecting in the catch basin from the weeping tiles? In your neighbour's home, it may quickly fill all the weeping tiles and catch basin and start to empty into the basement. That will be creating the same problems as before the backwater valve installation, only with clean rainwater this time. Your sump pump is the only proper protection from this occurring and the issue of having a catch basin valve will have no bearing on the outcome.

To address your neighbour's concern of full weeping tiles created by the catch basin valve and damage to the structure, it generally does not happen. Unless you have a valve installed at the top of the floor drain, rather than at the bottom of the catch basin, the extra weeping tile water will not cause extra pressure on the floor slab, it will just flow through the top of the floor drain into the basement. Your neighbour may not understand that the weeping tiles empty above the typical catch basin backup valve, not below. If you do have a backup device installed at the top of the floor drain, flush with the top of the basement floor, you should definitely remove it.

The final issue is the potential non-operation of the sump pump due to power failure or inactivity. I always recommend that clients test their sump pumps at least once a year, usually in the early spring, to ensure they are working. This can be done by simply filling the pit, partially, with water. As for protection from a power failure, I know numerous homeowners, mainly in Ontario, where power outages are a regular occurrence, who have a second battery-powered sump pump in the pit. This is normally hooked up to a typical marine battery situated near the pit. That may be the final part of the puzzle to ensure that you have the best protection possible in case of future sewer backups.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the president of the Canadian Association of Home & Property Inspectors -- Manitoba ( Questions can be e-mailed or sent to: Ask The Inspector, P. O. Box 69021, #110-2025 Corydon Ave., Winnipeg, MB. R3P 2G9. Ari can be reached at (204) 291-5358.