SCH 40 PVC PIPE—All the Time, Every Time!

By: Patrick Hooper

On my way to an inspection the other day, I pulled up alongside a pickup truck that was towing an excavator, and what appeared to be PVC drain pipe.After a closer look, I realized that the drain pipe this contractor was carrying—presumably to install underground for a customer—was Solid Smoothwall pipe, which is also called Double-Walled or Triple-Walled pipe. Having seen this kind of PVC pipe many times during downspout inspections, I usually refer to it as “Soon-To-Be Collapsed” pipe.

Solid Smoothwall Pipe is commonly used as downspout line. It’s essentially a light-weight  corrugated drain pipe with a black interior and white outer layer that’s suppose to increase its rigidity/resilience to soil pressure, as well as to protect it from heat, ultraviolet radiation and severe weather conditions.

As you may have picked up from one of my previous posts, there are many different kinds of PVC and plastic drain pipe available in varying thickness and diameters. Of all the inspections I have performed, there is only one kind of PVC pipe (other than SDR 35) that has the durability, strength and wall-thickness necessary to withstand the crushing weight and pressure of soil (even as shallow as six-inches deep) or of a concrete foundation—Schedule (SCH) 40 PVC.

SCH 40 is more expensive than most other drain line options, which is the only reason I can imagine why a customer or contractor would consider using an inferior-grade of underground drain line. However, if you take into account the costs involved in excavating and replacing inferior pipe when it eventually fails—as it almost certainly will—the savings associated with choosing SCH 40 from the start of your project is obvious.

I’ve come across contractors who insist that the reason thinner-walled drain pipe collapses is because it’s installed incorrectly, not because it’s the wrong product for the job. I couldn’t disagree more. In my professional opinion, when anything other than SCH 40 is used for underground drain lines, it’s a failure waiting to happen, no matter the installer. It’s got to be SCH 40, every time!