Downspout Drain Lines: SDR 35 or Schedule 40?

Should I use SDR 35 or Schedule 40 for my underground downspout and sump-pump drain lines? This question has been asked more then a few times and in this short article we will go over which should be used. Initially Schedule 40 looks better on paper. All around it is stronger, harder to crush. Should this not be the obvious choice? I mean when it comes down to it you always want to pick the stronger material, right? In order to answer that question we must first look at what strength means in this context and how it applies. Hold your conclusions until the end and lets get into it.

The Strength of Flexibility

When we think of strength we usually go right to the core of what strength is, which can take more punishment? While this may lead us to believe that Schedule 40 is a better choice we have to take a deeper look at the two types. SDR, or standard dimension ratio, was designed with the intent of being more flexible than Schedule 40. Compromising structural integrity for flexibility. Doing this does not seem like it would go along with what most people would want. Why would anyone want the line to have less strength? What would be the benefit? The quick answer is flexibility. Mother nature is always shifting and settling. Since these lines are installed underground they will be subject to these changes. Here is where the flexibility of SDR outweighs the strength of Schedule 40. SDR will bend with the shifting and settling. Having a higher flex tolerance means less breaks from the soil conditions. Schedule 40 is so rigid that in the event the ground shifts or settles this pipe has no give. It will simply snap or break from the pressure. In the winter Schedule 40 also becomes more brittle from being outside. After a few seasons the weather alone will have compromised the structural integrity of the schedule 40 pipe.

   To the Victor Goes the Spoils

So in the long run we recommend using SDR on the exterior of your home. The flexible nature of the line will help keep the line from breaking from these adverse conditions. Additionally these lines will utilize a solvent weld or gasket to ensure the connection points are secure. Completely closing the system between the entry and exit points will help keep roots from infiltrating your line. Furthermore SDR 35 is less susceptible to the elements. When installed correctly it is one of the top choices available on the market today! So make sure you are protecting your investment with a small investment into a superior quality line.