Scoria: An Alternative Fill For Your French Drain

Posted on: 19 June 2015

French drains are relatively simple drainage solutions, but when you install one, you have a few options that will make your drain work better and last longer. Most french drains are built using PVC pipes, a fabric liner, and gravel, which is usually crushed stone. However, you can replace the crushed stone in a french drain with various other materials to suit your particular house and land. One material you should consider is scoria. 

What is Scoria? 

Scoria is a highly porous rock that is formed when magma is expelled from a volcano. It is harvested and crushed into a variety of sizes for use in landscaping and construction and is commonly used when building drainage systems.  

How is Scoria Used in a French Drain? 

When constructing a french drain, your contractor will dig a narrow trench to the base of your foundation. They will then line the trench with fabric. After the fabric, a thin layer of scoria will be placed, followed by a large PVC pipe. The pipe will be covered with scoria until the trench is mostly filled, and then a thin layer of dirt will be spread on top. Because scoria is often considered an attractive, decorative rock, you may choose to fill the trench completely with scoria to create a ring around your home.

When water from the surrounding dirt comes in contact with the scoria, it will follow a path of least resistance and flow to the bottom of the drain, into the pipe, and away from your home. This prevents water from seeping through the concrete in your foundation and causing cracks or internal water damage.   

The Benefits of Scoria 

  1. Lightweight  Scoria weighs less than standard gravel. One cubic foot of concrete made with scoria weighs about 50 pounds less than a cubic foot of concrete made with crushed stone. The lighter weight makes scoria easier to work with if you are filling your drains manually. It also reduces the load that your foundation is supporting, which can help increase the longevity of your home's foundation. 
  2. Provides Insulation The tiny air bubbles in scoria are an excellent source of natural insulation. The pockets of air help retain a constant temperature inside your basement. If you do not have insulation in your basement, installing a scoria french drain could reduce your overall heating bill during the winter. 
  3. Can Often Be Locally Sourced Although Scoria is among the lesser mined rocks in the United States, there are several locations that produce significant amounts. If you live in an area with a history of volcanic activity, it is likely that you can locally source your scoria. This will reduce transportation costs, which will lower the overall cost of your project. If you are unable to locally source scoria, you should weigh the cost and environmental impact of transporting the scoria against the visual and insulation benefits of using it. You and your contractor may decide that a different rock that is locally available is a better choice. 

Using Scoria in Your French Drain

If you think that scoria might be the best choice for your property, then you should discuss it with your local contractor. Your contractor will be able to inform you about the specific cost of using scoria for your project. Alternatively, you can choose to source the scoria yourself and have it delivered to your home directly from the quarry. This has the potential to save you some money if your contractor does not usually use scoria on his or her projects. It is important that you educate yourself about the various options available for french drains to get the highest quality drain for your needs. For more informaiton about french drain systems, check out websites like