Roof 101: Low-Slope Roof Material Options

Low-slope roofs have 3 main options:

  1. Built-up
  2. Single-ply membrane
  3. Monolithic sprayed foam

To begin with, built-up roofs can be of two basic types and have a fabulous reputation at Schmidt Associates. Built-up roofs can be composed of coal tar or asphalt and the asphalt can be hot applied or cold adhesive applied. Coal tar roofs are the oldest low slope systems used in North America and are built to last for 40-50 years. The multiple layers create a built-in redundancy and a self-healing tendency. With coal tar, the layers of tar never fully harden and the heat from the sun softens the tar allowing it to naturally fill cracks and holes to prevent leakage. With the asphaltic type built-up roof, the layers are attached or adhered with hot asphalt or cold adhesives.

Another nice thing about built-up roofs is that they can be applied anywhere and are capable of being placed on all low-slope roof building shapes. Coal tar roof, however, while it is a great option, is not as widely used today as it once was due to the oil companies making tar less accessible and more expensive and attributed carcinogenic effects during installation, plus it requires hot (flame) application. Asphaltic built-up roofs are fairly common on industrial low-slope roofs.

Next we have the single-ply membrane system, which too is broken down into 3 subcategories- rubber (EPDM), thermal plastic (TPO), and plastic (PVC). EPDM has been utilized the longest and makes patching problems easy and relatively inexpensive. The newer options, TPO and PVC, are both made out of plastics that are melted together with heat. These options eliminate or reduce the possibility of leaks and also come in colors other than black, making them a popular choice. PVC roofs have been used since the 1970s while TPO has been used for the past 15 years. Both are expected to maintain the highest quality for approximately 20 years.

Lastly, we have sprayed foam monolithic roofs. These roofs are also known as “foam roofs” and are not recommended by Schmidt Associates. They are expected to last for 10-15 years, but historically Schmidt Associates has seen problems with the surface after only 3 years. The foam material was originally made for interior use and is extremely sensitive to ultraviolet (UV) light, causing it to deteriorate with sun exposure. The sprayed foam roofs must be covered with a thin coating to protect them from the UV light. The foam application is also difficult to control, which often creates bumps, unevenness, and other various cosmetic defects. Condensation on the substrate can be very detrimental to the ability of the foam to stick to it as well.

Of further concern is birds. They love to peck at the foam and eventually break through the top coat of the foam allowing for water to seep underneath. The water is then trapped under the top coat which expedites the deterioration of the foam in the sun. Thus, this roof is really only good for climates with little sun, rain, or snow.

Despite these issues, sprayed foam monolithic roofs do offer an advantage over other roofs in that they are monolithic, meaning no seams, and the ease of initial application and reapplication. To repair and replace, all you need to do is spray down another layer of foam.

What Schmidt Associates Prefers and Why

All in all, you can’t beat a roof with a long life expectancy that doesn’t require frequent repairs.

If choosing among steep-slope roofs, Schmidt Associates would recommend using the classic shingles because of its life expectancy and the minimal maintenance and repair required.

If choosing among low-slope roofs, Schmidt Associates would recommend the plastic option for 3 simple reasons. First, both TPO and PVC is heat-welded, giving it good seams that prevent leaks, thus also preventing expensive repairs. Second, the plastic membranes comes pre-made, making it extremely easy to apply during the construction process. Lastly, TPO is the most affordable option.

Have any further questions? Reach out to our experts!