Does Roof Thickness Matter?

If you own a home or commercial building, you’ve probably heard about roof thickness. Whether your roof is sloped or flat, thickness matters when it comes to choosing the right material for your roof. The choices are more plentiful for sloped roofs. Low slope or flat roofs are another story.

A low slope roof is anything under 2 ½ inches of fall per foot.

Well-known midcentury real estate developer, Joseph Eichler built many low slope or flat roofed homes in Marin and the bay area. Modern for their time, they do present a bit of a challenge when they need to be re-roofed.

When you think of flat roofs, the basic hot tar and gravel come to mind. One layer of waterproof material, built up upon another, alternated with hot tar, commonly referred to as Built-Up Roof (BUR).

The final coat is hot tar covered in gravel which keeps the UV rays of the sun and weather off the paper beneath, protecting it from splitting or cracks. More recently, other materials such as fiberglass membranes were developed.

The benefits of a tar and gravel roof are that it is usually the least expensive and is very fire retardant.


What Does PVC, TPO and EDMP Stand for?

When considering other roofing materials for flat roofs, you can get lost among the acronyms, whatever the thickness. PVC is made up of those materials created through a chemical reaction, known as polymerization. TPO stands for Thermoplastic Polyolefin and is made up of a range of rubber roofing materials which are a blend of polypropylene and ethylene-propylene rubber. EDMP stands for Ethylene Propylene Diene Monomer and is made from oil and natural gas to create a synthetic rubber.

Booth and Little’s, Darren Little points out, “Tar and gravel used to be the only viable alternative for flat roofs, but it’s falling out to favor in areas where houses are less accessible, like one we just finished. The house was on a pretty steep hill in Tiburon, so getting hot tar close enough and then up onto the roof was not a viable option. Besides, we moved away from tar and gravel because there are much better options, now. Early on we experimented a bit with new alternatives and we prefer Dura-Last, a polyvinyl chloride, or PVC material that is good for both residential and commercial low slope buildings. Yet, a thinner single ply membrane in Dura-Last offers more reliable protection than TBO coverings. So, it pays to talk to a professional.”

Flat roofs often have trouble with water that pools in one or two areas during downpours. TPO, according to RTN Roofing Systems, the Midwest Roofing Contractors Association committee, released an “Advisory on TPO”, noting TPO’s potential susceptibility to deterioration from exposure to high heat and/or UV (solar) loads. Heat and reflected/focused sunlight are the primary concern in this advisory.”

Many manufacturers won’t provide coverage for membrane damage when this happens. Duro-Last’s membranes are designed to handle standing water without leaking and include this in the warranty.

In most cases though, roofers will tell you, the thickness of the roofing actually does matter, as it affects the efficacy and long-term life of your roof. This is true with asphalt and composite shingles used on sloping roofs.

“The thickness of almost any roofing material can help to ensure its longevity. Thicker can mean more money up front, but thicker should last longer. When getting a material’s quote from a roofer, it is very important to be sure you are comparing materials of the same thickness and quality. I hear people say, ‘this other roofer says he can do my roof for $500 or a $1,000 less than you quoted me.’ When I ask about the materials quote, I find that the other roofer included a thinner, less expensive roofing material.”

If you have questions about which materials are right for your roof, give us a call today and talk with one of our roofing professionals.