What is Single-Ply Roofing?
When architects first began designing flat and low-sloped roofs for commercial buildings more than a century ago, there was basically only one way to cover those roofs: using a mixture of asphalt and tar in a built-up roofing system (BUR). However, over the past few decades, thanks to modern advances in technology and manufacturing, single-ply roofing systems have grown to dominate the commercial roofing market. Single-ply roofs are affordable, easy to install and maintain, and can provide excellent waterproofing and protection for many years.
That being said, there are now so many variations and applications of single-ply roofing systems on the market — each with its own distinct advantages — that it can be challenging for architects and roofing professionals to decide which system would be best for their project.
To help alleviate the confusion, let’s take a deeper look at single-ply roofing: what it is, how it came about, and what’s good (and bad) about it. We also consider the various ways single-ply roofs can be assembled and attached, along with the different types of membranes in use, and how you can determine the best single-ply system for your needs.
What Is Single-Ply Roofing?
The earliest use of single-ply roofing systems can be traced back to the mid-1960s, but they came into wider use in the late 1970s and through the ’80s, as different varieties of single-ply materials came on the market. As the name suggests, single-ply roofing combines all the waterproofing protection of the old multi-layered BUR roofs into a single sheet of material — a membrane that can be easily rolled out and attached to the roof deck. Over the years, single-ply roofing has grown exponentially in popularity — and today, while BUR roofing is still used in limited contexts, single-ply roofing systems have taken over as the industry standard in commercial roofing.
Advantages of Single-Ply Roofing
What caused single-ply roofing to dominate the industry over a few short years? Let’s highlight some of the key benefits that make these roofing systems so attractive to architects, developers, and roofers:
- Ease of installation keeps costs down. Single-ply membrane systems can be installed in a fraction of the time it takes to lay down a multi-layer system and is therefore much more affordable due to reduced labor costs.
- Durable and resilient. Single-ply roofing has a high tensile strength that provides superior waterproofing and resists damage, even in extreme temperature differences.
- Energy efficiency. Single-ply white roofing often has a “cool roof” effect that keeps the building cooler during summer heating.
- Long service life. Single-ply roofing holds up well against the elements and is resistant to UV rays, making it less susceptible to deterioration over time.
- Lightweight. A single-ply membrane weighs much less than a built-up roof, causing less strain on the building’s structure and requiring less reinforcement.
Weaknesses of Single-Ply Roofing
For all its benefits, single-ply roofing also has some drawbacks of which to be aware. These include:
- Prone to puncturing. While single-ply roofs are fairly easy to maintain and repair, they can also be punctured more easily. Many single-ply systems are not conducive to foot traffic for this reason.
- Seams subject to leakage. Single-ply installations have seams that can deteriorate and cause leaks, at which point they must be repaired.
Single-Ply VS. Other Roofing Types
Despite the popularity of single-ply roofing systems, they aren’t the only types of roofs we see on commercial buildings nowadays. Let’s compare single-ply systems with two other common roofing methods used on flat and low-slope roofs: built-up roofing and modified bitumen.
Built-Up Roofing (BUR)
Long considered the “old reliable” way of covering flat roofs, built-up roofing (BUR) consists of multiple layers of asphalt and tar, typically with a top layer of gravel (hence the nickname “tar and gravel roof”). While these roofs are effective, durable, and easy to maintain, BUR systems are much more labor-intensive to install than single-ply roofs. Additionally, the multiple layers make these roofs quite heavy, often requiring reinforcing the structure to support it. Perhaps the most common complaint of BUR systems is that they don’t hold up well in cold temperatures, so they often spring leaks in cold climates — and because there are no seams, it can be difficult to find the source of a leak in a BUR roof.
Another common roofing system for flat roofs, modified bitumen, is similar to single-ply roofing in that it is a membrane system. The membrane is usually made of asphalt (bitumen) combined with either plastic or rubber polymers and fabric reinforcement. Modified bitumen does better in temperature extremes than BUR roofing, and it’s a bit more resistant to tearing than single-ply roofing. Hence, modified bitumen is better for handling foot traffic. On the downside, these roofs have a lower life expectancy than other roof types.
Assembly Options for Single-Ply Roofing
One of the great things about single-ply roof systems is that there is more than one good way to assemble and attach the membranes. Depending on the type of roof and specific issues, roofing professionals can decide which assembly option works best for their project. Let’s turn our attention to the most common assembly options for single-ply roofs and the situations for which they are most recommended.
With ballasted assemblies, the membrane is laid out loose across the roof deck and held in place with ballasting material (e.g., gravel, stone, or concrete pavers). The ballast serves as a protective topcoat for the membrane and helps extend the roof’s service life. Ballasted assemblies are less common in new construction and reroof applications.
For mechanically-attached systems, the single-ply membrane is physically fastened to the roof deck by a series of plates and fasteners. Mechanical attachment is an ideal way to secure the roof membrane on a budget because of lower labor costs — and attaching it directly to the roof deck makes it resistant to wind uplift, making it a good choice for buildings that are subject to windy conditions.
With a fully-adhered roof, the single-ply membrane is attached directly to the base insulation layer using an adhesive. This can become a bit labor intensive if the adhesive is applied separately, although some manufacturers today make application easier by making self-adhered membranes. A fully adhered system offers excellent stability and resistance to the wind (though, some have argued, not at effectively as mechanically attached roofs).
A fourth popular application of single-ply roofing is to install it directly over an existing metal roof. With this assembly, insulation fills the roof’s gullies to make a level surface, and the single-ply membrane is installed over the top, either with adhesives or mechanical attachment. A metal retrofit system is an ideal solution for extending an aging metal roof’s life without having to do a full replacement. It is also used for purposes of improved energy efficiency and providing a quieter environment for building occupants.
Common Types of Single-Ply Roofing Systems
Not every single-ply roof type is right for every roof, and certain factors like climate, budget, and other practical priorities may come into play. The three most common types of single-ply membrane systems are Ethylene Propylene Diene Monomer (EPDM), Thermoplastic Polyolefin (TPO), and Polyvinyl Chloride (PVC).
Ethylene Propylene Diene Monomer (EPDM)
EPDM membranes are made from synthetic rubber material derived from ethylene and propylene and often reinforced with a polyester scrim to make them more damage resistant. EPDM roofs are known to last 30-50 years with proper installation and care. The downside is that EPDM typically comes in black, which absorbs heat and makes the building more difficult to cool. Some companies have addressed this issue by making a white version of EPDM, but this usually comes at an additional cost.
Thermoplastic Polyolefin (TPO)
TPO roofing consists of a thermoplastic polymer of polypropylene and ethylene-propylene rubber —similar in some ways to EPDM, but with the added advantage of greater reflectivity, making it a “cool roof” alternative to EPDM and saving on heating and cooling costs. The biggest complaint about TPO roofing is that it has a lower life expectancy than other types of single-ply roofing.
Polyvinyl Chloride (PVC)
PVC roofs are thermoplastic membranes made from ethylene and chlorine and reinforced with polyester or fiberglass. PVC is highly resistant to damage from fire, water, chemicals, mold, and wind, making it a good choice for buildings with grease traps (e.g., restaurants) and buildings that are prone to high winds. It is not a good choice for colder climates because PVC can become brittle and crack in cold temperatures.
Choosing the Best Single-Ply System for Your Needs
One of the reasons for the proliferation of single-ply roofing options is that every building is different and presents different challenges. Various types of membranes, application methods, and even sealing materials have been developed over time to address a wide range of issues and provide the best protection and coverage possible.
If you’re still uncertain about which single-ply roofing system would work best for your project, RoofSource can help. We represent some of the most trusted roofing material manufacturers in the industry today, and our trained team of experts can offer key advice to help you make the best decisions on materials and applications for your next roofing project. Contact us today to get started.