What Is The Difference Between EPDM And TPO?
There are many roofing systems available for homeowners and contractors to choose from in today’s market. Of these many options, the three most commonly used are EPDM, TPO, and modified bitumen.
There is no outright ‘best choice’ among the three because what you use on your roof depends on unique circumstances such as the climate, local regulations, your budget, and preferred roof style, among others. In this article we will take a look at the characteristics of EPDM and TPO roofing systems so that you are in a better position to pick the right roofing system for your home.
What is TPO?
TPO, is a single-ply roofing membrane that is one of the fastest growing commercial roofing systems on the market. TPO roofing systems are made up of a single layer of synthetics and reinforced scrim that can be used to cover flat roofs. TPO roofs are also known as white roofs due to their white upper surface and highly reflective finish.
To attach the TPO membrane to the sub roof or cover board, the contractor can either ruse adhesive or they can fasten it mechanically. Once the membrane is rolled out, the contractor then returns to use a hot air gun to hot air weld the seams together.
TPO is made up of two sheets with a scrim in the middle. Over time the fillers and calcium in the top layer weather away, which is when you may start getting leaks into your building.
TPO membranes are typically available in two thicknesses, 0.045 AND 0.06 inches. As opposed to EPDM and modified bitumen, TPO requires more experienced roofing technicians, and much more equipment.
How TPO came to be
Prior to the introduction of TPO in the market, PVC was the single-ply thermoplastic roofing solution employed by most contractors. PVC was liked because it could be molded to fit roofs of different shapes and sizes, and also because it was fairly resistant to chemicals, UV degradation and temperatures. However, in the long run, it is affected by weather conditions, leading to shrinkage and cracks. Another con is that PVC contains plasticizers which wash away over time, leading to soil pollution. These plasticizers also contribute to the cracking of PVC surfaces.
Given the challenges that PVC posed, there was a need to come up with a roofing system that would maintain flexibility of PVC, but that was more durable and didn’t leach chemicals to the environment. This new roofing material would be TPO.
Prior to being introduced to the United States, TPO roofing membranes were introduced in Europe in 1991 under the name FPO (Flexible Polyolefin), which conveyed the flexibility of the material. Since the early nineties, TPO has grown in popularity and now accounts for over 40 percent of installed commercial roofing membrane in the United States.
Pros of TPO membrane roofing
- In TPO roofing seams are heat welded rather than glued, therefore much less prone to separation
2. The white surface reflects light, keeping the structure below cooler.
3. If the contractor is certified by the manufacturer, the manufacturer rather than the contractor, honors the warranty
Cons of TPO
- Newer to the market than EPDM about 20 years old. Has a long track record of revisions and improvements due to surface and seam failure.
- TPO is known to shrink, and its rigidity causes stress on seams and flashing.
- Prolonged, excessive sun exposure causes UV light degradation.
- Contractors must calibrate their welding machines very carefully because improperly welded seams may come loose during the first freeze and thaw cycle, leading to water infiltration.
- Manufacturer warranty only 15-20 years.
What is EPDM?
EPDM is the most popular rubber roofing system and has been in use for over fifty years. Apart from roofing, EPDM finds use in manufacture of electrical insulation, tire tubes, pond liners, and industrial belts.
EPDM is produced in various thicknesses – 0.045, 0.06, and 0.09 inches. Most contractors use the industry standard of 0.06 inches, which is very close to the thickness of a quarter.
Some advantages of using EPDM on a flat roof are:
- First it is the least expensive flat roofing system on a per sq. ft. basis. According to Legacy USA, the average cost of an EPDM roof is $4.50 – $5.50 while a TPO roof costs on average $3.50 – $9.50.
- It is simple to install, with the use of rollers, anchors, and adhesives.
- EPDM weighs less than other single-ply membranes.
- EPDM is sold in wide rolls of 8 to 20 ft., resulting in less seams in the final roof.
Cons of EPDM as compared to TPO membranes:
- UV rays degrade the adhesives used on seams and flashing, leading to premature separation.
- The black membrane absorbs UV light causing shrinkage and brittleness, which drastically decreases the life expectancy of an EDPM roof.
- The thin membrane is susceptible to punctures due to food traffic or construction objects. For this reason protective mats are required.
How Is EPDM Manufactured?
EPDM, like other synthetic rubbers, is made by polymerizing the by-products of crude oil processing. One such by-product is isoprene, which is polymerized to produce cis-1,4-polyisoprene—a synthetic version of natural rubber.
However, EPDM, like other rubbers, has poor mechanical properties. To combat this, EPDM is usually compounded with fillers (such as fumed silica) and plasticisers (such as mineral oils) in order to increase its strength and flexibility.
Properties Of EPDM
- Resistant to high temperatures
- Adaptable to low temperatures
- UV resistant
- Steam resistant
- Resistant to weathering
- Flexible – 600% elongation and a tensile range of 500-2500 psi
EPDM vs TPO – The Choice Is Yours
Now that you know the differences, advantages, and disadvantages of both EPDM and TPO, you can pick the flat roofing system that best suits your home construction or renovation project.
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