Is A Thicker Roof Membrane Better?
In the roofing industry, there is much debate about whether or not a thicker single-ply roofing membrane is better than a thinner one. More times than not, however, there is a bias that can skew an otherwise objective opinion. Such bias can come from the product manufacturer or a supplier that has a vested interest in taking one side or the other.
It's not to say that I'm not capable of having a bias myself. But the goal of this article is to present as much of an unbiased response to the following key questions as possible: (1) If you're in the market to purchase a new single-ply roofing system, should you focus primarily on the thickness of the product? (2) Does the product itself matter or is it all about thickness? (3) Is it possible that a thinner product from one manufacturer can actually be better than a thicker product from a competing source? (4) Is thicker really better?
Consider the information and come to your own conclusion. You've got nothing to lose and at the very least, you'll add to your knowledgebase.
First Things First
So that I don't have to bore you with a bunch of roofing mumbo jumbo, let me cut right to the chase and say: Thickness matters with comparable products, but not all products are themselves created equally. If in the market for a new single-ply roofing system, choose a product first. Then worry about the question of whether you should go with a 40-, 45-, 50-, 60-, 65-, 80-, or 90-mil membrane. In the roofing industry, your product choice just may be more critical than the thickness of the membrane. With that out of the way, let's dig a little deeper.
A Familiar Comparison
It is an easy concept to focus on thickness and determine that thicker is automatically better. But ultimately it depends on what your are trying to accomplish with your new roofing system. Are you trying to "buy" time and put the cheapest system on your building? Are you looking for a compromise between cost and long-term durability? Are you looking primarily for an energy-efficient product, or are you concerned with possible hail damage? The questions could go on and on. But let me provide you with an illustration of why focusing on the 'thicker is better' mentality may not always serve you best.
If you're like me you're old enough to remember those 8-track tapes. Those where awesome. They totally outshined the reel-to-reel monstrosities. They were more portable than the vinyl records. You could get a 8-track player in your car and actually drive around while listening to your favorite music. Those were the days. But then came the cassette tapes. They were not only smaller, but they could be played in much smaller players - even those that you could carry with you. Did the smaller cassettes mean less quality? Not at all. In fact, the opposite was true. Then everything changed again with the introduction of the compact disc.
We all know that the compact disc is thinner than the original vinyl records and certainly much, much more portable then those clunky 8-tracks tapes or cassettes. But did the size truly reflect the quality? Again, not even close. Compact discs were a huge leap in quality, rivaling a live recording. Though these were smaller and THINNER than its predecessors, they outperformed - and still do - those other products. Why? Well, not necessarily because they are thinner, but because the product itself is better. A CD is made from a completely different material and is put together in a completely different way than a vinyl record, 8-track tape, or a cassette was. Those are the reasons that make it a superior product, not necessarily the actual size of the product itself.
So it is - or at least, can be - with a roofing system. Thicker does not always have to mean better. The product type and how it is "put together" can be just as significant, if not more so, than just the comparison of thicknesses. But with that being said, thickness does play a roll, especially among comparable products. Let's take a look at TPO membranes.
TPO Membrane Comparisons
TPO is a type of roofing membrane that can come in a variety of thicknesses. The most common thickness is probably 60 mils. (A mil is a unit of measure where 1-mil is equal to 0.001 inches. So, a 45-mil roofing membrane is actually 0.045 inches thick; whereas a 60-mil membrane is 0.06 inches thick, and so on.) So the first thing that may jump out at you is that going from a 40-mil product to a 45-mil product (0.005-inch difference) is not nearly as significant as going from a 45-mil product to an 80-mil product (0.035-inch difference). So if you are merely comparing comparable products with reasonably close milages, then you're not really gaining or loosing much in thickness. To be sure, you are gaining or losing something, but I think it is important for you to understand that you may not be dealing with such a significant difference that you need to fret over such a decision. This is one reason why product type may be more of an important factor to consider. But we'll get into that more in a bit. For now, let's go back to the TPO membranes.
Most roofing membranes - including many TPOs - have a reinforced area that is placed somewhere in the vertical architecture of the membrane. Though not necessarily in the middle of the membrane, the end result is that there is a certain amount of material above and below the reinforcement area. This reinforced area is usually accomplished by means of a scrim, which is an interlaced matrix of tiny treads. They work much like the iron rebar that is used to reinforce concrete. The more threads, the stronger the reinforcement, assuming they are placed in the proper pattern. (Note: Unreinforced membranes are not recommended and are therefore not considered in this article.)
When a membrane is made thicker, a certain amount is added to the area above the scrim - known as the wearing surface - and a certain amount is added below the scrim. What might surprise you, though, is how much of the overall thickness is above the scrim - that area that is truly protecting your roof.
A 45-mil TPO membrane, for example, may have a wearing surface above the scrim of only about 17-mils (0.017 inches). This means that 28 mils - or 62% - of the membrane's thickness is below the scrim. Compare this with a typical 80-mil TPO membrane where an average of 34-mils is contained in the wearing surface. The other 46-mils - nearly 60% - of the membrane material is once again below the scrim. What does that really mean? Well, it basically means that to increase just the wearing surface by only an additional 17-mils, you must increase the overall thickness of the entire membrane by 35-mils, or twice the amount of the wearing surface increase itself. So when talking of a membrane's thickness, it is important to know how this membrane thickness translates to the overall thickness of the membrane and that of the wearing surface. Shortly, we will discuss what this material below the scrim really is. But first...
The Wearing Surface
This leads me to another point that is best discussed later in this article when discussing how a product is "put together." But because of its relevance to the issue at hand, let's touch on it now. When evaluating the question of membrane thickness verses product type, it is important to fully grasp what a wearing surface is. This is the area above the scrim that "wears away" over time; this is due, not just because of foot traffic, but primarily because of the natural aging process of the product. Severe exposure to harsh weather elements will hasten the wearing away of the product. Most manufacturer's have to increase the thickness of the overall membrane in order to increase the thickness of the wearing surface. If too much of the wearing surface wears away, then the protective aspects of your roofing system go away with it. Typically, the thicker the wearing surface the more protection over a longer period of time is experienced. But there is another way of looking at this.
Most TPO membranes will chalk, which really is the process of the wearing surface wearing away. So if you were to rub your hand over the top of the membrane and then look at your hand, you'd see a white powdery chalk-like substance. That illustrates what chalking is. What you are actually seeing is deteriorated roofing membrane. The less a membrane looses in this process of chalking, the less need there is for a wearing surface. Now don't get me wrong, every single-ply membrane needs a wearing surface. But a well-engineered product that is "put together" to high levels of quality will not wear as much. If a product doesn't wear as much, there is less need to make it thicker in the first place. So the bottom line is that a superior product with a thinner membrane can actually be better than an inferior product with a thicker membrane. Thickness may actually indicate a weakness in the quality of the membrane. But we'll touch on this again in a little bit.
More About Thickness
Now getting back to our 45- and 80-mil TPO comparison... The overall thickness of the 80-mil TPO membrane was increased by 78% - or 35-mils - in order to allow an increase of only 17-mils of additional wearing surface. But you'd be paying for the entire thickness, not just the wearing surface increase. The cost of 80-mil is more than twice the cost of 45-mil even though your wearing surface increase is exactly twice the amount. You need to determine if that additional cost is really worth it.
But let's compare the standard 45-mil TPO membrane with the more common choice of 60-mil. As mentioned before, the 45-mil TPO membrane has an average wearing surface of about 17-mils. A 60-mil membrane has an average wearing surface of around 24 mils. So to increase the wearing surface a measly 7 mils (0.007 inches), the overall membrane thickness was increased by 15 mils, a full 34% more. Don't get me wrong, this can certainly provide more protection against such things as hail, snow, rain, or even burns (from fireworks, cigarettes, etc.) However, is the difference in wearing surface - 0.007 inches - worth the cost of the 34% increase of the overall membrane thickness? Remember, you pay for the total thickness, not just the difference in wearing surface. The wearing surface increase has some benefit, to be sure. But the increase in cost can be a deal-breaker for some, especially considering the difference in cost between a 45-mil and a 60-mil TPO membrane is usually more than 25% per SF.
To put the above into perspective, consider this: To put a 60-mil TPO membrane on a 10,000 SF area of roof would cost you about $1,400 more than a comparable 45-mil TPO product. These costs are estimates, but are based upon real prices at the time this article was written. They do not include the applicable taxes and permit costs charged against that amount. So the question comes down to whether or not spending $1,400 is worth the negligible increase of the wearing surface? Put like that, most don't see the benefit. Then again, going from a 45-mil TPO to a comparable 80-mil TPO product would increase your cost by about $6,000. In that case, is paying an additional $6,000 on a 10,000 SF area of roof worth having twice the wearing surface when that wearing surface is only around 34 mils (0.034 inches) anyway?
The above scenarios and costs are only averages; the particulars of the specific product you are looking at would need to be considered. Some may have more or less milage above the reinforcement. Some feel that even that little bit of extra protection is worth it, especially if the roof is to receive a lot of foot traffic. But could strategically-placed walk pads mitigate that issue? True, it's hard if not impossible to guarantee roof-top travelers will use the walk ways provided by these walk pads. But it should at least be considered.
There are some that feel that if a roof is to have heavy foot traffic, or as protection against hail damage, going with a 60-mil membrane instead of a 45-mil membrane is necessary. First of all, as specified above, your actual wearing surface protection may really not be that different between the two. Secondly, what is the membrane installed over? The underlayment can directly impact the durability of a roofing membrane. For example, a soft fiberboard can actually cause hail to penetrate the membrane because of the "give" in the material underneath. On the other hand, a hard cover board; i.e., Dens Deck or even a high-density polyisocyanurate insulation board, will not allow the same type of give. So your increased wearing surface could potentially be sacrificed because of an improper or bad choice in underlayment. Furthermore, a slightly thinner wearing surface could potentially be bolstered by a good choice in underlayment.
Ultimately, the owner will need to determine whether or not there truly is a cost benefit to spending more on what otherwise is only a negligible to moderate increase in wearing surface thickness. The more thickness, the more protection - assuming comparable products. The more thickness, the more cost. Is that cost worth the wearing surface thickness increase? As mentioned in the outset, there are potentially very many reasons to put on a new roof. It's not always just about stopping leaks. The best way to make sure you are getting what you want is to talk to your roofing contractor. Let them itemize the pros and cons, the benefits and drawbacks of choosing a particular product and thickness. Life-cycle requirements, amount of foot traffic expected, and other issues would all go into the mix. There really is no 'one size fits all' when it comes to spending your hard-earned money on a new roofing system. Call RTN Roofing Systems today at 970-593-1100 to help you make an informed decision.
None of this information is intended to portray a thicker membrane as inherently worse than a thinner one, as that's not necessarily the case. However, it is intended to help you think of the realities that exist when considering whether or not to use a thicker membrane. It's not always so clear cut when you get down to the nitty-gritty.
Seams Matter Too
Another point that is often neglected, but should not be lost in this discussion, is the seams. The most vulnerable part of any roofing system are the seams. In a very basic definition, the seams are where us imperfect humans bind two pieces of the roofing system together. An EPDM roof (rubber) is either glued or taped. In a TPO or PVC system it can be glued or taped, but is most often heat-welded. But in either case, the more seams you must create in the field, the more potential there is for problems. So your decision to put on a new roofing system should not ignore how the seams of that roofing system are addressed. It might be considered foolish to spend extra money on increasing the wearing surface and yet completely ignore how the seams are to be addressed. They are typically the most vulnerable and therefore, the most susceptible to any roof-top problems that may be encountered.
Maybe the Most Important Issue - The Product
This also sets up nicely the other point that needs to be addressed: the product itself. Is a thinner membrane from one manufacturer better than a thicker membrane from a different one? The answer: yes, no, maybe. Did you really expect any other answer? The fact is, all these answers are true. It really depends on what you are comparing. This is another reason why calling RTN Roofing Systems is the best way to get answers to your specific roofing needs - they are not the same for everyone. But I will cover a case where product type does matter, maybe even more than the overall thickness of the roofing membrane itself.
Take as an example the Duro-Last single-ply PVC roofing system. Duro-Last manufacturers 50- and 60-mil membranes. But would you be surprised to learn that it's best-selling product is their 40-mil PVC membrane? That's 5-mils less than the standard 45-mil TPO membrane. Also, would it surprise you that their 40-mil PVC membrane rivals a 60-mil TPO membrane? Remember the illustration of a compact disc verses an old 8-track or cassette tape? That illustration applies here. In that illustration I mentioned that how a product is 'put together' can be critical to that product's overall quality, making what is otherwise smaller - or thinner - better than its bulkier - and thicker - counterpart. So, how does it apply in this case? As discussed, most reinforced roofing membranes have a certain amount of material above the reinforcement area (scrim) and a certain amount below it. Unfortunately, most single-ply roofing membranes have below the scrim a different material component than that which is above it. The material above the scrim, which you may recall, is known as the wearing surface. This material below the scrim is often just filler material; its primary purpose is to increase the overall thickness of the membrane and provide a means to apply the reinforcement material (scrim).
These types of products are made up of conventionally-laminated material – the top material is fused together to a different bottom material with a reinforced area in-between. So these manufacturers are increasing overall thickness by increasing the amount of filler material below the scrim so that relatively small amounts of wearing surface can be added to the top of the scrim. Understanding that this can be a problem comes from the common-sense understanding that true roof product performance is found in balancing (1) the overall thickness of the membrane with (2) reinforcement that is tied together with a quality product that is the same from top to bottom. As mentioned, most of these roofing products are different from top to bottom.
Duro-Last 40-Mil Membrane
While the 40-mil Duro-Last membrane may be their best selling, RTN Roofing does not recommend it for hail-prone areas. Our experience is that the 40-mil membrane is more susceptible to UV degradation, which makes is that much more prone to damage from hail. We've installed 40-mil Duro-Last membranes in Florida that outlasted their warranty. But for one, Florida, while hot and humid, doesn't receive the level of UV rays as, say, Colorado. Furthermore, even though Florida is known for its rain and lightening, frequent hail storms are not nearly as common as Colorado and other adjacent states.
Therefore, when specifying Duro-Last in our particular climate, we recommend a 50-mil membrane. For added hail protection, we recommend a hard cover board be installed beneath the membrane. With this combination, we've seen virtually no hail damage common to other roofing systems
So if you are in a climate like Florida with less than severe UV radiation and infrequent hail storms, a 40-mil membrane may be something to consider. But here in moderate to extreme UV radiation areas with frequent hail storms, a 50-mil membrane with a hard cover board is highly recommended for the best results and overall protection.
A Different Product That Illustrates the Point
The Duro-Last single-ply roofing system is different. It is different for many reasons, but a major difference is in the fact that it is the same from top to bottom. There is no filler material. In practical terms, because the product above the scrim is the same as the product below the scrim, the entire membrane thickness is, in effect, a wearing surface.
So in the case of their 40-mil product, a full 17-mils is above the scrim. This is the same as many 45-mil TPO products. But once you get below the scrim, the Duro-Last membrane remains the same material as it was at the top. It's not laminated with different components. Therefore, the way the Duro-Last membrane is 'put together' significantly increases its quality, enabling it to meet or exceed products of greater overall thickness.
There are two other points that highlight that thicker is not always better, especially when you compare Duro-Last's membrane with other roofing products. Those points are the scrim (reinforcement) and the product itself.
The Importance of How a Product is "Put Together"
The Duro-Last scrim, which is really the source of the product's strength and durability, is weft-inserted at a density of 14 x 18 threads per inch. This is among the highest in the industry. Other comparable products – if there really are any – have woven scrims at a density rate of only about 10 x 10 threads per inch.
Also, the Duro-Last product itself equals, and most often exceeds, comparable products in tensile strength, elongation, flexibility, crazing, and cracking standards established by the roofing industry.
So when you combine all of these unique elements of the Duro-Last roofing system, you get a thinner, but better-engineered product. Please keep in mind that we are authorized installers of other roofing products - including TPO and EPDM. I have no vested interest in promoting one product over the other. But the Duro-Last single-ply roofing system well-illustrates the concept that product quality is possibly more important than membrane thickness. A better-engineered product can be thinner and still outperform a competitor's thicker product. This is why I started off with my opinion that product type needs to be chosen first, then worry about whether or not you want to spend more money on additional membrane thickness.
We offer commercial rooftop evaluations and can provide you with specific and significant insight into the needs of your particular roof. Call us today at 970-593-1100 to schedule for your commercial rooftop evaluation.
But what if you just cannot afford a new roof? Is all lost? Not necessarily. In fact, a roof restoration can usually be done if action is taken quickly. To find out more about roof restorations and whether or not your roof would qualify, please visit our roof restoration page.