Water is tenacious. It finds any crack or hole in an object and trickles through – no matter how small the blemish is.
That is a problem for roofing contractors and property managers – especially on large commercial roofs. With so much surface area and equipment on the roof, keeping a building cool and dry can feel like an impossible task.
We’re not here to crown a winner in the roofing materials category.
At Perry Roofing we do want to help you understand which options are available and which roofing material is best for your particular flat or low slope commercial roofing project.
So, let’s get started!
4 Flat Or Low Slope Roofing Challenges
Any roof deck is hard to keep dry – but waterproofing a flat or low slope is an extreme challenge.
Let’s find out!
Less Water Run-Off
Any roof with a slope naturally sheds water, which means that water won’t pool on the roof. This is not always the case with flat or low slope roofs.
Unfortunately, when water does not effectively shed from the roof, this standing water can lead to leaking and other damages to your property. Plus, it can also add more weight to your roof than the structure was engineered to support, which is extremely dangerous.
Because of these factors, newly installed roofs will not pass a final inspection if there is too much ponding water on the roof.
A good flat roof should have a drainage system that keeps water from ponding. Sometimes this requires tapered insulation or installing new roof drains to achieve.
Not many people regularly crawl on to the roof of their house. However, a commercial roof is often home to lots of equipment like solar panels, HVAC equipment, ventilation fans, and cooling towers
This equipment itself adds weight to the roof and creates more potential leak spots.
On top of that, servicemen will need to access them, which creates foot traffic on your roof. Unfortunately, every step holds the possibility of puncturing the roof by stepping on a sharp screw or shard of metal. Other trades are notoriously careless when it comes to working on the roof, and are one of the highest causes of leaks not related to workmanship and aging.
In other words:
The materials used on flat or low slope roofs need to be durable and able to resist punctures.
UV Damage And Degradation
The sun brings a lot of joy to humans, but roofing contractors know that it is one of the main things that degrade a roof.
And because commercial roofs are often so large they can act as huge UV absorbers. This breaks down the roof quickly, and leads to warm buildings underneath.
That’s why having a roofing material that reflects sunlight is important, especially in Southern climates.
Large Roof Size And Roof Weight
The sheer size of many low slope or flat roofs creates some unique problems.
First, traditional roofing materials like asphalt shingles aren’t a good option. They would take too long to install.
Plus, when shingles are placed on a roof with less than 2/12 pitch, the system is no longer effective because the water will pool up underneath the shingles.
Another problem is that such a large roof requires a relatively lightweight roofing material.
Since the roof deck is so large, an extremely heavy roofing material would not work well on a flat or low slope commercial roof.
As you can see, a lot is asked of roofing materials used in low slope commercial roofs. Ideally, these materials should be:
- Durable: flexible and strong
- Resistant to punctures
Now, let’s get into which low slope roofing system is best for your application!
5 Components Of A Low Slope Roof
Most commercial roof assemblies are made up of multiple layers.
The structural deck of a roofing assembly is the bottom layer and acts as a backbone for the entire system. Its primary job is to offer adequate support to all the materials placed on top of it.
The most prevalent roof deck in the U.S. for commercial buildings is steel. This acts as a good foundation that can eliminate concerns about a roof’s performance.
Vapor Control Layer
A vapor barrier can be an important layer in the composition of your roof. Its purpose is to help prevent water vapor from reaching building walls, ceilings, attics, or roofs, where it can condense and cause building materials to rot or grow mold.
On a commercial roof, the vapor barrier is usually made of plastic or asphalt and keeps condensation from forming inside the building when the exterior temperatures are significantly colder than the interior temperatures.
Some kind of vapor barrier is required in many North American climates, though Southern climates are less likely to require a vapor barrier.
Commercial roof insulation is a layer of material installed under the roofing membrane to create a thermal barrier between inside the building and the outside elements.
Roof Insulation plays a crucial role in reducing heating and cooling costs for residential and commercial buildings
A cover board is not required on every low slope roof, but they are often important in improving the quality of the roof.
A coverboad is a thin, dense substrate usually made of gypsum or high-density polyiso that is installed directly below the roofing membrane. However, the use of a cover board far exceeds that of a substrate.
It also serves as a critical component that helps to extend the life of a roof. Coverboards add much needed puncture and compression resistance which protect the roof against damage from hail, foot traffic, and tools used by other contractors on the rooftop equipment.
The roofing membrane is the top layer of a low slope roof. Its primary job is to provide waterproofing and UV protection to the roofing assembly.
In some instances, a layer of aggregate like river stone is placed on top of the roofing membrane to increase its durability and reflectivity.
There are many different kinds of roofing membranes, and this category is where we will focus next.
Let’s explore which roofing membrane is best for your roofing application!
Built Up Roofing
Built up roof membranes, referred to by the acronym BUR, have been in use in the U.S. for more than 100 years. These roof systems are commonly referred to as “tar and gravel” roofs.
The basic concept behind these roofs is very simple:
Multiple layers of reinforcing fabrics, or ply sheets are applied to the roof – each one fully adhered with asphalt or cold adhesive.
This creates a structure of alternating layers of reinforcing fabrics and asphalt.
You can create as many layers as desired (hence the name, built up roofing) but a fairly standard practice is a four-ply roof.
The final layer of asphalt is often topped with gravel or other chipped minerals for several reasons: to protect the asphalt from the sun’s ultraviolet rays, fireproof the material and add weight to secure the roof membrane
Benefits Of Built Up Roofing
- Time-tested technology. It’s hard to argue with more than 100 years of history.
- Redundancy. Built up roofs provide many layers of protection, so if the top layer is damaged, the additional layers below will continue to protect the building from water intrusion.
- Guarantees/Warranties. BUR systems may be eligible for guarantees or warranties of up to 20 years, depending on the materials used and the system installed. Check with the manufacturer for guarantee/warranty requirements and coverage.
- Reflective cap sheets available. White-coated cap sheets are available to help reflect the sun’s rays away from the building, which can help lower internal temperatures.
- Affordable: Built up systems are very affordable due to the relatively low cost of the materials.
Drawbacks of Built Up Roofing
- Hot, messy, and slow installation
- Heavy, adds weight to the structure, which must be accommodated
- Difficult to remove
- Difficult to detect and repair leaks due to multiple layers of material
- Manufactured on the roof, which can lead to inconsistencies in the install.
Modified Bitumen Roofing
Modified Bitumen (Mod Bit) roofing is an asphalt-based, close cousin of the Built-up-Roof (BUR) designed for buildings with low-slope or “flat” roof structures.
However, a modified bitumen roof generally consists of only two-three layers: one-two base sheets and a cap sheet.
The base sheet is often adhered to the roofing substrate. The cap sheet is either torched down, cold adhered, or self-adhered (Modified bitumen can also be applied in hot asphalt).
And though a modified bitumen roof may not have as many plies as a built up roof, it is still considered a thick and durable material.
- A modified bitumen roof has a thickness of about ⅜ of an inch. If you want to visualize it, that’s about 5 quarters thick.
- Single Ply systems (discussed later) are generally 60 or 90 thousandths of an inch. That’s equivalent to the thickness of one quarter.
Modified Bitumen is installed in one of three ways:
- Self-adhered: This means that each layer has a sticky backside that is covered in plastic. Upon removal of the plastic the layers stick down and seal when heated by the sun.
- Heat adhesive/welded: This usually involves a propane torch to melt the bitumen and seal it together. SBS and APP act differently when heated.
- Cold adhesive: Bitumen that is liquid at room temperature is used. This reduces potential fire risk and toxic fumes that can come from the heat adhesive.
Modified bitumen roofing can be broken into two small subcategories: APP (Atactic Polypropylene) and SBS (Styrene-Butadiene-Styrene).
APP vs. SBS Modified Bitumen Roofing
The basic difference between SBS and APP is that APP-modified bitumen is a “plastic asphalt” and SBS-modified bitumen is an “elastic asphalt.”
What is the difference?
APP-modified bitumen is modified with plastic in the form of APP (atactic polypropylene), and SBS-modified bitumen is modified with synthetic rubber in the form of SBS (styrene-butadiene-styrene).
APP is usually heat welded or torch applied and has a much higher “melt” point. This makes it much more difficult to overheat and damage. It also is a more rigid roof membrane.
SBS has a lower “melt” point and is much more flexible. It can be installed using cold adhesive or hot mopping of asphalt as well as a torch. However, it is more prone to overheating by inexperienced installers.
The great advantage of SBS bitumen roofing is that it can properly absorb the working of underlying structures (such as insulation) because it can stretch.
- APP bitumen roof coverings are most often installed in the northern states.
- SBS bitumen roof coverings are most often installed in the southern states.
Benefits Of Modified Bitumen Roofing
In general, a modified bitumen system works well. Here are a few benefits:
- Tear-resistant: The combination of fiberglass or polyester reinforcement layers make modified bitumen roofs hard to tear
- Energy-efficient: the top layer can be treated to add “cool roof” features such as solar reflectance and thermal emission
- Flexibility: modified bitumen expands and contracts without losing its shape (especially SBS)
- Strong: Because modified bitumen roofs have at least two plies, they are thicker than some options and more resistant to puncturing.
- Sealed system: Modified bitumen seals down to the roof so there are no seams. This makes it waterproof and resistant to leaks.
Disadvantages of Modified Bitumen Roofing
Like all roof types, a bitumen roof does have some drawbacks:
- Not the most inexpensive option
- Vulnerable to UV damage, especially without protective granules
- Torch applied membranes can be fire hazards (cold adhesive options are available)
- Ponding water causes modified bitumen roofing to break down, voiding warranties and leaving the roof susceptible to leaks.
Single Ply Roofing
Built up roofing systems require multiple layers of roofing material and asphalt in order to create a waterproof and durable surface.
Likewise, SBS and APP systems utilize multiple layers including a base ply, and an adhesive layer under the SBS or APP cap ply to finish the installation.
By contrast, single-ply roofing materials are carefully manufactured offsite and can be installed directly on the approved roofing substrate.
In other words:
They are manufactured with all the necessary components in one single role. All you have to do is apply one layer (singly ply) of the membrane to the roof.
However, there are different kinds of single-ply roofing – each with its unique strengths and weaknesses. Let’s explore the two main options so you can understand which is best for you.
Thermoset membranes incorporate principal polymers that are chemically cross-linked or vulcanized. Membranes that are vulcanized also may be referred to as “cured.”
One characteristic of true thermoset polymers is once they are cured, they only can be bonded to similar materials with adhesives.
The most common thermoset roof membrane is EPDM (ethylene propylene diene monomer).
EPDM is basically the modern version of traditional black rubber roofs. In fact, EPDM is considered a synthetic rubber and has the same feel as rubber used in inner tubes.
Traditionally, EPDM was available only in black, but in more recent years has become available with white coatings to increase reflectivity. In general, black is better for northern climates while white is a better option for southern climates.
EPDM membranes come in many sizes and are available as either reinforced or non-reinforced sheeting from 10 to 50 feet wide and up to 200 feet long. Depending on the roof design the larger sheets can be more economical to install, and they provide fewer seams, which are the most common places for water intrusion.
They come in varying thicknesses from .045 to .09 inches thick (about the thickness of one quarter).
Well-constructed, thoughtfully installed, and consistently maintained EPDM roof systems are very resilient.
They have been shown to withstand extreme weather patterns. EPDM is resistant to the ozone, as well as scuffing, abrasion and impacts from hail. The roofs are durable, even against thermal shock, and also resistant to heat and fire.
However, EPDM has always had one major Achilles Heel: the seams between the membranes are potential fail points. Adjacent sheets of EPDM are sealed together using tape or adhesives, which fail over time and allow for water to enter the building. This is even more of a problem in southern climates, where heat causes the adhesives to break down more quickly.
Pros and Cons of EPDM
So, let’s get down to the real business: what are the pros and cons of EPDM roofing?
- Cost: Compared to other types of roofing, EPDM is generally very low.
- Fire-resistant: This material actually slows down the progress of fires
- Long-lasting: You can expect an EPDM roof to last 20 years or longer, provided it is installed correctly.
- Environmentally-friendly: EPDM is 100% recyclable.
- Susceptible to puncturing
- Not pretty to look at: The utilitarian design is effective, but rubber isn’t pretty.
- Adhered seams break down over time
The second major category of single-ply roofing is thermoplastic roofing.
A thermoplastic membrane is a material made with a synthetic substance that softens when heated and rehardens when cooled – most similar to plastic.
Because of the way the material seals to itself, it is used as a single-ply roofing material—no other roofing layers are used during installation.
These single-ply roof membranes offer flexibility and can be installed using a variety of methods, including mechanical attachment, adhered and point-affixed (induction welded) installation.
There are two major types of thermoplastics used in roofing: polyvinyl chloride (PVC) and thermoplastic olefin (TPO). Let’s take a look at both!
PVC and TPO
Thermoplastic membranes—PVC and TPO—are similar to thermoset or EPDM membranes in application and usage, but the materials themselves are different.
PVC and TPO have a lower melting point and can be heated and melted again, whereas, once EPDM is vulcanized it can’t be re-cured.
For PVC and TPO the lap seams are heat-welded on site, to form an equally strong layer to avoid leaks and keep maintenance to a minimum. Plus, they always include a layer of reinforcing material.
Finally, they are most commonly a highly reflective white membrane, which is ideal for southern climates, where cooling costs are a significant concern for building owners.
So, which is better – PVC and TPO or EPDM?
EPDM is fire resistant, but can’t be remolded or reshaped after installation and has taped seams.
PVC and TPO have the advantage of being impact and chemical resistant, and they can be reshaped.
But what is the difference between PVC and TPO? And which is better?
The main difference between the two materials is that TPO does not use added plasticizers as PVC does.
Getting into the details of the difference can be a little mind-numbing, but we don’t mind making it simple:
TPO is generally less expensive, but PVC provides extra resistance to chemicals and animal fats (worth considering if you are roofing an airport, industrial building, or restaurant).
There are lots of roofing options to choose from when a commercial building needs a new roof.
But instead of being overwhelmed by the options, you can feel knowledgeable in choosing the right system for your application. And remember – your best source of information is a local roofing expert.
Local contractors know the conditions of your geographical area, and what is most important in choosing a roof.
We have skilled and experienced roofing crews, and we offer only the best roofing materials. We truly want to take care of your roof so you can focus on taking care of what matters to you.
And we make solving a problem with your roof easy:
- Get a free, no-obligation quote
- Get a roofing solution right for you
- Get the job done on-time and in-budget.
Contact us at Perry Roofing today. We look forward to hearing from you!