Building owners have many options when it comes to maintaining, repairing, or replacing their low-slope roof. One cost-effective option is to apply a maintenance coating system over an existing roof. If applied to a suitable low-slope roof membrane, a maintenance coating system can extend the useful service life and improve the overall performance of the roof membrane. Roof coatings can also be applied over a new roof to extend the manufacturer’s warranty and the expected useful life of the system.

This technical bulletin provides information on: 

• determining if an existing low-slope roof membrane is a good candidate for a maintenance coating;
• selecting an appropriate coating system; and
• preparing a substrate to receive a coating system.

These factors are all critical to the successful performance of a new and maintenance roof coating system.

Making A Cool Home More Comfortable

WEDGE ROOFING BRINGS STYLISH OLDER HOUSE INTO 21ST CENTURY

Developer Joseph Eichler and his Eichler Homes Inc. built approximately 11,000 single-family homes in California from 1949-66, mostly in the northern part of the state, and it’s easy to see why their innovative, California-cool design proved popular with homeowners.

Designed to bring the feel of the outdoors into the home, the typical Eichler house features glass walls from floor to ceiling, post-and-beam construction, large skylights, an open floorplan and an expansive atrium. The influential style became known as "California Modern," which now seems like a misnomer given that many of these midcentury homes still lack the modern comfort of air conditioning.

In recent years, one family in San Rafael had hired Petaluma-based Wedge Roofing to install roofs on several properties, so when it came time to upgrade their own Eichler home, they knew just whom to call.

For Wedge Roofing, the task was to help bring the home into the 21st century. Not only was there no air conditioning, but the original integral radiant heating system installed within the concrete-slab floors had failed due to water leaks in the inaccessible pipes. For several years, the family had resorted to using electric space heaters to warm individual rooms.

With winter approaching late last year, the family decided that it needed a modern HVAC system, so it hired an HVAC contractor to install hundreds of linear feet of small-diameter, highvelocity ductwork on the roof.

Given the home’s distinctive style, the homeowner wanted the roof to retain its original aesthetics, without large, above-roof ducting strewn about and visible from the street. So, Wedge Roofing was hired to essentially encase that ductwork in a new roof, creating a uniform surface about 8 1/2 inches above the original roof surface.

On similar projects, after the HVAC contractor completes the ductwork, Wedge Roofing would spray polyurethane foam over and around it to conceal it and create a flat roof surface. But in this case, the homeowner and HVAC technician were concerned that heat from the SPF application could damage the ductwork. Consequently, Wedge Roofing would have to use 328 sheets of closed-cell, 2.5-pound rigid foam insulation board to envelope each piece of ductwork on the 3,500-square-foot roof.

The sheets measured four feet by eight feet, and only 20 percent of them were installed as is, without needing to be individually carved or shaped to fit around ductwork. That fill board, including some pieces cut down to less than two square feet, was glued into place using low-rise foam adhesive.

The boards were two inches thick, so Wedge Roofing had to repeat the process of gluing boards in place three times to create a new surface six inches above the old one. After the final layer was applied, workers used masking tape to cover the seams between pieces of fill board.

Fortunately, Wedge Roofing’s finish carpenter, Eric Carreno, was onsite making structural modifications and curb installations for a new, electrically powered Rollamatic skylight, which can be opened and closed with the push of a button. His help in cutting the fill board into perfectly sized pieces proved invaluable, said Gary Harvey, general manager of Wedge Roofing.

"His layout skills in measuring and designating where to cut were worthy of fine craftsmanship associated with cabinetmaking," Harvey said. "After all the detail work was done, this application still required a one-inch-thick rigid polyisocyanurate cover board to be set in low-rise adhesive to provide a nice, smooth surface on which to spray."

Given that the roof was a spider web of trip hazards, Wedge Roofing used perimeter warning lines around the edges of the roof and the large skylight opening, and supervisors held a meeting each morning to reiterate the need to watch where literally every footstep landed on the rooftop.

"Our greatest fear was that we would inadvertently puncture or damage some minute section of the hundreds of feet of ductwork," Harvey said. "We tested the HVAC system prior to work commencement along with the contractor, and then we tested the system at the completion of the cover board and, finally, at the completion of our roofing project. We are happy to say there were no punctures or damage to the HVAC system or ducting."

Next, the crew used a Graco E-30 integrated spray foam machine with a Graco Fusion Air Purge gun equipped with a low-rise foam adapter kit. Workers sprayed 1.5 inches of Evercell 3.0 closed-cell, 2.7-pound SPF from Everest Systems. Harvey said one challenge involved spraying SPF directly onto rigid polyisocyanurate, which tends to pinhole and blister due to its construction with a paper backing.

"We sprayed a half-inch flash pass across the rigid insulation in the areas that pinholed or blistered, and then we would scuff or abrade it by lightly dragging a tear-off shovel across it or even scuffing it with our feet, which yielded a very suitable surface to spray to," Harvey said. "A small amount of cleaning and prepping was required, and then you could spray to it like any other surface."

The final step was to break out the Graco GH 933 Big Rig gas hydraulic airless sprayer and the Graco XTR-7 airless spray gun. The crew applied 2.5 gallons of GE Enduris 3500 silicone coating from Everest Systems along with C-93 gray granules supplied by Beacon Roofing Supply.

Wedge Roofing used nine workers in total, including members of its carpentry, demolition and preparatory teams simultaneously on the first two days of the project, which allowed the company to finish the job in six days instead of the projected seven or eight. The family moved back into the home just in time for Christmas, making for a happy holiday.

After almost a week of prep work and one day of spraying, Wedge Roofing had created a beautiful roof with a sky-high R-value of 49, ensuring that the home will stay warmer in the winter and cooler in the summer.

"Underneath the roof surface there is an incredible amount of plumbing lines and air-conditioning ducting, so to just simply look at it and think, ‘Wow, that’s a great roof,’ doesn’t take into consideration all of those components and the all the work that got you to that point," Harvey said. "Normally, the roof is just a roof, but in this case, it was so much more. We were proud to be chosen to protect and upgrade this timeless home."

By: Nick Fortuna

Article Courtesy of SPRAYFOAM PROFESSIONAL

CLICK HERE TO CONTINUE...

Greetings WSRCA Members,

As a follow-up to the Western Roofing Expo Seminar “Roof Wind Speeds: ASCE 7, Uplift Ratings & Warranties” Brian Chamberlain of Carlisle Construction Materials is releasing his PowerPoint presentation to the WSRCA membership for their roofing design library.
 
An ongoing issue that frustrates the industry as a whole is the confusion in how a roofing assembly will meet the building code, will meet an uplift rating, and be warranted based on local wind speeds. Since local wind speeds is the common factor in all three, an understanding of how wind speed is used associated to each needs to be clarified. This presentation focuses on the process, from uplift to warranty.

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LEGAL  DISCLAIMER

All rights reserved.  All content (text, trademarks, illustrations, reports, photos, logos, graphics, files, designs, arrangements, etc.) in this Technical Opinion (“Opinion”) is the intellectual property of Western States Roofing Contractors Association (WSRCA) and is protected by the applicable protective laws governing intellectual property. The Opinion is intended for the exclusive use by its members as a feature of their membership. This document is intended to be used for educational purposes only, and no one should act or rely solely on any information contained in this Opinion as it is not a substitute for the advice of an attorney or construction engineer with specific project knowledge. Neither WSRCA nor any of its, contractors, subcontractors, or any of their employees, directors, officers, agents, or assigns make any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or any third party’s use (or the results of such use) of any information or process disclosed in the Opinion.  Reference herein to any general or specific commercial product, process or service does not necessarily constitute or imply its endorsement or recommendation by WSRCA. References are provided as citations and aids to help identify and locate other resources that may be of interest, and are not intended to state or imply that WSRCA sponsors, is affiliated or associated with, or is legally responsible for the content reflected in those resources. WSRCA has no control over those resources and the inclusion of any references does not necessarily imply the recommendation or endorsement of same.

Courtesy of: George Daisey — The Dow Chemical Company

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Installing or restoring a roof can be a tremendously complicated endeavor. There are single ply membranes, roof systems, coatings, concrete, metal and many more variations to choose from, which leads anyone to ask what substrate do I choose? To add further complexity, within the coatings option alone there are a variety of product types available: silicone, acrylic, polyurethane, and asphalt? Each presents notable features, strengths, and weaknesses to consider.

ROOF COATINGS MARKET OVERVIEW

The roof coatings market in the Unites States is a growing, vibrant market. According to data from the US Census Bureau combined with Dow internal analysis, it’s estimated the total US Construction Market is valued at approximately $1.1 trillion. Roofing is a little over 1% of that total which still represents a staggering $14 billion value. Within the scope of roofing, is a bright and shining market called roof coatings. The roof coatings market is rapidly approaching 6% of the total roof market with a value of approximately $780 million (see Figure 1.). There are many factors contributing to this growth but I will mention just one: the ever-aging building inventory. As buildings get older it becomes more common that two roof systems have already been installed and doing a third roof system either means tearing the first two completely off and starting over, or applying a maintenance product like a roof coating. In terms of cost savings and less impact on the environment, roof coatings win that debate almost every time.

In terms of growth, all three of these market segments can be described as healthy and growing. The same sources of information describe the total construction market growing at a compound annual growth rate (CAGR) of 8.2%. The $14 billion roofing segment is growing at 5.2% CAGR, and the roof coatings segment is humming along at a 4.7% CAGR. Compare this to the US GDP (Gross Domestic Product) which during the same period grew at a modest 2.4% CAGR. During that same period the US GDP was valued at $17.9 trillion; the US Construction market represents over 6% of the total US GDP. All these numbers simply show that these markets are large, vibrant, growing and poised to continue delivering advancements.

In fact, if we look at data spanning 2011 through 2016 we see the US roof coatings market growing at a rate of 5.2% CAGR, and that rate appears to be steadily increasing year over year. Starting from a total market value of $653 million in 2011, the growth rate has steadily increased on average to reach an annual growth rate in 2016 of 7.8% CAGR.

The two fastest growing segments in the roofing market are Thermoplastic Polyolefin (TPO) membranes and roof coatings (see Figure 2.). The tightening regulations on energy efficiency and lowering Volatile Organic Compounds (VOCs) have fueled demand for energy-efficient and low VOC products like TPO membranes and roof coatings.

Roof coatings show steady growth but indicators express the fastest growing portion of the roof coatings market is in higher performing coatings. It is easy to drive volume with lower cost products, but when growth is seen in higher value portions of a segment, there is good news for all parties. This means the customer is moving towards higher performing products that will deliver more value and longer service lifetime. The contractor is able to capture more value by selling and installing higher value products, and the manufacturer is also benefiting by offering the contractor higher value and higher performing products.

WHY CHOOSE A ROOF COATING

With so many choices for roofing, why would you choose a roof coating? There is no one answer to this question. Roof coatings come in many varieties not limited to water-based, solvent-based, reflective, non-reflective, thick-film, thin-film, white, black and all colors in between. Where do I start?

First, let’s answer the question posed above; why choose a roof coating? The first answer that often comes to mind is sustainability. In the United States alone, more than 251 million pounds of waste finds its way to landfills and nearly 40% of that waste comes from construction projects1. According to a Construction and Demolition Recycling article published in March 2018, global construction waste will double from the 1.3 billion ton total in 2012 to 2.2 billion tons by 2025. Identifying volumes of particular waste products is often difficult due to the variety of classes assigned to waste products; although certain roofing materials like shingles, asphalt and concrete are often mentioned in published waste studies.

If we truly want to offer sustainable products that make a difference to our environment, roof coatings are a great way to accomplish this objective. The application of a roof coating can extend the life of an existing roof and minimize the need to tear off a roof and send those materials to a landfill. In fact, whether the roof coating installation is new or retrofit, regularly scheduled recoating of that roof can reduce the need to landfill the original roofing assembly and lead to a viable solution for that roof. Looking for a sustainable solution? Then roof coatings are your answer!

How about sustainability from the standpoint of energy consumption? Energy efficiency is becoming more important to everyone. From the building owner dealing with utility bills to the occupants dealing with comfort level of the built environment, energy efficiency and performance of buildings is important. One of the most impactful jobs I ever participated in was a production facility where the building owner needed eight HVAC units to cool the building and office areas still never reached below 76 degrees. The roof was a black surface and the owner hired a contractor to convert the roof to a reflective surface by applying a reflective roof coating. After the installation, the owner stated that he was able to shut down three of the HVAC units and maintain a comfortable 72 degrees in the office spaces. That’s a win for everyone involved from contractor to owner to occupant.

Climate change is a hot topic almost everywhere you go, from construction sites to conference room meetings; even to your social media conversations. Everyone is talking about climate change, the environment and our planet. We all want to live better. Whether you believe reports of global warming, global cooling, and climate change or subscribe to none of it, constructing sustainable buildings and saving energy enables us to build a better future. Roof coatings can be a huge part of any sustainable, energy efficient building design project.

A building owner or other key decision-maker is often confronted with the choice of maintenance versus capital investment for a roofing project. A capital investment often means the cost of that roof installation is depreciated over many years; whereas a maintenance project can often be deducted in the same tax year. Most roof coatings installations fall under the maintenance category which allows the building owner to deduct the costs immediately. Note, tax laws change frequently; always check with your tax advisor to verify. This life cycle cost analysis compares two roof maintenance scenarios to demonstrate the value of roof maintenance.

Easy – and quiet – installation is a winner and roof coatings can deliver this in almost every situation. When a tear-off and complete roof assembly installation is done, there is often major disruption of building activities as well as areas around the building. Large trucks hauling materials in and waste out.

Sections of the parking lots cornered off to allow for trucks and materials to be moved and stored. Let’s not forget the dust and debris generated during construction. But many roof coatings jobs can be done in “stealth mode.” Buckets, drums or even totes of roof coatings can be delivered to a job site and transported up to the roof without many people aware that it is happening. I’ve personally been on jobs where the buckets are transported up a service elevator to the roof and the occupants do not know the roof is being coated!

We choose products because we want them to perform well. Roof coatings not only protect the existing roof and extend its service life, but roof coatings can deliver measurable performance. A roof coating may offer one or more of the following performance benefits: extended service life, water resistance, waterproofing, enhanced solar reflectivity and/or thermal emittance. Often, a roof coating enhances the appearance as well be transforming a dingy, dirty roof into beautiful colors ranging from basic white or black to a variety of highly decorative shades.

Selecting a roof coating for its variety of benefits is a first step. Now comes the hard part – which type of roof coating do I choose? Let’s explore some of the most common options on the market today, including their benefits, challenges and typical service life.

ACRYLIC

Acrylic roof coatings can be based on 100% acrylic or styrene-acrylic copolymers. Focusing on 100% acrylic roof coatings, these coatings offer excellent durability as well as the following typical properties: UV resistance, good permeance, dirt resistance, water resistance, and abrasion resistance. Acrylic coatings are water-based, easy to apply, easy to cleanup, and cure times can be tunable from several hours down to several minutes. Acrylic coatings are often installed as coating-only, but a growing sub-segment of acrylic coatings is as part of a liquid-applied membrane. Those familiar with acrylic decorative paints are familiar with a wide color palette, but for roof coatings that can vary. Steep slope thin film roof coatings can be supplied in a diverse color palette, but low slope elastomeric acrylic roof coatings are limited to white or light pastel colors. Deeper colors in these elastomeric coatings are possible to formulate but these colors often do not hold pigment as well, which leads to other technologies being used when deep colors are required. Acrylic roof coatings are limited to good weather conditions during installation because they are water-based. Excessive humidity or extreme temperatures can limit the success of an acrylic roof coating installation. Constant exposure to ponded water is also challenging for most acrylic roof coatings, resulting in impaired adhesion, blistering and delamination. However, the formulating space for acrylic roof coatings is wide; hence coatings can be formulated into anything from an economy coating up to an exceptionally high performing, durable coating. This variety makes acrylic roof coatings a great choice for the contractor looking for anything from an economical, low service life roofing solution up to a multi-decade lifetime roofing solution.

STYRENE-ACRYLIC

Styrene-Acrylic copolymers are a subset of the acrylic roof coating technology and should be treated separately. At a fundamental level, the styrene monomer is not as UV stable as the acrylic monomers used in roof coatings. Combining styrene with acrylic monomers to form a styrene-acrylic copolymer can deliver good performance properties; however, notably high performance is difficult to achieve versus the juggernaut of acrylic-acrylic copolymer interactions. In the roof coatings market, styrene-acrylic coatings are usually found in the economy space or in the lower warranty products. The good news is that styrene-acrylic roof coatings do have some notable performance properties, including excellent adhesion to metal and concrete and re-coats over existing acrylic roof coatings.

SILICONE 

Silicone roof coatings are all the buzz in the roof coatings industry. These coatings are not water-based and come in either low solids (~67%) or high solids (~98%) formulations. Silicone roof coatings are extremely resistant to water absorption, with some products literally having 0% water absorption according to standard ASTM D471 tests. The silicone polymers used in these coatings are UV light stable, do not degrade when exposed to sunlight, and thus offer one of the highest service life guarantees of any coatings option per installation. For commercial roofing, ponded water areas are the most challenging space on a roof for any coating, but silicone roof coatings are specially designed to perform well in those high moisture situations. A few challenges do exist for silicone roof coatings; including the need for primers over most surfaces, poor asphalt bleed resistance, difficulty to recoat, and low abrasion resistance. However the long service life and water resistance make the silicone roof coating a popular choice for low slope commercial roofing. Due to the slippery nature of the surface on a silicone roof coating, they are often not recommended for steep slope roofs.

POLYURETHANE 

Polyurethane (PU) chemistry delivers some noteworthy properties versus the coatings already discussed. A PU roof coating will often offer exceptionally high tensile strength and elongation versus other technologies. In situations where high tensile strength, toughness and chemical resistance are desired, PU roof coatings are an excellent choice. Adhesion and water resistance are often very good with PU roof coatings. It is important to note that PU coatings can come in either aromatic or aliphatic type chemistries. Only the aliphatic type are UV stable and offer long-term durability. These coatings are solvent-based and do need specialized spray equipment separate from either silicone or acrylic.

ASPHALT

Asphalt coatings are the oldest technology discussed in this article. The use of asphalt can be traced back to the ancient cultures like Greece and Babylon2. In fact, the earliest known use of asphalt dates back to around 615 B.C. when King Nabopolassar paved the streets of Babylon with asphalt and burned brick so he could have easy access in and out of his palace. In modern day roof coatings, asphalt coatings come in a variety of forms. There is traditional hot mop asphalt where the solid asphalt is heated and melted before being rolled or broomed onto a roof. Newer versions of this black color coating are in emulsion form where the asphalt is emulsified in water either through mixing with surfactants or high pressure processes. Further differentiation is between traditional black asphalt coatings and the newer silver or reflective asphalt coatings. Both in solvent and water-based emulsion form, the reflective asphalt coatings fit in a niche space between non –reflective and highly reflective roofing products. Hot mop asphalt and cold-applied asphalt emulsion are often applied to the roof as the waterproofing layer. With their near-zero permeance and hydrophobicity, there is no better waterproofing coating for roofing than asphalt coatings. These basecoat/primer coatings can then be top-coated with reflective aluminized asphalt or acrylic roof coatings. In some cases, the desire is to have a black surface so the asphalt coating is the final coat as well. The reflective aluminized asphalt coatings have good solar reflectivity and low thermal emissivity giving them a significant energy value proposition. Lifetime expectancy of aluminized roof coatings have improved over earlier incarnation of the technology due to improved formulation quality and refinement of the aluminum flake. In climates or situations where both very high reflectivity and emissivity are not desired, the moderate energy performance of the aluminized roof coatings can be the best choice.

SEBS 

Styrene Ethylbutylene Styrene or SEBS coatings are solvent-based coatings that offer excellent water resistance and very low permeance. Often SEBS is positioned against acrylic roof coatings as having an extended season of use; not as subject to the cold temperatures encountered in the shoulder seasons. SEBS coatings can be described as super-hydrophobic and will have a moderate service life versus silicone or acrylic roof coatings. The challenges for SEBS coatings include high VOCs and limited color option; typically only sold in white according to leading distributors of the product.

POLYUREA

Polyurea roof coatings are a very small percentage of the roof coatings market, but they offer an excellent property balance and can be the right choice for many roofs. Polyurea roof coatings are great waterproofers, have excellent chemical, abrasion and corrosion resistance and have an extended application season versus water-based systems. Some of the challenges are high VOCs and the reactive chemistry. An acrylic roof coating will dry by evaporation of water typically over a few hours, whereas the polyurea chemistry is reactive causing the coating to cure in a matter of seconds. The applicator must have a high skill set to spray this type of coating. Exterior durability is moderate, but long service life is never the driver for polyurea coatings; it is usually the chemical resistance or waterproofing properties that drive the use of polyurea.

PVDF

Polyvinylidene Fluoride or PVDF coatings are different from the previously discussed coatings in many ways. First, they are not applied to commercial roofs in thick films. Often a PVDF roof coating is applied at 2 to 4 dry mils thick. The cost per pound of a PVDF coating is much higher than other technologies, but is counter-balanced by the performance it can deliver in a thinner film. The benefits of PVDF over other coatings include improved dirt pickup resistance, long-term reflectivity, long-term durability, water repellency and mildew/algae resistance. Colors are no challenge for PVDF as they can be supplied in a diverse color palette. The main challenge is balancing the hardness and toughness of the PDVF coating versus the flexibility of the elastomeric basecoats often applied before the PVDF coating. PVDF coatings have advanced over the years and though earlier versions suffered from cracking issues, newer offerings have improved their crack resistance. It is always a challenge to apply a hard, rigid coating over a soft flexible coating, which must be understood by the contractor/applicator.

CONCLUSION

There are a diverse variety of roof coating technologies available in the North American market. Each roof coating technology has its noteworthy balance of properties and features that need to be understood by the buyer and user to determine the best option for intended use. Beyond roof coating product properties, type of substrate, service life, maintenance planning, sustainability benefits, and cost are considerable factors to help the coating chosen to meet the needs of the job.

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1 Mike Hower, Marketing Communications Manager, Carbon Lighthouse, 2013

2 https://actionasphalt.net/storied-history-asphalt-pavement/

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LEGAL  DISCLAIMER

All rights reserved.  All content (text, trademarks, illustrations, reports, photos, logos, graphics, files, designs, arrangements, etc.) in this Technical Opinion (“Opinion”) is the intellectual property of Western States Roofing Contractors Association (WSRCA) and is protected by the applicable protective laws governing intellectual property. The Opinion is intended for the exclusive use by its members as a feature of their membership. This document is intended to be used for educational purposes only, and no one should act or rely solely on any information contained in this Opinion as it is not a substitute for the advice of an attorney or construction engineer with specific project knowledge. Neither WSRCA nor any of its, contractors, subcontractors, or any of their employees, directors, officers, agents, or assigns make any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or any third party’s use (or the results of such use) of any information or process disclosed in the Opinion.  Reference herein to any general or specific commercial product, process or service does not necessarily constitute or imply its endorsement or recommendation by WSRCA. References are provided as citations and aids to help identify and locate other resources that may be of interest, and are not intended to state or imply that WSRCA sponsors, is affiliated or associated with, or is legally responsible for the content reflected in those resources. WSRCA has no control over those resources and the inclusion of any references does not necessarily imply the recommendation or endorsement of same.

By Rick Duncan, Ph.D., P.E.,

Technical Director, Spray Polyurethane Foam Alliance (SPFA)

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The sustainability focus in buildings has shifted lately to one on energy performance. Not only have building codes become more stringent, with a much greater emphasis on energy efficiency, but many incentives have been introduced and made available to owners, providing them with tax credits and savings for the integration of renewable energy sources such as solar onto their homes and projects.

Increasingly ambitious movements, including Passive House and Zero Net Energy (ZNE), are also gaining in popularity as immediate issues like climate change, and the catastrophic effects of it, are top-of-mind and ever present in the news.

Even though ZNE is a bigger energy goal than what is currently highlighted for many structures, architects, builders and owners are increasingly integrating sound energy practices in their buildings. As a key component of the building enclosure, roofing systems tend to transfer (i.e. lose) significant amounts of energy if not properly designed or well maintained. Thus, it is unsurprising that they are a key focus in buildings designed to minimize energy use.

Spray Polyurethane Foam (SPF) and Photovoltaic (PV) systems are now, more than ever, utilized together on the roof as a complete solution for energy savings. SPF reduces demand for the energy generated by photovoltaics, which can make a significant difference in ZNE buildings. When combined, they provide a joint solution for the generation of renewable energy, the conservation of heating and cooling energy, and, ultimately, the elimination of the structure’s dependence on fossil-fuel consuming electricity sources.

Regardless of whether ZNE is the end goal, SPF and PV integrated in roofing are an ideal combination for many structures, providing unparalleled return on investment through energy cost savings, as well as numerous additional benefits. However, contractors should be mindful of some important installation considerations when looking to join these two powerful systems on the roof of a building, to ensure highest possible performance and lifespan.

PV System Overview

PV cells are the basic unit used to convert light to electricity. Many PV cells are bundled together to make a PV panel, or module. PV panels are grouped electrically to create a PV string. And depending on the system size, two or more strings are combined to create a PV array.

The dominant type of PV panel used with SPF roofing is cSi, or crystalline silicon. cSi is a typically rigid panel with glass frame and metal frame and may be applied, unlike other dominant PV panel types, via rack installation methods.

A photovoltaic system includes many components in addition to the panels. Components include racks, rails, rooftop attachment devices, grounding systems, wiring and wiring harnesses, inverter(s), and connection to the main electrical panel. Components may also include control modules and storage batteries for off-grid PV system installations.

Photovoltaic panels must be handled and maintained with caution. Electricity is produced when a single panel is exposed to light, however, because a panel is not part of a circuit, that electricity will not flow until the circuit is complete. A worker may complete the circuit by connecting the two wires from the backside of a PV panel.

When maintaining a PV system, it may become necessary at some point to disconnect or remove an individual panel from a string or an array. The whole system must be shutdown properly as a precautionary measure to prevent shocks from occurring to workers and arcing between electrical connections. This “shutdown” procedure must be followed with precision as part of a lock-out/tag-out program and is provided by the inverter manufacturer. Under no circumstances should SPF contractors ever disconnect or decommission a PV panel or system unless they are trained and qualified to do so.  

Rooftop PV Installation Types for Use with SPF

Rooftop PV systems can vary significantly in size. Large footprint buildings can employ PV systems rated from 50 kW to 1000 kW or larger while residential rooftop PV systems are commonly 3 kW to 5 kW solutions.

Rooftop PV systems may be installed either on racks or adhered directly to the roof surface. When looking to combine PV with SPF, it is generally not advised to adhere or place the PV panels directly onto the roof surface. Solar heat as well as water can accumulate between the PV and roof coating and can negatively impact coating performance.  Moreover, panels applied directly to a low-slope roof will, in nearly all cases, not optimally align with the sun, which will reduce energy production. 

Non-penetrating rack systems may be placed directly on a rooftop and held in place with ballast. Racks may also be installed with penetrating supports that require flashings. Each type provides advantages and disadvantages. For example, ballasted racks may block water flow and affect drainage, while penetrations require leak and maintenance-prone flashings. SPF is unique in that it easily self-flashes around penetrating supports.

Design Considerations

Rack-mounted arrays with penetrating attachments are fairly lightweight at two to three pounds per square foot, and ballasted arrays add four to six pounds per square foot. With the latter however, more ballast is utilized at the perimeters and corners of a PV array. Thus, localized loading from ballast may reach as high as 12-17 pounds per square foot, which must be considered. Most SPF roofing systems have a compressive strength of 40-60 psi. 

PV panels add weight to a rooftop and this must be factored into the design and installation. Existing structures should be analyzed by a structural engineer to determine if the additional weight of the PV system is acceptable.

Additionally, roofs are required by codes to provide “live load” capacity, a measurement, which includes people, snow, and other temporary weight-bearing scenarios that may occur. The weight of a PV system is typically below the live load capacity, however in the absence of a structural analysis, the live load capacity will be reduced by the addition of the PV system. A final consideration is whether a PV installation will create new locations for drifting snow, which may add considerable weight to a roof, and must be factored in.  When determining key considerations for wind load and fire safety, best practices require deferral to the PV supplier.

Drainage on rooftops is important for safety of the structure and longevity of the roof. PV arrays often have many points of contact with a roof, and these are possible locations that will block or slow drainage.  PV racking should be positioned to minimize ponding water, and/or include methods such as notched pads to allow drainage under points of contact, especially for ballasted systems. 

Photovoltaic panels convert approximately 15-20 percent of light to electricity, leaving the remaining unconverted energy to be released as heat. Additionally, PV panels are more effective when their temperature drops. It is for each of these reasons that the majority of rooftop PV installations are designed to encourage airflow under panels, which reduces the temperature of the panels, improves conversion efficiency and releases heat effectively. Photovoltaic panels installed 4 to 5 inches above the roof will not change the temperature of the roof and, instead, provide shade to the surface of that roof. This additional shade may extend the life of SPF roof coatings.

Service Life and Maintenance

Ideally, a roof system, whether SPF or another material, and the PV system should have the same expected service life.  Removal (decommissioning) and reinstallation (re-commissioning) of a PV system is costly, and the cost should be weighed relative to the residual service life of the existing roof and cost of roof replacement or recoating at the time of PV installation.  Ballasted, rack-mounted PV systems are difficult, if not impossible, to reroof (or recoat) under and around.  Elevated racks with adequate space beneath may be able to be left in place when reroofing.  A PV system that covers, for example, 10% of the rooftop will be easier to relocate during reroofing than a PV system that covers 75% of the rooftop.  Building owners should be advised of future reroofing and maintenance costs with roof-mounted PV systems. 

The life expectancy of the SPF roof system should align with the service life of the PV system, and coatings factor in as they can extend the life and improve performance of SPF on the roof.

Roof systems used as platforms for PV systems must be tough and durable, and generally speaking, SPF has greater compressive strength as density increases. Higher density SPF systems may be preferred, especially when ballasted support systems are used. 

An SPF system will be stressed during the installation of the PV system and coatings and granules will help protect the roof during this time, and during scheduled maintenance. Because a roof surface below PV panels will likely not dry as fast as non-covered portions, coatings that stand up better to standing water and biological growth should be selected.  Installation of PV systems on SPF roofing will inevitably create additional foot traffic. It is important to protect heavily trafficked areas with additional coating and granules or walk pads. The cost to do so is low and will protect the service life of the roof.

All roof mounted PV systems should be inspected and maintained at least twice a year. Wiring, attachment points and flashings should be inspected and cleaning of the top surface of the PV panels may be required.

To maintain and service the roof and PV system, workers must be able to access both. PV systems should not block access to drains, penetrations, flashings, mechanical units or other rooftop equipment. Similarly, PV systems should be installed so maintenance workers can access wiring, inspect panel-to-racking connections, and properly clean top surfaces without stepping on PV panels.

Summary

In closing, while there are many considerations to the application of PV systems in combination with SPF roofs, the complete energy generation and conservation solution provided by the two integrated systems performs notably well. The energy cost and earth saving benefits are both undisputable and hard to ignore.

About the Author

Rick Duncan, Ph.D., P.E is the Technical Director of the Spray Polyurethane Foam Alliance (SPFA), the industry’s leading organization representing contractors, material and equipment manufacturers, distributors and industry consultants. The SPFA promotes best practices in the installation of spray foam and offers a Professional Certification Program to all those involved in the installation of the product.

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