Substrate Boards

The third installment in my series on the roof system is about the substrate board. (To read my first two articles, “Roofs Are Systems” and “Roof Decks”, see the January/February issue, page 52, and the March/April issue, page 54, respectively.) For the purpose of this article, we will define the substrate board as the material that is placed upon the roof deck prior to the placement of thermal insulation. It often is used in part to support vapor retarders and air barriers (which will be discussed in my next article in the September/October issue).

The type of substrate board should be chosen based on the roof-deck type, interior building use, installation time of year and the cover material to be placed upon it.

The type of substrate board should be chosen based on the roof-deck type, interior building
use, installation time of year and the cover material to be placed upon it.

Substrate boards come in many differing material compositions:
• Gypsum Board
• Modified Fiber Reinforced Gypsum
• Plywood
• High-density Wood Fiber
• Mineral Fiber
• Perlite

Substrate boards come in varying thicknesses, as well: 1/4 inch, 1/2 inch, 5/8 inch and 1 inch. The thickness is often chosen based on the need for the board to provide integrity over the roof deck, such as at flute spans on steel roof decks.

TOUGHNESS

The type of substrate board should be chosen based on the roof-deck type, interior building use, installation time of year and the cover material to be placed upon it. For example, vapor retarder versus thermal insulation and the method of attachment. Vapor retarders can be adhered with asphalt, spray foam, bonding adhesive, etc. The substrate board must be compatible with these. You wouldn’t want to place a self-adhering vapor retarder on perlite or hardboard because the surface particulate is easily parted from the board. Meanwhile, hot asphalt would impregnate the board and tie the vapor-retarder felts in better. The substrate board must have structural integrity over the flutes when installed on steel roof decks. The modified gypsum boards at 1/2 inch can do this; fiberboards cannot. If the insulation is to be mechanically fastened, a substrate board may not be required.

It should be more common to increase the number of fasteners to prevent deformation of the board, which will affect the roof system’s performance.

It should be more common to increase the number of fasteners to prevent deformation of the board, which will affect the roof system’s performance.

The substrate board should be able to withstand construction-generated moisture that may/can be driven into the board. Note: In northern climates, a dew-point analysis is required to determine the correct amount of insulation above the substrate board and vapor retarder, so condensation does not occur below the vapor retarder and in the substrate board.

Substrate boards are often placed on the roof deck and a vapor retarder installed upon them. This condition is often used to temporarily get the building “in the dry”. This temporary roof then is often used as a work platform for other trades, such as masonry, carpentry, glazers and ironworkers, to name a few. The temporary roof also is asked to support material storage. Consequently, the substrate board must be tough enough to resist these activities.

The most common use of a substrate board is on steel and wood decks. On steel roof decks, the substrate board provides a continuous smooth surface to place an air or vapor retarder onto. It also can provide a surface to which the insulation above can be adhered. Substrate boards on wood decks (plywood, OSB, planking) are used to increase fire resistance, prevent adhesive from dripping into the interior, provide a clean and acceptable surface onto which an air or vapor retarder can be adhered, or as a surface onto which the insulation can be adhered.

PHOTOS: HUTCHINSON DESIGN GROUP LTD.

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Spray Polyurethane Foam Has Structure-strengthening and Energy-efficiency Capabilities

A high-performance building material, spray polyurethane foam (SPF) is widely used as an effective, lasting roofing solution. With positive benefits, including versatility, thermal insulation, resistance to inclement weather cycling and storms, strengthening of the building envelope, long life span and durability, spray foam has enjoyed increased use among builders and roofing contractors alike.

A roof’s primary purpose is to protect the structure underneath it. As a roofing material, closed-cell SPF acts as a protective roofing mechanism and a thermal insulator. The lightweight material is ideal as a roofing solution when:

 As a roofing material, closed-cell SPF acts as a protective roofing mechanism and a thermal insulator.

As a roofing material, closed-cell SPF acts as a protective roofing mechanism and a thermal insulator.

  • the roof substrate has many penetrations.
  • the roof deck is an unusual shape or configuration.
  • the roof is being applied to a structure located in a severe-weather environment.
  • a lightweight option is needed.
  • a slope application is preferred to provide extra drainage capabilities.
  • keeping the existing roof cover is desired.

STRENGTH AND DURABILITY

SPF is considered a highly durable building material. The physical properties of the foam change little with time, accounting for a life span up to 30 years with regular care and maintenance. SPF roofing systems also strengthen the roof in multiple ways. Roofing spray foams possess a compressive strength of 40 to more than 60 pounds per inch. Spray foam’s adhesion strengthening capabilities are key, especially in locations where severe weather cycling, storms, wind, hail and other conditions are prevalent and commonly cause structure damage. Coastal and hurricane-prone regions are prime examples.

When applied to the interior side of a roof, closed-cell SPF can increase a building’s resistance to wind uplift during severe storms. When SPF is applied to built-up roofing and metal substrates, it increases resistance to wind uplift even further. A study conducted by the University of Florida, Gainesville, in 2007 found that applying closed-cell spray foam under a roof deck provides up to three times the resistance to wind uplift for wood roof sheathing panels when compared to a conventionally fastened roof.

Spray foam is a good solution for unusual configurations and areas with many penetrations.

Spray foam is a good solution for unusual configurations and areas with many penetrations.

Spray foam also is resistant to progressive peeling failure. Caused by wind, peeling happens at the roof’s edges when wind pulls flashings and copings away from their installed positions. Peeling looks like a tin can after it has been cut around the perimeter. When this happens, a chain reaction may occur and lead to catastrophic building failure. After the roof membrane, panels or tiles pull away, the board-stock insulation is exposed, often with less resistance to the lateral and uplift wind forces. Then the sheathing below and the substructure are subject to movement and wind or water damage, potentially leaving the entire building interior underneath open and vulnerable. SPF roofing is continuous, so it provides a water-resistant layer that is well adhered to the substrate.

When the Gaithersburg, Md.-based National Institute of Standards and Technology examined roofs following Hurricane Katrina, it found buildings with spray-foam roofs performed rather well without blow-off of the SPF or damage to flashings. The 2006 “Performance of Physical Structures in Hurricane Katrina and Hurricane Rita: A Reconnaissance Report” found that only one of the examined SPF roofs incurred notable damage, and that damage was confined to only 1 percent of the total roof system. The report concluded spray foam kept the roofs intact, prevented moisture from entering the buildings, and protected the structures from hail and debris.

Hurricane Katrina played a significant role in one of the largest reroofing projects ever on one of the largest metal-framed domed structures in the world: the Superdome in New Orleans. Katrina destroyed the dome’s second roof; the structure’s original roof was constructed with polyisocyanurate foam covered with a fluid-applied elastomeric coating but was replaced in 1989 with a single-ply EPDM roofing system. After the damages suffered during Katrina, the EPDM roof system was replaced with a spray foam roof system.

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ASTM International and Sustainable Roofing

ASTM International is a well-known standard-writing organization for the construction industry and other industries. As the building design and construction industries have moved toward more sustainable methods and products, it follows that more standardization of sustainability is necessary. This is certainly true for the roofing and waterproofing industry. ASTM now has a group devoted to developing standards for sustainable roofing.

Organizationally, ASTM is divided into numerous committees, each having a specific focus. The ASTM D08 committee is responsible for roofing and waterproofing standards. Within the D08 committee, there are multiple subcommittees that focus on a segment of the roofing/waterproofing industry—from asphalt shingles to spray polyurethane foam to modified-bitumen membranes to single-ply membranes and more. D08.24 is the subcommittee that is developing standards specifically related to sustainable roofing.

Further division of each subcommittee into Task Groups allows narrowly focused groups to develop standards for very specific topics. There are currently four Task Groups within D08.24:

  • D08.24.01 Guidelines for Sustainable Design
  • D08.24.03 Recycling Practices and Reporting Methodology
  • D08.24.04 Durability
  • D08.24.05 Selection Criteria Vegetative Roof Membranes

Process

Standards are developed by Task Groups with active participation by attendees at the semi-annual meetings. Typically, a draft standard (called a work item until it is an approved standard) is initially sent out for ballot to the Task Group to obtain comments that will improve the draft standard. After balloting to the Task Group, the draft standard is balloted to the full D08 membership. At times, a standard is simultaneously balloted to the Task Group and the full membership. During the balloting process, comments and negative votes are reviewed and dealt with according to ASTM protocols. Standards development is a very linear process that works well to achieve a consensus in the D08 committee. Once a consensus is reached, the standard is published for use.

The background on the process is necessary to understand the activities of the D08.24 subcommittee. Because the subcommittee was only recently established, all standards are still in the development stage.

Task Group Specifics

The D08.24.01 Task Group is developing a new standard, work item WK26599, which is currently titled “New Guide for Design of Sustainable, Low-Slope Roofing Systems”. The current scope is:

  • This Standard provides guidance for designing sustainable low-sloped roofing systems, including exposed membrane roofs, membranes covered with vegetative (green) overburden systems, ballasted roofs and protected membrane roofing assemblies. A sustainable roofing system minimizes environmental impact, conserves energy, and has maximized service life.

The scope recognizes the roof’s primary function is to weatherproof the building’s top surface.

The document provides a sequential process for designing sustainable roof systems. The document does not provide a prescriptive approach, but “attempts to help the user define and consider roofing system demands and environmental life cycle impacts, and integrate these with features that contribute environmental, energy conservation, or other benefit in service” through a number of considerations, which include roofing demands, functional expectations, end-user requirements and site restraints. The document is big-picture, technology-neutral and process-based.

The D08.24.03 Task Group is developing a new standard, work item 24614, currently titled “New Guide for Recycling Practices & Reporting Methodology”. The intent of the document is to unify common practices and develop an industry-accepted reporting format for recycling common roofing materials, such as asphalt shingles. The document is in its infancy and has not been balloted to date.

The D08.24.04 task group is developing a new standard, work item 26595, currently titled “New Guide for Roof System Durability”. The task group is still evaluating the specific scope but will focus on PVC and EPDM membranes in two separate documents. The intent is to provide methodology to evaluate the variables that lead to increased durability of PVC and EPDM roof systems. Neither document has been balloted yet.

The D08.24.05 Task Group is developing a new standard, work item 29304, currently titled “New Guide for Selection of Roofing/Waterproofing Membrane Systems for Vegetative (Green) Roof Systems”. The document will provide technology-neutral considerations for selection of appropriate membranes for vegetative roofs. The Task Group is expected to begin the balloting process soon.

Liaisons

The ASTM D08.24 group works with other groups, like E60 on Sustainability and the Built Environment Advisory Committee, to ensure continuity of ideas with all ASTM committees. Specifically, E60.01 on Buildings and Construction and E60.80 on General Sustainability Standards are in the focus of the D08.24 liaison efforts.

The ASTM sustainability standards are intended to be used by the roofing, construction and design industries to formalize the efforts toward more sustainable roofs and roofing. It is hoped that other roofing groups, such as ARMA, CEIR, ERA, NRCA and SPRI, will reference ASTM’s sustainability standards in their documents.

I encourage everyone in the roofing industry to not only join ASTM, but to participate in the development of the standards our industry uses each and every day. ASTM D08.24 needs your input as the roofing industry moves further toward sustainable products and activities.

Are You ‘PV Ready’?

Commercial rooftops are an attractive platform for the installation of solar photovoltaic (PV) electricity-producing systems. These low-slope roofs offer an economical and sustainable structural foundation for renewable solar energy. As an example, one of the largest roof-mounted PV systems in North Carolina has been online for several months at the Old Dominion Freight Line Inc. vault logistics facility in Thomasville. Almost 7,700 solar panels completely cover the warehouse’s 160,000-square-foot roof and produce enough power (1.8 megawatts) to offset more than 90 percent of the building’s annual energy costs.

Success stories like Old Dominion’s are becoming increasingly common in the sunny Carolinas. However, it is important to remember a roof’s function is, first and foremost, to protect the building’s contents and people from the elements. In this regard, roofing professionals need to anticipate the potential risks associated with the installation of a roof-mounted PV system (array). This sort of due diligence is particularly important when installing PV systems on existing warranted roofs.

A broad selection of membranes and thicknesses are available for consideration when a PV installation is planned. Photo courtesy of GAF, Wayne, N.J., and Protech Roofing Service, San Diego

A broad selection of membranes and thicknesses are available for consideration when a PV installation is planned. Photo courtesy of GAF, Wayne, N.J., and Protech Roofing Service, San Diego

To help in these industry efforts, members of Waltham, Mass.-based SPRI—the trade association that represents sheet membrane and component suppliers to the commercial roofing industry—have developed “PV Ready” roof assemblies and guidelines designed to provide maximum protection for the roof (and maintain its warranty coverage).

In September, SPRI’s technical committee and board of directors also approved and distributed to its members Technical Bulletin 1-13A, “Summary of SPRI Membrane Manufacturer Photovoltaic (PV) Ready Roof Systems and Services”. The bulletin contains general guidelines from SPRI related to “PV Ready” roof assemblies. This article goes into more depth about issues related to PV installations, particularly on existing warranted roofs.

Ask the Right Questions

The installation of a PV system on an existing warranted roof raises many important questions for the roofing professional and building owner. For example, will the roof accommodate the added weight of the PV array? Logistically speaking, before property owners decide on a solar-power system, they will need to determine whether their roofs are sturdy enough to support
the additional loads put on the existing roof structure by the solar array.

An average solar panel and support system typically add a minimum of 3 to 4 pounds per square foot to the existing roof. It is the responsibility of the roofing professional to ensure this additional weight does not exceed the load limits determined by the building’s designer.

From an economic (life-cycle-cost) point of view, it makes sense the service life of the existing roof membrane will come close to matching the projected service life of the PV system. If not, a complex and costly reroofing project may be required long before the solar panels need to be replaced. In general, the underlying roofing system must provide the same minimum investment horizon—generally at least 25 years—to realize the full potential of the rooftop PV system.

Most PV arrays require penetrating the roof membrane. Even non-rack-type systems may include electrical conduits, wiring and other components that may need to be flashed in a professional manner. It is essential the responsibility for this flashing work rests with the roofing contractor.

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Green-building Innovation Is Important, But So Is Refinement

In March 2006, I swore allegiance to the wildly popular green-building movement. I even put the kibosh on my favorite joke about recycling in the landfill—you know, so not to deprive future generations of fossil fuels and diamonds. Nice.

I’ve worked in facility management at Duke University Health System for 26 years. In this profession, being overly pragmatic is an occupational hazard. So, why did an “old-school” guy (no pun intended) show up at a green love fest alongside folk with funny-colored hair and way too many bumper stickers? Quite simply, I came to the party to plea for intellectual honesty.

Unfortunately, early on, the sustainability movement offered myriad earth-friendly materials often with little thought to their durability or life cycle. Similarly, early building rating programs focused largely on the merits of individual products without factoring their proper integration into functional systems or assemblies. Consider, for example, the many thousands of squares of reflective “cool roofing” membranes applied over non-durable assemblies. A LEED-applicable roofing membrane that fails prematurely because of inferior quality or misapplication does not look very sustainable buried in a landfill.

It’s no longer 2006, and the greenie you’re partying with may be a blue-haired, retired architect. It’s encouraging so many in the building industry, and particularly the roofing industry, have embraced the concept of durability as the essence of green and sustainable building design. Moving beyond mere branding “strategery,” sustainability can be good for the bottom line. On the Duke campus, a 2007 roof replacement used forward-thinking design to divert 718 tons of solid waste. Salvaged materials from this effort included 296,000 board feet of XPS insulation, which was repurposed in new roofing construction on three Duke buildings. It’s our story. And it’s simply good business.

It has been said “architecture is storytelling.” The story of our 2007 roof replacement project settled forever how Duke University Health System will conduct itself in regard to sustainable roofing design and environmental stewardship. We distilled our story into the following “Guiding Principles of Sustainable Roofing”:

  • 1. Favor insulations or insulating assemblies that are highly resistant to water and physical damage.
  • 2. Favor roof assemblies that position the roof membrane directly over a permanent or semi-permanent substrate.
  • 3. Favor roof designs that prohibit or highly discourage the entrapment of water within the roof assembly.
  • 4. Favor membrane and insulation designs capable of in-place reuse or recycle in future roof iterations.

Through the years, these guiding principles have produced a dramatic improvement in roofing performance on our campus. In particular, our emphasis on adaptive reuse of materials will minimize our impact on the environment, as well as reduce future demand on hospital resources–resources best used in support of outstanding patient care or cancer research, not funding a premature roof replacement. Interestingly, the U.S. General Services Administration, Washington, D.C., has recently incorporated our guiding principles in facilities standards for future public building construction. Now our story has legs.

In April 2013, I attended the Energy Efficient Roofing Conference in Charlotte. I was invited to participate in the program, offering a building owner’s perspective about emerging roofing technologies. The focus, primarily, was energy-efficient roofing as a value proposition: how to achieve it and how to sell it. The format leaned heavily on panel discussions, which produced large amounts of banter and at times outright tension regarding the subjects at hand. It was as if someone handed a microphone to the elephant in the room. Has the proposition become a “solution” in search of a “problem”?

Don’t misunderstand; everyone can see the benefits in much (but not all) of the new energy-efficient roofing innovations and building codes. But should we be excited about reflective or solar membranes on massively thick R-30 minimum insulation while still far too many roof installations will fail prematurely because of shortsighted design and construction? If quality and durability are of utmost value, do you—the roofing contractor— know how to achieve it and how to sell it? Should you care?

Back in 2006, I believed everyone was trying to “out green” each other; durability be damned. Today, I wonder if the problem is that everyone wants to “out innovate” each other. As we’ve witnessed with green, the danger when innovation means everything is that it can soon mean nothing.

Innovation is exciting and necessary, but so is refinement. Refinement may be the most powerful strategy of all, yet it remains under emphasized. The most effective way to celebrate refinement is by creating new stories–new institutional memories. Roofing contractor, you are the biographer. Run with that.

Roof Maintenance, Sustainability and RoofPoint Life-cycle Management

The roofing industry knows good design, quality materials and proper installation are the key tenets to achieving a leak-free, long-term roofing system. Roof system maintenance is an equal part of the equation and should not be overlooked, even though there is a tendency for “out of sight, out of mind” by many building owners.

A technician from Sheridan, Ark.-based RoofConnect walks a roof and documents it as part of an annual maintenance survey. RoofConnect, which has locations around the country, including Monroe, N.C., has made maintenance contracts a major part of its business.

A technician from Sheridan, Ark.-based RoofConnect
walks a roof and documents it as part of an annual maintenance survey. RoofConnect, which has locations around the country, including Monroe, N.C., has made maintenance contracts a major part of its business.

Roof maintenance is not only important to long-term service life, it is a key factor for the overall sustainability of roof systems. RoofPoint, the Washington, D.C.-based Center for Environmental Innovation in Roofing’s Guide for Environmentally Innovative Nonresidential Roofing, emphasizes durability and life-cycle management for sustainable, environmentally friendly roof systems. Of the 23 credits within RoofPoint, nine are in the Durability/Life Cycle Management (D/LCM) section. It’s clear the roofing industry recognizes the importance of longevity when it comes to environmentally friendly roof systems.

Looking deeper into RoofPoint, one of the nine credits in the D/LCM section is titled “Roof Maintenance Program”. Establishing and maintaining a partnership with the building owner is a win-win for the roofing contractor and the building owner. Performing inspections
and maintenance provides the owner with an ongoing information resource, ultimately allowing better management of capital and the roof asset by extending the life of the roof system.

From a sustainability perspective, a longer lasting roof—extended by regular roof system maintenance—means roof replacement is appropriately postponed and with that comes a reduction in material and energy use, as well as reduced expense and waste. Roof system maintenance is a win for the owner, the environment and the roofing contractor.

PHOTOS: RoofConnect