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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The NRCA ProForeman Certificate Program Helps Roofing Contractors Invest in Their Foremen

High Life Speedboats was experiencing a problem with its newest model speedboat engine, which, when hitting top speeds, would frequently cut out. This resulted in boats that were traveling 60 mph to be almost dead in the water within seconds. More than once, someone had been seriously injured by being thrown off balance, crashing into onboard components or being thrown overboard.

Panache Speedboats also was trying to improve its engines. The company had been in business for two decades and was known for building reliable boats. With operations systematized and production running in turnkey mode, company engineers wanted to explore the possibilities of building a higher-performance engine and securing Panache a spot in the elite racing market.

There are two equal and opposite drives for improvement in both of these cases. High Life needs to improve; its product is unreliable and the company will ultimately go out of business—not to mention people may be hurt and killed if steps are not taken. Panache wants to improve; it has a reliable product but it’s not as good as it could be.

So, now you may be asking, “How does this relate to the roofing industry?”

Most reputable roofing contractors are not like High Life. Their roof systems don’t fail outright, causing damage and ruining companies’ reputations. Most roofing contractors are Panache engines. They are reliable and their roof systems serve customers well.

But if you have the itch, like Panache, to increase performance, then you have a drive to improve for the best reason— because you want to be better. You are not panicking. You are planning. You want to see whether you can shape your company to become an elite contracting company, known for its excellence.

Thoughtful contractors will consider what investments will yield the most significant returns for their companies. New equipment? A better facility? Increasing the types of systems they install?

Consider the following statement from Ethan Cowles of Raleigh, N.C.-based management consultant FMI: “World-class contractors all have incredible talent at the foremen level. That is not to say company leadership, business strategy, project management, etc., are not important, but operations without great foremen always struggle to achieve anything but mediocrity.”

HIGH-PERFORMANCE FOREMEN

Cowles’ quote resonates with what the Rosemont, Ill.-based National Roofing Contractors Association (NRCA) has heard from its contractor members, as well. Tom Shanahan, NRCA’s associate executive director of risk management, states that after asking hundreds of contractors over the years how much of each dollar flowing through a company is affected directly by foremen, he has safely landed on 85 cents. Eighty-five cents of every dollar.

Foremen drive your trucks, use your equipment, manage your labor, direct quality control, affect insurance rates and often are the face of your company for customers.

EIGHTY-FIVE CENTS OF EVERY DOLLAR.

It makes you want to ensure your foremen are high-performance engines, doesn’t it?

NRCA has been focused for years on providing education for roofing foremen. Recognizing that most foremen are promoted into their positions because of their roofing skills and work ethic, rather than for their leadership prowess, For Foremen Only has provided a venue for training thousands of foremen about leadership and communication during the past 15 years. Now, packaged within this larger ProForeman initiative, the classes provide a cornerstone for a well-rounded experience aimed at helping roofing-contractor operations to achieve world-class excellence.

Foremen need to be leaders, not just crew managers; therefore, they need to understand the whole picture—the process of selling and installing roof systems, their role in keeping employees safe, outside forces that necessitate compliance and more—if they are to understand the importance of their role.

The ProForeman program is designed to help roofing foremen shift their perspectives of their role from being roofing installation managers to company leaders. As leaders, the burden of responsibility is greater and, when understood, frees them to think differently about how to work with their crews and their supervisors.

The ProForeman program comprises six main topics:

    • General education
    • Roofing technology
    • Construction/business practices
    • Leadership
    • Safety
    • Training others

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Wind Loading on Rooftop Equipment

I recently attended a continuing-education conference for civil/structural engineers that discussed changes in the 2012 International Building Code (IBC) and the referenced ASCE 7-10 “Minimum Design Loads for Buildings and Other Structures”. During the seminar, the question was asked: “Who is responsible for the design of wind loading to rooftop equipment as defined in the IBC and Chapter 29 of ASCE 7-10?” The most accepted response was to add a section in the structural general notes that wind design on rooftop equipment is to be designed “by others”.

A structural engineer designed the metal support system and load transfer from the new HVAC unit down through the structure.

A structural engineer designed the metal support system and load transfer from the new
HVAC unit down through the structure.

The design requirements for wind loading on rooftop equipment have been included in previous editions of the IBC and ASCE 7, but significant changes have been included in ASCE 7-10. The increased attention is in part because of more severe wind events in recent years. While it is not the primary responsibility of the roofing consultant or contractor to evaluate the systems being placed on the roof, it is good to understand the code’s requirements for loading to rooftop equipment, how the load is determined and applied, and how the load is transferred to the building structure.

CODE REQUIREMENTS

The primary focus of the roofing professional in the IBC is concentrated on Chapter 15 (Roof Assemblies). While there are requirements in Chapter 15 addressing rooftop structures, these requirements, particularly in relation to wind loading, extend beyond Chapter 15. It is therefore imperative to be familiar with other sections of the code.

For instance, Section 1504 (Performance Requirements) refers the user multiple times to Chapter 16 (Structural Design) for wind-loading-design requirements. While roof manufacturers typically prequalify their systems based on various industry standards (ASTM, FM, ANSI, etc.), rooftop equipment supports are not typically prequalified because of the variability of placement and conditions. Similarly, new to this code cycle, Section 1509.7.1 includes the requirement for wind resistance for rooftop-mounted photovoltaic systems per Chapter 16 of the IBC. Other industries or trades have similar requirements. Section 301.15 of the 2012 International Mechanical Code and Section 301.10 of the 2012 Fuel and Gas Code require “equipment and supports that are exposed to wind shall be designed to resist the wind pressures in accordance with the IBC”.

Section 1609 of Chapter 16 (Wind Loads) applies to wind loading on every building or structure. Section 1609.1.1 provides two design options. The designer can use chapters 26 to 30 of ASCE 7-10 or Section 1609.6 of the IBC. Note however that Section 1609.6 is based on the design procedures used in Chapter 27 of ASCE 7-10, which does not address wind loading on rooftop equipment and thus is not applicable. Chapter 29 of ASCE 7-10 (Wind Loading on Other Structure and Building Appurtenances) contains the procedures used to determine wind loading on rooftop structures and equipment.

DETERMINING AND APPLYING WIND LOADING ON ROOFTOP EQUIPMENT

Properly specified ballasting blocks are designed and formed to better address the freeze/thaw cycle.

Properly specified ballasting blocks are designed and formed to better address the freeze/thaw cycle.


To determine wind loading on rooftop equipment, the first step is to identify the building Risk Category (formerly the Occupancy Category) and the building location. The Risk Category is determined from Section 1604.5 and Table 1604.5 of the IBC or Table 1.5-1 of ASCE 7-10. There are slight variations in the two codes but typically each will produce the same Risk Category.

The Risk Category and the location are then used to determine the design wind speed based on published wind-speed maps, available in Section 1609.3, figures 1609 A to C of the IBC, or Section 26.5.1, figures 26.5-1 A to C of ASCE 7-10. It can be difficult to read these maps to select the appropriate wind contour line, specifically along the East Coast. The Redwood City, Calif.-based Applied Technology Council (ATC), a non-profit that advances engineering applications for hazard mitigation, has digitized the maps providing a valuable resource for determining design wind speeds by GPS coordinates or the building’s address. Visit ATC’s wind-speed website. Note however that it is always advisable to cross check this design wind speed with the maps in the adopted code or with the local building authority.

PHOTOS: MIRO INDUSTRIES INC.

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The Success of Your New (Replacement) Roof Depends on Adjacent and Connected Elements, including Masonry

Although the name of this publication is Roofing, the roofing/waterproofing/construction industry recognizes more and more that the building envelope is a fully integrated and interrelated assembly of systems.

masonry cracks due to freeze thaw

Click to view larger version

As such, I feel the need to discuss the importance of water resistance and structural integrity in existing wall surfaces, which are adjacent and connected to your project’s new (replacement) roof system. The focus of this article is not how to design a replacement roof system but how to address adjacent masonry to ensure it doesn’t work against the success of the new roof.

These principles actually apply to any wall system that connects, generally above and adjacent, to your roof, but masonry poses some distinct concerns. Water intrusion, thermal movement and structural integrity of this masonry, along with locations of embedded flashing, all come into play as the new roof system is properly integrated into the adjacent rising wall, parapet wall or even perimeter edge wall beneath the roof.

COMMON MASONRY ISSUES

Thomas W. Hutchinson, AIA, FRCI, RRC, a regular Roofing contributor, has said, “long-term service life is the true essence of sustainability”. Moreover, designers specify (for owners to buy) warranties of 20, 25 years or more with new roof systems. It’s just good common sense that you can’t allow a new roof to be jeopardized by water intrusion from an adjacent system because of an oversight in the original analysis of the situation.

Many of us have been called by an owner who says his or her new roof is leaking, only to find roof-mounted equipment or an unrelated system is actually leaking. However, if the leak is stemming from another aspect of the building envelope, such as an adjacent parapet or rising wall, which is now jeopardizing the investment made on a new roof, that you (the designer) should have foreseen, it makes for a very difficult position. The roofing system manufacturer, who holds the warranty, and the owner are going to look at you as being responsible.

masonry

Click to view larger version

Let’s examine three common occurrences using actual case studies. All three situations, which occurred on schools in the Northeast, exemplify the condition of adjacent masonry was deficient and had to be corrected, adding a significant degree of scope and cost to the project to guarantee a roof design that would perform over the long haul. These three cases cover:
1. Repairing the masonry and covering it.
2. Altering the masonry to change the location of embedded flashings.
3. Replacing structurally unsound/failed masonry with another material.

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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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Forum-selection Clauses and Their Impact on the Construction Industry

With the national housing market poised for slow but steady growth in 2014, U.S. contractors expect a good year for business, and the number of contracts and subcontracts for construction work is expected to increase. Many of these contracts will contain forum-selection clauses, and a recent U.S. Supreme Court ruling brings to light the importance of these clauses and coming changes in their enforceability.

WHAT IS A FORUM-SELECTION CLAUSE?

A forum-selection clause is a contractual provision in which the parties establish the place for specified litigation between them. These clauses have become increasingly common in construction contracts, particularly with general contractors who do business in two or more states. Often, general contractors have a form subcontract agreement they require or ask all subcontractors on a particular project to sign. If general contractors work in multiple states, forum-selection clauses can help them make potential litigation less costly and easier to manage by guaranteeing the litigation will take place in the company’s home state, where its executives and attorneys likely work.

An example is a general contractor based in New York but working on a North Carolina project and entering into a roofing subcontract with a North Carolina roofer. The general contractor can present the subcontractor with a forum-selection clause mandating any legal claims arising from the subcontract may only be brought in a New York court. For a North Carolina contractor, finding counsel and filing suit in New York will likely be more difficult and costly than doing so in North Carolina, especially when evidence and witnesses are located in North Carolina. In this example, the forum-selection clause makes litigation more predictable and cost-effective for the general contractor and also decreases the likelihood the subcontractor will actually be able to sue, so it most likely favors the general contractor.

To protect local contractors, many state laws have declared out-of-state forum-selection clauses unenforceable in construction contracts. These states include Arizona, California, Connecticut, Florida, Illinois, Louisiana, Minnesota, Montana, Nevada, New York, North Carolina, Ohio, Oregon, Pennsylvania, Tennessee, Utah, Virginia and Wisconsin. Additionally, state laws in Nebraska, Rhode Island, South Carolina and Texas make forum-selection clauses unenforceable in certain circumstances that sometimes, but do not necessarily, encompass construction contracts. In the first category of states, local contractors have been able to file suit locally despite forum-selection clauses because courts in these states can apply the state laws and disregard the clauses. However, the U.S. Supreme Court’s recent decision on these clauses will severely limit the reach of these laws and will ensure that forum-selection clauses are enforced in many more cases.

CASE BACKGROUND

In December 2013, the U.S. Supreme Court issued a unanimous decision in the case of Atlantic Marine Construction Co. v. United States District Court for the Western District of Texas. The court held that defendants in federal court can use forum-selection clauses to transfer their cases to the state specified in the clause, even if the suit is brought in a state with a law deeming these clauses unenforceable. Essentially, forum-selection clauses may be enforced by a venue transfer motion.

The case involved Atlantic Marine Construction (AMC) Co., a general contractor based in Virginia. AMC won a federal contract from the U.S. Army Corps of Engineers to construct a building at Fort Hood, Texas. AMC subcontracted with J-Crew Management, a local Texas company, to perform some of the work. AMC’s contract, which J-Crew Management signed, included a forum- selection clause dictating that any legal disputes between AMC and J-Crew Management arising from the contract had to be brought in state or federal court in Norfolk, Va.

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Roofs Are a Potential Solution for Urban Stormwater-management Issues

Can stormwater management using rooftops in urban areas be the financial solution to our growing urban stormwater problem? Will public-private partnerships with building owners help to provide a government service—stormwater drainage—in a more cost-effective manner? As cities struggle with the high administrative and procurement costs and time delays to manage stormwater, should we be looking up to roofs as part of the solution? Can we avoid more regulations and instead look to market-based solutions? These questions are beginning to be discussed and tested as new, innovative approaches to solving difficult and expensive urban stormwater-management issues.

Consulting and engineering firm Geosyntec Consultants is monitoring and controlling runoff from an existing New York City Parks and Recreation facility green roof.

Consulting and engineering firm Geosyntec
Consultants is monitoring and controlling runoff from an existing New York City Parks and Recreation facility green roof.

STORMWATER MANDATES

Many cities and counties are dealing with more stringent stormwater permits issued from the Washington, D.C.-based U.S. Environmental Protection Agency (EPA) and state environmental agencies that implement the federal Clean Water Act. Many communities are operating under federal court orders and administrative consent orders from EPA to reduce stormwater runoff into rivers, lakes and streams. In addition, there are 177 communities in the U.S. where stormwater and wastewater-collection systems are combined, known as combined sewer overflows (CSOs). These CSOs result in billions of gallons per year of combined untreated stormwater and wastewater discharged into waterways during large rainfall events. Funding crises have developed in many municipalities as they create programs, hire new staff, and design and construct new infrastructure to meet these regulatory requirements.

Many cities have spent billions of dollars separating stormwater drainage from wastewater-collection systems by installing new, costly drainage systems. In addition, large underground storage tunnels and vaults have been installed by many cities at the costs of billions of dollars per installation. These tunnels and vaults are designed to collect, hold and slowly release the stormwater into the treatment network. Increasing stormwater pipe sizes and creating tunnels and vaults is extremely costly. For example, Washington, D.C., just broke ground on the construction of two stormwater tunnels that are currently projected to cost $2.6 billion dollars to construct. Just one of the tunnels will be 13-miles long and hold 157 million gallons of combined stormwater and wastewater in 23-foot-diameter tunnels, 100-feet below the surface.

Green-infrastructure approaches to stormwater issues are included in most municipal stormwater permits and orders. For example, New York City is spending $187 million on green infrastructure for stormwater control in CSO areas to control the equivalent of 1 1/2 inches of runoff from impervious surfaces by December 2015. Public and private areas are under consideration for green-infrastructure solutions, and the city expects to spend $2.4 billion in green infrastructure during the next 20 years.

As cities address urban stormwater management, stormwater fees are being assessed on private-property owners to help fund the programs to solve urban stormwater issues. Close to 1,500 stormwater utilities are now in operation in the U.S., and the number is rapidly growing. These stormwater utilities typically are assessing stormwater fees based on the amount of impervious surfaces by property owner. The fees can range from a few hundred dollars per year to tens of thousands.

Roofs are considered an impervious surface because they are designed to shed stormwater through drainage networks into the collection system beneath city streets. For example, in New York City alone roofs make up 11.5 percent of the total area, or roughly 944.3 billion square feet, according to the city’s Department of Design and Construction’s Cool & Green Roofing Manual. Rather than looking at roofs as part of the stormwater problem in cities, they should be viewed as a possible solution.

DID YOU KNOW?

Baltimore enacted a stormwater fee
in 2013. Currently a building with a
200,000-square-foot roof would be
assessed $11,400 per year.

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A Trade Association Brings Roofs to the Sustainability Discussion

Roofs, first and foremost, keep water and the elements out of a building. The roofing industry has done this quite well since the modernization of buildings began more than a century ago. Along the way, a number of trade associations—ARMA, ERA, MCA, NRCA, PIMA, SPFA, SPRI—have formed and evolved as materials and trends have changed. Each group provides excellent information relative to its mission and goals. Yet we know change keeps coming.

THE BYRON WHITE COURTHOUSE, DENVER, features a RoofPoint-certified high R-value (R-30) roof for energy savings. A dual-reinforced Derbigum modified bitumen membrane, 90-mil base sheet and a high-density coverboard were installed.

THE BYRON WHITE COURTHOUSE, DENVER, features a RoofPoint-certified high R-value (R-30) roof for energy savings. A dual-reinforced Derbigum modified bitumen membrane, 90-mil base sheet and a high-density coverboard were installed.

Since the turn of the century, the awareness and push for energy efficiency of buildings and the sustainability for materials and building design has grown substantially and has become an important topic in the public forum. Sustainability and environmentalism are universal topics.

Serving as a unified voice for issues involving roofing, energy and the environment, the Center for Environmental Innovation in Roofing was established in Washington, D.C., in 2008. The non-profit organization’s focus is to advocate and promote the use of environmentally friendly, high-performance roof systems, not just within the U.S., but in North America and globally. The center is a member-based association consisting of roofing manufacturers, roofing contractors, roofing consultants, raw-material suppliers and other trade groups within the roofing industry.

To promote the sustainability of roof systems, the center develops resources, products and educational information that can be used by the building industry to advance the longevity, durability and overall sustainability of roofs. Increased awareness of the importance of a building’s roof is critical to the center’s mission. The roof can be a large contributor to the energy efficiency of the building, a long-term asset and, increasingly, a location for energy production (solar, wind).

ROOFPOINT

The center’s premier program is RoofPoint, a guideline for environmentally innovative nonresidential roofing. RoofPoint is used to evaluate new and replacement roofs for commercial and institutional buildings based on their environmental performance during the life cycle of the building the roof covers. This provides a useful measure for what constitutes a sustainable roof during design, construction, operation and decommissioning.

RoofPoint is primarily a rating system, and when certain minimums are met, a roof can become a RoofPoint Certified roof. Certificates and plaques noting RoofPoint certification can be awarded and used to validate a commitment to sustainability and the environment.

RoofPoint is based on current state-of-the-art processes and methods, remaining technology neutral. It does not rank or prioritize materials or systems; however, RoofPoint emphasizes energy efficiency and long-term performance and durability as overarching key attributes of a sustainable roof. Material recycling and reuse, VOCs, water capture and reuse, hygro-thermal analysis, and operations and maintenance are a few of the categories within RoofPoint.

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Roof Decks: Don’t Underestimate the Backbone of the Roof System

NOTE: This article is intended to provide general information while conveying the importance of the roof deck as an integral part of a roof system. Additional information about specific effects and concerns in regard to roofing can be found in The NRCA Roofing and Waterproofing Manual and various roof-cover manufacturers’ design guides.

Wood plank decks can provide a dramatic exposed roof deck.

Wood plank decks can provide a dramatic exposed roof deck.

The roof deck is the backbone and an integral component of all roofing systems. Its main function is to provide structural support for the roof system and, therefore, is a building element that needs to be designed by a licensed design professional because proper support of the roofing above is critical to the roof system’s success.

Roof decks also add thermal performance and fire resistance and ratings, provide slope for drainage and enhance wind-uplift performance. They must accommodate building movement and often determine the attachment method of the vapor retarder, insulation and membrane.

Roof Deck Types

There are many types of roof decks being installed today:

  • Steel
  • Precast concrete panel
  • Structural concrete
  • Cementitious wood fiber
  • Wood planking
  • Plywood/OSB
  • Poured gypsum

Some decks are covered with topping fills that become the base for the roof system and may also be an integral structural component:

  • Concrete
  • Lightweight insulation concrete topping
  • Lightweight aggregate concrete topping

Other deck toppings are available, such as poured gypsum and lightweight concrete with integral insulation, but these are considered substrate covers and not roof decks.

The most prevalent roof deck in the U.S. for commercial buildings is steel. On the West Coast, plywood/OSB is very popular. In addition to the roof decks already mentioned, in the course of roof-replacement work the designer may come in contact with the following:

While the “plate” test is not a preferred method, it can quickly and inexpensively give an indication of retained moisture in lightweight aggregate concrete roof deck covers.

While the “plate” test is not a preferred method, it can quickly and inexpensively
give an indication of retained moisture in lightweight aggregate
concrete roof deck covers.

  • Book tile
  • Lightweight precast concrete planks
  • Precast gypsum planks
  • Transite

Collaboration with the Structural Engineer

Because a roof deck is the foundation for the roof system, the designer needs to coordinate the roof system design requirements for the roof deck with the structural engineer to ensure the performance of the roof system. For example, the roof deck may need to extend to the roof edge. In this example, the roof deck may not need to extend to the roof edge for structural concerns but is needed to support the roof system; the roof designer must address this. If the roof deck is structurally sloped, the designer and engineer must determine whether the low point is a potential drain location. Are there steel beams in the way of the drain location? The roof deck must be attached to the structure to prevent uplift. And the designer and engineer must determine what the deflection of the roof-deck span may be between structural supports. For example, steel deck is sometimes installed with spans of 7 feet between joists and flexes (deflects) under foot traffic. This typically is not a good condition onto which a ridged roof system, such as a bituminous one, should be installed. It cannot be expected to accommodate such deflection. PHOTOS: Hutchinson Design Group Ltd. [Read more…]

Several ‘Sandwich’ Roof Assemblies Mitigate Sound Transfer

We all want a roof over our heads to protect us from the cold winter months, hot summer months and precipitation year round. How much thought goes into the sound-control construction of a roof, though? Have you considered the acoustic properties of your roofing system? Admittedly, acoustics is not a topic that many roofing contractors think about. The construction of a roof, however, can have a significant impact on the sound quality of the building interior. While this may not seem important in every project, it can be a critical element of the design for concert halls, theaters, auditoria and even school classrooms.

Sound Isolation

The acoustics of a space depend on many criteria, including sound isolation, sound reflection, impact noise and sound transfer. In many cases, particularly in noisy, urban environments, there is a need to prevent loud outside noises, such as traffic, sirens and airplane noise, from entering quiet spaces. Sound isolation depends on the entire envelope of a space, including external walls, windows and roofs.

Green roofs, particularly the “intensive” version, which includes several inches of heavier-weight soil, can provide effective sound control.

Green roofs, particularly the “intensive” version, which includes several inches of heavier-weight soil, can provide effective
sound control.

Historically, roofs over sound-sensitive spaces have been built with fairly dense materials, such as concrete, which by themselves are relatively effective in blocking sound transfer. As construction methods have developed, however, more lightweight construction is being used. If thought and care are not given to the assembly, these lightweight construction methods can cause serious issues with acoustics. Rain noise, mechanical noise and other exterior sounds can all transfer readily through a thin, lightweight roofing system.

In an effort to use lighter-weight construction, a “sandwich” assembly may be used to mitigate sound transfer. Similar to an Oreo cookie, a sandwich assembly’s outer layers are comprised of a heavy, dense material, and the inner filling consists of insulation and/or airspace. The materials of this assembly can differ from concrete to roofing board, rigid insulation to fibrous insulation, gypsum board to acoustic ceiling tiles. The components can be combined in a variety of ways, each with varying levels of sound isolation.

One of the principle phrases often heard when discussing sound isolation is “mass air mass”, which refers to the separation of two bodies of mass by an air space. The greater the mass and the deeper the air space, the more sound isolation will result. For this reason, a heavy mass, such as 5-inch concrete, followed by a deep air space, such as an 18- to 24-inch ceiling cavity in which ducts are run, followed by a continuous layer of drywall ceiling will provide a high level of sound isolation. Additional steps, like adding sound-absorptive material to the air space and/or using resilient connections when supporting drywall, further improves the sound isolation of the assembly.

Sandwich Roof Assemblies

Several sandwich roof assembly approaches are possible, including:

Good: Multiple layers of dense roofing board (at 2.5 psf per board, a final density of 10 psf or four-ply is often recommended) on either side of insulation, which ideally would be a sound-absorptive fibrous fill, like mineral wool, can reduce sound transmission. This approach is similar to a “floating floor”, often used in interior spaces to isolate sound transfer from one room to another. (Equivalent Sound Transmission Class, or STC, ratings can range from low 50s to low 60s, depending on whether a ceiling is included below the deck.)

Drywall ceilings hung on resilient hangers in conjunction with a lightweight roofing system provide even greater sound isolation by virtue of the resilient connection or “decoupling” of the drywall layer from the rest of the building structure.

Drywall ceilings hung on resilient hangers in conjunction with a lightweight roofing system provide even greater sound isolation by virtue of the resilient connection or “decoupling” of the drywall layer from the rest of the building structure.

Good: Green roofs, particularly the “intensive” version, which includes several inches of heavier-weight soil, can provide effective sound control. These can be part of a sandwich approach with airspace or rigid insulation between soil and a more-dense roofing material, similar to the roofing board described in the previous example. The mass-air-mass combination is similar to the approach just mentioned, and the benefits of green roofs appeal to many building owners for a multitude of reasons, including minimizing urban heat islands and storm-water management.

Good: A 5-inch slab of normal-weight concrete (150 pcf) has a density of 62 psf. This tried-and-true method is still used regularly and often proves to be the most cost-effective method of enclosing a space. The best sound isolation will occur if this is used in conjunction with a ceiling below, but on its own it still provides a reasonable level of isolation in many environments. This isn’t technically a sandwich system unless paired with a ceiling below or a green roof above. (Equivalent STC ratings can range from low 50s to low 80s. The highest ratings require pairing a resiliently hung ceiling with the concrete, as described under “Multi-function Roof Assemblies”.) IMAGES: Threshold Acoustics LLC [Read more…]