Retrofit with high R-value insulation

Reroofing with high R-value insulation can provide energy savings

At the end of 2009, President Barack Obama urged Congress to provide funding to building owners and homeowners to improve energy efficiency in buildings by replacing doors and roof systems and adding more insulation. He likened the current lack of energy efficiency in most homes and buildings to watching "$20 bills float though the window and into the atmosphere." And he went so far as to say the idea "may not be very glamorous," but he finds insulation "sexy."

As the president so eloquently stated, insulation is one of the most important components in a building when it comes to reducing energy costs and decreasing carbon footprint. Much of the existing building stock still has 30 or more years of service life and could be vastly improved during the long term if owners consider reroofing with high R-value roof systems.

A high R-value roof system can save a building owner money, increase a building's energy efficiency and reduce greenhouse gas emissions. And in the retrofit roofing market, high R-value roof systems present a 50 billion-square-foot opportunity for roofing contractors.

A high R-value roof system provides a level of thermal resistance, or R-value, higher than current minimum levels required by building code standards and practices. The most effective way to achieve this performance level is by using more insulation than is required by code.

The exact insulation level needed to achieve superior performance with a high R-value roof system varies according to the criterion applied, but most high-performance building guidelines suggest the level should be up to 30 percent above minimum required values.

Executive Order 13423, Strengthening Federal Environmental, Energy, and Economic Management, which sets sustainability goals for federal agencies, provides a good benchmark, setting a building's high-performance target at a minimum 30 percent improvement in energy efficiency by 2015.

Based on data compiled by the Department of Energy's Office of Energy Efficiency and Renewable Energy, the Center for Environmental Innovation in Roofing estimates there are more than 50 billion square feet of low-slope roof systems in the U.S. For every roof system installed on a new building, about three additional roofs are installed on existing buildings to replace older, less energy-efficient roof systems. As a result, the roofing industry's reach exceeds new commercial construction by a factor of three, accounting for more than 4 billion square feet of total low-slope roof system installations annually.

According to the center, if low-slope roof systems' insulation levels were upgraded from their current R-values to high R-value roof systems, annual energy savings would exceed $2 billion.

Energy savings

You may recall that in 2007, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Inc. increased required insulation levels for low-slope roof systems in ASHRAE 90.1-2007, "Energy Standard for Buildings Except Low-Rise Residential Buildings." The standard raised the minimum insulation value of commercial roof systems insulated above decks to R-20 for most of the U.S. and Canada with the exception of Climate Zone 1, which is the U.S.' southernmost region.

Currently, ASHRAE 90.1-2007 is the most referenced baseline for commercial buildings' energy efficiency and also is incorporated into the 2009 International Energy Conservation Code (IECC). IECC and ASHRAE 90.1-2007 rapidly are being adopted by state and local code jurisdictions throughout the U.S. In fact, all 50 state governors, as part of optional block grants under the federal stimulus bill enacted in 2009, have committed to making state energy code upgrades a priority.

Furthermore, ASHRAE is expected to again increase the minimum R-value for building envelopes in ASHRAE 90.1-2010. The goal is to improve minimum prescriptive targets by 30 percent from the standard's 2004 edition.

Projected energy savings resulting from specifying and installing a high R-value roof system can be determined with available software modeling systems.

For example, NRCA's EnergyWise Roof Calculator Online can demonstrate how a high R-value roof system can offset or pay for the costs of the upgraded insulation. The EnergyWise Roof Calculator Online, available at, is a Web-based application that provides a graphical method of constructing roof assemblies to evaluate thermal performance and estimates energy costs in normal operating conditions. The application determines annual energy cost values associated with the roof system only (not the walls), which are useful when comparing energy costs and savings with the cost of upgrading and installing various insulation amounts.

Roof retrofitting

As I mentioned, one of the most significant opportunities to increase buildings' energy efficiency lies with the 50 billion square feet of low-slope roof systems currently available for retrofit annually. Energy-efficiency gains can be obtained whether an existing roof system is torn off to the deck or re-covered.

Moisture concerns

The decision to replace an existing roof system often is driven by roof leaks and moisture intrusion associated with such leaks, which may degrade an existing roof system and perhaps other parts of a building. Therefore, understanding the condition of an existing roof system is critical for successful high R-value retrofit roof system installation—even if the existing roof system is removed in its entirety.

There are several important actions you should take to minimize moisture concerns in existing buildings and roof systems.

First, inspect critical building and roof interfaces. Common entry points of moisture intrusion into a roof system are at interfaces between the roof system and other building elements such as parapet walls, penthouses, roof edges, penetrations and elevated roof curbs. All interfaces should be inspected by a roofing professional, and any deficiencies should be corrected before reroofing.

To ensure latent moisture will not adversely affect the long-term performance of a re-cover roof system, a roof moisture survey should be conducted, especially for any building that has experienced observable water leakage. Moisture surveys can be conducted using various nondestructive technologies, including infrared and nuclear scanning; these technologies can be combined with roof core cuts to validate the results.

Thermal breaks

Numerous studies have demonstrated the energy savings provided by an insulated roof system may be compromised by thermal breaks in the system, especially at joints and gaps within the insulation layers, at mechanical fasteners, and at intersections with building walls and penetrations. Certain practices can minimize energy losses at these locations when retrofitting with a high R-value roof system.

Careful measurement, cutting and fitting of insulation materials is necessary. Most modern insulating materials easily can be cut in the field, and significant thermal value can be retained through proper measuring and fitting of materials around roof penetrations and flashings. Also, spray-applied insulations may be used to eliminate board joints and cutting and fitting.

You also should install insulation boards in two or more staggered layers. Polyisocyanurate Insulation Manufacturers Association (PIMA) Technical Bulletin 113, which can be accessed at PIMA's Web site,, identifies the benefits of multilayered roof insulation boards and their ability to reduce the potential for thermal loss at board joints.

Flashing and drainage

Because insulation levels recommended for high R-value roof systems require greater total roof system thickness compared with older roof systems, wall and curb flashings may need to be raised to maintain minimum flashing heights. Additionally, a roof system's existing drainage pattern may need to be modified to ensure effective drainage and prevent ponding. And adding drains may be required to accommodate a roof system's modified drainage patterns.

To minimize flashing and drainage concerns in existing buildings and roof systems, a topographical survey of the existing roof surface may be conducted to determine existing drainage patterns. A proper understanding of the roof surface's drainage pattern is important because building settling and deflection of the roof structure over time may significantly alter intended roof drainage patterns. A roof's existing elevations and contours may be easily determined using conventional land survey instruments and methods or a visual survey noting locations of ponding or inefficient drainage on the roof surface can be performed.

Also, for roof system tear-off (not re-cover), remove less-efficient roof insulation types. Many roof insulating materials used before the development of high R-value insulations provide a relatively low R-value per inch of thickness. Polyisocyanurate, XPS, EPS and spray polyurethane foam are high R-value insulations. Removing less-efficient insulation materials and replacing them with high R-value insulation effectively can "free up" additional roof thickness to help preserve necessary flashing heights.

Parapets and curbs may need to be reconstructed to maintain minimum flashing heights. If the distance between the tops of roof flashings on walls and curbs and the top of the new roof surface is inadequate to prevent water intrusion (8 inches minimum is recommended), reconstructing parapets and raising curbs may be necessary.

A high priority

Retrofitting buildings to improve their energy efficiency has been deemed a high priority by U.S. policymakers, economists, building scientists and the design community. You have the opportunity to help lead the movement toward more energy-efficient buildings in the right direction with emphasis on high R-value retrofit roof systems.

Jared O. Blum is president of the Polyisocyanurate Insulation Manufacturers Association.


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