Contractors Face Challenges for Roof Attachments on Energy Efficient Buildings

May 11th, 2012

Green building rating systems are anticipated to increase their minimum energy efficiency requirements as demand for greener buildings grows and building code updates become stricter. As the energy efficiency requirements increase, so will the amount of polyiso roof insulation installed by contractors as design professionals strive to meet the requirements of the rating systems. Attaching thicker layers of polyiso insulation in roof systems comes with a variety of issues to consider and the following article covers several challenges for contractors.

Codes and Rating Systems:

The LEED program from the U.S. Green Building Council will require more stringent building energy performance. Some building codes are or will become stricter about minimum energy performance, including the International Green Construction Code (IgCC), an overlay code based on ASHRAE Standard 189.1, Standard for the Design of High Performance, Green Buildings Except Low-Rise Residential Buildings.

Stringent state regulations include the California’s Green Building Standards Code, or “Calgreen.” Alignment of the ASHRAE standard, IgCC and the Calgreen are all likely to occur in coming years as these non-code rating systems and adoptable standards become building code at the state and local levels.

Voluntary or mandated, these codes and rating systems will present greater challenges for contractors as they are required to attach increasingly thicker insulation layers in the roofing system. While polyiso insulation will play a big role in more energy efficient buildings, contractors will also need to know how to use newer products being developed for green buildings, including low-VOC adhesives.

In the past, roof system attachment methods have included adhesives containing VOCs, hot tar or asphalt-based materials, or they were held in place with pavers or stone ballast. Mechanical fastening systems have also been improved in recent decades and now dominate the commercial roofing industry.

Inadequately secured installation can be costly. The Single Ply Roofing Institute (SPRI) provides technical papers on proper attachments as well as strong warnings about not following proper installation methods. According to SPRI, “Roof substrate and insulation materials insufficiently restrained within a roof system may experience some dimensional change or shifting under certain in-service conditions. The result may be cupping, curling, or rafting that can be a concern with respect to drainage, thermal efficiency, membrane damage, and aesthetics.”

Green Roof Considerations:

Adding more insulation is good but how they are attached also needs to be addressed when using newer green adhering products.

In addition to green building programs resulting in thicker insulation, the rating systems also are transforming the roofing industry in other ways. For example, new roof insulation adhesives have been developed to replace older generation adhesive that are odorous and contained harmful Volatile Organic Compounds (VOCs). The Ozone Transportation Commission (OTC) has lowered the VOC limits to reduce materials contributing to ozone, an ingredient known for increasing the potential for smog. Working with the latest generation of adhesives also presents challenges for contractors trying to please building owners, occupants and others who are part of the project team.

Care has to be taken, for example, with some of the Low-VOC adhesives, because the heavier particulates in these green adhesive products have unintentionally caused strong odors inside a building as a re-roofing project progresses. Until these new Low-VOC products have been perfected to create fewer odors, activated charcoal filters can be placed over air intake vents on the roof for a reduction in complaints about odors during re-roofing from the occupants inside the building.

The odor issue with water-based adhesives is just one of the potential unintended consequences that can occur even when good intensions such as green building practices are the goal. Because some climates contain high amounts of moisture especially in the rainy season in states such as Florida, water based adhesives may not be the right choice or their use must be conducted according to the manufacturer’s instructions.

Integrating Positive Drainage and Energy Efficiency:

In addition to attachment considerations, it is best to work with a professional from a  roof insulation manufacturer that is also experienced in tapered roof insulation and can help the architect and contractor design the rooftop for the proper drainage and meet the project’s energy performance requirements. Regarding energy performance, the Atlas Roofing Corporation’s LTTR Calculator can assist with meeting the energy efficiency requirements that meet the applicable ASHRAE 90.1 requirements for the building’s climate zone.

As R-Values are increased in ASHRAE standards and the IgCC, insulation thickness in excess of 5 inches will be necessary. Determining the insulation volume and design of the roofing system based on ASHARE can be achieved with the Atlas interactive LTTR Calculator at its www.greenzone.com Web site. The calculator gives users in all climate zones across North America instant access to polyiso roof insulation solutions that will enable them to reach any R-value requirement. The new LTTR Calculator enables contractors, specifiers, roofing consultants, building owners and others to easily design for a specific R-value, building code, or determine how to meet the ASHRAE 90.1 standard in specific climate zones.

LTTR is a scientific methodology for predicting Long-Term Thermal Resistance of polyiso (polyisocyanurate) insulation. Using LTTR, the R-value of a polyiso product is determined as a 15-year time-weighted average.  During the last 20 years LTTR became the accepted standard among polyiso users and manufacturers, enabling more accurate predictions of the actual energy efficiency achieved in a building insulated with polyiso in a given climate zone.

Polyiso (polyisocyanurate) is the insulation of choice among commercial roofing contractors, roofing materials manufacturers, roof consultants and construction specifiers. Its combination of low installation cost and lifecycle payback makes it an economical choice for new construction or re-roof applications. With certain high performance facers, Atlas polyiso can be used without a thermal barrier or cover board in many roof systems and its high temperature stability prevents melting when mopped with bitumen. Atlas ACFoam polyiso products are third-party QualityMark Certified through the Polyisocyanurate Insulation Manufacturers Association (PIMA) and use blowing agents with Zero Ozone Depletion Potential (ODP) and Zero Global Warming Potential (GWP).

Atlas Roofing’s tapered insulation services group supports contractors and other project team members during the bidding process by generating quotes and shop drawings based on everything from architectural bid documents to faxed rough sketches. The design phase is the best time to specify the attachment system and a strong representative from the roofing product manufacturer can make life easier for the contractor before and during installation day.

With drainage and energy efficiency requirements established, Atlas Roofing then provides the project team with quick delivery of its Atlas ACFoam® polyiso products to keep the project schedule on time and on budget. With additional layers of insulation to achieve the R-Values, the attachments of insulation layer for various roof decks needs to be addressed. Always check with the insulation manufacturer and the roofing membrane manufacturer for any additional requirements and all current standards  relevant to the application.

Attachment Techniques:

For steel and wood roof decks, mechanical fastening with self-tapping screws and plates on steel and wood roof decks is very common and an approved technique for attaching insulation.

Mechanical fastening is also acceptable on cast-in-place concrete, cementitious wood fiber, and gypsum. Mechanical fastening requires pre-drilling pilot holes and the use of specialty fasteners for insulation attachment.

When a contractor is pre-drilling holes this means more labor is involved. There is also the risk of damage to the deck and the noise involved can disruption occupants inside the building during office hours. For these reasons, mechanical fastening can be less desirable when compared to other attachment options.

If the deck is not steel or wood, hot asphalt can be used. It is an approved method for insulation attachment on concrete roof decks and over mechanically attached base sheets on nailable decks such as gypsum, wood, cementitious wood fiber, and lightweight concrete. Hot asphalt is also acceptable on cover boards or subsequent insulation layers over a mechanically fastened base layer of insulation. Hot asphalt is not approved for insulation attachment directly to steel decks.

Low-rise polyurethane adhesives are approved and can be substituted for hot asphalt to provide insulation attachment. Polyurethane adhesives are advantageous for use where asphalt odors are objectionable or asphalt delivery to the roof is impractical.

Polyurethane adhesives are applied as either full coverage or as bead/ribbon installations. Bead-applied adhesive is placed in 0.75- to 1-inch ribbons over the substrate. Bead spacing is typically 12 inches on center in the field of the roof, with increased bead spacing (6 inches and 4 inches) in the roof perimeters and corners, respectively.

For insulation attachment directly to steel decks, polyurethane adhesive, in conjunction with mechanical fastening on steel decks, is approved for use and required to achieve the higher wind-uplift resistances in hurricane-prone regions. The ASCE/SEI 7-05 is a standard for Minimum Design Loads for Buildings and Other Structures should be followed.

In a ballasted roof system, the insulation and roof membrane are typically loose laid and then covered with the weight of washed river gravel or concrete pavers. The required weight of the ballast varies by wind zone, but, at a minimum, is 10 to 12 pounds per square foot in the field of the roof, increasing at the roof perimeters and corners. Ballasted assemblies are not allowed in high wind zones and various municipalities throughout the United States.

As the contractor starts to attach the polyiso insulation products, there are SPRI standards available to ensure proper performance, for both mechanical and the newer Low-VOC adhesives, solvents, primers and cleaners, which are very new to the marketplace.

A roofing contractor required to practice more sustainable installation methods can add value to their services when they use best practices in the field, resulting in such benefits as zero indoor air quality complaints because they are aware of the potential for odors and have procedures in place to combat odors. Ordering more polyiso insulation is the easy part, installing it presents challenges that are easily addressed when the roofing contractor and manufacturer work together.