Raise the Roof!
- By Amy Milshtein
- December 1st, 2012
Roof insulation, admittedly, is one of the least sexy parts of a building. But, when done right, the insulation helps keep a facility warm in the winter, cool in the summer, and remains intact despite workers, and the occasional wayward student, stomping on the roof. However, choosing the right material can be tricky.
In a 2010 article for FacilitiesNet
, registered roof consultant (RRC) and senior consultant with Benchmark, Inc. Alvin Nunnikhoven identified six kinds of rigid insulation types, which include: wood fiber, perlite, polyisocyanurate (PIR or polyiso), expanded or extruded polystyrene, cellular glass, and gypsum board. Each choice has its own properties, along with their own pros and cons. What they have in common is that they need to become “an integral part of the roof assembly and must function in concert with the membrane and the structural deck. Wise insulation choices result in successful roof systems that perform over the long term, while poor choices can be detrimental to roof performance,” according to Nunnikhoven’s piece.
Making a Choice
Choosing the right material is a process that takes many factors — like membrane compatibility and insurance and code requirements — into account. However, “There are two primary concerns when it comes to roofing insulation,” says Tony Matter, marketing communications manager, Carlisle SynTec Systems, “R-value and compression strength.”
R-value is a measure of thermal resistance used in the building and construction industry. The higher the number, the greater the insulation. Compression strength relates to how much pressure the material can take. “There’s a lot happening up on a college roof,” says Matter. “Mechanicals are found up there and workers have to clean and service them, which means they are walking up on the roof and potentially harming it.”
“Polyiso is the industry standard,” Matter continues. “It has a high R-value and it’s easy to install. In fact, gypsum board has a 0.5 R-value, while the same thickness polyiso has a 2.5 R-value. Expanded or extruded polystyrene foam (EFP) is a less expensive option, but it has a lower R-value, so you have to use more of it to get the desired effect.”
That desired effect changes every few years. “There is nothing new in insulating products,” says Mark Graham of the National Roof Contractors Association (NRCA). “The only thing that is changing is the amount of insulation we use.” Graham reports that in the last seven or so years the energy codes and standards have grown more stringent.
Take a Look at Energy Efficiency
“If we compare energy codes through time, we find that the 2006 standard asked for a 30 percent increase in efficiency over the 2000 standard, and the 2012 standard asks for a 30 percent increase over that,” explains Graham. “This doesn’t mean that we’re asking for 60 percent more insulation, but we do need a 60 percent increase in energy efficiency in less than the life span of a roof. If the products remain the same, that means that we just use more of them to bump up the value.”
If you think that getting a LEED certification will help with your roof’s energy efficiency, Graham cautions you to think again. “You can get enough points to have a LEED Silver rating and still not have a building that meets energy codes,” he says. “And mind you, the codes are just the bare minimum.”
Reflective, or white, roofs are another factor that has changed with the times. “There used to be a credit for reflective roofs in the code, meaning that if you used a reflective roof you could add less insulation,” says Graham. “That has been eliminated. Now you have to have the same amount of insulation no matter what color the roof.”
“White roofs were considered a panacea for energy efficiency for a while,” agrees Matter, “but it’s not true. Generally speaking they cut down on air conditioning costs, but in the colder months you spend more on heating. Roof color should always be secondary to insulation. Insulation is the great equalizer.”
How Green Is My Roof?
Vegetated, or living (green) roofs, comprise another fairly new roofing option. “EFP remains a great option for vegetated roofs,” says Matter. “It can be formed into different shapes to look like rolling hills, valleys, cubes, columns, or whatever the architect imagines. Then an engineered growth media holds the plants. It lasts longer than topsoil, doesn’t pack down, and is lightweight and porous.”
Unfortunately, vegetated roofs do nothing for R-values. “Its greatest benefit is stormwater management,” explains Matter. “If it’s thick enough it can work as a sound barrier, but it doesn’t add to energy efficiency. It is aesthetically pleasing, though.”
“Vegetated roofs help with the urban heat island concept,” continues Graham. “Here in Chicago, we have the most square footage of vegetated roofs in the U.S. But that shouldn’t count towards any insulation benefits.”
Graham is hoping that a change will happen in roofing insulation in the 2015 codes. “Right now all roofing products are rated at 75° Fahrenheit,” he says. “But some products have a lower or higher R-value at different temperatures. Hopefully in the next few years the codes will recognize that and not penalize the products that work better in the cold weather.”