There are many factors and considerations that go into creating a low-slope roofing proposal in terms of the insulation. In 2015, the IECC raised the amount of insulation needed on a roof for much of the United States. It is critical that you choose the right amount of insulation to meet the R-value set for your climate zone. These higher standards can be met more easily with ISO than any other insulation. Polyiso has the highest design R-value (5.7 at one inch thickness) compared to XPS and EPS, which make it the most efficient insulation board on the market. However, in addition to the required R-values, there are three other significant issues that need to be addressed in every proposal. Condensation, puncturing, and ponding water can negatively impact the life expectancy of a roof if they are not considered when the roof is being designed.
- Condensation. Avoiding condensation in a roof design is critical for protecting the interior of a building and maximizing the life of the roof system. It can damage the substrate and potentially shorten the life expectancy of a roof. Polyiso is an effective vapor retarder compared to fiber/wool insulation, which is not. In addition, by using two layers of staggered polyiso insulation coupled with the right thickness of insulation, you are not only preventing thermal bridging but also limiting the pathways that moisture can travel along to the membrane.
- Puncturing. Compressive strength of the insulation serves two purposes: to provide a level substrate for a membrane to be attached and to protect the roof membrane. Foot traffic is inevitable on any roof, so having a higher psi insulation provides more support to the membrane to help extend its life. For roofs that have heavy roof traffic, a cover board is recommended. Polyiso comes in a high-density cover board with a psi rating of 80 psi and up to help meet that specification. And since it is lightweight and easier to fabricate than a gypsum board, it offers an outstanding installed cost advantage. Another benefit of using an HD cover board is that it helps in absorbing impact during a hailstorm unlike a gypsum board, which crumbles due to its rigidity. Polyiso and HD polyiso require less equipment, time, and labor to install compared to other insulation or cover boards.
- Ponding Water. If water doesn’t evaporate after 48 hours or longer it is considered ponding water. This is bad news for a roof as it increases the weight load, which can cause leaks or even a deck to collapse. It also collects dirt and debris that can damage or accelerate erosion of the surface of a roofing membrane. Integrating a tapered polyiso system into your roof design, which provides slope to the membrane above, allows you to direct the water off the roof to the gutters and drains and help improve the roof’s life expectancy.
Understanding and proactively addressing these issues will result in building a stronger relationship with a building owner as they will know that you are protecting their investment. To learn more about the benefits and uses of polyiso insulation, please visit the Polyisocyanurate Insulation Manufacturers Association website at www.pima.org.