Every client: “I want a roof that lasts forever, doesn’t leak, and doesn’t break the bank.” So how do we provide our clients/building owners with a roof that performs, especially in Hawaii, while also being mindful of their budget? Two terms that come to mind when designing and implementing a roofing solution are resiliency and sustainability. These terms get tossed around a lot in the roofing industry but what do they really mean? Dictionary definitions trend to the common uses of the words. Simply put, resilience is the ability to bounce back, and sustainability is the ability to continue over time.

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    ASTM Committee E60 on Sustainability developed standard E3341, General Principles of Resilience, which includes a definition of “resilience”. It states: “resilience, n—the ability to prepare for anticipated hazards, adapt to changing conditions, to withstand and limit negative impacts due to events, and to return to intended functions/services within a specified time after a disruptive event.” Also, E60 developed standard E2114, Terminology for Sustainability, which defines sustainability as “the maintenance of ecosystem components and functions for future generations.”

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     The dictionary and ASTM definitions are certainly correct, but not all that helpful when it comes to designing a roof. So, how does one implement resiliency and sustainability when it comes to buildings, and specifically roof systems? The roof on a building is arguably one of the most important elements required for a building to remain usable for long periods of time and after extreme weather events. When we look at what it means for a roof to be resilient, we are talking about a roof that is able to withstand the harsh conditions and abuses thrown at it on a daily and periodic basis, such as UV exposure, wind and rain, extreme weather events such as hurricanes, foot traffic, and potential physical damage such as mechanical equipment either deliberately or accidentally impacting the roof surface. And not just on the short term or once-off basis, but for its anticipated service life (i.e. a 20-year roof system). This leads to what it means for a roof to be sustainable. While the obvious definition of sustainable is that it lasts a long time, what other aspects of sustainability apply to roofing?  Material selection is critical, not just in the initial installation but also when the time comes for the roof to be removed and replaced.  The ability for the roof to reduce or absorb energy/heat, such as reflective surfacing or the ability to implement solar energy generation (solar PV) into the roof is also an aspect of sustainability. Lastly, and often overlooked, is the ability for a roof to be easily brought back into service (i.e. repaired) following any negative event, such as a hurricane causing physical damage from wind-borne debris or rooftop mechanical units. 

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     So, how do we design roofs that are resilient and sustainable then?  It’s actually easier than it sounds provided you are able to look at all the factors that affect a roof’s performance and lifespan. First, how does a roof handle wind? Wind resistance simply means two things–is the roof designed to withstand the increased frequency and intensity of storms, and is the design considering the performance (wind loads and pressures) with the same look to the future? The standards we use to design roofs are based on historical data, not on the anticipated needs of the future. But anticipating future needs is a key component to sustainability and needs to be considered in the initial design of a long-lifespan roof. 

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     Impact resistance, often referred to as hail resistance, is another factor for longevity. Hail, foot traffic, maintenance and modification work, and debris from a storm can all damage a roof. Very importantly for long term resilience and sustainability of a roof, don’t let the coverboard get removed because of the dreaded “value engineering”. Traditional gypsum, cementitious, and HD polyiso coverboards all provide toughness and durability, critical components to ability for a roof to “bounce back” from physical impact. 

Roofs are required by the IECC (and local building codes) to have minimum levels of roof insulation, such as Expanded Polystyrene (EPS) or Polyisocyanurate. While we all know the impact of Styrofoam on our environment, EPS is a very inexpensive material to manufacture and is made locally in Hawaii. However, its impact on the environment both during installation and when recycling counters its sustainability.  Another type of insulation that is sustainable due to its longevity and ability to be reused is lightweight insulating concrete (LWIC). LWIC’s sustainability characteristic comes from the fact that it can be reused when the roof is re-roofed; there is generally no need to tear off the LWIC when replacing the roofing membrane.

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     Another component to a roof’s resiliency and sustainability is tied to the roof reflectivity requirements of the IECC as well.  Roofs are required to meet minimum levels of reflectivity, which results in two factors: roofs reduce the heat island effects and they also reduce the solar energy absorbed, i.e. keeping the building cooler, particularly when the there is no power to run things like fans and AC.  

The choice of materials we use in our roof also plays a role in the resiliency and sustainability of a roof. Initial material selection, such as type of insulation, membrane, coverboard, and accessories, all have to balance the cost-benefit ratio in the upfront cost of a roof. However, if we choose materials that get removed and replaced often because of costs, the energy and resources needed to remove and replace those materials is definitely not good for the environment. Secondly, designing roofs that utilize not just long-lasting products that are environmentally friendly but also can be easily rehabilitated (i.e. their life extended) can lead to a more sustainable roof design that is also more resilient. Additionally, evaluating the recycled content of roof materials as well as the reusability and recyclability of roof materials ties into a sustainable roof design.

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     The last component to designing a sustainable and resilient roof is often the one that is the driving factor: cost. While initial cost is always important, a resilient and sustainable roof usually is not one that costs the least.  Life cycle costs and replacement costs are critical aspects when analyzing the financial investment in a roof. Roofs designed to last only 10 to 15 years before complete replacement are not very environmentally friendly.  Additionally, a roof that costs 15% more may have a 25-30% longer life expectancy, reducing the per-year cost of the roof.  Longer life, reduced energy costs, and little or no interruption to a building’s operations are factors that should be included in the discussion about a roof’s long term resilience and sustainability.

About the Author:  Jonathan Shick is the Owner of Pono Consulting Group, a full-service Construction Management Consulting Firm based in Honolulu, HI. He is an experienced construction professional, having served roles in all aspects of construction as general contractor, consultant, designer, quality assurance manager, construction manager, project manager, and expert witness over the course of almost 20 years with a primary focused on the building envelope and roofing. This broad depth of experience allows him to work closely with clients from the very start, guiding and educating them along a path towards a successful completion of a high-quality, cost-effective, and lasting project He can be reached at jonathans@ponocg.com or 808-213-0533

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