Facility owners, architects, and other key decision-makers are tasked with making critical choices that impact not only the sustainability of buildings but also the operational costs. Roofing systems are one area that can significantly affect these outcomes—particularly in terms of how they impact operational carbon and energy efficiency. Read on for more information about how roofing materials, system design, and maintenance strategies can influence operational carbon throughout a facility's life cycle.
What Is Operational Carbon?
Operational carbon refers to the carbon dioxide (CO2) emissions generated by a building's energy consumption during its occupancy phase, including heating, cooling, lighting, and powering equipment. Since roofing systems help regulate building temperature and energy use from heating and cooling, a building's carbon emissions and its roof's long-term durability and thermal efficiency are directly related. A well-designed roofing system can help lower operational carbon emissions, aligning with both environmental goals and reduced costs.
The Importance of Total Carbon
To fully understand the impact of roofing decisions, it's important to consider the concept of total carbon, which is defined as the sum of operational and embodied carbon. Embodied carbon refers to the totality of CO2 emissions from all stages of a building's life cycle except the operational phase, including raw material acquisition, manufacturing, transportation, construction, maintenance, and disposal/demolition. While embodied carbon can be significant, operational carbon often makes up the largest portion of a building's total carbon footprint.
How Roofing Materials Affect Carbon Emissions
A properly designed and installed roof is key to helping minimize a building's carbon emissions. Consider these factors when designing and choosing roofing materials for commercial facilities.
Polyiso Insulation
Insulation is generally considered the only building material that directly offsets operational emissions, so choosing the right product is critical. Polyisocyanurate (polyiso) insulation is a popular choice for commercial roofing due to its low cost per R-value, high insulation performance per inch, and compatibility with adhesives. Since electricity is typically more expensive than gas used for heating, polyiso's greatest value is seen during the summer months when air conditioning usage peaks, as well as during seasonal transitions in the spring and fall. In addition, if electricity is used for heating, polyiso's value is seen during the heating season, as well.
R-Value
When specifying insulation, it is advisable to consider the building's lifespan and polyiso's long-term thermal resistance (LTTR) values. The climate zone and building code applicable for the project will dictate the minimum required R-value for roofing systems, but that doesn't mean the minimum is necessarily the best solution. Increasing insulation at the time of a roof replacement may lead to a substantial decrease in operational costs and carbon emissions over the building's lifetime. Many factors, such as building proportions, roof reflectivity, and geography, directly affect the overall benefits of polyiso insulation.
Vapor Retarders
Vapor retarders can also play a role in optimizing energy costs. The use of a vapor retarder may be necessary to prevent air from moving from the building's interior into the roof system. Moisture-laden air can bring heat and moisture, and, under certain conditions, the moisture can condense within the roof system, especially in buildings with high humidity levels when it is cold outside.
If a vapor retarder is not used, the dew point location should be situated in the upper portion of the polyiso insulation layer to lower the risk of condensation occurring within the roof system or on the underside of the roofing membrane. A building science professional can help determine whether a particular project might benefit from a vapor retarder and what type should be used, depending on the building's use, location, and surrounding climate.
How Installation Methods Affect Insulation Performance
As one of the only products with use-phase benefits for a building, insulation isn't discretionary—it's an asset. Insulation helps prevent heat transfer (loss or gain) and helps reduce the energy needed to heat or cool a building, thus reducing carbon emissions from fossil fuel use. Furthermore, the method used to install insulation can affect its efficiency and performance.
Fasteners vs. Adhesives
Mechanical fasteners can be thermal bridges, reducing insulation value and energy efficiency. Mechanically attached roof systems use fasteners through the full insulation thickness when installed in the membrane seams. These fasteners create pathways for heat transfer. Adhered insulation systems in conjunction with adhered membranes, on the other hand, do not use full-thickness fasteners to attach insulation and membranes. This helps to significantly reduce thermal bridging, and it may help lower the potential for condensation by reducing air flow through the roof system.
Adhered systems generally have higher initial material and labor costs, but the risk of thermal bridging is effectively eliminated compared to mechanically fastened systems.
Another type of attachment using fasteners is induction-welded systems. These systems use induction welding to attach roof membranes to special fasteners that also secure the roof's insulation layer. Induction-welded systems can help uniformly distribute wind loads. This application method doesn't have temperature restrictions during installation so that contractors can use it regardless of cold weather conditions. However, concerns about thermal bridging and reduced energy efficiency persist. Therefore, it is important to examine the potential increase in energy use and operational carbon relative to roof systems with all or most layers adhered.
Design and Maintenance Strategies
A roofing system's design and maintenance can significantly influence its carbon emissions.
Proper Design
A well-constructed roof system helps prevent air leakage and minimizes thermal transfer. When using two layers of polyiso, contractors should install them in a staggered pattern with offset joints to help prevent air from migrating through the roof assembly. Burying fasteners within the roof system and adhering the upper layers of insulation and adhering the membrane can significantly increase the effective R-value of the roof's insulation layer.
Maintenance and Inspection
Routine roof maintenance is essential for maintaining optimal performance. Remove debris regularly and repair any damage that may have occurred since the prior inspection.
Regular professional inspections can identify issues early, assessing the roof's condition. Inspections from both inside the building and on the rooftop will help evaluate the system's overall functionality and repair requirements. Catching defects while they are small can help prevent costly repairs, ranging from extensive roof replacement to potential leakage that can disrupt a building's operations. The goal of roof inspections and maintenance is to prolong the service life of a roof system. A long service life helps reduce the energy and embodied carbon that is associated with removal and replacement of a roof system.
Long-Term Benefits of High-Performance Roofing Systems
A high-performance roofing system is an investment that can minimize environmental footprints and offer long-term financial benefits. Architects, building owners, and other key decision-makers should consider the following benefits when designing roof systems, selecting materials, and overseeing roofing installation and subsequent maintenance.
Reduced Energy Costs
Enhanced thermal performance reduces energy consumption by lowering heating and cooling demands. Insulation helps offset the embodied carbon released during building construction by minimizing carbon emissions throughout its lifespan. Often overlooked is how vapor retarders and air barriers also help reduce energy costs by managing moisture and air movement.
Vapor retarders, especially when installed as air barriers, limit moisture migration and help prevent condensation, which can lower effective insulation R-value. Air barriers restrict air flow, reducing energy loss from air leakage and helping maintain consistent temperatures. Both help ensure insulation performs optimally by minimizing air movement and helping to prevent condensation. High performance roofs help lower the workload on HVAC systems and reduce energy consumption. When designed and installed correctly, these systems work together to achieve long-term energy savings and prevent the negative effects of moisture and air infiltration.
Extended Roof Life
Quality materials and proper maintenance help extend a roof's lifespan. Most commercial facilities are typically long-term commitments. Investing upfront can help extend the roof system's service life, reduce maintenance and repair costs, and avoid more frequent roof replacement projects. All of these extend a roof's service life and help to reduce the embodied and operational carbon.
Making Informed Choices About Carbon Reduction
Understanding how to assess operational, embodied, and total carbon can help facility owners, architects, and other decision-makers identify optimal roofing solutions—including materials, system designs, and maintenance practices—to reduce their buildings' carbon emissions. Ensuring the roofing system is well-maintained can further help minimize the building's environmental impact, reduce the risk of costly repairs, and lead to a long service life.
