The Material Ecology of a House: Roofing

The spring season has arrived in the northeastern United States bringing with it lots of continuous and steady rains. The cabin-like Air-BnB that I live in will have some small leaks at the wood beams where there are spots on the exterior roof that need to be patched and repaired. Luckily there is a responsible property owner who already had some contractors assess the conditions to make the repairs soon. This is not uncommon with older structures, and typically most roofing systems are warranted for about 20 years, but then will most likely need to be replaced in a reasonable timeframe after the warranty expires (though many roofing materials can last beyond 30 years with proper maintenance). Thus, it is a timely discussion to share on the material ecology of roofing materials. As a reminder, the material ecology considers the life-cycle of the building material, from sourcing, manufacturing, implementation, maintenance, and end-of-life alongside the reciprocal labor, health, and environmental impacts. 

The roofs of houses are perhaps one of the most important elements for providing adequate shelter – giving cover from the weather and keeping our interior spaces dry. Roofs provide multiple functions in this role depending on various climate conditions. They shed water and redirect heavy rainfall to valleys, gutters, and downspouts. They provide shade from intense sun with deep overhangs and eaves. They insulate from extreme cold or hot temperatures and often sustain the greatest amount of annual direct radiation on their surfaces. Because of the important role that roofing performs for our homes, it will often be designed with durable materials that are up for the task.  

Roof systems for residential construction are most frequently made with wood framing members. The wood framing may be composed of trusses, beams, or joists to create the appropriate spans across the open spaces below. The connections for wood framing are made with aluminum or steel brackets, angles, and hangers. On top of the wood framing will almost always be sheathing boards, which are typically plywood or oriented-strand board (OSB). On top of the sheathing will be a waterproof membrane, which also serves as an underlayment barrier for the finish roofing material. It is difficult to find a fully eco-friendly roof underlayment since these are typically made from asphalt-saturated felt paper, rubberized asphalt, or polyethylene sheets. However, there are a handful of more sustainable options on the market now, so informed selections can be made! Finally, on top of the underlayment is the finished roofing material. The exterior roofing materials are the most diverse and vary greatly depending on regional availability and application context. Here we review the following roofing finish material groups: natural materials, ceramics, polymers, metals, and composites. 

Let’s begin with natural materials. Within this category, we are addressing materials that are comprised of wood or plant-based compositions. The main roofing materials present in this group include cedar and redwood shakes. Shakes are square-shaped wedges that are layered into place on the roofing substrate and waterproofing, creating a sort of cascade effect for water runoff. The lapping of the shakes generally prevents water and other debris from penetrating to the substrate layer. These renewable materials, when sourced from responsibly managed forests, are some of the most sustainable roofing options. Wood shakes have a natural resistance to decay and insects. The drawback is that they are often prohibited by code in areas that are prone to wildfires. 

Next, we have ceramic roofing materials such as clay tile, terracotta tile, and slate. These offer a timeless choice for homeowners seeking both durability and aesthetics. Clay and terracotta tiles, made from natural clay fires at high temperatures, embody tradition and sustainability with their long-lasting performance, fire, rot, and insect resistance, and beneficial thermal properties for certain climates. Slate tiles, quarried from natural stone, add a touch of elegance with their textures and color variations, lasting over a century while requiring minimal maintenance. Clay and terracotta tiles are recyclable at the end of their lifecycle, and slate tiles are naturally returned to the earth without negative impacts. These materials contribute to the eco-friendly options for sustainable roofing. 

We can’t skip over polymer roofing materials, which are typical for low-slope or flat roofs that consist of concrete slabs, metal decking, or wood decking substrates. While these roofing materials are some of the most prevalent for flat roofs, they are also some of the most toxic in their chemical compositions. Let’s review the benefits and challenges of these options. Common polymer roofing materials include options such as Ethylene Propylene Diene Monomer (EPDM), Polyvinyl Chloride (PVC), and Thermoplastic Polyolefin (TPO) membranes. The benefits of these polymers are that they offer durability, flexibility, and great water-resistance properties. However, its manufacturing process involves non-renewable fossil fuels contributing to greenhouse gas emissions, and the material releases VOCs causing health risks to the manufacturing laborers and construction site installers.   

EPDM is a synthetic rubber that has exceptional resistance to UV rays and weathering, ensuring longer lifespans of 30 to 50 years. PVC is a widely used roofing material that offers good durability and fire resistance but is plagued by environmental challenges in its production and disposal, including toxic phthalates and harmful dioxins. In contrast, TPO emerges as a better option among these polymers. It is highly reflective, providing good emissivity for the “cool roof” effect, which reduces the cooling load on the home by reducing the direct heat gain across the roof’s surfaces. TPO does not contain phthalates or chlorine, and it is more easily recyclable. Nevertheless, the manufacturing of each of these polymeric roofing materials still involves the use of fossil fuels, promoting a continuous need for improvement in balancing their performance and environmental impact.  

Metal roofing is often a preferred choice for both residential and commercial buildings due to its remarkable combination of performance and sustainability. Various metal roofing materials, such as aluminum, copper, zinc, and stainless steel, are available in different forms including corrugated, ribbed, and flat or interlocking panels. These materials are known for their remarkable longevity, lasting up to 70 years or more, significantly reducing the frequency of roof replacements and associated environmental impact. Primarily composed of recycled materials, metal roofs contribute to a circular economy by reducing the demand for virgin resources and diverting waste from landfills. Depending on the surface coating, most metal roof materials are excellent at reflecting solar radiation resulting in minimal heat absorption and decreasing building cooling loads. Metals in general have high emissivity values allowing for heat to be more rapidly released from the material back into the atmosphere. Furthermore, metal roofs are usually 100% recyclable at the end of their long service life. Additionally, they tend to resist the growth of mold, mildew, or algae, reducing required maintenance and promoting a healthier living environment. 

Aluminum, copper, zinc, and stainless-steel metal roofing materials each offer unique benefits. Aluminum is lightweight, corrosion-resistant, and highly reflective. Copper is renowned for its striking appearance and unparalleled longevity, often lasting over a century with minimal maintenance. Zinc is celebrated for its self-healing properties and distinctive aesthetic appeal, though tends to be higher cost upfront. Stainless steel offers exceptional strength and corrosion resistance, ensuring long-lasting performance in various climates while providing a sleek and modern appearance.  

Finally, we have the group of composite roofing materials, which have emerged as a versatile and practical solution through a balance of affordability and durability. Among the commonly used composites are asphalt shingles, the most prevalent in North America, composed of a fiberglass or organic mat base and asphalt. While these shingles offer ease of installation and typical lifespans of 15 to 30 years, their production from petroleum-based asphalt contributes to greenhouse gas emissions and reliance on fossil fuels, making them a less environmentally friendly option. Built-up roof systems, consisting of multiple layers of asphalt and a top layer of gravel, are durable and weather-resistant but face similar concerns due to the use of asphalt and are more difficult to repair. Tar and gravel roofing is a traditional choice and offers good weather resistance but is falling out of favor due to concerns about toxic runoff. Stone-coated steel roofing is a hybrid option that combines the strength of steel with the aesthetic appeal of stone granules, providing durability and longevity. This composite may be the closest to an eco-friendly option from this category but still makes use of toxins in the adhesives and bonding agents.  

In selecting roofing materials, regional climate variations play a pivotal role, especially in the potential longevity and maintenance requirements that will be incurred. Natural materials such as wood shakes thrive in temperate and mixed climates with moderate rainfall, while slate’s density and durability make it an excellent choice for cold climates with heavy snowfall. Clay tiles and ceramic roofing materials do well in hot-arid climates due to their heat capacitance, absorbing the sun’s energy and storing it, then releasing it back into the atmosphere at night to create an overall cooling effect for the home. Polymer membranes are common in temperate and hot-humid climates because of their waterproofing performance but can also do well in hot-arid climates when they are white and reflective. Metal roofing materials do well in any climate region, as long as they are properly treated for corrosion resistance in wet conditions or near saltwater ocean locations. Composite materials, such as fiber cement shingles and plastic composite tiles that are designed to mimic natural materials but with enhanced durability, are also versatile and can be used in temperate and hot-humid climates. Ultimately, the choice of roofing material considers not only the ideal climate applications but also factors like roof slope, insulation needs, local building codes, costs, and aesthetic integration with the overall design of the house.  

Future blogs about the material ecology of a house will cover the MEP (mechanical, electrical, plumbing) systems and eco-friendly interior finishes. If you are planning for any new home construction or renovation and are interested in a healthy material ecology, reach out to AIDA LLC today for a consultation. You can always find more information and resources for creating your own healthy home and workspace at Aletheia Ida Design and Architecture, LLC (AIDA LLC) by visiting www.aletheiaida.com.