Design for the Environment/Residential Roofing Materials

This page is part of the Design for the Environment course  Project Information 

Group 10A - Lec 01

Daniel Loureiro(loureiro1)

Samuel Melamed(melamed1)

Simon Murray(simon.murray)

Jakub Telatnik(Jtelatnik)

This article outlines the results of an environmental life cycle assessment performed on three possible options of roofing material for residential applications. Recently, an increasing focus has been placed on the green design of buildings. This article will attempt to present information on the complete life cycle of products available to home builders who wish to offer a greener house to their customer.

Fiberglass felt asphalt shingles
The baseline for this assessment, asphalt roofing products make up as much as 90% of the residential roofing market in Canada. This assessment will focus on the fiberglass based shingles due to the lower material input required for production, compared to organic (cellulose) based shingles. This option is assumed to have a lifespan of 20 years based on warranties provided by various manufacturers. The material is produced by coating a roll of fiber mat with binder (a mixture of asphalt and aggregate) and one side is surfaced with mineral granules of desired colour. The rolls are then cut to size. The primary environmental concerns that exist with this alternative are the large amount of waste that is produced in the production of the shingles (cut away) and in re-roofing. Several possibilities exist for post-use asphalt shingle waste. This assessment will assume that 100% of the material is recycled as an additive to hot mix asphalt. In Toronto, asphalt waste is deemed private waste and must be disposed of by a private construction and demolition company; therefore, the possibility exists for the waste to be diverted from landfills.

Stainless steel roofing panels
Metal roofs are becoming more popular for residential homes. The common style and grade of steel used for urban homes is known as standing – seem, 18/10 stainless steel. This fraction represents stainless steel composed of 18% chromium and 10% nickel, 2 – 2.5% molybdenum, and 69.75% iron. The lifespan being considered for this analysis is 50 years. The processes required to extract theses metals is energy intensive and can have significant impacts on the environment. These impacts will be analyzed in this report. The roofing panels are made by taking the refined stainless steel from the mill and casting it into slabs and then rolling it into hot rolled coils. The hot rolled coils are then cold reduced and coated with a polymer coating known as Polyvinylidene Fluoride (PVDF) for protection]. One of the benefits of stainless steel roofing is that it is 60% recyclable at the end of its life. Stainless steel recycling is one of the world’s most widely recycled materials which can reduce the energy needed to produce stainless steel roofing. This will ultimately reduce the environmental impacts associated with manufacturing stainless steel roofing.

Extruded concrete roofing tiles
The alternative product analyzed is a flat extruded concrete roofing tile. The tile is made via a concrete extrusion process and is called an extruded concrete roofing tile (ECRT). The inputs from the economy represent the estimated total demand for the five life cycle stages analyzed. The life expectancy of the ECRT is 60-100 years. This analysis will account for the worst-case scenario of 60 years. The ECRT has been approved by the American Society of Mechanical Engineering Building Codes to withstand the elements of the physical environment of the scope for this report. For a single home of average 2500 sqf roof surface are it is calculated that 2016.8 tiles are needed. The weight of the roof is 23193 lbs (10.52 MT). It is assumed that by weight the tiles are comprised of 100% concrete because the weight of the paint and adhesives is negligible in comparison to the tiles themselves.

For the recycling stage of the life cycle several assumptions are made in order to make the analysis possible. It is assumed that 100% by mass of the concrete is recycled into aggregate. It is also assumed that the recycling occurs in the manufacturing plant therefore the distance of trucking the recycled concrete is the same as the distance traveled by the ECRT to the construction site. Since no mass is disposed the trucking demand is the same as the trucking demand for the installation stage. Finally it is assumed that the electricity needed to make aggregate from raw material is the same as the electricity used to make aggregate from recycled concrete. This assumption can be justifies as the process of generating aggregate from recycled concrete is the same as making aggregate from raw material.

Details about the Functional Analysis
The scope of this project applies to residential roofing in the Toronto area. All options considered conform to Ontario Building Codes and associated CSA standards. A roof is only one component of a building envelope. Other such building envelope components are doors, windows, walls and the basement. The functional purpose of each envelope component is to separate the indoor environment from the outdoor environment. Some of the outdoor environmental effects that must be considered when designing a roof are wind, rain, snow, temperature gradients, and solar radiation. Toronto experiences four seasons; therefore, each roof must be able to withstand the intense summer heat, the cold harsh winters, and the rain and wind of spring and fall.

Details about the Cost Analysis
The area of roof being considered is 2500 ft2. Transportation costs are considered over a trip of 100km. This assumes transportation from the manufacturer to the building site. These costs are determined based on weight of the materials. All costs are calculated in 1997 dollars.

The following table summarizes the direct costs anticipated by this assessment:

In addition to these costs, this assessment takes into account the of energy savings due to differences in thermal performance of the materials. The following is an assessment of annual energy used in cooling of unwanted heat gained through the roof.

As can be seen from the analysis above the extruded concrete roofing tiles are the least expensive alternative considered and have the potential to save the most energy in use.

Details about the Streamlined Life Cycle Assessment
Asphalt shingles received a low score in the material selection category because of the mining process involved in the pre-manufacturing stage and the energy required it convert the petroleum into the finished product in the manufacturing stage. With regards to transportation and packaging the effects are similar. Asphalt shingles received a score of 1 for the installation and use stage because of their short life span compared to the other two alternatives. Asphalt scored poorly in the end of life stage because it is an energy intensive process to sort through the nails and the shingles.

The reason that asphalt shingles scored better than the other alternatives in the pre-manufacturing stage is because less material is required for an equivalent area to be roofed. The process for converting petroleum into asphalt shingles must be done at a high temperature. Cement is tough and needs to be crushed in order to make concrete, which is energy intense. The manufacturing stage for steel panels requires stamping, which does not require large amounts of energy compared to the other alternatives. As stated above, the short lifespan and poor solar reflectance of asphalt shingles are the major reasons for it receiving a low score in the installation and use stage. Steel panels and ECRT have long life spans and high solar reflectance values.

Burning fuel to make the concrete in the manufacturing stage is to account for the mediocre score. Asphalt shingles received a poor score because the petroleum processing releases gaseous residue. There are no gaseous residues required to stamp the steel panels. Installation and use of the three alternatives require manual labour and no process that results in gaseous residue.

Mining of iron and extraction of petroleum can result in acid mine drainage (AMD) and the release of harmful drilling fluids. Aggregate extraction for ECRT does not release harmful liquid residues. The liquid residues associated with the pre-manufacturing of ECRT is from the process of making the cement. Asphalt shingles are coated with granules and water runoff from the roof may contain these granules and be contaminated.

The solid release associated with steel panels is the flashing from the steel shape forming. Asphalt shingles and ECRT do not have excess solid waste in the manufacturing stage. Asphalt shingles deteriorate over time. The granules that cover the asphalt shingles break off as the shingles deteriorates over time.

Details about the Hybrid Life Cycle Assessment
The primary resource in this evaluation, the Hybrid Life Cycle Assessment, was performed using the EIOLCA software to analyze the economic activity generated by the direct costs in various sectors and thus the associated environmental impacts. Each alternative was analyzed by controlling the sectors in which economic activity exists to accurately model the life cycle of each material. The following charts show the economic activity generated by each alternative:

Fiberglass felt asphalt shingles
It can be seen that most of the economic activity is a result of the first three life cycle stages. This first image shows the environmental impacts incurred by the economic activity in the first three life stages of asphalt shingles. The installation life cycle stage of this alternative incorporates the production of additional materials needed for installation (underlay, flashings, fasteners) where as the assessment of other materials include this in the manufacturing life stage.

As can be seen considerable amounts of energy input and environmental outputs come from the relatively small amount of resources extracted for this alternative, this is mostly due to the petroleum and mining sectors. For this alternative it can be seen that most of the energy is used in the manufacture of both the shingles themselves and the materials required in the installations. Analysis of processing of waste asphalt shingles to be used as an additive in hot mix asphalt showed that the additional energy required for processing results in an overall reduction in environmental outputs due offset virgin material that would otherwise need to be extracted. The overall reduction in pollutants is insignificant compared to the rest of the life cycle but analysis shows that recycling is a viable alternative to disposal in a landfill.

Extruded concrete roofing tiles
Production of extruded concrete roofing tiles results in less total economic activity than the baseline alternative. It can be seen that most of the economic activity occurs in the pre-manufacturing life cycle stage. The premanufacturing life stage involves the production of cement and the mining and processing of rock aggregate. High temperature furnaces are required to produce cement. The production of cement thus has a high economic demand from the petroleum refining industry. As can be seen in the following figure, the largest energy demands and highest production of greenhouse gases occur in this sector. The manufacturing process involves the mixing of the cement and aggregate and the extrusion process. This requires a high demand from the petroleum refining industry and the power generation industry. Both of these industries have high greenhouse gas emissions. The installation stage is minimal in economic activity and environmental impact in comparison to the premanufacturing stage and the manufacturing stage. This is because only the transportation of the extruded concrete roofing tiles is factored, and therefore most of the environmental impacts come from the fuel burned during the operation of transportations trucks. Even with the least economic activity, the energy intensive process of concrete roofing tile production results in energy inputs and environmental impacts comparable to those of the asphalt shingles. Overall, the energy inputs and the resulting greenhouse gas emissions are less than those of the asphalt shingles.

The disposal sector has a small impact on the economic activity compared to the pre - manufacturing and manufacturing sectors. A certain amount of aggregate is recycled back into the market which creates a credit in the Stone Mining and Quarrying sector and reduces the economic impact that this sector has on the environment. Studies have revealed that roughly 5% of the aggregate market comes from recycled concrete. This 5% of recycled concrete reduces the economic and environmental impact by reducing the demand needed from the aggregate mining industry.

Stainless steel roofing panels
Production of the stainless steel roofing panels creates the most economic activity of the three alternatives. As a result the energy inputs and environmental impacts are the largest for this sector. The pre – manufacturing and manufacturing sectors account for the largest portion of the economic activity, energy requirements, and environmental outputs. The combined economic activity level for both sectors is $204,132 or 97.9% of the total economic activity as seen in the corresponding chart. Both sectors contribute 1,978,000 MJ of energy and 175 MTCO2E. The total land releases are 6,274 kg. These values are significantly larger for than those for asphalt and concrete roofing materials. This is because metal extraction is an energy intensive process that is almost always a non–local activity. The industries associated with pre–manufacturing are iron ore, chromium, nickel, and molybdenum mining, and iron and steel milling. Surface mining and underground mining are typical mining methods for minerals such as iron ore and the precious metals mentioned. Both can have detrimental effects to the environment. Erosion, sinkholes, and contamination of ground and surface water by chemical waste are some of the few environmental issues facing the mining industry. Acid Mine Drainage (AMD) can unbalance the natural pH levels of an ecosystem which can destroy organisms. AMD results from the acidic waste left by abandoned mines. The next part of the pre–manufacturing section is the production of stainless steel. Electric Arc Furnaces (EAFs) are a popular type of furnace used for stainless steel smelting. Large amounts of electrical energy are needed to produce stainless steel. Approximately 360 - 400 kwh are required to melt one ton of steel. Other environmental impacts associated with using an EAF are high sound levels, dust and off–gas production, slag, and cooling water. Metals such as steel are in high demand. Therefore, they require large amounts of transportation for moving scrap and product. The trucking and rail industry contributes greatly to Global warming potential (GWP). All of these environmental impacts are the reasons the production of stainless steel roofing is more harmful than the production of asphalt and concrete roofing. The disposal sector represents a small portion of the total economic activity, but it is still important to acknowledge this sector. Recycling steel is very beneficial. There were 20 million tones of stainless steel produced in 2002 and 12 million tones out of the 20 were recycled material. The energy saved by recycling reduces the annual energy consumption of the industry by 75%, which is enough to power eighteen million homes for one year. Recycling one ton of steel saves 1,100 kilograms of iron ore, 630 kilograms of coal, and 55 kilograms of limestone. The process for producing stainless steel is the same as the recycling process. Both utilize an EAF to melt down the steel. A benefit of steel recycling is that steel can be recycled many times. Its material properties are not affected by the recycling process since the process is the same as the production process. The advantage to using an EAF is that steel can be made from 100% recycled scrap material. This is known as Cold Ferrous Feed. When stainless steel is recycled it reduces the amount of virgin material that is needed for production. This will reduce the amount of economic activity, energy, and (GWP) that is produced by manufacturing stainless steel roofing. These savings are known as recovery. The inputs for recovery can be subtracted from the final demand of production to get the actual production outputs. By recycling steel, 37.3% less virgin iron ore will be needed per household. The EIO – LCA model can be used to calculate a savings of 2.57 billion dollars of economic activity. This will ultimately lower the amount of energy consumption and GWP for stainless steel roofing manufacturing.

Final recommendations
Based on the above analysis, extruded concrete roofing tiles have the lowest environmental impact over their entire life cycle and are the lowest cost to the installer. The high durability of the roofing tiles results in a longer lifespan of this product. This helps in avoiding the large environmental impacts associated with production of the material and results in concrete tiles having the lowest energy inputs. Green house gas emissions and environmental releases produced are slightly smaller than asphalt shingles and much smaller than stainless steel panels. It was also determined that the concrete roofing tiles resulting in the greatest energy savings. These factors combined resulted in the conclusion that Ontario home builders who wish to offer a environmentally friendly design should employ extruded concrete roofing tiles in the construction of their homes.