Design for the Environment/Ontario Residential Roofing Materials

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Roofing shingles are important to residential units as they protect the roof of a house from outdoor elements. With the large selection of styles, colours, and materials, shingles must not only withstand extreme seasonal conditions, but compliment the architecture of the home. Shingles vary in cost, thus a more expensive material choice can result in increased property value and higher social standing.

Summary[edit | edit source]

This study focuses on three common forms of residential roofing materials, and compares each alternative based on their function, environmental impact and cost to the user. The three types of shingles that will be further compared include asphalt fibreglass composition, wood, and aluminum. Fibreglass-based shingles are composed of a fibreglass reinforced mat saturated with an asphalt mixture. Asphalt roof shingles have been designed to protect a roof through their manufacturing and installation process. Wood roofs most commonly come in the form of red cedar shakes. Along with their natural resistance to decay, red cedar roofs are chemically treated to improve sustainability. The high strength and toughness of aluminum makes it a viable roofing option by resisting damage from the impact of hail and other solids.

This study can be useful to anyone looking to re-roof a residential house. On a large scale, a home building company may find the following recommendations and conclusions particularly interesting. The motivation behind this analysis was to look at the current trends in residential roofing materials, and decide whether the most common forms of roofing have functional, environmental and cost advantages. The comparison can serve as a basis for the final recommendation of one design alternative for residential roofing materials.

Project Information[edit | edit source]

MIE 315 Section 02

Group B22

Holly Johnson (Holly)

Kyle DuPont (Kdupont)

Shyra (Shyra)

Mark (Mark.Osmokrovic)

Highlights and Recommendations[edit | edit source]


Asphalt and fibreglass composition shingles are currently used in the majority of homes, and thus served as a baseline for comparison. Two alternatives to asphalt shingles are aluminum and Red Cedar Tapersawn Shakes, which will be referred to as cedar shakes.

Asphalt shingles have been the standard among homes in North America for several decades. Information for the figure to the right was provided by The Freedonia Group, and shows the detailed breakdown of the material used in roofing residential homes in the United States from 1992-2007. This analysis was completed to revaluate the use of asphalt, and determine if either aluminum or cedar is a better alternative. It was assumed a house in Ottawa, Ontario, Canada with a roof of 1500 square feet was being protected for 50 years. A conclusion was recommended based on a functional analysis, a qualitative life cycle analysis, a quantitative life cycle analysis, a cost analysis, and society’s perception.

After analyzing each of these factors, it was determined that asphalt should continue to be used as a primary roofing material. However, this conclusion is only valid for the upcoming 25 years, after which time the net consumption of oil will reach the net production. After year 25, the production of asphalt shingles will be detrimental to the environment because it will involve a depletion of a fossil fuel.

For the long-term, cedar shingles are optimal for the environment, but aluminum shingles are best suited for the consumer. This is because the cost of cedar shingles is more than twice that of aluminum. Despite scoring lower in the SLCA, aluminum shingles produce less total global warming potential, releases, and require less energy than cedar shingles. Therefore, it is recommended for the long run that aluminum be used as the primary roofing material.

Functional Analysis[edit | edit source]

The primary purpose of residential roofing shingles is to protect the house and its inhabitants from the vast array of outdoor elements. Drastic changes in temperature, precipitation, and wind can occur over a short period of time. In terms of a house located in Ottawa, Ontario, the roof must be able to withstand the cold weather and abundant precipitation associated with a frigid winter, as well as the scorching heat of the summer sun.

Asphalt, aluminum and cedar roofing options have their own advantages and disadvantages when looking at the full spectrum of their purpose; for example, asphalt shingles are most easily installed, aluminum’s toughness makes it resilient to the impact of hail, and cedar’s natural appearance provides an aesthetic appeal to the house. However, these benefits do not alone justify a level comparison between the design alternatives. In order to ensure asphalt, aluminum and cedar roofs have comparable functions, each roofing material is analyzed in terms of their tolerance to extreme weather conditions.

Upon researching the functionality of each option in varying weather conditions, it was determined that each of the design alternatives could fulfil their year round purpose on the roof of a house in Ottawa, Ontario. However, the major variable within the comparison deals with the expected lifespan of each option. Aluminum shingles can typically last 50 years without replacement, while standard asphalt and cedar options can only be functional for 25 years. Thus, in order to accurately compare the three options, this study will look at a 50-year time period. In this time, aluminum shingles will be installed once and last until the end of the study, while both the asphalt and cedar roofs will be installed once at year 0 and then again at year 25.

It is concluded that with this consideration of varying life spans, the three options for residential roofing materials can be accurately compared against each other in cost, environmental and societal analysis. More details regarding the advantages and disadvantages of asphalt, aluminum and cedar roofs can be found here.

Economic Input-Output Life Cycle Analysis[edit | edit source]

The Economic Input-Output Life Cycle Analysis allows for the comparison of design alternatives by quantifying the environmental impacts corresponding to an economic input into a specific economical sector. This analysis model considered resource extraction and manufacturing as one stage, transportation as a second stage, and end of life as a third stage. In analyzing the output for each of these three studies, the largest environmental impacts are ranked according to the top five contributing sectors.

The environmental impacts between alternatives are evaluated through: substance releases, such as the equivalent metric tonnes of carbon dioxide for Global Warming Potential gasses (GWP), carbon monoxide and dioxide emissions; the Tera Joules of energy used; and kilograms of all toxic releases and transfers (land, water and air).

The results of this showed that in fact, asphalt shingles produced the least environmental impact overall. Aluminum had the highest impact of the alternatives during its manufacturing and end of life stage (recycling) in total releases. Cedar shakes had the second highest impact, which was trailed closely by asphalt shingles. The same rank followed in the other two sectors, except asphalt was clearly the best alternative by a larger margin. Based on this analysis, the asphalt shingle produces the least environmental effects for a 25 year life span. More detailed information regarding each roofing alternative can be found here.

EIOLCA - Releases.JPG


Streamlined Life Cycle Analysis[edit | edit source]

A streamlined life cycle analysis considers all the stages in the life cycle of shingles: Resource Extraction; Product Manufacturing; Product Delivery; Product Use; and Disposal and Recycling. Each stage was then evaluated on the following criteria: material choice; energy use; solid residues; liquid residues; and gaseous residues.

The product delivery phase was ranked based on the energy used to transport the shingles. The energy used is dependent on the distance the truck travels from the manufacturing plant to the distribution centre in Ottawa, Ontario. Asphalt shingles travel from Brampton to Ottawa within Ontario, but with a weight of 230 pounds per square. Aluminum smelters are located in Quebec along the Saguenay River, and it is assumed the shingle production plant is located close to the smelter, the product would be transported 670 km by truck to Ottawa, Ontario. The weight per unit area of aluminum roofing is five times less than that of asphalt or cedar at 40 lb per square. Cedar shingles weigh 205 pounds/square and need to be transported from British Columbia to Ontario.

The matrix assesses asphalt, aluminum, and wood shingles and the results are summarized in the following table.


Resource extraction and product manufacturing were weighted at 30% because they have the biggest impact on the environment. Since product delivery and use were similar to all alternatives, they were each weighted at 10%. The disposal and recycling phase was weighted at 20%. The final results for asphalt, aluminum, and cedar shingles were respective rankings out of 100 of 59.5, 61, and 77.5. Details on each of the alternatives can be found below.

Cost Analysis[edit | edit source]

Cost Summary.JPG

The economic analysis was completed on the assumption that a house in Ottawa, Ontario, Canada with a 1500 square foot roof was being protected for 50 years. All costs were converted to present worth assuming a 2% inflation rate. During the 50 year lifetime, the roof composed of asphalt shingles, as well as the roof with cedar shakes, will be replaced at year 25. The costs considered are considered from the perspective of the home owner and included the installation, maintenance, and end of life costs.

It was found that asphalt shingles require no maintenance, but had a total installation cost of $3509.05 and a disposal cost of $222.84. Aluminum shingles require no maintenance, but had installation costs $3634.05 and had a return of $0.05 for disposal. Cedar shakes require $6741.45 for installation, $1494.31 for maintenance, and $250.83 for disposal. From these results, it is clear that aluminum shingles are the most cost effective because it does not require two disposal or installation fees. The costs for each design alternative are summarized in the graph located to the right. More details regarding the advantages and disadvantages of asphalt, aluminum and cedar roofs can be found below.

Societal Analysis[edit | edit source]

Due to the nature of the product, its effect on the greater part of society is mostly aesthetic. Society’s perception of a roofing alternative will affect a homeowner’s purchasing choice. Also, the affordability of the product for the homeowner is also a major factor.

The widespread use of asphalt was attributed to its relatively low cost. The comparatively greater expense for aluminum or cedar roof was justified by aesthetic appeal; cedar shingles have a natural, authentic appearance; aluminum shingles are versatile in terms of graphic design. Aluminum shingles also involve the benefit of convenience due to low maintenance. The details for each alternative can be found here.

Details about the Functional Analysis[edit | edit source]

Asphalt[edit | edit source]

Sudden variations in ambient temperature cause the shingles to rapidly expand and contract, resulting in thermal stresses. Hail can fracture or cause a significant loss in the asphalt granules, which may result in short term leaks or reduce the lifespan of the shingle. Since asphalt shingles are installed with an overlapping double layer, the damaged shingles do not need to be replaced immediately. Strong winds are likely to lift the edges of shingles resulting in warping and possible tearing. This can lead to water damage as more shingles are torn from the roof, thus exposing the roof deck.

Aluminium[edit | edit source]

Aluminum shingles employ a four-sided interlocking installation system. The tight seal from interlocking helps resist wind damage and prevent leaks. The interlocking and slippery aluminum surface work to shed snow and ice rapidly, preventing damming and, in turn, leaks. Installing aluminum shingles is less labour and energy intensive compared to the other alternatives because they are five times lighter per unit area than either alternative [1].

An aluminum roof inhibits moss growth, retards the spread of flame, and is not liable to rust, slit, rot or curl [2].

A disadvantage to aluminum shingles is a higher noise level upon the impact of hail or heavy rain on the metal surface. While asphalt and wood are better at absorbing the noise, aluminum shingles depend on the felt layer below the shingles to dampen the sound [3].

Cedar[edit | edit source]

Wood has been a competitive option as a roofing material for a significant portion of building history. Red cedar shakes can last up to 40 years if the roof is properly maintained and the wood is chemically treated to protect against decay and fire [4]. It costs approximately $40 per square to fire-treat the wood, which is often required by law in high-risk forest fire areas [5]. After being treated, typical cedar shakes can withstand 1 ¾ hail and winds as high as 200 mph [4]. To prevent water build-up or damage due to snow and precipitation, cedar shakes are best suited for a roof with a minimum slope gradient that increases in height by four feet for every twelve feet away from the eaves [6].

In terms of maintenance, red cedar shakes require cleaning every five years to remove any mould growth and mildew [7]. Although cedar shakes are generally suitable for most geographic regions, cracking and warping are possible in harsh climatic changes due to water seepage into the wood grain [6]. This risk can be reduced if the shakes are initially treated and properly maintained, making cedar an aesthetically pleasing option that is suitable for all climates.

Details about the Economic Input-Output Life Cycle Analysis[edit | edit source]

Asphalt[edit | edit source]

For the manufacturing stage of asphalt shingles, the highest contributor to GWP emissions was power generation and supply because this is an energy intensive process. The total toxic releases and toxic transfers are attributed to copper mining as this is a highly toxic process and the copper is used for the algaecide in the asphalt mixture.

Petroleum refineries have a high impact due to the release of toxic chemicals during the distillation process. However, because asphalt is a by-product of crude oil refinement, the environmental impacts do not need to be considered, as they occur regardless of whether the asphalt is used or not. This argument is valid for gas and oil extraction.

The transportation of shingles from the manufacturing location in Brampton, Ontario produces almost equal amounts of GWP emissions as the manufacturing stage. The remaining contribution is due to the releases from refining petroleum to produce gasoline and diesel fuel and the mining of the materials needed to construct the transportation vehicles.

The end of life of shingles after 25 years requires their disposal in landfills. The total weight of the refuse is approximately 1.667 tonnes, which is only solid waste. However, according to the model, disposing this waste in a landfill produces enough economic activity in the waste management sector to produce the highest releases of GWP emissions of all life stages at 0.499 metric tonnes. The total releases (including toxic substances) is also the highest of the three phases, making the disposal of asphalt shingles the highest contributor to the negative environmental impacts.

Aluminium[edit | edit source]

For the manufacturing stage of aluminum shingles, a custom analysis was used that combined several industry sectors that make up the steps within the manufacturing processes. Those industry sectors included; “Aluminum sheet, plate, and foil manufacturing”; “Sheet metal work manufacturing”; and “Electroplating, anodizing, and coloring metal” with corresponding inputs in 1997 USD of $142.16, $800.44, $1 320.54, respectively. The second analysis was completed for product transportation from the manufacturing plant to the distributor, a total of 670 km away in Quebec. Using the traveling distance and tonnage of product, the cost of transportation was calculated to be $35.57 1997 USD.

The third analysis describes the environmental impact of recycling the used aluminum at the end of life phase. The salvage cost for the material of $413.96 1997 USD was input for the Secondary Smelting and Alloying of Aluminum sector.

The EIOLCA predicted a total of 26 MJ of energy used for the manufacturing process. The manufacturing process showed a total of 4.79 kg of toxic releases; 3.64kg of which were solid residues. This quantity can be attributed to aluminum hydroxide sludge produced in the anodizing process. The most prominent form of GWP releases by far for the manufacturing process was shown to be CO2. At 1.74 MT it was almost ten times more prominent than the next gas and represented over 80% of the total GWP. CO2 was also significant for product delivery and recycling, as it is produced from combustion engines and smelting facilities.

Cedar[edit | edit source]

A custom model was used for the manufacturing of cedar shakes, in order to account for both the cutting of the wood and the preservation treatment of the cedar. In total, the production and treatment of cedar shakes contributes 1.68 metric tonnes of C02 equivalent (MTCO2E) of GWP, where power generation and supply accounts for nearly one third of this value. This value may be larger than in reality, since the model is based in the United States where more than 44% of the power plants are coal-fired, which emit large amounts of SOx, CO2, and NOx [8]. In Canada, the percentage of coal-fired power plants is much lower at 6.3%, as a large fraction of our power comes from refined petroleum, hydroelectricity and nuclear power [9].

The manufacturing of cedar shakes contributes 0.631 kg of toxic releases, which is primarily due to the mining of copper, nickel, lead and zinc. Mining requires a large amount of land removal for a small quantity of usable metal [10], contributing to toxic land releases such as lead, which is found naturally in the earth’s crust and is a dangerous neurotoxin to humans [11].

In considering the delivery stage of cedar shakes, truck transportation is the major contributor of conventional air pollutants, releasing 0.083 metric tonnes of CO. This impact is most likely due to the incomplete combustion of the gasoline and diesel powered engines of the tractor-trailers used to transport the products [12]. The significance of these engine releases is also depicted in the GWP index, where the truck transportation sector is the second highest contributor of CO2 and other greenhouse gases.

The disposal of the red cedar shakes upon removal contributes most negatively to the environment in terms of methane emissions and toxic land releases. Waste management and remediation services accounts for 98% of the methane emissions at this stage, emitting 0.742 MTC02E of the total 0.75 MTC02E. As a greenhouse gas, methane is produced by the decomposition of landfill materials in the absence of air. The toxic land releases associated with the disposal of the cedar shakes can be accounted for by the chemicals used to treat the wood. CCA (chromate copper arsenate) is a common wood preservative, which contains the poisonous chemical of arsenic [13].

Details about the Streamlined Life Cycle Analysis[edit | edit source]

Asphalt[edit | edit source]

The resource extraction of asphalt involves petroleum refinement, which has heavy crude oil as a by-product, which asphalt is made from. Fibreglass matting is used as a base to support the asphalt within a shingle. The energy necessary to create fibreglass involves high temperatures of 2000°C [14].

Asphalt shingles are reinforced with fibreglass, both of which must be virgin materials during manufacturing. The asphalt then needs to be oxidized, which involves heating the material to above 200°C [15].

In Canada, approximately 1.25 million tonnes of asphalt based roofing material is discarded annually in landfills [16] However, there are many alternatives to this process. According to Alberta Construction Magazine, Nova Scotia uses shredded shingles as a main ingredient in gravel on multi-use trails. Halifax C&D Recycling Ltd. currently shreds asphalt shingles into grit and flake, which is then sold to Lafarge as an alternative fuel for its cement kiln. However, the use of asphalt as a fuel source has not been pursued aggressively due to public anxiety and possible waste products.

Lafarge uses scraps from the manufacturing line as an additive in its concrete mixture. There are possibilities for the use of waste shingle in highway material, but pilot studies have yet to be conducted. As it remains, the fee of dumping asphalt shingles in landfills is much lower than the cost of recycling, and unfortunately will probably remain this way without some form of government regulation [16]

Aluminium[edit | edit source]

29% of aluminum products manufactured in the United States are made using recycled material[17]. Therefore, this analysis will assume that 29% of the material used to manufacture shingles is recycled, and the remaining 71% is virgin material. The use of recycled aluminum requires 5% of the energy to be produced and results in less than 5% of the emissions than virgin material [17]. [18].

On average, 7 to 12 kWh of power is required to produce one pound of aluminum [17]. A large amount of energy is used to heat and pressurize the digesters that separate aluminum oxide from the minerals in bauxite ore. An electrometallurgical smelter releases approximately around 1.223 metric tonnes of carbon dioxide for every metric ton of aluminum produced.

The product manufacturing stage involves sheet metal forming which is easily formed and does not require excessive amounts of energy. The aluminum shingle then goes through a protective coating process, which normally involves an anodized finish [19]. This process requires 0.5245 kWh of energy for 1500ft2 (Sulfuric, 2008). Anodizing produces large volumes of aluminum hydroxide sludge, although, by reusing the acid baths, this amount can be reduced by 85% for every subsequent dip ([20]. The only liquid and gaseous residues released for the manufacturing process are potential non-point discharges of sulphuric acid. If dissolved in water it can have moderate short term toxicity on aquatic life [21].

Aluminum shingles require no maintenance during their lifetime and are expected to last for 50 years or more. The thermal conductivity and ability to reflect radiant heat minimizes the heat dissipated into the home from radiant sunlight. Aluminum shingles reflect 70% of the sun's energy, resulting in a reduction of 34% in heat increased, when compared to asphalt shingles [3].

Aluminum shingles are fully recyclable. However CO2 is released during the re-melting process. Used and coated aluminum can be sold for approximately 90¢ per lb [22].

Cedar[edit | edit source]

The resource extraction phase of cedar shakes is very environmentally friendly because wood is a renewable resource, non-toxic, biodegradable and recyclable [23]. The most significant form of residue during this stage is the sawdust from saw milling operations, which can be used as a rooting medium and for construction purposes [24].

In the manufacturing phase, the chemicals used to treat the wood against insects, decay, and fire are classified as Chromate Copper Arsenate (CCA). Arsenic is a known carcinogen to humans, and if not handled properly, even small amounts of residue could be dangerous [13].

Wood accounts for 47% of the raw materials market in the United States, yet it utilizes only 4% of the total energy used for raw materials manufacturing, making it very energy efficient [25]. However, the chemical treating requires the shakes to be kiln dried at temperatures above 100oC for as long as 24 hours. The chemical impregnation takes place after the wood has been dried in a vacuum, and occurs at pressures around 1000 kPa [26].

In the product use phase, cedar shakes require a chemical re-treatment every 5 years to prolong the life of the roof and prevent against common threats to cedar such as mould and mildew [27]. This treatment can be painted on after power-spraying the roof, emitting a gaseous residues consisting primarily of ammonia [28]. Another significant environmental impact during the use phase of shakes deals with heating and cooling costs of the house. Tests have shown wood shingles are able to keep an attic 15°C cooler in intense summer heat, when compared to a roof with asphalt shingles, reducing energy costs by nearly 20% [4].

At the end-of-life stage, wood has the advantage of being recyclable and reusable with little additional energy. Wood is also biodegradable, so it will eventually break down if it does end up in a landfill. Alternative disposal options include selling the scraps to companies who can convert it to cedar ground chips and hog fuel. This option is currently only commercially viable in the United States [29].

Details about the Cost Analysis[edit | edit source]

Asphalt[edit | edit source]

The cost of asphalt shingles was taken as today’s prices. However, when the shingles are replaced at the 25 year mark, the cost of shingles will have increased at a rate higher than inflation due to the increasing cost of crude oil. It is difficult to predict how the price of asphalt shingles will be affected as there are several contributing factors, including potential growth in the shingle recycling market. However, based on 2006 Crude Oil prices [30], which are fairly stable, a modest 5.4% increase was used to calculate the cost of shingles in 25 years.

The maintenance required on an asphalt roof is minimal, which is one of the reasons why it appeals to so many consumers. As long as precautions are taken, such as proper installation, attic ventilation and trimming of overhanging trees, the roof should require no maintenance until replacement. The disposal costs amounted to $222.84. The total cost of the project, in present worth, is $3731.89.

Aluminium[edit | edit source]

The major cost to the homeowner associated with aluminum shingles is the cost of installation. The cost of materials (shingles, nails, and felt matting) is $3132.09 US and the labour of installation was calculated to be $501.96 US giving a total of $3634.05 US. There are no maintenance costs for aluminum shingles, and the disposal, in fact, provides a return with the sale of recycled aluminum. However, considering an inflation rate of approximately 2%, the return on secondary aluminum amounts to less than 5¢ US in present value.

Cedar[edit | edit source]

The initial cost of the cedar shakes, felt matting, galvanized nails, and installation labour were taken from a distributor in today’s prices. It was assumed that the cost of cedar shakes will not rise more than the inflation rate over the next 25 years, since this renewable resource is in abundant supply due to Canada’s sustainable forestry management [23]. After considering this, the total initial costs from years 0 and 25 equal $6741.03 CAD.

Maintenance of cedar shakes includes the cost of labour and the materials required to clean the roof and re-treat the shakes with a cedar wood protection treatment. These maintenance costs will occur every five years between year 5 and year 20 and then again between year 30 and 45. During the use phase of the cedar shakes, mould and mildew can form on the roof surface if not properly maintained and treated. Cedar shakes are more prone to decay by mould growth and insects than any other roofing material. If mould has initiated the decay of the shakes, the resident of the home must pay to have the roof pre-maturely replaced. This indirect cost is highly subjective on the owner’s habits, and is therefore unquantifiable. If proper maintenance instructions are followed, the total cost over the 50 year time period is $1,454.30.

Disposal occurs at the end of each 25 year segment. The disposal costs at years 25 and 50 include the labour to remove the roofing material as well as the local landfill cost. In the end, the total disposal costs amount to $250.81.

In considering the present worth of the initial, maintenance and disposal costs, the total expense of purchasing and maintaining a cedar roof for a 50 year period is $8,446.17.

Details about the Societal Analysis[edit | edit source]

Asphalt[edit | edit source]

The use of asphalt shingles in North America is vast, with over three quarters of residential homes using asphalt shingles. The main reason for this is because they are the most economical method of roofing a home. As the shingle market became more competitive, this forced shingle manufacturers to produce more aesthetically pleasing shingles, in a variety of different colours. However, because asphalt shingles are very economical they do not add much value to a house, as other means of roofing are more expensive and usually more aesthetically pleasing.

Aluminium[edit | edit source]

Homeowners pay a significantly greater amount of money for an aluminum shingled roof than the asphalt baseline. There are several motives for this. As explained in the functional analysis and SLCA, aluminum shingles require no maintenance. From this perspective, the consumer is paying for convenience. Aluminum shingles also have the versatility of being made to look like other types of roofing. They can be formed into various shapes, and dyed with a wide range of colours during anodizing, to appear as cedar shakes, slate, stone or tile. The extra cost pays can also be attributed to this aesthetic value. Both factors increase the value of a home and, therefore, could help increase the resale value of the house.

Cedar[edit | edit source]

Aside from its functional advantages and technical specifications, a cedar roof adds significant monetary value to a residential home. The “Residential Cost Handbook” suggests that a cedar roof increases the value of a house by $2.00 per square foot [31]. According to this estimation, a cedar roof would add $3000.00 to the value of the house. This increase would greatly benefit the homeowner at the time of resale, and might encourage residents to choose cedar when re-roofing their house.

References[edit | edit source]

  1. Mar. 2008. The Aluminum Shingle Company. [Accessed on 10 Mar. 2008] <>
  2. "Residential Metal Roofing System." Mar. 2008. Permanent Roofing Systems. [Accessed on 10 Mar. 2008]<>
  3. 3.0 3.1 "Metal Roof Facts." Mar. 2008. Metal Roofing of Canada. [Accessed 10 Mar. 2008] <>
  4. 4.0 4.1 4.2 "Products and Overview." 2005. Cedar Shake and Shingle Bureau. [Accessed on 21 Mar. 2008] <>
  5. "Fire Retardant Wood." Nov. 2006. Wood Preservation Canada. [Accessed on 10 Mar. 2008] <>
  6. 6.0 6.1 "Roofing Materials and Roof Structure." Metroplex Roofing, Inc. 6 July 2006. [Accessed on 22 Mar. 2008] <>
  7. Pinney, Cindy, and Art Winkler. "Executive Summary." Parkside Roofing Committee Report. 28 Dec. 2006. Parkside Roofing Committee. [Accessed on 22 Mar. 2008] <>
  8. McClevey, Kenneth. "Inventory of Electric Utility Power Plants in The." Energy Information Administration. Mar. 2008. U.S. Dept. of Energy. [Accessed on 22 Mar. 2008] <>
  9. "Energy Supply and Demand, by Fuel Type." Statistics Canada. 29 Feb. 2008. Canada's National Statistics Agency. [Accessed on 10 Mar. 2008] <>
  10. "Mining and Primary Processing: Process Description." Metals Advisor. [Accessed on 2007. Feb. 2008] <>
  11. "HomeSafe: Lead Poisoning Facts." HomeSafe Environmental. Summer 2002. [Accessed on 20 Feb. 2008] <>
  12. "Carbon Monoxide." NCTCOG. 2006. North Central Texas Council of Governments. [Accessed on 7 Feb. 2008]<>
  13. 13.0 13.1 "Arsenic in Drinking Water." It's Your Health. 14 Dec. 2006. Health Canada. [Accessed on 5 Mar. 2008] <>
  14. "The Manufacturing Technology of Continuous Glass Fibers." New York: Elsevier Scientific, 2-94.
  15. "Asphalt Shingle with Fibre Mat 4468430." Paul P. Ruede. 23 Dec. 1982. United States Patent Office [Accessed on 15 Mar. 2008] <,M1>
  16. 16.0 16.1 "Discarded Roofing Material Gets Second Life in New Applications." Paul Stastny. Jan. 2007. Alberta Construction Magazine [Accessed on 15 Mar. 2008] <>
  17. 17.0 17.1 17.2 "Aluminum Markets." Mar. 2008. The Aluminum Association. [Accessed 10 Mar. 2008] <>
  18. "Metals - Aluminium and Steel Recycling." Mar. 2008. Waste Online. [Accessed 10 Mar. 2008] <>
  19. Mar. 2008 Interlock Roofing. [Accessed 10 Mar. 2008] <>
  20. "Recycling Chemicals on the Anodizing Line." Apr. 2001. [Accessed 10 Mar. 2008] <>
  21. "NPI: Sulfuric Acid Fact Sheet." Feb. 2008 [Accessed 10 Mar. 2008] < profiles/78.html#environmentaleffects>
  22. "Coated Aluminium." 2006. Recycler's World. [Accessed 10 Mar. 2008] <>
  23. 23.0 23.1 Home Depot Canada. 2008. [Accessed on 23 Feb. 2008] <>
  24. "Western Redcedar." Sept. 2007. Tennessee Log Homes. [Accessed on 22 Mar. 2008]<>
  25. "Tackle Climate Change: Use Wood." 2006. European Confederation of Wood Working Industries. [Accessed on 22 Mar. 2008] <>
  26. Keefe, Donn. "Kiln Drying: a Part of the Treatment Process." 2006. [Accessed on 22 Mar. 2008] <>
  27. Deboer, John. "Cedar Roof Maintenance." Cedar Roofs. JD Wood Revival. [Accessed on 28 Feb. 2008] <>
  28. "Ammonia-Based Life." The Internet Encyclopedia of Science. 2005. [Accessed on 28 Feb. 2008] <>
  29. "Cedar Shingle Recycled Roofing Products." American Roofing Recyclers. 13 Nov. 2007. [Accessed on 26 Feb. 2008] <>
  30. "New Mexico Price Sheet." GO-TECH Oil Prices. [Accessed on March 2008] <>
  31. "Choosing the Right Roofing Material." Unicrete Roof Tiles. 2002. [Accessed on Mar. 2008] <>