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Insulated corrugated roof construction
The use of metal as a roofing material has been in practice for thousands of years. The first metal roofs were made out of copper or tin, and later with steel, which is much more durable. Metal roofs provide a number of benefits:
- Durability - While asphalt roofs may last only 10-20 years before they need replacing or maintenance, metal roofs may last upward of 50 years with almost no maintenance. If coated with a non-oxidizing alloy, metal roofs may last 100+ years.
- High strength-to-weight ratio - Metal roofs, especially steel, provide an extreme amount of strength in comparison to their weight. For this reason, they are especially useful for large buildings where heavier materials would otherwise provide stress on the supports.
- Resistance to elements - Metal roofs are fireproof, resist hail, and shed snow easily as there is little friction between the metal and snow.
- Recyclability - Metal roofing is often available from recycled materials, and can be recycled over and over without a reduction in strength or effectiveness. This is especially beneficial for aluminum, which is much easier to produce from recycled content than from aluminum ore (bauxite).
- Design flexibility - Metal roofs can be easily fit to almost any shape
- Energy efficiency - Coatings with high reflectivity can help save on cooling costs, especially in high-temperature areas.
- Labor efficient - Metal roofing is easily installed and can be installed in large pieces.
- Resists algae and mildew growth
- Environmentally sound - does not leach petrochemicals into runoff like asphalt shingles, and can be recycled over and over.
Today, a number of metals, alloys, and combinations are used for roofing material. These include:
- Galvanized steel - This is by far the strongest material available for metal roofing. Proper galvanization resists oxidation.
- Aluminum - A relatively cheap and lightweight material, though not as strong as steel. Does not oxidize.
- Aluzinc - A combination of aluminum and zinc, which is relatively inexpensive and more durable than aluminum.
- Copper - Costly and usually only used for its aesthetic appeal. Will oxidize if not properly coated.
- Tin - By far the most inexpensive material available, though it is also the least durable.
Oxidizable metals are coated with zinc (galvanization). It refers to the act of coating an oxidizable metal with a thin layer of molten zinc. A thin layer can also be formed by electroplating. When this zinc layer is exposed to the atmosphere it forms zinc carbonate. This layer is quite impermeable and insoluble, and makes the metal more resistant to rust.
Corrugation greatly improves the bend strength of the metal perpendicular to the corrugated ridges. Corrugated panels are installed with the "valleys" parallel to the slope of the roof. This reduces bending due to impact or wind.
Types of Insulation
Metals have low R-values. They absorb heat very well and therefore can make living underneath a metal roof very uncomfortable, especially in hot climates. A few things can be done to improve this. Coating the roof with a reflective barrier can decrease the amount of solar radiation absorbed by the roof. Light-colored paints improve the reflectivity, and more costly synthetic barriers can be applied to reflect even more. Venting can also help, but often the roof must be insulated to improve the R-value of the roof. There are many types of insulation that are applicable when using corrugated metal for construction:
- The fan-fold foam which provides air infiltration and liquid water protection.
- The foil-faced air bubble insulation which provides heat and flame protection.
- Sprayed foam insulation which provides: no maintenance, and stops air and moisture infiltration.
- Foam board or rigid foam: no maintenance, and stops air an moisture infiltration.
- Manufactured cellulosic insulation provides many of the same benefits, but can be costly in some areas and impossible to find in others.
- Blue jean denim can be shredded and used as insulation. A number of companies manufacture this type of material.
- Just about any type of fibrous agricultural waste can be used to insulate. Straw/hay is commonly used, but may be a fire hazard and will grow mold if not kept dry.
- Shredded newspaper is effective as an insulator, but can be a fire hazard. Mold may also be an issue.
- A green roof (growing plants on the roof) can greatly increase the R-value and increases green space as an added benefit.
- Wool is readily available in many places and provides a high R-value for insulating homes.
- Rigid wood fiber can be used but has a low R-value than fibrous insulation types.
- Coating fibrous material with a thin layer of clay can help decrease deterioration.
Example of Use