Roof Energy Considerations speaks to what are roof energy considerations and why roof energy considerations.
It speaks to the functions of roofs, roof insulation as well as low slope membranes and steep roofs.
A roof can capture rainwater and snowmelt and conduct them to a cistern, tank or pond for use as domestic water, industrial water or irrigation.
A properly proportioned overhang can shade south facing windows from the high summer sun but admit warming light from the low winter sun.
A light covered roof covering id kept clean, can reflect half or more of the solar radiation striking its surface, improving occupant comfort and significantly reducing the heating load on the occupied space below. Even darker hued roof materials, when coated with specialty formulated cool colour pigments can reflect 25 percent or more of solar radiation. Such cool roofs can reduce cooling energy costs for buildings by 10 to 25 percent and extend the life of the roofing materials.
Reflective roofs that reduce the absorption of solar heat can decrease the elevation of air temperatures in densely built areas, thereby reducing a building’s indirect contribution to smog, degraded air quality, environmental discomfort and other heat island effects.
In a hot climate, a shading layer above a roof, with a freely ventilated space between, can eliminate most solar heat gain through the roof surfaces. The shading layer might consist of latticework, fabric or corrugated metal but the exact material is less important than providing both shading and ventilation.
A roof surface can support flat plate solar heat collectors used to reduce building heating costs or arrays of photovoltaic cells to provide electrical power. Electrical power for building use can also be produced from thin film photovoltaic materials laminated directly onto a variety of conventional roof coverings.
Insulation Roof Energy Considerations
Thermal insulating materials in roofs and walls are probably the most cost effective, planet saving materials used in buildings. They increase occupant comfort by moderating the radiant temperatures of ceilings and walls. They reduce heating and cooling energy requirements to a fraction of what they would otherwise be. They pay for themselves through energy savings in a very short period of time.
Other environmental implications of thermal insulation materials are more complex.
Cellulose insulation is the most environmentally friendly thermal insulating material. It can be specified to contain not less than 85 percent recycled material, primarily newspapers. Its embodied energy is only about 150 BTU per pound (0.35 MJ/kg). The borate compound used to make it fire resistant is generally not harmful to human beings.
The binder used to hold the cellulose fibers in place is usually a simple glue that does not outgas. Installers should wear breathing protection, but the fibers are not known to be carcinogenic.
Glass wool and mineral wool can be manufactured primarily from waste materials, recycled glass and blast furnace slag, respectively. The embodied energy in glass wool is about 13,000 BTU per pound (30 MJ/kg), but a pound of it goes a long way. The binders used in some glass fiber insulations give off small quantities of formaldehyde but nonoutgassing products are available.
In a large number of scientific studies, glass and mineral wools have not been shown to be carcinogenic. However, they do irritate and congest the lungs and installers must wear breathing protection.
Polystyrene foam is made from petroleum and has an embodied energy of about 50,000 BTU per pound (120 MJ/kg). It can be made from recycled styrene and polystyrene. Expanded polystyrene foam (bead foam) is made using pentane gas, which is not an ozone destroying substance, as a blowing agent.
Extruded polystyrene, polyisocyanurate and polyurethane foams were formerly manufactured using ozone depleting blowing agents. All are now manufactured using pentane or other chemicals less harmful to the atmosphere.
Low Slope Membrane Roof Energy Considerations
Low slope roof membranes have varying impacts on the environment:
Bitumous roofing is largely based on asphaltic compounds derived from coal and petroleum.
Roofing operations with hot asphalt and pitch give off plentiful quantities of fumes that are decidedly unpleasant and potentially unhealthful, but once the roof has cooled, these emissions subside.
Most roofing felts today are made with cellulose or glass fibers, but very old felts in buildings being demolished or reroofed may contain asbestos, a proven carcinogen.
The various rubber and plastic formulations used in single ply membranes generally utilize petroleum as the primary raw material. Each has its own characteristics with regard to embodied energy and outgassing.
Adhesive bonding, solvent welding and heat welding of seams may give off volatile organic compounds (VOCs). Some single ply membrane materials emit VOCs.
Materials from demolition of built up roof membranes are generally incinerated or taken to landfills. Thermoplastic single ply membranes can be recycled, although most are not at the present time. Thermosetting membranes cannot be recycled.
Low slope roofs may be developed as green roofs, in which the membrane is covered with soil and plants. These living constituents of the roof consume carbon dioxide, generate oxygen, shield the membrane and the inhabited place below from temperature extremes, cool the roof surface by evaporation and transpiration, delay the passage of stormwater into sewers and reduce its volume and create a pleasant roofscape.
Steep Roof Materials for Roof Energy Considerations
Steep roof materials, shingles, slates, tiles and sheet metal come from a variety of sources with different environmental impacts.
Asphalt shingles consist mostly of petroleum.
The environmental impact of wood shingles is much the same as other wood products.
Slates are quarried stone and concrete tiles are made of concrete.
Copper, stainless steel, aluminum, terne and lead roofing materials originate as ores that must be mined, refined and manufactured into finished form, all at various environmental costs.
Metal roofing materials can be recycled. There is little recycling of the other steep roof materials. There are available,, however proprietary shingles made almost entirely of recycled tires or other recycled materials.
Roof Energy Considerations