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Metal Roofing

For an environmentally friendly building, metal roofing is one of the better choices.  One of the main reasons is that at the end of it’s lifespan, which is considerably longer than asphalt shinges, metal roofing can be easily recycled, keeping it out of the waste stream.  Asphalt shingles, on the other hand cannot be recycled and end up in the landfill when they are removed after their comparably shorter lifespan.  The roofing on a typical house would have to be replaced after 20-30 years with asphalt shingles, whereas with a metal roof, there are many that are 75-100 years old and most will last a minimum of 50 years if they are not damaged by wind.  Another advantage is that metal roofing is available in a number of light colours that will reflect the light and reduce the cooling load on the house.  Metal roofing is also recommended if you intend to collect rainwater for household use, as it will not leach chemicals and lose granules as asphalt shingle will.  Metal roofing also has the highest fire rating available for a roofing material and can reduce the chance of fire from flying embers, such as from a forest fire.

The most common types of metal roofing are corrugated steel sheets, standing seam and roofing tiles.  The least expensive is corrugated steel roofing.  It comes in sheets that run vertically from the peak of the roof to the fascia and are overlapped and screwed down.  Standing seam roofing also runs vertically from the peak of the roof, but the sheets of metal clip together to form a tight seal and the metal is held down with concealed clips.  Standing seam can be made of different metals including steel, aluminum or copper.  Metal tiles, which can be formed to appear more like a shingle, tile or shake roof, are made of smaller sheets of metal that are made with interlocking connectors.  The metal tiles are the most expensive of the metal roofing materials as they are often made of aluminum.

The sheet steel roofing can be protected with a galvanized coating covered with a coloured polymer, or with a zinc/aluminum coating, also often covered with a coloured polymer.  The two types of coatings are not compatible and should not be used in contact, as it may result in premature corrosion of the metal.  There are also some metal roofing materials that are coated with a special coating that reflects most of the heat from the sun.

If you are interested in installing the roofing yourself, the choice is between corrugated sheets or some metal tiles.  Standing Seam roofing requires specialized equipment and is only recommended to be installed by trained contractor.  You can install metal roofing yourself but you must take more precautions than with asphalt shingles, as the metal roofing materials are usually much more slick and present a slipping hazard.  Falling off a roof is not a fun experience.  The corrugated steel sheets can be quite large and can be difficult to handle, this is not a project for one person.

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Passive Solar Design

Passive solar design is about the orientation of a building and the placement of windows and mass in order to capture the heat from the sun and then to store it in the mass of the building.

One of the first things to consider when designing a house is the orientation to the sun.  The long axis of the house should be oriented directly east-west, with one of the long sides of the house pointing south.  The south wall should then be designed so that the majority of the windows in the house are on that side and that there is a minimum of windows on the north side.  One of the errors that many people make when doing a passive solar design is to have too many south facing windows.  In the average house you want no more than 15% of the floor space as windows on the south side of the building.  If you have more windows then you are prone to overheating, particularly in the fall and spring. When specifying materials you need to look for a window that has as high a Solar Heat Gain Coefficient (SHGC) as possible if you are in a northerly climate. The SHGC is a number between 0 and 1 that is the portion of the solar heat that is allowed through the window. A window that allowed all the heat through would have a value of 1. Most windows have a value of between 0.3 and 0.6. In addition you want to design overhangs that will shade the windows in the summer and let in as much light as possible during the winter (I will cover this more in depth in a later post)

In addition to the windows you want to have thermal mass in the building.  Thermal mass acts like a flywheel for heat.  If the sun shines on it, or the air around it is warm, it will store some of the heat, and once the air temperature drops, it will release some of that stored heat to the air. Once again, however, you can have too much of a good thing.  If you have too much thermal mass, it can never get above room temperature and will not contribute to heating the house, as in order for a thermal mass to be effective, it has to reach a temperature that is greater than the desired air temperature in the house.  This is because heat will always travel from a hot object to a cool object.  If the thermal mass is at the desired air temperature, it will only transfer heat to the air when the air temperature is below the desired temperature.  Also, with concrete, the most common thermal mass, the active zone is only about 4 inches deep, so there is little to no advantage having a 10 inch thermal mass.  A thermal mass will be most effective if it is directly exposed to the sun and is dark in color, as dark colors absorb more heat and light colors reflect the heat.

If the thermal mass is in an exterior wall, it is best if you can insulate on the exterior of the wall and leave the interior exposed to the air.  If you insulate the thermal mass on the inside of the house, such as in an Insulated Concrete Form (ICF) the heat will have to travel through the insulation first before it can heat the concrete, resulting in a less effective transfer of heat.  In my house I used 4 inches of Roxul Drainboard for the insulation. It has an insulating factor of R4.3 per inch, which is comparable to foam, and it has the advantages of being cheaper, being a more environmentally friendly product and providing a drainage plane for the walls. The only drawback I could see is that it has to be protected from the weather (I used concrete board).