Metalbased Materials

Basic info is found in Chapter 6.

For climatic purposes metals are commonly used for flashings. Flashing is used on exposed parts of a building's external skin, such as between the roof and parts that penetrate the roof such as chimneys, ventilation units, vent stacks and roof lights, and on valley gutters and

snow guards. Not all metals are usable as flashing, as some corrode. Combinations of different metals can create galvanic corrosion.

Metals are also used in vapour barriers and heat reflecting surfaces. These are often aluminium products. In vapour barriers, an aluminium foil is often laminated on to a building paper. Heat-reflecting sheets are often reinforced with films of polyethylene and often comprise up to six layers, with layers of foamed plastic in between, though wool can also be used.

Stainless steel sheeting is produced from an alloy with chrome and nickel. In aggressive environments an addition of molybdenum is also found. Stainless steel can be used in combination with other metals.

Galvanized steel sheeting needs about 275-350 g/m2 zinc. The material should not be used with copper. Gutters are often coated in plastic.

Aluminium sheeting normally has 0.9-1.4% manganese in it. The products are often covered with a protective coating through anodizing. They can also be painted with special paint. They should not be used in combination with copper or concrete.

Copper is usually produced in a pure form without any surface treatment or other alloyed metals.

Zinc is most often used in alloys with copper and titanium, and should not be used in combination with copper.

Lead is soft and malleable. It should not be used in combination with aluminium.

In terms of raw materials, the use of metals should be reduced to a minimum. Flashings are very much exposed to the climate and therefore to deterioration. Zinc corrodes quickly in an atmosphere containing sulphur dioxide, which is common in towns and industrial areas; the spray of sea salt also causes corrosion. The zinc coating on galvanized steel is exposed to the same problems, but its durability is better in the long run. In particularly aggressive atmospheres even aluminium, lead and stainless steel will begin to corrode.

Production of metals is polluting and energy intensive. For the people using a building, metals are mainly neutral, even though a large amount of metal is assumed to strengthen the building's internal electromagnetic fields. Metal ions may also be released into the soil around buildings from weather exposed products. This can cause an environmental problem, depending on the amount and type of metal in question; lead and copper are the most troublesome. Metal can normally be recycled when it becomes waste, but this may be complicated by additives and coatings.

The best way to reduce use of metals on the outside of buildings is through a good design that avoids complicated roof forms and number of chimneys, roof windows, etc. Metal fittings on doors and windows can normally be replaced by high quality timber.

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