Roof decking is the material between the structures trusses and joists, the insulation and other waterproofing layers such as breathable underlayment. The roof deck must be extremely durable and strong enough to bear the weight of roofing materials installed overtop, such as metal tiles. Other factors that are important to consider are the weight of air conditioning equipment, rain and snowfall. For residential buildings, the most common material used for roof decking is plywood. Wood normally stands up to the weight of almost any type of roofing material placed overtop, but metal tiles may require additional reinforcement. As a matter of fact, spruce wood strapping is installed on the roof deck beneath metal tiles to act as support and facilitate ventilation in the attic space. In any case, roof decking must be installed by a professional roofing expert since it must bear the weight of all other roofing materials.
Wooden strapping is installed horizontally and vertically along the trusses of the roof. They are typically spaced out a specific distance apart and metal roofing panels are installed over them. While metal roofing tiles are commonly installed over wood strapping, standing seam metal roofing systems are applied over solid roof decking. An important feature of metal roofing systems is that all attic ventilation is redirected up and through established ridge vents. In the past, residential buildings were not constructed nearly as airtight as they are in present day. Naturally, there was more ventilation within the building envelope. In present day, we strive to be more energy efficient, thus making buildings are air tight as possible through the use of energy efficient windows and doors. Activities like showering and cooking all introduce a lot of moisture into the interior of the home. If that moisture is not adequately vented up and outward and instead comes into contact with the cool underside of a metal roof, condensation issues will occur.
Regardless of the material used, ventilation is the biggest factor in ensuring that you have an effective and long-lasting roof. A proper attic ventilation system facilitates continual flow of outside air though the attic in order to protect the insulation from humidity and help lower temperatures in the living space.
In the summer, a properly ventilated attic may help reduce your air conditioning costs by moving heated air out of your attic. In the winter, various household appliances, showers and cooking vapors can contribute to excess moisture build-up. If your attic is not properly ventilated, moisture will collect and cling to the underside of the roof.
A high flow ridge venting system will give you the best possible ventilation. The determining factor is to have enough peak to support the amount of air that needs to be extracted. Meaning, you cannot put ridge vents on a high pitch roof with limited ridge. For these types of roofs, box venting is recommended and you need one box vent for every 300 sq/ft of attic space.