Roofing is an underappreciated art and science. Construction industry professionals refer to roofs as roofing systems. Seemingly simple, a roof is a complex, highly engineered system for keeping the weather out of your home and the energy inside.
Roofing a home starts with rafters. These rafters are joined together to form trusses, which give the familiar V shape to most roofs. The trusses are engineered systems designed to withstand the weight of roofing materials, water, snow and wind. Once in place, they must be protected from the weather. Weather, especially winter weather, is the enemy of your roof.
The roofing material that repels the weather is applied in multiple layers. The first layer is plywood or other sheathing to provide a foundation for subsequent layers. This provides a solid layer for further sheathing and helps anchor the rafters in place.
Over the plywood is laid another layer of roofing. This is tar paper or felt. The purpose of this impermeable layer is to provide a moisture barrier to prevent air exchange through the roof. Limiting the air exchange keeps expensive conditioned air being lost to the outdoors. At this layer leaks begin to be a concern. Typically the felt or paper is laid down with the upslope edge fastened and the remaining fastened down with adhesive. Construction adhesives that are long lasting and resistant to temperature change are used.
The outermost layer is what most people see as roofing. It is the visible layer that can be seen from the outside of the house. A wide variety of materials may be used. Historically, people have used whatever durable materials were at hand to roof their homes. In Europe thatch, stone, slate, wood and copper were commonly used roofing materials. In America, shingles were used very early and have lasted until current day. Advances in roofing material have included asphalt shingles overtaking wood shingles in widespread use. Galvanized metal made its debut and has become widely popular for outbuildings and barns.
The outermost layer of roofing is critical for preventing leaks. Water is the enemy of any roofing system and the outer layer bears the brunt of the weather. Not only must it be laid in a manner that prevents the infiltration of water, but it must withstand temperature changes and all sorts of weather without fasteners loosening. These requirements make roofing a skilled job and roof systems remarkable structural accomplishments.