The roof is what makes your home an actual building. It protects the interior from the outdoor elements, keeps the warm air inside, and adds strength to the supporting walls. Although a roof can be made with very dense, heavy materials, its design allows tension to be balanced out by compression. In other words, the framing of the roof is crafted in a way that keeps all inward, outward, and downward forces in balance.
Understanding the Design of Your Roof
Most roofs are of the gable type. An elevated roofline is in the center, and the sloping sides extend to the outer walls of the house. At the base of the roof are the ceiling joists. These are located just above the ceiling. The thick joists are what you climb over when you crawl through your attic.
The joists are connected to the uppermost level of the exterior walls. Many homes have ceilings that include a series of rafters. These are the supporting frames that extend upward from the exterior walls to the roof's peak. Rafters that run parallel to the exterior walls are known as purlins.
Rafters that run perpendicular to the top of the exterior walls are fastened at their peak to a very large, heavy board known as a ridge beam. Many homes are built with smaller roof sections that are constructed at ground level, raised above the ceiling level, and fastened together.
Manufactured homes often have pre-fabricated roof sections made with truss supports. These are triangular wood frameworks that support the weight of the roof. The trusses are fastened directly to the ceiling joists.
Think of roof framing as a set of triangles. The three sides of the triangle are a ceiling joist and two rafters that join together at the ridge beam.
Covering the Roof
Once the framing is in place, the roof is covered with wood, aluminum, or composite material. The rectangular sections of the covering are fastened directly to the rafters. A small triangular strip is added to seal the cracks adjacent to the ridge beam.
If plywood is used as the roof covering, it is topped with tar paper and/or a creosote-like tar layer. Shingles are then added to complete the roof structure. Additional wood planking may be added near the top of the outer walls to ensure complete protection against intrusion by outside air.
Insulating the Roof
Fiberglass, wool, or other insulation is used to protect against heat loss. This can be placed on the floor of the attic as well as fastened to the underside of the roof covering. If a fireplace chimney or other ventilation system outlet protrudes above the roof, a metal flashing is placed around the pipe or chimney stones.
Your roof is subjected to intense solar rays, rain, sleet, snow and pollution particulates. Shingles will eventually crack because they expand and contract with the changing temperature. Water percolation may be a result, and this is the most common problem with residential roofs. Roofs should be visually inspected each and every year to check for signs of water intrusion. Buildup of moss, mold, or dirt will speed the process of roof cover deterioration, so it’s important to keep the shingles clean.