The shape of a roof helps to define a building's form while the roof materials define its character. The roof provides a structure's protective covering and its proper care is of critical concern for the overall maintenance of the building.
Types of Roofs
Shed roofs often appear as a flat roof from the street. They can be metal, membrane, shingles, or built up. Walls that project above the roof are known as parapet walls.
Gable roofs are comprised of two sloped surfaces and create a triangular piece of wall at the ends (the gable). The pitch of these roofs is usually steep.
Cross-gable roofs are formed by two intersecting gable roofs.
Hipped roofs are sloped from each wall and do not have the gable ends.
Complex roofs combine hipped and gable forms and may also have turrets or towers.
Flat Roofs occur primarily on commercial buildings and are usually
surrounded by a parapet. They typically are built up roofs or have been
covered with an elastomeric membrane.
Fiberglass or asphalt shingles are an impregnated felt material covered with colored granules. These types of shingles indicate either a building constructed in the early twentieth century or later or an older type of roof material that was replaced at a later date.
Built up roofs consist of layers of tar or asphalt-saturated ply felt over sub roofing. Many commercial buildings have these types of roofs.
Membrane roofs are increasingly used in place of built up roofs. This type of roofing consists of a long-lasting elastomeric material.
Metal roofs are usually made of a galvanized steel but can also be copper. This roofing consists of rolled sheets of metal with standing seams. Metal roofs are painted, except for copper roofs whose patina serves the same protective function. Earlier roofing materials, such as wood shingles or shakes, were often covered with metal.
Metal shingles are found on some residential buildings and consist of pressed sheet metal shingles of galvanized steel.
Slate roofs are constructed of shingles made from slate. These roofs are extremely durable but expensive to replace in-kind.
Asbestos shingles are also an extremely durable roofing material. They usually consists of large square shingles that are sometimes installed in a diamond pattern.
Wood shingles are still found on some houses and consist of split wood.
Dormers add space, light, and ventilation to an attic space and are readily characterized by their roof shape - gabled, shed, or hipped. Dormers can also be arched and/or inset. A dormer with a half-round window is called an eyebrow dormer.
There is a distinctive Fredericksburg-style dormer where the roofing material extends up the dormer sides. Many dormers were thus clad in slate and metal although there were still many dormers covered in wood. As older roofs have been replaced, dormers have often been resided in wood (often beaded siding in an unfortunate attempt to give a historic appearance). Care must be taken to maintain the historic integrity of the local dormers and reside them in a material that is compatible to their original construction.
Maintenance and Repair
Some roofs are quite durable and will hold up well for 100 years. Slate will last that long, for example, as will metal if it is kept painted. Fiberglass shingles, in comparison, will last from 15 to 30 years, depending on their grade.
1. Inspect roofs periodically for signs of deteriorated roofing materials as well as deteriorated or improperly functioning flashing, gutters, and downspouts.
2. Ensure the coping on top of parapet walls is watertight.
3. Keep gutters and downspouts clear of debris to ensure they function properly to move water away from the building. Cleaning gutters two or three times in the Fall and once again in the Spring is a basic first step to preventing leaks, deterioration, and even basement seepage.
4. Repair leaking roofs, gutters, and downspouts as soon as possible. Repair deteriorated roof supports and underlayment, as necessary, Use metal fasteners in metal roofs and flashing that is compatible with the roofing material (to avoid deterioration due to dissimilar metals).
5. Ensure attic spaces are properly vented to prevent condensation.
6. Avoid applying paint or other coatings to roofing materials which have historically been unpainted and uncoated.
7. Avoid using materials that are physically or chemically incompatible and which would cause accelerated deterioration or corrosion.
8. Avoid replacing roofs with a substitute material that does not convey the same visual appearance of the historic roof. Replacing a metal shingle roof with standing seam metal, for example, alters a defining architectural characteristic. If replacement of a roof is not technically or economically feasible, the substitute material should convey the same visual appearance of the original roof as much as possible.
9. Avoid reducing the visual integrity of the roof by removing original chimneys, skylights, light wells, or other elements that contribute to the style and character of the building.
10. Install new elements such as vents and skylights without diminishing the original design of the building. New skylights, for instance, should be installed so as not to be visible from primary elevations.
11. Maintain the visual integrity of dormers through repairs that
retain their original type of covering. Avoid removing slate, for
example, and replacing it with wood.
1. Roofs of new dwellings should relate to neighboring historic buildings in type, materials, and complexity.
2. In general, the roof pitch of new houses should reflect the steeper pitch of most older dwellings rather than the shallow pitch of new suburban type houses.
3. New commercial buildings should incorporate a roof form that relates to the roofs of the buildings within the block in which it will be located.
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