A roof is the top covering of a building that prevents the ingress of weather into the building interior. Roofing comes in sloped or 'flat' form, however roofs are never really truly flat. Flat roofs are often covered with tar and gravel and provided with drains to run off rain and snow. Other shaped roofs are built to shed water easily, these include:
Ridged roof types
- single-sloped or shed roof
- pitched or gabled
- shaped gable
- Dutch gable
- crow-step gable
- corbie-step gable
Some building styles, for example, geodesic and A-frame, blur the distinction between wall and roofs. Pitched roofs are often covered with asphalt shingles (in the US) although thatch, wood shake, steel, corrugated galvanised iron, slate and tile roofs are used elsewhere. Newer systems include solar shingles which generate electricity as well as cover the roof.
Several systems of construction transmit the weight of the roof to the walls of the building and tie the roof into the structure. These include: ashlar-piece, brace (can be arched or wind), collar-beam, crown-post, hammer-beam and -post, king (or queen) post, purlin, rafter (common or principal), ridge beam, ridge-board, strut, tie-beam (Tie rod), truss, and wall-plate.
A roof has different areas. For example, the eaves are the area where the rafter ends form the edges of the roof that run horizontally across the fašade.
By extension one can speak of the roof of a tent, automobile, etc. A convertible is an automobile built with a folding, retracting, or removable roof.
An attic is the story under a non-flat roof.