Flat Roof Framing Basics

The run or half the building span is the base of the triangle.

Flat roof framing basics.

Snap all layout lines on the floor before cutting any wall plates then cut every wall plate in the house before framing. The most important thing to know about a flat roof says tom is that it s not flat to prevent water from pooling and eventually invading the home flat roofs are always built on a slight incline at least 1 8 inch per foot. The inherent strength and integrity of the triangular form makes the roof a sound structure. The framing of a basic gable roof is based on a right angle triangle and the various roof framing components fit the triangle.

Collar tie also collar beam in profile the framing of a conventional pitched roof forms a triangle. The rise or height of the roof at its peak is the altitude of the triangle. Flat roofs are always built at a slight incline at least 1 8 inch per foot. You can do this with a foam layer that exactly fits your roof.

When framing a flat roof you will need to create a slight incline. If you re cutting studs or headers and cripples make a cutlist for the entire project and cut them all at once. This will help you create a flat roof framing plan. There must be some momentum for the water to move into the flat roof drainage system.

From there the flat roof system you choose will determine the materials you apply. Underneath the basics flat roofs are usually constructed with a ceiling nailed to joists which support a deck usually wood in residential construction a vapor barrier insulation and a roof board. Stick framing combines roof rafters with ceiling joists. Flat roofs operate with the same basic principle but of course their lower angles mean that gravity isn t quite as effective in shedding water rapidly.

Another possibility is to cut a fall into the roof insulation something several businesses now offer it s often referred to as tapered insulation. Like wall studs and floor joists rafters and trusses are spaced every 16 or 24 inches from center to center. The butt of a shingle is the end that faces down roof. Photo by russell kaye.

The rafters are usually positioned directly above the wall studs. Some roofs actually slope in several directions ensuring optimal water runoff. Tie all the intersecting walls together before starting to straighten and brace the walls. The framing style of the roof refers to the actual components of each roofing truss and the design of the structural foundation of that roof.

A far more common method is to use firring strips which are battens cut at an angle and placed on top of the roof joists. Most roofs utilize 16 inch spacings for strength and rigidity. Mirrored pairs of rafters meet at a ridge and are connected across the base by a ceiling joist.