Flat Roof Framing Basics

And the line length measurement from the roof peak to the building wall is the hypotenuse.

Flat roof framing basics.

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. Partially these will depend on the style of roof you ve selected but you ll also have some wiggle room depending on the design elements of the house. If you re cutting studs or headers and cripples make a cutlist for the entire project and cut them all at once. Flat roofs are always built at a slight incline at least 1 8 inch per foot.

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. The rise or height of the roof at its peak is the altitude of the triangle. Like wall studs and floor joists rafters and trusses are spaced every 16 or 24 inches from center to center. From there the flat roof system you choose will determine the materials you apply.

Snap all layout lines on the floor before cutting any wall plates then cut every wall plate in the house before framing. The inherent strength and integrity of the triangular form makes the roof a sound structure. The run or half the building span is the base of the triangle. Stick framing combines roof rafters with ceiling joists.

Mirrored pairs of rafters meet at a ridge and are connected across the base by a ceiling joist. Tie all the intersecting walls together before starting to straighten and brace the walls. The framing of a basic gable roof is based on a right angle triangle and the various roof framing components fit the triangle. The butt of a shingle is the end that faces down roof.

This will help you create a flat roof framing plan. The rafters are usually positioned directly above the wall studs. Photo by russell kaye. Most roofs utilize 16 inch spacings for strength and rigidity.

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. A light rain or drizzle for example remain remain on a flat roof for a short period of time. There must be some momentum for the water to move into the flat roof drainage system. Some roofs actually slope in several directions ensuring optimal water runoff.

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. 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.