Friday, February 18th, 2011
Let’s Learn About Metal Roof Framing
Various metal types and alloys are used in metal roof framing, and it comes in different forms and styles as well. The roofing can be steel, stainless steel, aluminum, special alloys, or copper, with steel being the most common. It is possible to construct a roof using metal roof materials in shingle or panel form, pre-manufactured panels, or rolled sheets.
Site Framing Installation and Weight Considerations for Metal Roof Framing
Typical site-installed metal roof framing is made up of joists, purloins, beams and trusses or rafters. The spacing of framing members is determined by several factors related to the decking used; load carrying capability of the decking or structural roofing panels, it’s deflection allowables, and requirements at decking joints for support all come into play. The size of framing used is determined by allowable bending and shear stress for short spans, and by deflection allowables in long spans.
Weight is a big factor when framing a metal roof. Most types weigh from 50 to 150 pounds per 100 square foot, compared to 240 pounds 100 sq. ft for 3 tab asphalt shingles, 400 lbs per 100 sq/ft for wood shake, 900 lbs/100sq ft for concrete tiles, or 1,100 lbs/100sq ft for glazed clay tiles. Roof rafters or trusses for supporting a metal roofing system can be of less strength than those required for slate roofing for example.
Do You Need a Decking Underlayment?
Some manufactured metal roof panels used in framing metal roofs do not require decking underlayment, since they are rigid enough to be considered structural members of the roof, while others require full sheathing or decking. In either case, installing metal roofing over OSB plywood decking and felt, plus a layer of insulation, will help deaden noise (rain, hail, etc.) and further eliminate condensation problems.
Call Metal Roofing Systems Toll Free: 1-866-Wis-Metal (866-947-6382)
In Madison, Call: 608-663-2687
In, Milwaukee, Call: 414-727-1810