A water-shedding, or hydro-kinetic roof, also known as an architectural roof, relies on a steep slope to shed rainwater immediately. These roofs typically incorporate the water-shedding capabilities in the architectural design of the roof itself, which gives rise to the term used to describe them. This roof is ideal for buildings where aesthetics are important, because the inbuilt water resistance is less obvious and just as secure.
Water-shedding roofs need an optimum gradient of at least 3:12 to begin with, which allows the water to run off down to the downspouts and drainage system. Dramatic visual effects are created using low profile standing seam panels with little to no exposed fasteners. The structural design of this style of metal roof is particularly important to provide adequate support for the shape and load of the roof, and installation usually includes an underlayment such as a 30-lb roofing felt or an adhesive-backed ice and water shield.
This article appears at the website of Whirlwind Steel:
How can MBCI claim in court that their roof to be water-shedding only but state on their website that the minimum slope is 1/4:12. Is MBCI right and everyone else wrong? Every where I read, a water shedding roof is to be installed on a minimum 3:12 slope. The right people have not seen this information yet.
Found some interesting information that will help educate the public. The following are definitions from MBMA (Metal Building Manufacturers Association) Metal Building System Manual. The definitions define the 2 basic types of standing seam roof panels.
Metal panel systems that are designed to withstand being submersed in water for a period of time are called hydrostatic panels. Hydrostatic roof details rely on sealant to keep water from infiltrating the joints and seams. Hydrostatic roof details can be used at almost any slope (1/4:12 minimum).
Metal panel systems that are designed to shed water are referred to as hydrokinetic. Hydrokinetic roof details are typically devoid of sealant and rely on water to freely shed over the joints. Hydrokinetic roof details are not to be used on roof slopes below 3:12.
Also found the following information at ehow.com.
Define a Structural Standing Seam Roof
By Ann Salter, eHow Contributor
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Standing seam roofing systems are composed of durable , overlapping, preformed panels secured with concealed fasteners and can be divided into two basic categories: structural and architectural. Structural standing seam roofing benefits from increased strength, water-tightness and design flexibility over architectural panel systems.
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o Structural, standing seam roofing panels have greater spanning capabilities and resistance to wind uplift. Designed for structural stability, they can be installed spanning over purlins instead of a solid deck, allowing for a lighter roof.
o The structural standing seam roof’s taller seams, mechanical joining and factory-applied sealants combine to form a water-tight system, even at extremely low slopes. Structural panels, unlike architectural, can be installed on slopes as low as 1/4:12, and can even be mounted vertically as a wall panel.
o Structural standing seam panels are available in much longer lengths than architectural. Factory-formed sheets can be shipped in more than 80-foot lengths, and the lengths of field-formed sheets are virtually unlimited. Clip attachment systems allow for necessary thermal expansion and contraction of longer panels
In conclusion….my opinion is that if a company claims that their standing seam roof is water shedding only, it should not be installed on any slope less than 3:12. I know there is at least one company that claims their standing seam roof panel is watershedding roof and not hydrostatic, but yet they still install sealant in the panels during fabrication…….?….what’s that all about. They also sell this panel for applications of less then 3:12 slope. They may deny knowing it was to be installed on a slope of less than 3:12 and at the same time will sell along with this panel the support purlins manufactured to a slope of less than 3:12 along with accompanying gutter. It is not hard to see what’s going on here. SELL THE PRODUCT….THEN REFUSE WARRANTY BECAUSE OF IMPROPER INSTALLATION…..AND PLAY DUMB ABOUT ANY BEFORE HAND KNOWLEDGE.