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2:12 pitch and open-beam construction - what are potential problems?

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Guest User
2/21/2006
We want to replace our existing tar + gravel roof with a metal roof. We will be tearing off the t+g. In our area we get heavy rain in winter, every now and then some pea-sized hail, and no snow. In reading the posts in the roof pitch category, it sounds like we can use only a vertical panel, standing seam style metal roof on this shallow 2:12 pitch. Is this correct? Can you recommend some roofing systems that we should evaluate for this installation? Since the house is open-beam construction and has no attic, would a metal roof be prone to a high level of noise during rain/hail? If so, what precautions can we take to dampen the noise? We will be installing 3" rigid-foam insulation on the roof between the tongue & groove ceiling decking and the roofing material. Do we need to put OSB or plywood sheathing over the foam insulation? Do we need to use some sort of underlayment or felting? Do we need to provide an air space between the metal roofing material and whatever is underneath it? How do we compensate for the expansion and contraction of the metal? The roof has existing skylights. Do manufacturers offer flashing kits for skylights and similar penetrations? Are there any particular problems associated with metal roofs and skylights, especially on a shallow slope, that we should be aware of?
Allan Reid
Dura-Loc Roofing Systems, Inc.
2/21/2006
The building code generally splits steep steep slope to low slope at a 2/12 pitch. For residential construction I always recommend ventilation as required for steep slope which is a 1" minimum vented air space between the insulation and roof covering. Certainly most vertical rib panels are better suited for the lower slope application. Do choose a panel and then ask to see tyhe ICC-ES product evaluation report which will indicate it has been tested and approved for your application. Once you have the system selected make sure they have the flashing kits for the skylights. usual;ly the skylights need to be mounted on curbs higher than 6".
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