Metal Roofing
Posted on Sep 18th, 2009 by Doug Marsh VP, CR, CAPS, GBP | 0 Comments
One of Clients requested a metal roof upgrade to their home and so I started delving into the ins and outs of this type of roofing. I am not a stranger to this type of roofing as I have installed a copper roof and a number of standing seam and screw down roofs over the years. However, now on virtually every project, we are converting or building unvented attics (foamed roof deck- attic is within building envelope) and the roof is another component that works in conjunction with the rest of the building as a system. In Texas the normal metal roof installation is over either felt paper (15 lb or 30 lb) or synthetic underlayment on top of a solid roof deck. Now that we are all becoming more educated about HVAC, attics, and heat gain, the contributing factors of roofing reflectivity and roofing installation have come more to the forefront. An interesting technique that is beginning to be specified on projects is to put 1 x 4 slats on top of the roof deck at 45 degrees to the eave and then install the metal on those. In between the slats goes a 3/4" tall by 1.5" venting material called Coravent. This venting at the perimeter combined with a ridge vent allows for venting radiant heat coming through the metal roof and venting out over the deck. This is a great idea and would obviously work if there was foam insulation sprayed on the underside of the deck (unvented attic) or if there was a conventional vented attic below. A further technique would be to install foam baffles to the underside of the deck before shooting the foam onto the deck and utilize existing soffit venting and install ridge vent to allow air to pass over throught the soffit vents, over the foam, and out the ridge vent.
However there are a couple of downsides to this venting and roofing installation technique. Any future work including solar installation that requires walking on this elevated metal roof is tricky because one wrong step dents a panel. The other concern is hail following on a mostly "hollow surface". These are definitely important issues and lead us to decide to just go with a standard installation right on the roof deck. We already have a foam unvented attic and felt that this was a good enough upgrade plus the reflectivity and sustainablility and recylcibility of the metal roof itself.
Of cours once your metal roof is installed you are ready to go for rain water collection. There are many affordable options available for gutter however I suggest you start with where your rainwater storage tanks would be and then work downspout location relative to the roof
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