Do battens result in energy saving benefits that justify cost

Guest User
1/7/2014
I have a builder whose general practice is to install metal roofs (paint grip) over 1x2 battens for air flow and a thermal barrier. There will be spray foam applied to the undersude if the roof in the attic. My architect says that their analysis in talking with building scientists is that the energy savings of adding battens are not justified by the additional costs. They are also conscerned from an aesthetic point of view as they were going for a thin profile and claim that this would increase the bulkiness of the eaves. What are your thoughts on this? And what about other positive effects of a raised roof deck? including condensation control and some noise reduction?
Todd Miller
Isaiah Industries, Inc.
1/7/2014
I am not aware of any studies exactly relevant to the construction you have described. I'd say that the spray foam will to some degree minimize the effectiveness of the battens. However, air spaces do help. They behave as a thermal brake. We have seen the effectiveness in studies of metal shingles (which often have an integral air gap by design) and other metal roofs installed on battens. When battening, if you cross batten with vertical battens first and then actively ventilated the area, the effectiveness is enhanced. Using a metal roof that is light colored or else has reflective pigment in the coating (meeting Energy Star standards) will also be helpful. Look at the data for 2001 on the graph of page 2 of this report: http://www.classicmetalroofingsystems.com/info/FSEC-Summary.pdf Note that formed metal shingles, because of their integral airgap, even in a darker color (with reflective pigment) kept the attic cooler in the summer than did highly reflective white standing seam, which does not have the airgap.
Eric Novotny
An informed customer is the Best Customer!
1/7/2014
+1 Totally depends on the climate as well. In a more cooling dominated climate, the impact is greater. I, personally, love the idea of over deck venting and air space. I think it is the most bulletproof approach to venting and does help with the insulation/conduction question.
Jim VanO
8/24/2015
Cross battening seems like an effective BUT expensive solution to providing venting between the deck and the metal roof. Matt Risinger has used a single layer of diagonal lath to provide venting and to provide a quasi-horizontal surface for connecting the roof panels (https://youtu.be/LM6zv3A4JjI). Would this be an effective AND less expensive solution than cross battens?
Eric Novotny
An informed customer is the Best Customer!
8/25/2015
As compared to the diagonal lath that he demonstrates, a horizontal and vertical combination will not be that much more expensive at all. I also don't care for that vent strip that he uses. A stainless mesh would work better combined with some insect screening. While, in theory, the water will drain out, the fact remains that water wants to flow down. By putting the purlins/battens on the diagonal, you are not letting the water take the path of least resistance to get out and it will be backing up against the purlins/battens as well as wanting to come in around any of the fasteners in those spaces. For the small investment of additional materials and labor, I don't think this makes good sense and especially when you are putting a lifetime roof over the home.

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