Do battens result in energy saving benefits that justify cost

TOPIcs: Energy Efficiency

Do battens result in energy saving benefits that justify cost

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?

Guest User

2014-01-07 06:07:51.000000

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.

Todd Miller

2014-01-07 07:55:16.000000

Many times I have seen wood shingles removed, the roof decked, and new roofing installed ... and homeowners saw an increase in energy bills. That was largely because they neglected to add ventilation (both intake and exhaust) to the attic during the process. I know that Decra has also worked some with radiant barriers beneath their battens and that seems helpful as well.

Todd Miller

2018-06-08 11:56:50.650468

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?

Jim VanO

2015-08-24 19:19:41.000000

+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.

Eric Novotny

2014-01-07 08:05:36.000000

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.

Eric Novotny

2015-08-25 08:30:01.000000

I doubt you will find a direct study that will reference your exact scenario to assist in the justification of that application.

Are they paying for the complete replacement of a cedar roof?

Usually if you are dotting all your "i"s and crossing your "t"s, you have a decent amount of money in the project to cover the full replacement and perhaps the incorporation of some additional insulation or cross batten design for air flow. Add in some radiant barrier and you have a great combination for rejection of heat from the roof assembly.

Eric Novotny

2018-06-07 18:36:03.896080

I read the Decra website study by the Oakkridge national laboratory. I'm just a homeowner but it seems that the study says counter batten installation helps remove about 30% of the heat in summer.
http://www.decra.com/technical/sustainable-roofing
It appears to show asphalt injects the most heat into the house 45000 BTU/ sq ft/ day, stone coated steel on various installs, 2k to 3K/ btu/ sq ft and stone coated steel over a cedar shake roof only 1100 BTU Day. The Cool Roof Council rates now banned cedar roofs as one of the roofs that put the least energy into the home.
Does anybody know of any research or build plans that can cut the amount of energy a stone coated steel roof injects down to the level of a cedar roof. If I can find a credible tested plan or research, I could use that to justify building it to my insurance company because they will pay for items proven to be necessary to make the replacment roof perform in a like kind ( AC cost) roof. The reason I need a proven documented source insurance companies won't accept anything unless it's documented research or from an engineers wet stamp plan.

Larry g

2018-06-07 18:24:31.041248

For those coming to this thread, the merits of various roof deck insulation are a much debated an analyzed topic over at Green Building Advisor. Building Science Corporation has also done a ton of work on them.

Bryce Nesbitt

2019-10-09 22:37:26.375572

Cool roof designs (ventilated ones) are a hotly debated topic over at Green Building Advisor, https://www.greenbuildingadvisor.com/
And sometimes tested by Building Science Corporation for commercial clients.

These might be good resources for you.

Scott Bitstream

2019-10-15 16:52:46.059555