#31 – Should a Metal Roof be Installed Over Battens?

April 26, 2017 | Filed under: Battens or No Battens, Metal Roofing 101 Series, Roofing Help Videos, Roofing Installation

We frequently are asked whether metal roof should be installed on batten’s or direct to the roof deck. By design, some metal roofs must be installed over battens, some must never be installed over battens, and some can be installed over battens or over solid decking. So first and foremost, it’s critical to choose the right product and install it according to manufacturer’s specifications. Keep in mind for residential applications, we never suggest installations over battens unless there’s a solid deck beneath the battens.

Installations over battens alone are just an invitation to condensation issues in the attic.

Next, we highly advise the use of a layer of underlayment over the old shingles or decking whether or not battens are used. We interpret the international building code as requiring this, and it’s just good practice. We normally suggest a layer of one of the higher quality synthetic underlayment and ice and water shield if required by code. Now, if your home’s existing shingles are pretty curled you could install text you metal roof such as a metal shingle, shake or tile directly over those curled shingles along with underlayment. You also could install a corrugated through-fastened metal roofing product and probably not have issues with that either. However, a true standing seam – especially one without any sort of striations or stiffening beads in the center of the panels – will probably show oil canning as the result of going over old shingles. In that case the old shingles should be removed or batten’s could be installed over those old shingles.

Now as to the potential benefit of batten’s, they do create a thermal break to help minimize heat transfer from the metal to the roof deck. That’s a good thing. However, if you choose a metal roof that is either light in color or has reflective pigment in the paint (meeting energy star standards) that will be very helpful as well. Your attic ventilation and insulation will also help with Summer Energy Efficiency.

One effective way to use battens is to cross batten. This involves putting down vertical battens first, attaching them through the roof deck to the rafters, and then you put down horizontal battens for the roof panel attachment. The resulting vertically-oriented Chambers can then be ventilated by bringing fresh air in at the bottom, and exhausting it out at the top. This has very positive results as far as keeping heat out of the attic, and it can also help avoid rooftop Ice Dams in the winter. However, cross battening significantly raise the roof level. This means gutters will have to be rehung, and it also could interfere with skylights, clearstory windows, dormers, even chimneys and plumbing stacks. Again if you have good attic ventilation and insulation, those things alone are very helpful and can be more than adequate for most homes. One thing to remember is that many of the products that are installed over battens have exposed fasteners. Those can be something many folks want to avoid. As a great option to the expense and bother of battens, there are concealed faster metal shingles, shakes, and tiles available. These products usually have an integral airspace or an insulated cavity between the metal and the roof deck. This creates a thermal break which is very similar to a vertically seamed metal roof installed on battens. The dead air space in the hollow beneath these panels acts like the dead air space between two panels of glass in a thermal pane window. This blocks conductive heat transfer and helps keeps attics cooler during the summer.

Finally, if a structure has very limited insulation and ventilation – especially ventilation in the attic – battens can be helpful. Especially if a vertically seamed metal roof is being installed. Again this is from a thermal break / thermal bridging standpoint. A home with limited attic ventilation is at high risk that moisture originating inside the living space can migrate to the attic, and cause condensation there. If that moisture hits a cool surface it will condense. Condensation will lead to mold etcetera, which of course is not good. While you’re home I have been fine with asphalt shingles and no ventilation, the addition of a vertical seam metal roof will reduce the roof deck temperature even just a slight bit. That can be enough to be the straw that breaks the camel’s back and causes condensation in the attic that never existed before. Additionally we want to point out if you install tighter windows, house wrap and siding, those things will reduce the ability for moisture inside the home to exit through the walls. So if you plan those kinds of improvements in the future, don’t do something now to the roof that can make it more prone to condensation once those other things are done.

In conclusion, battens can sometimes be helpful, but we find those occasions to be few and far between (limited primarily to homes with insufficient attic insulation and ventilation. And, a great alternative to battens are the metal shingle, shake, slate, and tile products which have an integral dead air space between the metal and the roof deck, serving a function very similar to that of battens.

8 responses to “#31 – Should a Metal Roof be Installed Over Battens?”

  1. dorothy says:

    hi .I have a sunporch that is attached to the back of my mobile home and have taken off the old plastic that was attached.I put up wooden battens and was wondering if i could just put metal on top.I live in nanaimo and i have many trees around my property which makes me want to go with metal as the trees have been like spears going through the plastic.Is it possible to put metal with plastic for light ?any info would help ?

    • Todd Miller says:

      Thank you. There are metal panels that can be installed over battens. However, it might be necessary to add battens to what you have now. The spacing of battens will be determined by the design of the exact metal panel which you select. Also, yes, some metal panels will have translucent fiberglass or polycarbonate panels that can be worked into the field of metal roofing. I would suggest checking in with Westwood Metals there in Nanaimo and seeing what they have available for you.

  2. Elishka Tischuk says:

    Hi, so do I understand right, that under metal roofing is better to install air cavity for air ventilation and asphalt shingle doesn’t need ventilation? Is the air cavity actually something what is understanding by itself, that the company installing the metal roof will do it or should I make sure that they will make it there. Is it possible that it will increase the price of the roofing – material or labor? Thank you

    • Todd Miller says:

      Thank you. This is a bit of a complicated question. In most cases, there is nothing about a metal roof that increases the need for ventilation beyond what is needed for an asphalt shingle roof. Metal roof installations without an air gap are done all the time. The key in most cases is having a properly vented attic beneath that. A properly vented attic requires intake and exhaust vents.

      This is a topic you should discuss with your contractor. Do not make any assumptions as to what they might be doing, nor any assumptions that all contractors will do it the same way.

      Here is a link to a video and article that I think will help you: https://www.asktoddmiller.com/roofing-help-videos/metal-roofing-101/metal-roof-installed-battens/

  3. Beth says:

    Todd, i live in Western North Carolina Carolina have two homes I will be having metal roofs installed on in the next year. The first is a 1960s ranch with a 4/12 pitch, not much tree cover and decent wind exposure. The home has new windows and tends to be reasonably energy efficient. I am unable to access the attic prior to decking removal to determine amount of insulation, but a if it’s puny, we may blow extra in there. The current plan is to remove the asphalt shingles, replace any decking that is damaged, warped or weak removing whirlygig turbine vents and replacing with a full length ridge vent (there are existing soffit vents) and reroofing with vertical rib, fastener based sheet galvalume metal roofing. Contractor wants to use felt, and I’ve convinced him to go with an adherent synthetic vapor barrier. He also wants to use 29g steel and no battens. I wonder if it’s wiser to upgrade to a 26g and use 1×4 battens? It would complicate the ability to install solar light tubes, but I am more concerned about the humidity here as I moved from Colorado and the more i research the more confused I am about air gap vs no air gap in this case.

    • toddmiller says:

      The risk is warm moist air hitting the cool underside of the roof deck and condensing. When metal roofing is applied direct to the roof deck (with underlayment), it does drop the deck temperature a bit. This can be enough to cause condensation inside the attic — on the bottom side of the roof deck. That said, if you have good ventilation to let the warm moist air out of the attic, then it doesn’t condense. Additionally, a vapor barrier behind the ceiling and also insulation on the attic floor will be helpful. Normally, battens are not needed but if you are concerned about a lack of good attic ventilation (consisting of intake and exhaust vents), then battens can be wise. I hope this helps.

  4. Nancy Bishop says:

    Great article, thanks for all the information. One area where we are getting contridting points of view is OSB -vs- Plywood.

    We have a new construction build. The house is 36×46, with a 24×24 garage, and a wrap-a-round porch except where the garage attaches.

    The roof pitch on the house/garage is 8:12 and the porch is 3:12

    I have had two roofers tell me that if we use OSB we must use battens, one said that if we install plywood on the roof, even 1/2”, we can skip the battens. He has also told us that with battens the roof will have dents if walked on unless they stay on the battens.

    Thank you for taking the time to give me your thoughts.

    • toddmiller says:

      As long as the attic is properly vented, you can use OSB or plywood and both either with or without battens. I personally am not a huge fan of battens and keep in mind that not all metal products can be installed on battens. However, except in the case of conditioned attics, if there is not good attic ventilation, then battens can be helpful. The concern with OSB is that it can be moisture sensitive.

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