Does A Metal Roof Need To Be On Battens?
September 25, 2010 | Filed under: Battens or No Battens, Misc, Roofing Answers, Roofing Installation
Q: I have removed all the old shingles from the roof boards (not plywood) the roof is in great shape and have installed an ice shield over the roof. Can I install the metal roof over the Ice shield or do I need the 1 X 4 battens every 2 feet as well, It’s a low slope roof thus the ice shield for extra protection.
Ed
A: Ed, that is a great question. Thanks for contacting me. I have several thoughts:
1) Not all metal roofs can be installed over battens like that. Before even considering it, make sure the product you’re installing is approved by its manufacturer for that type of application.
2) Basically all metal roofs that can be installed on battens can also be installed on solid decking with underlayment. Well, there are some exceptions with some of the batten mounted tile and shake profiles but that is about it.
3) Ice and Watershield products are a vapor barrier – they do not breathe. This makes attic ventilation a special concern when those products are used. They can trap moisture inside an attic and that moisture can then find a place to condense.
4) It sounds like the metal panels you’re installing probably have a great deal of contact with the underlayment, unless they are installed on top of battens. This is the case with most vertical seam products.
5) If you do not have good ventilation in the attic, then I have some concern about installing the metal roof without battens. The low pitch of your roof indicates to me that perhaps you may not have much ventilation. And, keep in mind that good ventilation requires both intake of fresh air (usually at the bottom of the roof) and exhaust (usually at or near the ridge of the roof).
6) Installing metal panels without battens can reduce the temperature of your roof decking during cool evenings. This is because the metal panels touch the underlayment which touches the decking and cold is transmitted by conductance. This could cause the decking to reach dewpoint and especially if you have a lot of moisture in the attic (caused by inadequate ventilation), this will set off condensation in the attic. Having the metal panels up on battens though stops that conduction of cold and can help avoid this situation. Keep in mind also that some metal roofs have airgaps between the metal and the underlayment / roof deck … and those airgaps can serve the same purpose as battens in this scenario.
I hope this helps.
Todd Miller has spent his entire career in the metal building products manufacturing industry. He is president of Isaiah Industries, an organization recognized as one of the world’s leading metal roofing manufacturers. Todd is currently Vice President of the MRA (Metal Roofing Association) and a Past Chair of MCA (Metal Construction Association). Through his website, he strives to raise the bar on standards and practices to provide property owners with the best possible products for successful roofing projects.
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We had asphalt roofing damaged by April 27th tornado. Roof was covered with felt under metal. On three occasions we have had very loud “noise” that seemed to be in attic but find nothing. Could it be that the extreme daytime heat is causing expansion and then contraction in the metal during the nighttime cooling? We have searched the attic, inside house and under house but find nothing. I have soffit vents and vents at each end of attic – any other ventilation recommended?
I would ieally like to see the soffit vents and a ridge vent rather than the existing gable vents.
That said, I would be surprised if the noise is from the roof. Have you had the contractor back out to take a look at it though?
I live in baton rouge Louisiana. I would like to install my metal sheets directly over the roofing felt without putting down 1×4 runners on the felt. The metal has air gaps for ventilating. Will I be okay? Thank you very much
In most cases, what you are doing will be fine. The thermal break created by battens is nice but not essential in most cases. If your home has limited or no attic ventilation, though, let’s discuss this further. There could in that case be a condensation concern to discuss. I would suggest a light colored metal roof or a metal roof with reflective pigment in the coating, to achieve greater energy savings.
I had a metal roof replaced and the contractor is upset with me as I did not tell him that I did not have a covered roof (plywood, etc) and that the old metal roof was installed on 1X4 inch boards and now that I have leaks he states it’s because I don’t have a solid roof. I’m not a roofer and most things I see on the web indicates that a solid roof is NOT required to install or replace a metal roof. My old roof only leaked in one spot where it rusted through and created a 1/8 inch hole. We had a little extra money at the time and decided to have roof replaced and which should last us a lifetime as wife and I are both in our 70’s. Thank you for a reply.
Thanks for your question and I am sorry about the problems you have experienced. First of all, it was the contractor’s responsibility to ascertain what was beneath the old roof, either through attic inspection or asking you. Next, when he found that the situation was atypical when he started the job, he should have brought his concerns to you. Next, some metal roofs can be installed over spaced boards. Some can’t. The manufacturer of your roof should be able to tell you which yours is. Finally, I am a little curious why this would cause leaks … not entirely sure that it should. Can you email photos of the roof installation to me by chance? tmiller@classicroof.com
I am looking to install metal roof on a small summer cottage. It is an old building, not airtight by any means. I was going to install the metal over battens but never thought of using any underlay. The cottage is seasonal, however in the shoulder off seasons months it is heated by a stove when the nights get very cool. There isn’t really an attic space other then the space for the rafters. Do you think something like this would require underlay. If so which type would you recommend. Thanks
In this case, I think you are wise to install the metal over battens. Make sure the metal panels you buy are approved by their manufacturer to be installed over battens. Without battens, I am concerned about dropping the roof deck temperature enough to cause condensation inside.
As for underlayment, many people would not use underlayment. I personally interpret the International Building Code as requiring it but not everyone interprets it that way. I would use a quality synthetic underlayment such as RoofAquaGuard UDLX. Please contact me anytime.
I am building a single pitch roof for a shed. It is in an areas that gets large amounts of snow and temperatures hovering from just below freezing to just above freezing all winter (Cascade Mountains in Washington State). It has a 4/12 pitch. Can I put the metal roofing down on OSB with a vapor barrier or do I need battens? I’m using the Home Depot roof metal in brown.
If the area beneath is unheated, you should be fine without battens. If it is heated, assuming there is no insulation nor a well vented attic, then battens would be wise.
I am installing a galvalume roof in central Florida. It is a 2 in 12 pitch roof. I have given it 3 inches of ventilation on each side of the ridge. I have also installed 2 inches of iso board in between battens on the roof. I am planning on installing peel and stick directly on top of the battens and iso board and installing the galvalume directly on top of the peel and stick. will I need any air gap between the galvalume and the underlayment or will it be ok long term to be installed directly on top.
Thanks Paul. I assume the ridge ventilation is for the attic and being fed fresh air from soffit intake vents. If so, I think you’re okay but make sure you use a non-granulated high temp ice and watershield (peel and stick) underlayment.
I have a similar situation. I live in western Washington where it’s rainy and windy. I have a standing seam metal roof that I want to install on my new shed. It is a single 3:12 slope with 15/32 sheathing. It is a single story shed with a roomy enclosed loft/attic. I’m thinking of putting down a water/ice underlayment on the entire roof since it is low pitch, then add 1×4 battens horizontally, 2 feet spacing. Are the battens necessary? For ventilation I’m going to add 12” square vents near the eave and ridge. There are already small gaps under the sheathing at the eave and ridge.
Thanks for your question. Is this Greg? Someone named Greg left me a message today about a similar situation. Your situation raises several questions for me. Will this be a heated space? So, the attic / loft will be directly vented with intake and exhaust vents that move air through the attic space?
Hi Todd,
Sorry, not Greg.
This is a storage shed with no heat. I’m not totally sure on ventilation yet, but they will be wall vents. Possibly, an intake vent on the lower attic wall on the low side of the roof and an exhaust vent on the upper wall of the ridge side. Another, maybe relevant detail, There are two 2×5’ windows on the main floor.
Because of no heat, you are probably fine without battens. The main role of battens would be to keep the roof deck from getting as cold. A very cold roof deck over a structure that has warm moist air inside of it and little ventilation will create condensation on the underside of the roof deck.
Thanks Todd for the swift and clear responses. I have decided on using a hi temp underlayment, Polyglass MTS, with no battens. It may be another month before the weather conditions are acceptable for installing. Enjoy your weekend.
Good luck with everything. Please feel free to contact me anytime.
I have a concrete block commercial building in central Florida that was originally a flat roof. It leaked, so an A frame was built on top of it with Batten boards and metal corrugated panels. That is now ~40 years old and is rusted and leaking. I plan to replace it with a new metal roof. My question is this: I have 2 estimates.. One to replace the metal on Batten boards as originally done.. The second estimate is to lay plywood down, then replace the metal. Which should I do?
Thank you for the advice..
My advice is plywood. However, I also encourage you to verify what local building code and your insurance company require.
What do you think about painting my roof deck with aluminum reflective paint, then add Synthetic Underlayment, then metal roof on top, I have ridge & eave venting, thanks, Mike.
A radiant barrier must face an airspace in order to be effective. Painting the underside of your deck would actually be more effective than the top side. There are metal roofs with reflective pigment as well as products that can be installed with an integral thermal break. Another option would be a reflective underlayment of some sort.
Greetings, and thank in advance to considering my question.
Here’s the situation: a 3/12 low-pitch roof on a renovated, 850 sq. ft. 1971 bungalow with 4″ of closed-cell foam spray on the underside of the roof sheathing (ie., an unvented attic); simple gable (no valleys); Zone 6; cold clear winters with modest rain in summers.
Here’s my problem/question: I’d like to install standing seam metal or metal shingles (Oxford metal shingles by Classic Metal Roofing Systems) but due to the presence of the impermeable closed-cell foam cannot because the metal would not allow sufficient drying of the roof deck/sheathing.
Yes, it might be possible to use cross-battens above the existing sheathing (and even an additional layer of sheathing) but due to the low pitch of the roof (3/12) there would be insufficient airflow (ie., insufficient stack effect).
So, in sum, I feel I cannot put the metal directly on the sheathing, nor can I use battens.
I should add that there is intense night sky radiation. For example, a couple of days ago the air temperature early in the morning was -7C (19F) and the temperature of the underside of my gutter measured with a good quality IR themometer was -22C (-8F), and indeed there was frost on the underside of the gutter because of this. I assume it would be the same for both standing seam and metal shingles, too: frost/condensation on the underside.
So what to do?
Any suggestions or insights would be very much appreciated. Thank you so much!
Thank you. Because closed cell spray foam is a vapor barrier, I am not sure why your roof decking would ever get damp or need to dry out? Can you help me understand that please?
That said, one option would be cross battens — vertical battens installed first following the original rafters, and then horizontal battens before your roofing material and/or another layer of decking. The metal products that you mentioned require solid decking and underlayment. Some metal panels, though, can be installed over horizontal battens.
I hope this helps.
Thank you for your quick reply.
Regarding your question, indeed the closed-cell spray foam should prevent moisture from inside the house reaching the underside of the roof deck / sheathing. Hurrah! That is one common roof problem solved.
However, night sky radiation can cause massive temperature differentials (see my measurements above) between the metal (both top and bottom) and the relatively warmer outside air, causing condensation or frost on the underside of the metal roof, which could drip down on the sheathing below.
In the case of cross-battens, because the roof is low pitch (3/12) building science research—if I am understanding it correctly— seems to suggest that the stack effect cannot be relied upon to move air from the soffit to the ridge vent so as to dry out the sheathing moisture (due to the above). If the roof was steeper, this would not be a problem…I wish I had a steep roof ;-(
Hence my problem: a low pitch roof with limited ventilation and drying potential. So, what to do? I really would like a metal roof, but more than that, I would like a roof that functions well. Thanks again!
Hi Todd, based on further reading it appears that condensation (and frost) due to night sky radiation under a metal roof on battens is a well known and unavoidable fact. Just in case I was unable to communicate this clearly, here is someone else saying essentially the same thing:
“Condensation due to night sky radiance: Step back and ask what is condensing on the underside of the roofing? Moist air from the gap created by the battens. If the roofing panels were attached directly to an impermeable underlayment on sheathing, there would be no moist air to condense – any more than there would be moist air condensing below the underlayment.”
So, with an unvented, impermeable closed-cell foam attic, one possible way to avoid condensation (or frost) associated with night-sky radiation and battens would be this stack up:
metal roof
——–
synthetic underlay
——–
sheathing
———
battens (for air movement and drying
——–
existing asphalt shingle roof (in my case I’d like to leave it on)
——–
underlay
——–
sheathing
——–
closed-cell foam
Yes, you would end up with two layers of sheathing, but for peace of mind, this would be acceptable to me.
Can you think of any reason that would NOT work, or anything small details that should be considered?
I do not see why that would not work. That said, I still stand on saying that, if you have a vented area beneath the metal, then you will not get condensation on the back side of the metal because the ambient conditions (temperature and humidity) on both sides of the metal will essentially be the same.