Should a Metal Roof be Installed Over Battens? – Metal Roofing 101 with Todd Miller
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Call Us
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Working Time
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Best construction video I’ve ever seen told me what i wanted to hear confirmed it and then made sense of why in terms i could understand. Awesome Video!!!
So I’m building a single pitch saddle stall with a couple of small awnings on either side. Oh on a budget of course. Could i run the synthetic underlayment over the frame then batons every 3′?
Can i lay metal roof on top if zip sheathing(treated OSB) with maybe an underlayment on top of the sheathing? Seems like the screws will make a water leakable hole?
@Isaiah Industries Ah I see thanks. U know ..i am in Los Angeles. I cannot remember the last time we had rain. Yet alone “wind driven”..:>)
The problem is with wind-driven rain. The water can’t get off the roof quickly enough and can therefore “flood out” panel overlaps and snaplocks. Mechanically seamed standing seam would work. If not, a TPO or other quality single ply membrane is a good option.
@Isaiah Industries So what do u recommend for a 1.5% say slope…i thought at that slope water would flow…not puddle. ..I am confused bv that….if the water flows…why would it leak..flows to slow? EPDM?
I strongly encourage never installing a panel at lower than its manufacturer’s recommended minimum pitch. Manufacturers would like to sell as much product as possible – if their panels worked successfully at lower pitches, they’d allow it. Metal Sales’ “Classic Rib” panel requires a 3:12 pitch. Most industry “R” and “PBR” panels require 2:12. For roof slopes less than 2:12, mechanically seamed standing seam should be used, or else another panel designed specifically for that purpose. Without decking, you will sometimes have condensation dripping from the back of the panels. There are people who use panels at lower than their recommended minimum pitch and, eventually, it comes back to bite them. Also, there are some panels manufactured specifically for carports and patio covers, such as “W” panels, that can be used on very low slope roofs. Again, always adhere to manufacturer specifications.
@Isaiah Industries Thanks…actually I am in the idea phase. My previous roof which i just ripped off was 1/2 plywood, tar paper, and asphalt tiles. The roof has a 1% slope so that did not last. I am thinking just metal panels over battens..I mean its only two cars…but a question I have. ALL the websites that sell metal panels…like the classic rib..all of them recommend a much greater slope it seems…so why is it I see so many carports and patios with classic rib panels? Do they all just leak..thanks in advance…
Great Video – thank you! I am building a seasonal home in Maine, where it is getting very hot in the summer these days. My face screwed metal roofing is on the way. I was going to directly screw it to the rafters over Duponts ‘roof protector’ underlayment, because it’s cold now, and we want to get the roof on fast! I am concerned that I will regret not using the mylar looking reflective underlayment under battens, and that the area under the roof, which is to be a dwelling area in the summer, may be unbearably hot. Do I need battens in this case? No other insulation is planed.
Please email me direct at todd@asktoddmiller.com and tell me more. You would not be able to install roofing direct to vertically oriented rafters. I in fact never suggest residential applications without solid decking, even if battens are installed on top of the solid decking. Do you have good attic ventilation? I will await your direct email reply. Thank you.
Is there a problem using Treated Battens under a Galvalume metal roof
Yes, the chemicals used to treat the wood will corrode the metal. Only untreated lumber should be used.
For “Long Term” use, Remove the Shingles, check and tighten the deck and install over a synthetic under-layment. Use of lathe or batons is in most cases done poorly with too few fasteners and fasteners not attached to frame. I have seen dozens of roofs installed that in essence were only fastened to the structure with a few nails – bad idea for wind load.
Don’t forget screws hold way better in solid backing like battans rather then ply or sob.also the air gap helps kill the sound the rain and r value.fyi I put syntitic felt on top of battens to block metal sweat
Here in Canada we regularly put metal roofing over purlins (battens) when building outbuildings and agricultural buildings. We always lay down roof underlayment first as dripping onto the insulation due to condensation can be a problem. My home is built this way too, but that’s very unusual.
Have questions. Mountain Cabin, 7/12 pitch, cathedral ceiling/ no attic, old cedar shakes are torn off. Car decking underneath. Is the process 1). Peel and stick. 2). 1″ foam board. 3).1/2″ plywood. 4). Standing seam metal? Do I need 1×4 battens?
1. 2″ or 4″ XPS foam board 2. peel and stick 3. battens or OSB screwed through foam to rafters 4. steel
Larson Home Inspection
Thank you!
Sorry for the delayed response, sarobinson56. Based upon what you’re telling me, yes, some form of thermal break is probably wise. Call me at 1-800-543-8938;201 if you’d like to discuss it.
– Todd
Mr Miller! I am building a house with 6″ of open cell spray foam under the roofline with a sealed attic. I am also installing a raised seam metal roof which the installer uses 30# felt for underlayment. My question is, what type of underlayment should I use and I was going to use a perforated roofing foil over the underlayment with 1″ battens that the metal roof. Is this an acceptable roof system? I want to meet code and prevent any moisture issues. I am in Clark county NV in zone 9A Hot Desert I believe. Any help is appreciated.
Closed cell foam of course is better as a vapor barrier but, if you’re using the foam everywhere, I still think you will be okay.
If you wanted to ventilate at all, I’d ventilate the attic rather than just beneath the roof system.
If you can put a vapor barrier behind your ceilings and walls, that would be very helpful as well.
As far as the roof underlayment, I would suggest a synthetic underlayment rather than 30# felt. The felt, in hot temperatures, will want to stick to the back side of the metal panels and that could lead to problems. The synthetic underlayment will breathe only through the seams, not through the product itself. There are breathable synthetics available but they are pretty expensive and I don’t feel you need them. That said, my company is beginning to stock a good breathable product from Europe. If you’re interested, email me direct at tmiller@isaiahindustries.com. This product is a little more expensive than standard synthetics but would work well.
Todd, thank you so much for the fast reply. I was planning on using open cell foam on the entire house including the underside of the roofline. My quote for closed cell foam was over $9K more for just the roof line over the cost of closed cell. Is this a problem? Also, do I need a breathable or vapor permeable underlayment under the metal roof?
Hi LeeMan 20s!
The potential problems when it comes to moisture and condensation with roofing stem in virtually all cases from moisture that originates inside the structure (from bathing, cooking, laundry houseplants, etc.) migrating into the attic and then condensing on a cool surface, often the back side of the roof deck. The reason we see more of this in recent years is not because of the roof assembly but because we have made the walls / doors / windows of our homes much tighter. Moisture that used to migrate out through those things now ends up in the attic.
Your use of a sealed attic and closed cell foam should be plenty to prevent moisture originating inside the home from reaching the back of the roof deck and condensing.
I would use a standard roof underlayment over the plywood decking on your roof (such as a synthetic underlayment) and I see no need for battens or anything like that.
That said, if you’re seeking increased energy efficiency, then battens can be helpful by creating a thermal break. You can make things even more effective by putting down vertical battens and then horizontal battens before the roofing … allowing the resulting vertically oriented air chambers to be actively vented with intake and exhaust vents using convective airflow. This will help carry heat radiating off the back of the roof to the outside before it reaches the home.
If you use battens, make sure the roof panels you’re installing are approved by their manufacturer for installation over battens. –Todd
I have a new out building that has a 12 degree slope on a 16 by 24 foot roof. I live in Index WA. We have a little bit of snow every year, and lots of rain, and temps in the summer run mid 70’s to high 80’s occasionally. The OSB is on 2 foot center roof joists. In other words, the 2×4 roof joists are on 24 inch centers blocked every 2 feet, so the largest section of unsupported area of OSB is 2′ x 2′. There are 1 x 4’s on the 2×4 joists and blocks to increase the fastener areas, and increase load spreading. The OSB is covered with two layers of #30 tared felt. The room under this roof is one large open vaulted ceiling room. I was planning on attaching some Metal Sales Classic Rib 3-ft x 12-ft Ribbed Metal Roof Panel right on the felt. Is that advisable, or should I put some horizontal 1 x 4 on 2′ centers to attach the roofing too? I really don’t see the need or necessity but would really appreciate an opinion here.
@Isaiah Industries Thank you…
@Kim Davis Thank you for your comment. We went back and looked at our response to this individual and it got very complicated as we sorted through his exact situation. Generally speaking, we’re not a fan of battens on top of solid decking as the battens can weaken the roof system and also impact things like dormers and gutters. However, in situations where there is limited ventilation and subsequent condensation concerns, putting the metal panels on battens (with spacing as prescribed by the manufacturer) can help keep the underside of the roof deck warmer, which helps prevent the possibility of condensation. We are always happy to address specific questions and they are best handled if sent to todd@asktoddmiller.com Thank you again.
@Isaiah Industries It would be nice if you commented here instead of offline privately, several of us are watching and have the same question, thank you.
Hi, I received your email as well and sent you a response. Please let us know if you did not receive it.
Have a great weekend!
Todd
Should I put the tar paper down before I put down battens or should I put it over the battens? Thanks
@Isaiah Industries yea…with that logic is saying moisture will be then trapped under the batons to really speed up the rot. Best case is to strip everything, felt then metal. By the time u put purlins, felt then metal your out about the same cost
Both !! But on top is better.. The metal can sweat and if the felt is under the battens, the battens will collect moisture … The last roof over I did was shingles felted over it , then battens then felt, then metal,, I am getting to the point I’d just use shingles Fewer headaches ..Most places/code and warranties require the metal screws be placed into 1 1/2 in battens. 3/4 battens will crack and slpit over time allowing the screws to come loose..
the every 8-10 years get ready to change the screws ( the seals go bad) the screws come loose etc .. Just stick to plain ol shingles , its better in the long run…
Though it’s not ideal either way, my recommendation is underlayment on top of the shingles before the battens are installed. The problem with installing it on top of the battens is it tends to sag between them and the sagging areas can hold moisture which causes the underlayment to rot. I do suggest spacing your battens a tiny bit so that if water is ever trying to drain down the roof, it can run between the battens. There are also battens available with drainage slots milled into them.
You can just tell he knows WTh hes talking about.
Thanks.