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cobragrover
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# Posted: 23 Mar 2013 08:32pm
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We are still in the planning stage of our cabin. Clearing a spot and doing general cleanup.
I talked to a metal roofing installer about "barn" metal roofing vs standing seam. I was worried about all the holes and the rubber washers being the only thing between you and a leak. He said with the 10/12 or 12/12 pitch I have planned the "barn" roofing would not be an issue.
It is much cheaper than standing seam so it would be a cost savings.
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Anonymous
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# Posted: 24 Mar 2013 12:29am
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Standing seam for flatter roofs, WAYYYYY flatter. With 10/12 and 12/12 why are you worrying about leaks?
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bldginsp
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# Posted: 24 Mar 2013 12:49pm - Edited by: bldginsp
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I looked into standing seam, and concluded that it's really best for large areas with a minimum of penetrations and roof valleys, hips, and other intersections. It's used a lot in commercial work where there is a large area with no penetrations and few if any intersections. It's difficult and expensive to install, and other exposed fastener roofing is successfully used in probably 90% of all metal roofing applications.
The fasteners are going to eventually loosen, but now there are better underlayments that supposedly seal around the screw shank to keep moisture out from under. All metal roofing gets condensed water under the roofing itself, so the underlayment has to be intact to keep the wood below dry. Tar paper does this well, and seals well around fasteners well until the tar dries out or the fasteners move with heat and cold expansion and contraction of the metal roofing. The newer underlayments supposedly hold the seal better.
The question I haven't been able to answer is whether it's worth doing a Z bar installation with exposed fastener roofing. Instead of screwing the metal roofing to the roof deck, you put 1" high Z bar on the underlayment, then screw the roofing to the Z bar. In theory, when the metal expands and contracts it just bends the Z bar slightly and does not loosen the screws holding the roofing to the Z bar. Nice theory, but does it work? If so, it might set your mind at ease about leaks, but it costs more to do a Z bar installation.
One other advantage to standing seam is that snow slides off it more easily because it has no exposed fasteners, so you can actually reduce your load calcs for snow load in some cases, making your rafter costs lower.
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oldgringo
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# Posted: 24 Mar 2013 02:07pm
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Would the Z bar installation be self-ventilating, resulting in cooler decking?
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Anonymous
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# Posted: 24 Mar 2013 04:41pm
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Good question gringo, I don't know. Seems like it would have to help. But you got to let the air in both top and bottom, and keep the critters out
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rayyy
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# Posted: 25 Mar 2013 12:53pm
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I choose 8 in 12 pitch for my roof.Good quality steel roofing from the lumber company(not from Lowes or Homedepo)with colored matched screws.It goes up quick and easy,look's great.I figure in 50 year's It won't be my problem.I'll be long gone.Done my fair share of shingles and felt over the years and at best,you might get 10 or 15 years out of them befor it's time to replace them.Heck with that.I'm getting to old for that,Lol.
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grover
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# Posted: 18 Jul 2013 09:50pm
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Thought I'd get back to my post of a few months ago. We will be having the materials for framing and roofing delivered the next week or so. Have decided to go with the pole barn type metal mainly because of the 12/12 pitch.
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bldginsp
Member
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# Posted: 18 Jul 2013 10:48pm
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I bet you are going to be fine. I think what it comes to is that exposed fasteners eventually loosen and the you got to get up there and replace them with larger gauge and do other repairs.
I'm going to use medium quality R panel, but I'll research underlayments and use the best available.
Good luck
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rootwad
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# Posted: 19 Jul 2013 12:19am
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bldginsp-
I saw a setup that seems to be similar to the zbar mentioned (if I'm understanding you correctly), except 1x4's were used in placed of Z bar. A water/ice barrier was attached to the roof deck, and 1x4's were attached over that at a 45 degree angle, with maybe a foot or two of space between each board. The metal roofing was attached to the 1x4's, creating 1" high channels between the boards. There was a double fascia, with a long rectangular vent between the two that ran the length of the fascia boards. Air was drawn up this vent between the fascia boards, ran up the channels created by the 1x4's, and escaped through a vent at the ridge. Couldn't see the ridge vent, so not sure what that looked like, but supposedly this method helps with condensation issues and preventing leaks generally caused by attaching metal roofing directly to the roof deck. Not sure about the expansion/contraction issues you were talking about though.
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Kudzu
Member
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# Posted: 19 Jul 2013 06:19am
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Metal is the way we went, have it on our house and cabin, not one bit of a problem.
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soundandfurycabin
Member
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# Posted: 19 Jul 2013 07:08am
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Grover, were you talking about the snap-lock metal roofing or real standing seam?
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bldginsp
Member
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# Posted: 19 Jul 2013 09:50am
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rootwad- what do mean that the the 1x4s were attached at a 45 degree angle? Cant' visualize what you mean.
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jrbarnard
Member
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# Posted: 19 Jul 2013 10:22am
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I have 2 cabins on my place. One is 12x24 and has no metal roof. It is an oven when the sun is up, without the A/C going full blast.
The other is 24x32 and has a metal roof and radiant barrier. It is a good 10-15degrees cooler under that roof due to the metal roof and we had 8 inches of rain last month alone with zero water inside.
I would not go with anything but metal roof.
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creeky
Member
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# Posted: 19 Jul 2013 10:42am
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as I understand it, the 45 degree angle on the purlins is to allow air to move more freely up to the roof ridge vent. this allows for significantly lower roof temperatures as the roof draws cooler air from below and vents the hot air at the ridge.
as jbarnard confirms with his experience.
my washroom has a metal roof with radiant below and it stays at essentially ambient temp. even when in direct sun.
of course this week has been 34 and high humidity, so it's hot!
(34C = 93F)
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rootwad
Member
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# Posted: 19 Jul 2013 07:43pm
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bldginsp-
Here is the process:
http://www.youtube.com/watch?v=LM6zv3A4JjI&list=PLDYh81z-RhximAqGVU4FToZp23f4u8jgt.
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bldginsp
Member
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# Posted: 19 Jul 2013 11:22pm
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Rootwad- I watched the video. The reason he ran his 1x3s at 45 degrees was just because of the lay of the hips and valleys on that particular roof. Had he run them perpendicular to the eave, the channels between the 1x3s would not have passed through from the eave to the ridge, providing ventilation. So it was a job specific design.
The galvalume roofing he was using is standing seam with no exposed fasteners, so the whole issue of exposed fasteners loosening is mute. That's the big advantage of standing seam, the down side is cost.
Standing seam can screw down directly to 1x3s as in the video. Since the fasteners are hidden under the roofing, even if they loosen they can't cause a leak.
When you screw R-panel roofing directly to the roof deck through the roofing, leaving the head of the fastener exposed, the expansion and contraction of the roofing with heat and cold will tug and pull at the fastener, loosening in eventually. When water gets past the fastener head gasket, it is sitting on the screw shank that passes through the roof deck. If expansion and contraction have compromised the seal of the underlayment against the screw shank, water gets past the underlayment onto the roof decking.
With a metal Z bar installation, the roofing is screwed to the Z bar, not the roof deck. The Z bar is screwed to the roof deck. The Z bar spaces the roofing off the roof deck about an inch. If the roofing screw leaks, the leaking water hits the underlayment under the Z bar, and drains toward the eave. The leak does not occur where a screw penetrates the underlayment.
Since the Z bar can flex, the expansion and contraction of the roofing itself causes the Z bar to flex, thus not stressing the screws that hold the roofing to the Z bar. Supposedly this keeps them tight through many cycles of expansion and contraction.
At least, that's the theory.
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rootwad
Member
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# Posted: 20 Jul 2013 01:29am
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bldginsp
I didn't know the fasteners weren't exposed in standing seam. Not sure how I missed that, but when I went back and watched the video I saw that I was wrong on a few other key points as well. Thanks for clearing things up.
So Z bar and the 1x4's are similar because they create an airspace under the metal and they provide a surface other than the roof to attach the metal to. However, Zbar is superior to the 1x4's because of it's ability to flex, correct?
Z bar sounds like it would be the best choice since it's ability to flex prevents the fasteners from loosening so quickly in the first place. But do you think that 1x4's could still be effective, even if they didn't flex like the zbar? I admittedly have tons to learn about construction, but it seems that any leaks created by attaching the metal roofing to the 1x4 wouldn't penetrate the roof deck.
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creeky
Member
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# Posted: 20 Jul 2013 08:50am
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right. i did see angled purlins for roof venting.
what do you think the % of roofs using wood purlins with metal roofs is? by the far the majority ...
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jrbarnard
Member
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# Posted: 20 Jul 2013 08:56am
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FYI - Remember, keep it simple.
If this were your main home, I'd say do all the fancy stuff. But this is a cabin and the energy efficiency of a cabin done simple vs all the fancy stuff you can do would not really save money, unless over the long haul.
Those guys in Texas doing all the foam between the roof layers etc are doing so on a large house where energy conservation is important.
Lay down radiant barrier for the base and then put tar paper over it and then use metal roofing. That will get the most energy efficiency you can get for the buck and you won't spend a ton of money on all the other fancy schmancy stuff.
Take it from someone that has been at this for a year and a half, you can think it, do it.. or think it think it think it and spend more money than you need to.
It's a cabin.. go enjoy it ;)
Russ
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bldginsp
Member
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# Posted: 20 Jul 2013 09:21am
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rootwad- the THEORY behind Zbar installation is that the fasteners won't loosen, and if they do, they don't compromise the roof deck. But I have to tell you I don't really know what the practical reality is. I've never seen it done, just read about it on cyber space.
I've only seen a few references to a Z bar installation of R panel roofing. I think it's not done very often. Could be I'm splitting hairs here- most people that use R panel just screw it to the deck. If that lasts a good 30 years with no problems maybe it's the way to go.
I have a bunch of good quality R panel that I plan to use to roof my cabin. I'm going to talk to the most experienced roofers in my area to see if they think the Z bar idea is worth the extra effort. Maybe I should just spend extra money on the best quality underlayment and screw it to the deck.
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bldginsp
Member
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# Posted: 20 Jul 2013 09:48am
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Link to a good site with instructions on metal roofing installation:
http://www.bestbuymetals.com/how-to-install-metal-roofing.html
Specifically for exposed fastener R panel installation:
http://www.bestbuymetals.com/pdf/r-panel-installation-guide.pdf
I think there is no reference to installing R panel on Z bar in these manuals. I'm beginning to conclude that it is an obscure method rarely used. What's most important is the details of installation at corners, eaves, gables, penetrations, hips, etc.
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rootwad
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# Posted: 20 Jul 2013 02:03pm
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Russ, you sure are right about the "think it think it think it" thing. With so much info at my fingertips it's easy to get caught up in all the possibilitites and end up blind to the simplest solution. I'm learning so much along the way, though, so hopefully it all evens out in the long run.
So what would you all do if you were in my shoes? My cabin will be 12x12, constructed out of recycled materials (as much as possible), and it will be my full-time off-grid residence. I'll eventually get solar panels, but my first year will be spent truly off grid with no electrical devices whatsoever. Since I won't have ac or fans to cool in the summer, I initially set out to learn how to build a metal roof that wouldn't turn my cabin into an oven. But through this thread I also discovered the additional issues of condensation and of leakage caused by expansion/contraction of metal (which I wasn't even aware of before).
Long story short....what sort of metal roof system would you use if this were your full-time residence? I'll be taking advantage of other natural cooling available on the land (shade trees, positioning cabin/windows for good cross-ventilation, etc), but if there are some simple building techniques I can do to add to that benefit, I'm all ears.
On a side-note, here's a cool option for recycled metal roofs: http://www.instructables.com/id/Make-Shingles-and-Siding-Out-of-Aluminum-Cans-Bee/#. Wouldn't use it for a cabin, but might be a cheap option for an outhouse.
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grover
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# Posted: 22 Jul 2013 05:45pm
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soundandfurycabin,
My choice was basically between metal roof with exposed fasteners and metal roof with the hidden fasteners. My worry was about all those holes in the metal where you could get a leak.
I'm being told I'm worrying too much.
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