I spoke with a framing carpenter yesterday who told me that under standing seam steel roofing one must use rubber membrane (aorund here they call it bitathane) rather than roofing felt, as roofing felt would deteriorate without the ventilation that he claimed asphalt shingles give.
This made no sence to me. Does it to you?
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Replies
Stef,
Sounds like roofing advice from a framing carpenter. (g)
The suppliers I deal with recommend felt.
KK
Thanks,
Glad to have my feelings confirmed.
Stef
I put #30 felt under the standing seam roof (over plywood sheathing) on my own house along with a few others and have had nary a problem.
About 4 years ago I tore down an old house on a windy coastal bluff that had metal roofing (not standing seam...hi-rib as I recall) on felt on plywood. Felt looked as good as new and the metal ended up being put on another building. Roof was about 35 years old.
Why put anything underneath? I've torn down houses for a living, a bunch with standing seam, and 5 vee, and, never saw one with any roll goods underneath. The only leaks were lack of maintenance, like sealing up where a limb went thru the roof. Since tar paper isn't self sealing, I can see how the bituminous stuff would have an advantage, but that would only be with a sub-standard standing seam installation...I've got 5vee on my own house, no roll stuff, 1x4 strapping on 16" centers, plenty of ventilation (plywood is counter productive in that area), neoprene gasketed capped screws, no leaks...you might want to talk to your roofer, and, best of luck, I love metal roofs... EliphIno!
I've heard that red rosin paper is the standard thing to put under copper. Have you ever taken off a copper roof?
-- J.S.
Nope, never taken off a copper roof, nor have I ever seen rosin paper under metal...that doesn't mean it isn't done. But, I can't see how any paperish underlayment could be put on skip sheathing and not end up with a bunch of knee, elbow, and foot holes in it... EliphIno!
Copper over skip sheathing would also -- because it's soft -- be subject to getting dented and rippled down. I'm going to be doing some copper roofing this summer, and the plan is to go over full plywood sheathing and red rosin paper. I'd be interested in any experience or suggestions from someone who's done copper.
-- J.S.
John,
Back when I started roofing in the Dark Ages, I was on several Flat roofs on Govt specifications. We used pitch for the BUR and copper flashing, soldered. We always put red rosin behind the copper on those jobs, but I never knew why..
Excellence is its own reward!
The rosin paper under a copper roof is there to allow for copper's high coefficient of expansion. It keeps the copper from adhering to the underlayments in mid span (between attachment points).
It seems like there are places where allowing that movement instead of stitching it down would create more cracks and splits..
Excellence is its own reward!
The trick with copper is to allow for expansion where it will not do harm, ie. between attachment points. Keeping in mind that these points are spaced so as to allow for the expansion that occurs between them to be absorbable without damage, hence small pans. For flat locked soldered seam copperwork the SMACNA manual recommends no larger than 20"x28". There are innumeralble expansion considerations on every copper job, and experience is the best key to where to allow expansion to occur. As I said before the rosin paper makes it happen where I want it.
How do you attach the copper, and at what spacings to deal with that expansion? What is the rosin paper put down with, adhesive? copper staples?
Thanks --
-- J.S.
Sounds to me like something he made up while standing on his head after drinking one too many beers.
Excellence is its own reward!
I have the same question about felt under standing-seam roofing. I am building a 48'x48' shop in NH--snow country--and will be using a metal roof over Advantec sheathing (5/12). Both panel manufacturers I am looking at recommend felt under the panels, with Ice and Water along the eaves and valleys, etc. The eave detail is to bend the roof panel down and under an applied drip edge flashing and crimp. Additionally, they want to use a double bead butyl sealant between the underside of the panel and the drip-edge flashing under it--all along the eave line, thereby creating a very watertight seal. It seems to me that water will inevitably get in under the panel, perhaps a heavy rain on top of a snow-covered roof, travel down to the eave and be trapped by the sealant. Am I wrong?
http://www.unioncorrugating.com/pdfs/adv_lok_install_03-02.pdf
http://www.metalsales.us.com/TechSheets/VerticalSeam-Install.pdf
Not really. The whole idea of underlayment is that it is essentially a secondary roof, separate from the main surface roof material.
You do the felt and ice, water shield thing so that any water that hits it will run over the edge of the eave trim. That functions aas a temporary roof / watershed while you perform the finish work with whatever the choice of materials is.
Then you install that finish material as tight and snug as possible. You don't want it to leak and don't expect it to but if or when it does, you have the confidence of an underlayment that will shed a few drops of water.
With a detail like yours, you would not want the ice and water shield over the drip edge. I haven't finished yet with the downloads but I expect this as you describe is for a low slope roof where water is more prone to bleed back up via capillary action from the eave. A steeper roof would be less likely to require the butyl seal there.
I have now seen both pdf files and see multiple suggestions for eave treatment, per above. Study those documents thoroghly..
Standin seam detailing is much more intensive, labor wise, than most other roofing but worthwhile when done right. Be sure you have the right craftsman with understanding of the process and the thermal expansion of the materials and you will long be rewarded with the quality of the job..
Excellence is its own reward!
It hasn't been mentioned here yet, but it's been my understanding that, when laying a metal roof on sheathing, the felt paper serves mostly as "pad" to reduce any friction between the metal and the sheathing, as both materials will 'move' with changing temperatures. How much of a secondary water barrier the felt provides is debatable because it's been my experience that a properly installed, quality metal rood is unlikely to leak in the first place unless it gets damaged by a tree falling on it or something. But if it gets compromised by an event like that, the felt is probably damaged too.
I have seen felt installed over furring (a friend of mine always does it that way), but it's pretty vulnerable to damage during the install.
The framer invited me out to see the log house whose roof and interior he framed. I now know why he said what he said. Not because he knew anything, but because this $5 Million (yes thats right 5) house has the entire roof covered with the bitathane.
Now, get this. this house is a log one, the best I have ever seen as far a the log work is concerned, with every conceivable dodad and appurtenance inside. Copper flashing everywhere, copper clad windows, real stone work everywhere, three coats of hand sanded and applied exterior finish. BUT, for Gods sake, they put on PLASTIC shingles. They look like shakes but are three dimensional pressed plastic. Polyethylene, it looked like.
So, I guess they had no faith in the shingles, and effectively roofed the thing in Bitathane. Unbelievable.
BTW, My house is a log one, which my wife and I are building. I have surmised from another of your posts that you are also a log builder? (Notchman?)
Thanks for the responses to my original question.
Edited 3/18/2003 6:33:29 PM ET by stef
EPDM Rubber certainly has a more modern aesthetic to it and is much smoother and flush when installed correctly. It will not have the unsightly seams you see in a felt roof.Unlike felt, rubber roofing doesn't scuff or mark easily. It also is less likely to crack or warp in the sun and less likely to blister or rot. That is probably the reason why it's claimed to have such a long lifespan!
Doesn't make any sense, I guess.
Underlayment products for use beneath standing seam metal roof. metal roof is non-perforated, asphalt-impregnated felt underlayment.
Hey there,
Hmm, that sounds a bit odd to me too. I've always heard of folks using roofing felt under standing seam steel roofing without any issues. Not sure why ventilation would be a problem, especially since standing seam roofs are usually installed with an air gap underneath.
Maybe get a second opinion just to be safe?
Take care!
Using roofing felt under standing seam steel roofing can be a point of contention for construction professionals. Some may argue about the necessity of rubber membrane because of ventilation but to others they find this unreasonable. Perhaps, it would help to consult other experts.
You all realize the original post is from over 20 years ago?
Or did you just reply to the title?
It is common to use a rubber membrane such as Bitathan under a steel standing seam roof to provide an additional waterproof layer and protect against potential leaks. Roofing felt can degrade over time without sufficient ventilation, but which one you choose will largely depend on your specific project requirements and local building codes.
I just did a "standing seam" metal roof on a shed. It's the snap lock type standing seam, sort of a "fake" standing seam (looks great and it's easy). I used Sharkskin underlayment over plywood sheathing. It's been fine.
Using rubber membrane like bitathane under standing seam steel roofing instead of roofing felt is indeed common practice, as it provides a better seal against water infiltration. While asphalt shingles allow for ventilation, the design of standing seam steel roofing differs, requiring a different approach to prevent moisture issues. This method helps maintain the integrity of the roofing system over time.
Using a rubber membrane isnt a bad thing it is good if you give it a good ventilation to prevent leaks
that does seem abit odd
Roofing felt under a standing seam roof acts as a secondary barrier, providing additional protection against moisture ingress and extending the life of the roof. Acts as a damping layer between the metal panel and the roof deck, reducing noise and preventing wear. Proper installation of roofing felt is important to ensure optimal performance and weather resistance.
This discussion regarding underlayment for standing seam roofs is interesting. The traditional asphalt felt approach has its drawbacks, and the concerns about ventilation raised by the commenter are valid.
However, the synthetic underlayment options mentioned in the replies seem like a more suitable solution for modern metal roofing.
Are there specific types of synthetic underlayment materials that are generally preferred for use under standing seam metal roofs?
Perhaps mentioning some key features to look for in a synthetic underlayment, like breathability or water resistance, could be helpful for readers considering this option.
This thread highlights the importance of proper ventilation for a metal roof system, and the considerations for choosing the right underlayment material.
Here in the Intermountain West (Colorado) the last few standing-seam metal roofs we've been involved with have had full Ice & Water Shield HT specified under the roofing. The HT (high temperature) is necessary to withstand the high temperatures that metal roofing can reach in summer months. Since quality standing-seam roofing is more expensive than asphalt shingles and these houses were built to high standards it made since that we followed best practices. From the previous comments some may think this is overkill but our roofing subs won't even warrant metal roofs without it.
it's a couple of bucks a square foot in material for the high temp peel-and-stick but often required by manufacturers for their water-tightness warranty. Grace/GCP; Henry and Sharkskin are usual suspects, but some standing seam manufacturers require their own "grey label" membrane.
Ice and water shield has been state of the art since about 2014. There’s several kinds of standing seam, some are water resistant summer waterproof