Junor Cobb
2/3/2009
Sorry if this has been asked before but I couldn't find the specific topic. I'm having 26 guage metal installed over 1 layer of shingles. What is your opinion on putting Tyvek house wrap over #30 felt for a slip sheet. I've checked on the cost difference between felt/Tyvek vs. synthetic underlayment and it seems like it runs about 3 to 4 times the cost. Also do you think 26 guage is overkill for residential purposes? Great website!!
Guest User
2/4/2009
Are you asking if you should have both 30# and synthetic? My opinion I would say neither. When we reroof we install a purlin system, this way the screws have a solid surface to fasten to.If you do want underlayment use synthetic because it wont rip on the uneven surface. If you use hand nails or slap stapler you will rip the felt. As to what gauge you are installing 29ga is fine for an ag or classic rib panel. 26ga may be to light if you are doing standing seam. It just depends on your opinion on what the "oil canning" effect looks like. To reduce that as much as possible usually we install 24ga.
Guest User
2/4/2009
My question was, what is your opinion on 30# felt with Tyvek on top of the felt for a slip sheet. Does anybody use it this way? If not a good idea I will use synthetic underlayment as this will be the only roof I hope to ever need. I'm not doing the standing seam, just the "barn type" metal. I've also heard it called classic metal . And since you bring it up is there any problem with oil canning with the classic metal? Is a purlin system you refer to 1x4 wood stripping?
Guest User
2/4/2009
I would just go with with synthetic if you want to. We normally only use purlins on a recover. I use 2x4 but many people use 1x3 or 1x4. There isnt an issue with oil canning because there are striations in between the 3x4 high ribs. 29ga is structural 2'o.c. so you will have to install your purlins 2' o.c. and that is fine for your application.(it is also less money)If you would like 26ga it is heavier but not needed in my opinion.
Todd Miller
Isaiah Industries, Inc.
2/7/2009
You can also install over the existing without strapping in many cases.
Guest User
2/7/2009
why would that be a good idea? I only see problems that way. You are never going to get a good base and the shingles will possible crumble resulting in a loose fastener. When you fasten to a purlin you will get a good tight fastener. If you are spending the time putting quality roof on does it make sense to have an inferior base???? Just my thoughts...
Guest User
2/7/2009
First of all, I don't want to raise my roof any higher than I need to. If I use 2x4s it would raise it up 1 1/2 inches. Seems like that would give rain and wind a place to enter between the roof and gutter. Am I right or wrong on this? Second of all, my original question hasn't been answered about the Tyvek installed over 30# felt. My shingles are 8 years old so I don't think I'll have a problem with crumbling.
Guest User
2/7/2009
Junior, A few years back (before all of the mass produced synthetic underlayments),I checked into using Tyvek as an underlayment and the rep told me that water molecules can pass through house wrap and not to use it for that purpose. Even though it is a synthetic it does not have the water resistance of a synthetic underlayment, it is a breathable material. Looking at it from that standpoint, when you do the underlayment, you also want it to work as a vapor barrier and being able to breathe would negate that. And before anybody reading this starts in about water and vapor being two different things, it can be the same thing. Our number one greenhouse gas is WATER VAPOR.
Todd Miller
Isaiah Industries, Inc.
2/7/2009
Thanks Wade
Guest User
2/8/2009
Yes you are wrong about giving the rain more exposure to enter the roof system. If you want to but an ARMANI suit with WALMART shoes good luck....
Guest User
2/8/2009
I think I'll just do what I started to do in the first place and go with synthetic underlayment over shingles and the 26 guage metal. Thanks to all the great answers from everybody.( even the smartass answer from dlc ) My Walmart shoes do me just fine.
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