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Old 05-08-2010, 07:28 AM   #1
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Tyvek and roofing felt


I've seen some discussions about Tyvek vs. roofing felt. Most preferring Tyvek house wrap. My question is whether they can be used together. I.e. Can Tyvek be applied over existing felt on an exterior wall? Or does that defeat the purpose of Tyvek's breathing characteristic?

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Old 05-08-2010, 08:30 AM   #2
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Tyvek and roofing felt


You do not install one over the other
That creates 2 vapor barriers

I use Tyvek for wood shingle siding
If I use roofing felt it discolors & darkens the wood shingles

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Old 05-08-2010, 09:42 AM   #3
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Tyvek and roofing felt


It defeats the abilty of the Tyvek to allow wall moisture to vacate.

Use only the Tyvek, or other brand house wrap - not both.
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Old 05-08-2010, 10:22 AM   #4
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Tyvek and roofing felt


I couldn’t tell you how many LP, Vinyl, and other sidings I’ve ripped off over Tyvek and other House wraps to find it soaking wet behind the wrap.

One problem is water weeping in at the nail holes. Every nail creates a tare where water can get in, unlike felt (tar paper) that actually seals around the nail.

Water can get behind siding.

Caulking , flashings, and siding (LP is one example) can and do fail.

Tyvek and other house wraps don’t claim to be a moister barrier and they aren't. Typar (Tyvek's cuz.) claims to be a moister/vapor barrier but I’ve found soaking wet sheathing behind that too.

Tar paper keeps the water away from the wood. Oil and water don’t mix.

So what’s it going to be, let the house breath or keep it dry? I vote dry. Tyvek in the desert, great.

I have never seen felt bleed through and darken wood.
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Old 05-08-2010, 10:26 AM   #5
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Tyvek and roofing felt


shingle sided quite a few houses always felt with no problems. dave the felt goes under the shingles
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Old 05-08-2010, 01:48 PM   #6
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Tyvek and roofing felt


Here are two of the best discussions I've seen on Tyvek, felt, building papers, and the importance of rain-screen walls:

http://www.greenhomebuilding.com/pdf/RainScreen.pdf

http://www.dickseibert.com/martin.pdf

I'd summarize, but it's really, in my opinion, worth the few minutes to read the articles.

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Old 05-08-2010, 02:24 PM   #7
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Tyvek and roofing felt


I would use real asphalt 30# felt paper over a house wrap any day. For this one fact----- ďFans of felt note one of its advantages over housewrap:
If water gets behind felt ó either
due to a flashing leak or condensation
from solar-driven moisture ó the felt
can soak up the liquid water and gradually
dry to the exterior. Plastic housewrap
is not absorbent; any water
trapped on the wrong side of plastic
housewrap can only pass through to the
exterior as vapor.Ē

Read the whole article: http://www.dickseibert.com/martin.pdf

Cedar siding bleed-out has more of an adverse effect on house wraps than it does on felt- even 15#, drainage plains are important, and this article again states my reasoning: ďAs it happens, I have felt paper on my own home, and if I could choose between felt and housewrap and do it over again, Iíd still choose felt. Thatís because I believe that under certain circumstances, felt outperforms housewrap. For example, an ice dam or roof leak may allow liquid water to get behind the felt or housewrap. Itís also possible for the sunís heat to drive water vapor through the housewrap from the outside, where it can condense on the sheathing. In either of these cases, you now have liquid water on the wrong side of the wrap. Under these conditions, the liquid water would be trapped by the housewrap, which is permeable only to water vapor. Felt, on the other hand, will absorb the water, and more quickly dry to the outside.Ē From: http://bct.nrc.umass.edu/index.php/p...tion-barriers/

In the real world, the installation makes a huge difference. Be sure to back prime any reservoir siding; cement board, wood, anything but vinyl. House wraps and felt papers are water resistant---- water retarders Ė not barriers, with a permeability rating to pass water vapor. I would not double them and if using a house wrap- get an embossed or raised- to pass the liquid water down effectively. http://www.energysavers.gov/your_hom.../mytopic=11300

Be safe, Gary
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Old 05-08-2010, 03:53 PM   #8
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Tyvek and roofing felt


Some good reading there, learned some stuff but all in all they just confirm what Iíve been seeing in the field for years. I have removed a lot of siding (a special thanks to LP) and have seen first hand (more than most) how these different barriers have preformed on homes. Some that were sided 100 years ago and some just 4-5 years and without hesitation felt wins hands down. I read in one of the articles that all barriers including felt will allow water to pass through after being wet for a day. I have to say ďIĒ havenít see that with felt. In times were there was water damage on a felt covered wall itís always been from a breach in the paper (a tear, not lapped properly, improper flashing detail) and not from soaking through. At least thatís been my observation. I use nothing but 30lb. ASTM. ďLeather BackĒ we call it.

I have to agree that a rains screen in the way to go but unfortunately (in my area at least) itís just not done. Most of the new construction is done by developers buying up 50-100 acre plots and building neighborhoods of unsold houses and if isnĎt specked out it doesnít happen. New owners canít even pick out the color of there house let alone those kind of details. Using 3/8 ď ac plywood for the firing strips Iím not so sure about. What happens when that all rots away?
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Old 05-08-2010, 04:10 PM   #9
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Tyvek and roofing felt


I agree with your comment on the AC plywood. Cor-a-Vent is now available in a screened version, with matching plastic vertical units to replace furrings strips.
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Old 05-08-2010, 04:16 PM   #10
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Tyvek and roofing felt


Quote:
Originally Posted by Scuba_Dave View Post
You do not install one over the other
That creates 2 vapor barriers

I use Tyvek for wood shingle siding
If I use roofing felt it discolors & darkens the wood shingles

Neither is a vapor barrier so you wouldn't have 2.

Tyvek is incompatable with cedar so don't use with cedar shingles. It eats up the Tyvek.
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Old 05-08-2010, 04:35 PM   #11
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Tyvek and roofing felt


Quote:
Originally Posted by jogr View Post

Tyvek is incompatable with cedar so don't use with cedar shingles. It eats up the Tyvek.
Word. I've seen Tyvek pretty much destroyed in as little as 3 years under cedar. Might be a different story with a rain screen, but nearly everyone in this area has switched back to felt under cedar.
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Old 05-08-2010, 04:49 PM   #12
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Tyvek and roofing felt


Quote:
Originally Posted by seeyou View Post
Word. I've seen Tyvek pretty much destroyed in as little as 3 years under cedar. Might be a different story with a rain screen, but nearly everyone in this area has switched back to felt under cedar.
never heard tyvec incompatible. the reason for just cedar?
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Old 05-08-2010, 04:54 PM   #13
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Tyvek and roofing felt


The tannins in the wood react with the coatings on the Tyvek. Read the above linked articles for complete info
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Old 05-08-2010, 05:07 PM   #14
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Tyvek and roofing felt


It amazes me how a mega corporation such as DuPont is able through master marketing and armies of sales rep’s can convince an entire industry to quit doing what has worked for a 100 years and buy what they have to sell.

Pure Genius.
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Old 05-08-2010, 05:45 PM   #15
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Tyvek and roofing felt


Amen, Ron. I wish there were a Consumers Report for these types of products. Too much of a lack of backbone from even ASTM, I presume. From the above-referenced Sheathing article:

Some professionals who have made noble attempts to clarify the muddy waters appear to be failing. In an effort to make it easier to compare the products, an ASTM task force has been working for the last two years with scientists and manufacturers’ representatives in hopes of developing common standards and test procedures for plastic housewrap, asphalt felt, and building paper.


“We hoped we could write a specification, with tests to measure the performance of any of these products, but it’s just not going to happen,” says Thomas Butt, an architect from Richmond, Calif., who chairs the committee. “There are a lot of competing interests from some very economically powerful manufacturers. There is a lot of political pressure for something not to happen that would make one product look better than another," he says.


So much for Hope and Change.

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