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Old 09-21-2011, 09:06 PM   #1
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Synthetic vs felt over wall sheathing


I used Grace Tri-flex for my roof underlayment and really liked it.
Is there a downside of using it for wall sheathing covering before hanging vinyl siding. It's only about $2/sq more than 30# felt in my area.
Just not sure if it would have a disadvantage vs felt on the walls.

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Old 09-21-2011, 09:36 PM   #2
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Synthetic vs felt over wall sheathing


Walls should really be covered with Tyvek homewrap or the such, not felt paper.

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Old 09-21-2011, 09:54 PM   #3
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Synthetic vs felt over wall sheathing


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Originally Posted by gregzoll View Post
Walls should really be covered with Tyvek homewrap or the such, not felt paper.
Although I find this to be an understandable opinion in many jurisdictions 2 layers of Grade "D" paper are required as an under-layment.

If this is required in your local then the Tyvek would be redundant and un-necessary. That is especially true for stucco but also required for vinyl and wood lap siding as those materials can allow driven rain to get behind them.

But to answer the OPs question, I wonder if your BD would require two layers of the Tri-flex? I can't hink of any other disadvantages other than the extra cost though.

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Old 09-21-2011, 10:16 PM   #4
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Synthetic vs felt over wall sheathing


triflex has a perm rating of 0.54 which classifies as a class 2 vapor retarder

do not use this on the sidewall as a wrb
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Old 09-21-2011, 11:09 PM   #5
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Synthetic vs felt over wall sheathing


Interesting.......the norm here (California) is two layers 15# felt or 1 layer 30# or stucco tar paper....
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Old 09-21-2011, 11:51 PM   #6
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Interesting.......the norm here (California) is two layers 15# felt or 1 layer 30# or stucco tar paper....
Actually the CRC calls out for only one layer 15# felt or other approved WRB, you have go into the other chapters to find out what else is approved, many jurisdictions including every one of the Orange and LA county cities that I have so far dealt with are calling for 2 layers grade 'D'.
It has become rote for me to spec this out now.
Point is you never know until you you submit for permits wherever you may be.

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Old 09-22-2011, 11:03 AM   #7
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Synthetic vs felt over wall sheathing


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triflex has a perm rating of 0.54 which classifies as a class 2 vapor retarder

do not use this on the sidewall as a wrb

Ok, I'm seeing where felt would be a better choice over the wall sheathing due to its ability to absorb and pass through water as well as vapor.

Actually, I was planning at first on not using anything since the sheathing is Zip panels with the joints taped with Zip tape. The makers of the Zip panels say felt or house wrap is not necessary, but I thought a second barrier would be just extra protection. Maybe I should just put the vinyl siding directly on the Zip panels after all.

I do know that the Zip roof panels held up pretty good through the 6 months of weather before I got the metal roofing on, but I think maybe the membrane on the roofing panels is different than on the wall panels. (roof panels say for roof only, wall panels say for walls only).

Before putting the metal roofing over the roof Zip panels, I did apply synthetic underlayment even though the makers of Zip panels said it was not necessary. The advice I got from roofers was to use an underlayment anyway. So I went ahead and applied the synthetic thinking that a backup layer of protection would be a good idea in case the Zip tape did not hold up over the years.

But I hope I didn't mess up using the synthetic instead of felt on the roof. However, it seems the roof would be a different situation than the walls (not dealing with a wall structure and permability issues).

So, the questions now are:
Should I go ahead and put felt over the Zip wall sheathing (maybe at least one layer of 15# felt) or should I just install the vinyl siding directly over the Zip panels ?

Am I ok on the roofing underlayment, or should I have used felt instead of synthetic ?
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Old 09-22-2011, 12:22 PM   #8
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Synthetic vs felt over wall sheathing


The last I checked, the IRC calls for 1 layer of 15# felt for the weather barrier in zone 5 (Connecticut).

Can't confidently remember what code now (I deal with multiple states) , I'm thinking it's Mass....but I do remember the weather barrier requirement was noted as 10 times the permeability of the vapor retarder at the interior. So if you have kraft paper on your batts (1 perm) your weather barrier had to be 10 perms min.
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Old 09-22-2011, 07:08 PM   #9
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Synthetic vs felt over wall sheathing


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Originally Posted by Arky217 View Post
Ok, I'm seeing where felt would be a better choice over the wall sheathing due to its ability to absorb and pass through water as well as vapor.

Actually, I was planning at first on not using anything since the sheathing is Zip panels with the joints taped with Zip tape. The makers of the Zip panels say felt or house wrap is not necessary, but I thought a second barrier would be just extra protection. Maybe I should just put the vinyl siding directly on the Zip panels after all.

I do know that the Zip roof panels held up pretty good through the 6 months of weather before I got the metal roofing on, but I think maybe the membrane on the roofing panels is different than on the wall panels. (roof panels say for roof only, wall panels say for walls only).

Before putting the metal roofing over the roof Zip panels, I did apply synthetic underlayment even though the makers of Zip panels said it was not necessary. The advice I got from roofers was to use an underlayment anyway. So I went ahead and applied the synthetic thinking that a backup layer of protection would be a good idea in case the Zip tape did not hold up over the years.

But I hope I didn't mess up using the synthetic instead of felt on the roof. However, it seems the roof would be a different situation than the walls (not dealing with a wall structure and permability issues).

So, the questions now are:
Should I go ahead and put felt over the Zip wall sheathing (maybe at least one layer of 15# felt) or should I just install the vinyl siding directly over the Zip panels ?

Am I ok on the roofing underlayment, or should I have used felt instead of synthetic ?

yes you did fine,unless the wrb is integrated into the window sill flashing i don't think i would add it
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Old 09-23-2011, 06:36 AM   #10
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Synthetic vs felt over wall sheathing


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Ok, I'm seeing where felt would be a better choice over the wall sheathing due to its ability to absorb and pass through water as well as vapor.
?

would you buy a raincoat that passed more moisture the wetter it got?
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Old 09-27-2011, 10:54 PM   #11
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Synthetic vs felt over wall sheathing


Zip system water-resistive barrier (resin paper facing) = 12-16 perms.
OSB with tape = 2-3 perms http://docs.google.com/viewer?a=v&q=...ZoxkKEMlmyCNhg

Optimum perm rating of a WRB to dry wet OSB sheathing = 18-24 perms Page #17, here; http://repository.tamu.edu/bitstream...pdf?sequence=4

Just don’t ever get a water leak as the OSB with the low perm facing will take 40+ days to dry compared to plywood’s 15 days. A lot more time to develop mold….

If you must use OSB, try not to use aspen, pp.13, don’t know the species Zip uses, here: http://www.fpl.fs.fed.us/documnts/pd..._carll001.pdIf you have to use OSB, combine it with a felt or building paper = 5-60 perms when wet, or Tyvek = 58 perm., not Typar = 11.7 perms.

I’d sure use another WRB under vinyl, Zip or not, with OSB.

Gary
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Old 09-28-2011, 05:15 AM   #12
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all hypothetical...show me damage not caused by improper flashing details

osb can handle occasional wetting[as long as it has a chance to dry]much better than ply
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Old 09-28-2011, 08:18 AM   #13
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Where in that spec does it mention 2-3 perms?
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Old 09-28-2011, 07:32 PM   #14
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Synthetic vs felt over wall sheathing


zip wall is an engineered system,improperly ''adding''components may do more harm than good,unless an additional wrb is integrated with the zip tape at the sill your bound to get water behind the paper and unless Huber shows it as a detail i would think before deciding to install it
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Old 09-28-2011, 08:27 PM   #15
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Synthetic vs felt over wall sheathing


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would you buy a raincoat that passed more moisture the wetter it got?
Did you ever wear a raincoat when it's not raining? You sweat your a** off.

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