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Old 02-24-2013, 09:47 PM   #1
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Building Science- Perfect Wall Questions


My questions are in direct response to this article: http://www.buildingscience.com/docum...ct-wall/#Fig01

It makes sense to me why the author says your "control layers" should be on the outside of the structure but in regards to the "residential" wall type it seems to me a lot of people get this wrong. I worked residential for awhile and at an exterior wall your typical design had cladding, tyvek air barrier, osb or plywood sheathing, 2x6 wood framing, batt insulation, then a plastic vapor barrier and drywall sheathing. In that design, wouldn't the vapor not be able to dry from the inside?

My other question is really more of an observation, but to me there is no way you can prevent vapor from getting to the inside of the wall so then you should make sure you never use any kind of non-vapor permeable paint on the inside, correct?

Lastly, the author says the best place to control air is on the outside of the structure but underneath the insulation layer so the air does not change temperature when discussing Figure 1. I don't understand why this is important...why could you not have these layers switched in what order they are applied?

Thank in advance for the help!
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Old 02-24-2013, 10:04 PM   #2
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Re: Building Science- Perfect Wall Questions


You had to pull something done by:

Mr. Lstiburek.

This is a very complex question and has to do with many "layers" of the house.

I referred to an article he wrote on "two way" or "re-breathing" roofing underlayment, for certain roofing application we were doing with a "different" substrate. I got a lot of useful information, but it also raised a few questions for me that I don't think (In my opinion,) have universal answers for.

I will be interested to see some responses, and if none arise, I am willing to contribute, what I believe to be true.

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Old 02-24-2013, 10:18 PM   #3
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Re: Building Science- Perfect Wall Questions


Your example assumes your in the Northern climate. The plastic prevents the vapor from passing into the cavity because cold climate have more heating degree days that make moist air.
As an overall plan I would like a vapor retarder not a plastic barrier so if there is a moisture leak it isnt trapped.
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Old 02-24-2013, 10:59 PM   #4
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Re: Building Science- Perfect Wall Questions


Vapor barrier (paper face of insulation) goes towards the living area or heated space. Tyvek on the outside stops air flow, but allows vapor to escape from the wall.
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Old 02-25-2013, 07:32 AM   #5
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Re: Building Science- Perfect Wall Questions


[QUOTE

Lastly, the author says the best place to control air is on the outside of the structure but underneath the insulation layer so the air does not change temperature when discussing Figure 1. I don't understand why this is important...why could you not have these layers switched in what order they are applied?

Thank in advance for the help![/QUOTE]

there will be moisture from condensation at the point were the air gets cold. In his ideal wall the cold point is the out side of the ridged foam. So the tyvek is between the foam and the osb to protect the osb from the condensation moisture on the foam. Any other order of application would result in moisture on the osb.
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Old 02-25-2013, 07:40 AM   #6
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Re: Building Science- Perfect Wall Questions


I think once the house is framed and sheathed the whole thing should be sprayed with Rhino Liner problem solved
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Old 02-25-2013, 07:52 AM   #7
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Re: Building Science- Perfect Wall Questions


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Originally Posted by Tom M View Post
Your example assumes your in the Northern climate. The plastic prevents the vapor from passing into the cavity because cold climate have more heating degree days that make moist air.
As an overall plan I would like a vapor retarder not a plastic barrier so if there is a moisture leak it isnt trapped.
Tom, I agree that's what I've been taught in the past...Vapor barrier goes on inside of wall in cold climate areas and on the outside in warm climate areas. Why is that not addressed in the article though? Based on the article you'd always have your vapor barrier on the outside of the wall, regardless of wall type. So which is correct or are there just different schools of thought?
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Old 02-25-2013, 08:22 AM   #8
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Re: Building Science- Perfect Wall Questions


down here in Texas we don't use a vapor barrier at all. Air barrier, but vapor permeable.
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Old 02-25-2013, 10:13 PM   #9
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Re: Building Science- Perfect Wall Questions


Yeah, I see that 'order' of layers in a lot of literature, but I think it is developed in a lab, not real world.

Separating vapour and air is lame. You stop one, you stop the other.

The control layer(s) is what gets under my skin...so, you install the control layer (air and water stop) under insulation on a roof/wall....so, how do stick on the insulation without piercing the control layer...or better yet, what about the cladding on a wall. Your going to make a hole, one way or another in the control layer, and I'd rather it be on the outside, so the dew point is in the insulation (make it thick enough)...if in XPS, then no moisture as it is closed cell. If UV rays is the problem, then make a control layer that withstand it.

Same goes for slab...I don't want moisture/air migrating into insulation...defeats purpose of insulation.

Lastly, I suspect the 'order' is more to do with off-gassing of the new wonder insulation...anytime you stick a concoction of chemicals in your wall or whatnot, you want an air barrier to protect the interior.
And that would be plastic...

Sorry, I am skeptical of regurgitation without seeing 'new' test results...btw - NRC did publish a great study on walls...have the link somewhere...
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Old 02-26-2013, 07:48 AM   #10
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Re: Building Science- Perfect Wall Questions


I went to a contractor training with the city last Thursday and the presenter was saying closed cell spray foam applied directly to the underside of the roof decking is now starting to fail because the osb is rotting from the condensation that accumulates and can not escape. I know a guy who spray foamed the underside and used ice and snow on the entire roof deck surface. I hate to imagine what that osb looks like.
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Old 02-26-2013, 11:52 AM   #11
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Re: Building Science- Perfect Wall Questions


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I went to a contractor training with the city last Thursday and the presenter was saying closed cell spray foam applied directly to the underside of the roof decking is now starting to fail because the osb is rotting from the condensation that accumulates and can not escape. I know a guy who spray foamed the underside and used ice and snow on the entire roof deck surface. I hate to imagine what that osb looks like.
The question would be where the moisture came from? Entry from top or bottom?
I would loathe to spray foam because one tiny hole can spell disaster (from top or bottom). Plumbing, electrical holes are prime entry points.
Wall, floor, roof assemblies should be designed with failure in mind, that is, there should be a way for the assembly to dry out, and having a barrier up against wood is asking for it.

I was asked to build a deck on a roof assembly that was a torch on on top, and spray foam underneath. Height above roof deck was an issue...only 1-1/2" to work with (undulating deck with 1/2" min sleeper at spots) and they wanted hidden fasteners. Thank god I turned it down. One little mistake with a screw and it would be all over. Even the Architect/builder turned down the job...
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Old 02-26-2013, 01:50 PM   #12
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Re: Building Science- Perfect Wall Questions


I'm in a cold climate, and I see three major problems on structures that cause wetness / rot:

1) improperly detailed exterior penetrations (windows, doors, etc)
2) Vapor barrier use on the inside, without making the structure airtight on the inside (again, penetrations)
3) roof leaks, or interior moisture sources (like bathrooms) or other maintenance issues. These vapor barrier systems work if you don't have a leak of any kind and no excessive source of inadequately vented interior moisture.

As to the ideal wall, keeping everything on the outside, no insulation in the walls, and having having some king of humidity control in the structure would be my ideal.

Last edited by hdavis; 02-26-2013 at 01:53 PM.
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Old 03-02-2013, 08:22 PM   #13
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Re: Building Science- Perfect Wall Questions


[QUOTE=tenon0774;1715128]You had to pull something done by:

Mr. Lstiburek.

This is a very complex question and has to do with many "layers" of the house.

I referred to an article he wrote on "two way" or "re-breathing" roofing underlayment, for certain roofing application we were doing with a "different" substrate. I got a lot of useful information, but it also raised a few questions for me that I don't think (In my opinion,) have universal answers for.

I will be interested to see some responses, and if none arise, I am willing to contribute, what I believe to be true.






I do not know how much stock i would place in the view points of Joe Lstiburek and his gang. He has written many articles in both FINE H.B. and JLC. I have been a subscriber to both publications since their inception. Having said that,Joe appears to be a bit of a chameleon,at first,he was all gung ho for wood everything,now his "perfect wall " is a huge flip flop. Several short years ago,he ran an article in FHB admitting to the problems in his own office complex.


These are just some of the issues that give me pause,aside from the fact he is arrogant and likes to present himself as the self proclaimed guru.
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Old 03-02-2013, 09:05 PM   #14
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Re: Building Science- Perfect Wall Questions


Shoot I am surprised I only just saw this one - so first in answer to the OP

First off please repeat after me - TYVEK is NOT an air barrier (it can be one but the detailing required is hardly ever done & can result in other issues)

Plastic is finally going bye-bye in the 2015 code (mainly due to Joe L & crew) as the premise behind it was flawed (diffusion). You are correct condensation can form on it & it would not be able to dry out inwards but as hot moves to cold the bulk of the drying does happens the other way.

Vinyl wall papers & other similar coatings also can cause the same issues, but this is generally an issue for those of us who live down south - the biggest way to avoid moisture issues in the wall is by blocking the flow of air, especially when using FG products - also see hdavis's answer

As for the final, where do I install my layers - the Tyvek should be integrated into the flashing of the window - so if you have the window outboard of the foam then that is where the Tyvek should be. If you have an inboard or recessed window the Tyvek should be under the foam board. For more - To Tyvek or not to Tyvek (a look at WRB)

As for Closed Cell & the roofs - yeah I am not buying that (let me guess the presenter only installs open cell). With that and assuming it is factual you are either looking at installer error or not spraying enough on. Depending on the location you need anywhere from 3 to 8 inches to eliminate condensation issues.

I&W & CC mix - I see no issues with that unless water is getting into that area which means something got damaged or someone screwed up on installing it.
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Old 03-02-2013, 09:52 PM   #15
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Re: Building Science- Perfect Wall Questions


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As for Closed Cell & the roofs - yeah I am not buying that (let me guess the presenter only installs open cell). With that and assuming it is factual you are either looking at installer error or not spraying enough on. Depending on the location you need anywhere from 3 to 8 inches to eliminate condensation issues.

I&W & CC mix - I see no issues with that unless water is getting into that area which means something got damaged or someone screwed up on installing it.
That's the big problem with any correctly designed system. Damage, poor install, poor detailing, poor maintenance, and for some cases you'll never see the resulting moisture problem until it's too late (without specialized equipment).
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Old 03-02-2013, 10:09 PM   #16
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Re: Building Science- Perfect Wall Questions


Quote:
Originally Posted by Friend View Post
I went to a contractor training with the city last Thursday and the presenter was saying closed cell spray foam applied directly to the underside of the roof decking is now starting to fail because the osb is rotting from the condensation that accumulates and can not escape. I know a guy who spray foamed the underside and used ice and snow on the entire roof deck surface. I hate to imagine what that osb looks like.
Cold OSB Syndrome?
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Old 03-02-2013, 10:31 PM   #17
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Re: Building Science- Perfect Wall Questions


[QUOTE=fjn;1719850]
Quote:
Originally Posted by tenon0774 View Post
You had to pull something done by:

Mr. Lstiburek.

This is a very complex question and has to do with many "layers" of the house.

I referred to an article he wrote on "two way" or "re-breathing" roofing underlayment, for certain roofing application we were doing with a "different" substrate. I got a lot of useful information, but it also raised a few questions for me that I don't think (In my opinion,) have universal answers for.

I will be interested to see some responses, and if none arise, I am willing to contribute, what I believe to be true.






I do not know how much stock i would place in the view points of Joe Lstiburek and his gang. He has written many articles in both FINE H.B. and JLC. I have been a subscriber to both publications since their inception. Having said that,Joe appears to be a bit of a chameleon,at first,he was all gung ho for wood everything,now his "perfect wall " is a huge flip flop. Several short years ago,he ran an article in FHB admitting to the problems in his own office complex.


These are just some of the issues that give me pause,aside from the fact he is arrogant and likes to present himself as the self proclaimed guru.
Not to defend Joe Lstriburek but it is Building "Science'and it is a work in progress.

Knowledge in science is gained by a gradual synthesis of information from different experiments, by various researchers, across different domains of science; it is more like a climb than a leap.

This is relatively new way to look at buildings brought on by the increasing price of energy.
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Old 03-02-2013, 11:20 PM   #18
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Re: Building Science- Perfect Wall Questions


[QUOTE=bconley;1719944]
Quote:
Originally Posted by fjn View Post

Not to defend Joe Lstriburek but it is Building "Science'and it is a work in progress.

Knowledge in science is gained by a gradual synthesis of information from different experiments, by various researchers, across different domains of science; it is more like a climb than a leap.

This is relatively new way to look at buildings brought on by the increasing price of energy.
Building USED to be purely experimental (for hundreds of years). Moisture control in traditional balloon framed structures was understood and documented, as was moisture control in chicken coups (huge moisture source in chicken coops).

Balloon frames allow air to travel from the basement through the walls and ceilings and out through the attic. Very tolerant to moisture sources on the inside or coming from the outside of the building. If a wall was known to be in an area that would be very moist, they'd strap the wall before plastering to increase airflow through the wall. Penetrations were not well air sealed, so these areas (which tend to get wet) had pretty good drying ability. From an engineering point of view, this all ran off the stack effect, so sometimes you'd have more airflow than needed and less than needed at other times. They used better wood, were basically forgiving of moisture, and tended to have netter craftsmanship than seen today.

For current building, the science has been there for some time, and the modeling capability was put in place in the 1990s. It's just a long way from the nice models to a practical building in all it's details and all the materials and craftsmanship to make it actually work.
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Old 03-03-2013, 12:28 AM   #19
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Re: Building Science- Perfect Wall Questions


/\/\/\
Yes exactly, but those houses were cold and drafty so you would have to stoke the fire or crank up the furnace for them to be comfortable.

The increased cost of energy has forced us to insulate and air seal to conserve those oh so precious energy sources.

So being human beings we tinkered with the design to try to improve upon it.

The results of these "improvements" has lead to the building ailments that building science is working to understand.

So it is still an evolving science and body of knowledge, and there will surely be many new vanguards to come.
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Old 03-03-2013, 11:52 AM   #20
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Re: Building Science- Perfect Wall Questions


Hey guys,i can appreciate that building science is an on going field. I do not have a problem with that. The part that gives me pause is if we "try" one of these cutting edge ideas out on a customer's house and it comes back to bite them. We have egg on our faces in the best case scenario,it could get real ugly from there.


That is the point i was making,i do not want to be his labatory.

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