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How tight can a home be built?


Scottpat
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It has been years since I have seen a builder installing plastic sheeting over the inteior stud walls of a home. Paper faced insulation has been installed with the paper facing the exterior. The home has OSB substrate that is covered with Tyvek and then brick veneer.

Does anyone have a cite or site that would confirm that it is not good building practice to place plastic over the studs like this?

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Keep in mind that there should be two layers of vapor type retarder behind the brick veneer. I feel that the best practice for allowing vapor diffusion through the brick is installing a impermeable type of membrane such as dri-core (a continuous plastic membrane with dimples on the back side to promote drainage)

Matt

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When moisture is absorbed into the brick veneer and the sun or heat of the day heats the veneer the vapor pressure increases. Therefore heat goes to cold and wet goes to dry and a vapor retarder only slows the progression it just makes sense to install a material that will allow the wall / brick area to wick the moisture away.

Thanks,

Matt

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When moisture is absorbed into the brick veneer and the sun or heat of the day heats the veneer the vapor pressure increases. Therefore heat goes to cold and wet goes to dry and a vapor retarder only slows the progression it just makes sense to install a material that will allow the wall / brick area to wick the moisture away.

Thanks,

Matt

Well, what I was going for is, why two layers? And why do you say vapor retarder? It should be a vapor barrier/moisture resistant barrier.

There has to be a moisture barrier under brick veneer, detailed into the through wall flashing. There's nothing about two layers, or dimpled layers. That same material is not what causes moisture to wick away. The through wall flashing, if properly installed, will divert water back to the exterior.

Point being, you have the physics correct, but your material description isn't.

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Marc and Matto are both right. Dr. Paul Fisette at U of M Amherst has done a lot of research on solar drive and it's affects on various building material.

Matto,

You said two layers of a "vapor type retarder." I think you meant to say that there should be two layers of WRB - 60 minute paper.

ONE TEAM - ONE FIGHT!!!

Mike

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When did the two layer recommendation come out? It's the first I've heard of it.

Capillary action can be substantially, and in some cases almost completely, negated with the right mortar mix, i.e., high lime mortars.

Does any of Fisette's research address lime content?

Question being, there are local folks, and Dave Parette England, who are doing research that tends to refute or counter some of the current research in the US, and most of this new information is pointing at lime content and mortar additives as the means for controlling moisture, not two layers of WRB, dimpled layers, or other membranes to handle volumes of water.

Yes, you need a WRB, but real moisture control comes from mortar content and mortar-brick compatibility. Yes, these things are not addressed by anyone famous. Yes, they are obscure and not well understood by anyone outside of a few mortar and masonry bugs.

I'm restoring the front of my bungalow right now with high lime mortars, and until folks start using this stuff and see how it works, all the current research that folks are doing is interesting, but not necessarily correct. Not necessarily correct, and in some cases, completely off the mark.

How did all that brick last for so many centuries without 2 layers of WRB? I'm wondering if anyone thinks about that........

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Marc and Matto are both right. Dr. Paul Fisette at U of M Amherst has done a lot of research on solar drive and it's affects on various building material.

Matto,

You said two layers of a "vapor type retarder." I think you meant to say that there should be two layers of WRB - 60 minute paper.

ONE TEAM - ONE FIGHT!!!

Mike

I was thinking of two layers of 15lb builders felt WRB.

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True. I misspoke. Water in brick around here means brick that's falling apart from freeze/thaw, i.e., if water's getting all the way to the interior, something is very wrong in the first place.

The two layer thing was also miscommunicated; I've always recommended double lapped 30# felts, so that's two layers. My mistake. The way Matto described it, it sounded like 2 layers of Tyvek, or a dimpled drainage plane material.

Other factors greatly effecting the mix is cavity size. I'm finding that none of this stuff matters at all if the masons aren't striking the rear of the brick; most of them let the mortar drop down into the cavity, meaning there's now a fully grouted wall and it doesn't matter how many layers of moisture barrier or drainage weeps you install.

And no, not all masonry is porous; some high fire bricks don't absorb water, and some super hard mortars with additives don't either, so this stuff gets confused with various folklores about masonry always soaking up water.

What happens now is a homeowner chooses a brick dependent on whim and aesthetics, and the mason uses the same mortar mix (type n bag mix) regardless of brick composition. When I'm dead and gone, and the world has figured out all the things that need figuring out, they'll have figured out that high lime mortars, and intense study of mortar-brick compatibility, is necessary before any new masonry gets built.

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Well, OK.....at some point, everything has some porosity and absorbency, even Pre-Cambrian Shield granite. I was overstating it.

There are glazed bricks, and other high temperature fired bricks, that I've tested by soaking in a bucket of water for a year, with no measurable or apparent moisture absorption. That doesn't mean they don't soak up some water.

Then there's mortar. I've found wildly varying amounts of absorbency in mortars, ranging from hardly any to the stuff soaking up water like a sponge. There's all sorts of variables that effect absorbency, not the least of which is lime content.

Where the real absorbency occurs is in the micro-capillary pathways between the brick and mortar; water can suck through those joints like crazy. This isn't based on any scientific or laboratory analysis; it's based on my looking at thousands of masonry buildings.

The current industry is looking for the holy grail for water control, when all the while the material they're looking for was already in mortar, and now largely taken out, and that's lime.

Anyone ever handled any lime putty, or mixed up their own high lime mixtures, knows what I mean; the stuff feels like plastic putty (sort of), it's sticky, and it holds in joints like glue with very little, if any, micro-crazing and cracking that effects most mortars. What little cracking does occur gets "repaired" because of the autogenous healing characteristics of lime putty mortar.

Don't expect this to show up on the HI test exams..........

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Kurt is right, every time it rains, lime mortar heals itself. The only maintenance is about every hundred years it needs re-pointed, because it wears away.

I also think that detailing is of utmost importance when building a brick veneer wall, "Rust Resistant Ties, Cavity Spacing, and Through Wall Flashing", none of which I have ever seen (other then in books) in my area of Ohio.

Down the line someone else will pay the price for our current (lack of) building practices.

Ezra Malernee

Canton, Ohio

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