Waterproof and breathability?

I get a little confused when reading about CEB, Cob, strawbale, etc when these two terms come up. On the one hand, these natural building materials are supposed to be allowed to breath....but on the other hand, they need to be treated so that they will be water proof/resistant and will be more enduring. How can both of these co-exist?

Hi Tom,

That is a fair observation that I am sure may confuse many folks. I think often this comes from the use of improper language used when some folks "try" to describe a process or method.

I am fine with the term "breathable" though many professionals in the building science trade take umbrage with the term...Often stating buildings don't have lungs. That may be true...but humans and animals occupy this space...and they do have lungs, which in turn could be looked at as the building also needed to and/or actually breathing. So for the peace of all readers I will say "highly or very permeable," which is the goal of most (all?) natural-traditional building modalities.

The concept of "air tight" architecture is probably, IMO, one of the worse steps taken in modern building...Breathable yes...Airtight...absolutely not a good concept. Water proof is another issue that is perhaps great in "concept" yet seldom if ever achievable, and it it is has repercussions and impacts to other building materials within the system that are very often poorly thought out..

So the goal should be highly repellent or resistant while still maintaining permeability. In the example of cobb this is why we use a earth plaster, lime or similar system instead of concretes, and other "proofing" materials.

Hope that sheds some light on this.

Regards,

j

I agree with Jay that these issues can be confusing and terminology can overlap. Iam sure it gets old to readers as we disagree over certain details but I dont feel good about myself without adding my opinions and what I hope is clarification.

Yes I think breathability is a terrible term for discussing wall or house properties. If you want to improve or replicate a construction detail there needs to be some amount of measurement going on. You cant measure breathability because it has no agreed upon meaning. Like Jay said, you probably meant "vapor permeability" which is the ability for a material to dry. I think this is a good thing for above grade walls but a bad thing for below grade walls/floors and usually the protective roof membrane as well. Permeability is typically measured in perms.

http://wncgreenblogcollective.wordpress.com/2013/11/04/should-we-eliminate-the-term-breathable-from-our-discussion-of-walls-and-buildings/

I feel Jay does a disservice to the community by constantly dismissing the importance of airtight construction. If you are using energy to heat or cool your home this is probably the most important detail you can consider. Insulation is practically meaningless without addressing airtightness first. The best thing about airtightness is that its easily measured. Its probably the easiest home performance metric available and has the biggest impact on the energy needed to heat and cool a space.

With an airtight envelope in place, its easier to control outdoor air introduction. Outdoor air is almost always healthier than indoor air. You dont want your building envelope and the weather conditions to dictate when, if or how much outdoor air is supplied and indoor air exhausted. Uncontrolled air leaks waste energy, increase probability of condensation/mold and can introduce dangerous sources of air like soil gases, combustion flue, and garages.

All homes whether leaky or tight benefit from controlled outdoor air supply and indoor air exhaust. Its probably the best way of making a beneficial, measurable impact to a home's indoor air quality. Permaculturists should be striving to save resources, especially the fuels needed for supplying energy to heat and cool our homes. This energy can represent the biggest portion of most folks environmental footprint. Airtightness is arguably the biggest performance factor impacting this energy use.

I will give a longer reply later...

Hi Brian...

I have a bag in front of me made of a house wrap material...

It does not have lungs...but is said to be permeable (what some call breathable.)

If I put that bag on my head and seal it...how long will I be able to breath?

Now lets all wrap our houses in it...

Really, Brian, again I remind you, this is a natural building forum and these modern "green concepts" out of the LEED and other industries pushing their wares and products is not going to fly here with great wind under its wings.

I am not really clear how many fully natural builds you have designed and done, but not to sound too challenging, you really have to know a system well to understand its challenges, and since I have been doing and observing these systems for almost 4 decades...I am pretty certain that these "modern" and "very new" concepts of wrapping houses in plastic and other industrial products until they are actually "air tight," is really not a good idea for the most part... When (and if) this style of architecture is done well, the level of technology dependence for these homes to work properly with there "air to air mechanical lungs" and other devices, puts them closer to being a "space ship" than a natural and sustainable building practice...

I appreciate your reply Jay but I dont think I mentioned LEED, plastic, housewrap or anything "un" natural. There is nothing un-natural of airtight construction. Plenty of people are achieving airtight construction with natural materials. Those projects use much less energy to heat and cool than projects ignoring the benefits of airtight construction and they have better indoor air quality than those ignoring outdoor air introduction.

...There is nothing unnatural of airtight construction. Plenty of people are achieving airtight construction with natural materials...

Folks are achieving "draft proof" architecture...not airtight. This is the huge distinction in the guidance we are sharing with folks. I will own I brought up the "house wrap," apologies for that.

j

Waterproof means the material can be submerged completely underwater for long periods of time, and there won’t be one single drop of water that enters the interior. Even concrete is not waterproof.

Now from what i gather so far anything that compromises breathability of cob will destroy it due to moisture accumulation.

The way to deal with it from what i read is to minimize the exposure to water trough good roof and foundation.

I've been wondering if putting some sort of breathable but water resistant (able to withstand prolonged exposure to water) siding (like wooden panels) would strengthen or weaken a cob wall. I mean if restricting the air movement on the outside of the cob wall would compromise moisture dissipation.

Tom Connolly wrote:I get a little confused when reading about CEB, Cob, strawbale, etc when these two terms come up. On the one hand, these natural building materials are supposed to be allowed to breath....but on the other hand, they need to be treated so that they will be water proof/resistant and will be more enduring. How can both of these co-exist?

When the above mentioned systems are plastered and rendered, they are airtight and draft proof. There is no reason to deviate from this with high tech methods but when it comes to stick framed homes, I must agree with Brian that it is very important not to have air blowing between floors and around knee walls. Even though these would not be drafts, they would severely impact thermal performance.
Breathable to me is how I would describe a wool sweater and vapor impermeable is like rain gear. I pretty much live in a wool sweater in the winter because it is warm and dry inside all the time. Vaporized moisture follows heat until it hits a vapor barrier, at which point it condenses and accumulates, which is why no one wears rain gear to ski in, even though it would be warm. So if water vapor from the interior enters a wall assembly in winter time, it will travel towards the outside of the house until stopped, then condense and accumulate.
Around here there is an epidemic of latex painted masonry. The paint is the vapor barrier, so moisture condenses inside the brick, freezes there and spalls the face of the brick, eventually causing the wall to fail.
Clay and lime both have interesting phase changes that occur with the addition of moisture. This allows the wall to be water resistant, but still completely vapor permeable. Like I said before, I see no reason to deviate from this.

Bill Bradbury wrote:
Breathable to me is how I would describe a wool sweater and vapor impermeable is like rain gear. I pretty much live in a wool sweater in the winter because it is warm and dry inside all the time. Vaporized moisture follows heat until it hits a vapor barrier, at which point it condenses and accumulates, which is why no one wears rain gear to ski in, even though it would be warm. So if water vapor from the interior enters a wall assembly in winter time, it will travel towards the outside of the house until stopped, then condense and accumulate.

I like how you illustrated it. Let me just add that waterproofing the surface of breathable material would be like skiing in rain gear over wool sweater. The end result would be not so pleasant for the nose.
When water encounters vapor barrier it stops moving and stagnates. And that would provide housing for un-beneficial energies which would be free to travel back inside through the breathable wall.
It can be seen as providing environment for anaerobic bacteria which being capable of extracting nutrients from the wall material would provide the foot in the door for more complex forms of life like mold for example.

Voy G. wrote:Waterproof means the material can be submerged completely underwater for long periods of time, and there won’t be one single drop of water that enters the interior. Even concrete is not waterproof.

This is a very succinct description of "air tight", and for all practical purposes is what is meant by "hermetic," which is exactly what many modern Architects and Designers are suggesting should be built as good practice. Many have even used the term hermetic in their discription of rendering a structure "airtight," yet still suggest the buildings are still breathable...which I have not found one yet to be such.

Bill Bradbury wrote:When the above mentioned systems are plastered and rendered, they are airtight and draft proof. There is no reason to deviate from this with high tech methods...

Sorry, these plasters and other natural builds do not render a "hermetic," finish or encapsulation and though could be construed as "air tight" they simply are not, nor should the be considered or designed as such...They are...very much "draft proof."

Bill Bradbury wrote:...it is very important not to have air blowing between floors and around knee walls. Even though these would not be drafts, they would severely impact thermal performance...

If air is "blowing" anywhere from outside the thermal envelope of the roof, wall floor diaphragms, be it from the "floors and around knee walls," let us be very clear...these would indeed be drafts...unless I missed the meaning.

Bill Bradbury wrote:Breathable to me is how I would describe a wool sweater and vapor impermeable is like rain gear. I pretty much live in a wool sweater in the winter because it is warm and dry inside all the time. Vaporized moisture follows heat until it hits a vapor barrier, at which point it condenses and accumulates, which is why no one wears rain gear to ski in, even though it would be warm. So if water vapor from the interior enters a wall assembly in winter time, it will travel towards the outside of the house until stopped, then condense and accumulate.

Wonderful analogy, and exactly the same one I have tried to use many times to illustrate exactly the same points about plastic paints, plastic house wraps and the related modern architectural elements that have become understood as a "mandate" of architecture, not just a created element of modernity in the current mainstream building treads; often without clear understanding of how they actually work, and a very short history of application.

Bill Bradbury wrote:Around here there is an epidemic of latex painted masonry. The paint is the vapor barrier, so moisture condenses inside the brick, freezes there and spalls the face of the brick, eventually causing the wall to fail. Clay and lime both have interesting phase changes that occur with the addition of moisture. This allows the wall to be water resistant, but still completely vapor permeable. Like I said before, I see no reason to deviate from this.

Bill, that epidemic of "plastics" and "over sealing" is in just about everything in construction is rampant around the globe in historic restoration work, and causing huge issues there and in modern construction as well. They absolutely do not belong in natural and traditional building systems.

Great post everyone...thanks...

j

I dont really think the clothing metaphors do it for me. Heres one of my own. As an avid whitewater kayaker, I have used many dry suits and drytops. The best performance in my experience are those that have goretex brand membranes, one of the highest perm rated fabrics that also keeps out the bulk water. Its amazing how you can do very physically demanding work in these suits only to unzip to find the insulation layers bone dry inside with no sweat accumulation whatsoever.

I know I must sound pretty "cocky" sometimes, and perhaps a bit too "done that" for some folks, but I can't help the life I live.

I have been guiding wilderness, rock climbing, caving, and tour kayaking for going on 4 decades. I have used every breathable cloth manufactured and routinely sleep inside a Gore-tex or related "breathable" fabric on a regular bases as I sleep outside year round. I sleep under an "8000 meter down parka" most nights her in Vermont just to stay warm and it too has a Gore-tex shell. There are different grades of Gore-tex and related fabrics, some more "breathable" than others. I have used seal skin, fish skin, seal gut and other "Native water gear," as well so have a good handle on the many systems.

Is Gore-tex and the related breathables better than the old "rubber suits?" No doubt.

Nevertheless, just like house wraps, 99.9% of the folks in them get soaked from their own sweat. I might get one student/client out of hundreds that just does not sweat like normal folks. They are anomalous and the exception...they are not the rule. I can, as most folks I have guided or worked with, just sit and do nothing with this material on and get much wetter than if I didn't have it on at all. Most of the Guides I know have a running joke that we wear Gore-tex and related because you only get slightly less wet than if you didn't have it on in the first place. In the past few decades we have really upped the game in material layering systems to the point that many (most?) gore-tex and related materials are always combined with a fleece or related micro fabric that facilitates an air layer between the gore-tex and the human skin, which also creates a "physical transport of moisture" away from the skin. This is very much like the "rain screen" effect in some regards, like we find in architecture. Hydor fleeces and other tech fabrics are also improving a great deal, yet I still don't find a huge difference between a silk layer, merino wool layer, heavy wool and maybe another wool or buckskin garment being much different. Frankly, very little different and I feels better as well.

So, whether ice climbing or caving, (probably the only to other supper soaking activities past white water) Gore-tex is going to render the "average" wearer very much damp at a minimum, if not down right soaked. This is not subjective...just the averages...and there are folks that just don't seem to generate, "the wet" like the rest of us.

As for architecture...again...most of this plastic, and "air tight" nonsense is not necessary to build a warm efficient and sustainable "natural" structure to live in.

With that written, if folks want to buy into all the "new age," "high tech," industrial laden wizardry of modern architecture...by all means, go for it...but please...don't suggest it has to be done this way or that there isn't traditional/natural alternatives that are just as good...there are...and some of us do it that way...

I dont think you sound cocky Jay and Iam sure many of us are envious of your life's experiences. If youre suggesting that Iam the 1 in a thousand I would say Iam more like one in a million! Talk about cocky..

Iam not the only one who gets excellent performance out of a drysuit made with goretex though and its not just a little better than a non-breathable fabric, its completely different. All my friends seem to have the same results and drysuits made with goretex enjoy the same reputation across the entire paddling industry.

As much as I dont like clothing analogies for our homes, this one seems pretty pertinent to our usual quibbles. Breathable housewraps have broad ranges of permeability, some of them are much more permeable than natural materials like wood and stone. Some researchers feel that some of the most permeable housewraps are TOO permeable in some situations.

There seem to be to questions posed here:

1) Should air be allowed to move freely through the wall?
2) Should moisture be allowed to move freely trough the wall?
3) Can moisture be allowed to move freely through the wall without allowing air to go trough?

Here's what i think so far:

1) No unless maintaining a temp difference between inside and outside is a concern.
2) Nobody seems to claim that moisture accumulation inside the structure or the wall would be a good idea.
3) The wall material needs to be porous In order to be able move moisture, some air is likely to follow. The air movement seems possible to manage through increase in wall thickness until it doesn't exceed what's required to maintain proper ventilation.

Haven't been paddling like I use to, yet will still do some cold weather swimming and a gore tex dry suit with microfleece I agree is awesome and much better than what we use to have...Everyone I know still gets very soggy in there own sweat...a few don't seem to as much as the rest.

As much as I don't like clothing analogies for our homes, this one seems pretty pertinent to our usual quibbles. Breathable housewraps have broad ranges of permeability, some of them are much more permeable than natural materials like wood and stone. Some researchers feel that some of the most permeable housewraps are TOO permeable in some situations.

Now the above is something I can make a point with...

Stone...most not all...are not permeable to any great degree at all. The lime and/or cobb mortars used with them are what is permeable. So, stone we will just leave out as not really applicable to this conversation.

Wood on the other hand is something worth looking at.

I would agree...make note of this folks...that 1 inch of wood is not as permeable in pore structure, and/or over time as many of the house warps present as being in laboratory conditions (the real world is where the rubber isn't meeting the road with these wraps.)

So...if wood is less permeable, how could it be a better material?

Well, like wool, and cobb, lime, cellulose and other materials it doesn't form a "condensing surface" and it has a huge capacity to take on "free water" while still presenting as dry. Then it does something else, as most of these natural materials do...it can effectively (and much better that plastic house wraps) transport both vapor and liquid water away from a living space and out to a drying surface such as the gap in a rains screen or cold roof designed venting system.

The real only point of most of my ramblings on this subject...and...the one I really try to get across to builders of both natural-traditional architecture, and those trying to move into more sustainable architecture is...

These wraps do not perform as intended...never have...and I fear...never will...in the real world and the way they are being used...

They do not offer as much as they claim and often contribute to interstitial issues that go unnoticed for decades...well after the damage to inner walls and insulation has taken place.

and most importantly!

They can be completely omitted on builds without ill effect if others design criteria is met (and should be on all natural and traditional builds.)

Simply put...you just don't need them to achieve a super insulated, thermally efficient structure, that will be both completely "draft proof," (think buck skin, and three layers of wool and/or down) and have no need of any more plastics being manufacture and later added to the waste stream...

I agree!

Voy Grabiec wrote:There seem to be to questions posed here:

1) Should air be allowed to move freely through the wall?
2) Should moisture be allowed to move freely trough the wall?
3) Can moisture be allowed to move freely through the wall without allowing air to go trough?

Here's what i think so far:

1) No unless maintaining a temp difference between inside and outside is a concern.
2) Nobody seems to claim that moisture accumulation inside the structure or the wall would be a good idea.
3) The wall material needs to be porous In order to be able move moisture, some air is likely to follow. The air movement seems possible to manage through increase in wall thickness until it doesn't exceed what's required to maintain proper ventilation.

Hello! I felt the need to chip in, bear in mind most of my thoughts are based on a large greenhouse attached to a house. All a mixture of cob, strawbale, timber framing, etc.
1) I believe one of the greatest benefits of cob is that air is able to pass through freely enough. As far as retaining a certain temperature, i feel that this is more relative to the thermal mass & banking properties. Permeability is a natural benefit of many natural earthen structures. Maintaining a good temperature through winter can be achieved using a number of thermal banking strategies (rocket thermal mass stoves, worm farm composting, attached chook-coop.). Of course you have to take care to ventilate and maintain a balanced internal ecosystem.
2) When coated with a lime render/plaster, from my understanding moisture naturally 'wicks away' out of the walls interior (through principles of osmosis).
3) Air and water molecules both vibrate at frequencies higher (or faster) than say; clay, sand or straw. This allows these elements to eventually move through these materials (as long as they aren't to dense, too much clay will cause cracks. Water always finds a way (; ). Due to this, the process of Osmosis will balance out areas of greater concentration (of whichever element) into areas of lesser concentration. So, it's best to have large overhangs and a foundation that keeps cob out of standing water. Otherwise, don't worry about the moisture, as one hot & dry day will surely dry out your walls thoroughly. This is the same principle in thermal dynamics which causes a thermally charged (hot) cob wall to radiate it's energy out into a room that is cooler than itself. If excessive moisture is truly a concern in your clime, I would suggest a de-humidifier indoors.

Tom Connolly wrote:I get a little confused when reading about CEB, Cob, strawbale, etc when these two terms come up. On the one hand, these natural building materials are supposed to be allowed to breath....but on the other hand, they need to be treated so that they will be water proof/resistant and will be more enduring. How can both of these co-exist?

Says who?
Where this stuff has been used for millennia, they either don't have much rain, or they keep it well away with overhangs and sloping ground. They often have a render (also cob) with straw, but that's it really. Even flat cob roofs (in good repair) can cope with occasional heavy rain; although they do need to be built with care to avoid pooling and damage at run off points.
More and more roofs were being coated with tar/pitch with no apparent ill effects, but not walls, and even if the cob did get, say, frost damaged around the interface, the disintegrated material can't go anywhere anyway, whereas on a wall it would slump.


Off topic, wow this is a touchy subject!

Hi Marion,

You are quite correct that in many climates, there is no need for external treatments to a clay surface, but earthen architecture is in some very wet climates as well. Then a breathable render that gets harder with wetting is not necessary, but definitely desirable.

I helped plaster a 350 year old church in New Mexico that had never had any render besides clay. The walls were about 10 feet thick at the bottom and maybe 6 at the top from all the times the building has been replastered(every 3-10 years), giving it a really cool look, but very labor intensive upkeep. My own adobe home in northern Utah is 120 years old with a lime render; it has only been re-plastered once.

Here's what clay plaster looks like after a bit of neglect.

That's a very informative pic, ty for posting.

It shows a number of not so good design points and the resulting effect on the walls. ops:

e.g. I had been wondering if the oft stated 2ft overhang was really enough, as I am used to much bigger overhangs.