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Recently I heard another comment from a builder who wants to build a house that breathes. I started to reply in an e-mail, and then decided to write a blog instead.
What we are doing nowadays in the world of high-performance homes is based on studying hundreds of thousands of houses built in the last half century that have failed — including the majority of superinsulated and passive solar homes built in the 1970s and 1980s in the Northeast — and applying those lessons to building a durable house.
Houses from before that time period that failed for one reason or another are mostly gone, and many of those that remain are piggy banks for big oil. We put our money in and the oil companies take it out. Simple. (Usually, I like simple, but not in this case.)
For the past few decades, most builders in the Northeast have been living in a vacuum, while builders in northern European and Canada paid much more attention to how houses fail, learning from them and adapting. Now the conversation is opening up again, and we are taking a seat at the table.
A house has to breathe? Really?
I have lived in houses that breathe my whole life. It sucks.
Aside from the part where you have to give your money to someone else just to prevent freezing to death in the winter, there is the comfort aspect of things. Houses I have lived in have never been all that comfortable, whether in terms of temperature or moisture levels or even wiping mildew off the window sills.
Now, with two children, I worry about the air quality and mold issues inherent in my “house that breathes.” I would rather be able to seal up the house in the winter and be confident that I was breathing fresh Vermont air all the time than have to step outside for a breath of fresh air or open up the doors and windows if I screw up on getting the wood stove going.
Six months out of the year, I would still have the choice to open the windows and turn off the HRV.
We do seem to have more summer moisture and humidity problems than we used to, but we also have access to more durable and proven materials and building methods. Some builders and architects are taking advantage of this, but most are building the same way they did 20 years ago, despite all the failures.
A house that breathes and has little or no insulation is a barn. And If you want to heat it, that means coming to terms with giving your money away. Jesse Thompson says, “People breathe air through their lungs, not their skin. Why should houses be any different?” If you want your house to breathe, give it a set of lungs — in other words, provide it with a mechanical ventilation system.
There are a range of options for doing this, from exhaust-only bathroom fans and range hoods (simple and cheap, but where does the makeup air come from in a very tight house?) to a full-on heat-recovery ventilation (HRV) system. These are also fairly simple and effective, although significantly more expensive. But they have the added advantages of recovering much of the heat from the outgoing air as well as providing fresh incoming air exactly where you want it. For more information, just type “HRV” or “house ventilation” into the search box on Green Building Advisor, and start reading.
Robert Swinburne is a part-time architect and full-time homemaker living on 49 acres with his wife and two young children in Halifax, Vermont. He was a carpenter for several years after architecture school and is now a licensed architect and passive house designer with over 100 completed projects in the Northeast. Bob maintains a blog (primarily for therapeutic reasons) under the moniker “Vermont Architect.”
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8 Comments
Open-Cell Foam
I recently completed a remodel that I completely spray-foamed with an open-cell product. I asked my insulator if an HRV system would be necessary afterwards. He claimed that this open-cell foam does allow the house to "breathe!"
Response to Matthew O'Leary
Matthew,
I've noticed that people who use the "walls have to breathe" vocabulary often confuse vapor permeability with air leaks -- one more reason why the analogy with respiration is misleading and confusing.
Articles like this completely miss the point
This basis for bashing the idea of "breathable" is typically based on this kind of concept: "People breathe air through their lungs, not their skin. Why should houses be different?"
I invite you to encapsulate every square inch of your skin with foam, or with 6 mil poly, or with any other kind of impermeable plastic. And then see how comfortable you feel. Assume that the foam doesn't interrupt your breathing through your lungs.
Skin is airtight, but vapor permeable. Skin "breathes". Most modern-day proponents of "breathable" are also seeking an airtight house, but one that "breathes" by virtue of some (carefully designed and placed) vapor permeability. They are not proposing to build a leaky barn that feeds big oil.
I wish writers of articles like this would actually entertain an intelligent discussion of permeability and the wisdom of building materials OTHER than foam or other totally impermeable plastics. Rather than perpetuating the notion that the best solution for building envelopes is the generous use of foam (from Big Oil, surprise, surprise).
At the very least, they should carefully define what it is they are bashing, by explaining exactly what they think "breathable" means.
It's not whether a building should "breathe" or should be tightly sealed. What you don't want to do is trap moisture in the walls. Houses that "breathe", while it mitigates moisture in the walls by allowing moisture to evaporate, it often comes at the cost of draftiness especially with historic buildings. If you start sealing up those old historic houses, you will start running into a problem, trapping moisture. That is moisture in the walls long enough to promote mold growth and wood rot (mold is a major contributor of wood rot). It's not just moisture, it is bio-chemical processes that mold (a fungi) excretes that breaks down wood fibers. One of those bioscience stuff. Now, sealing houses can also be bad if done wrong. Early on, we wrapped the outside really really tight but did things wrong. How? Well, forgot the moisture from the inside. Did fine blocking out rain but outside isn't the only source of moisture. You got sinks. You got the bathroom toilet. You got the showers (the biggest singular source of moisture getting into the walls (eg. diffusion for example), and not properly vented out. Then you have the stove where you may be boiling water for cooking a meal. Then you also have the people. We're what how much percent of our mass is water? It would be surprising if people didn't breath or exhale moisture.
So once you start wrapping, you need to mitigate moisture inside and out and Keep moisture from being trapped in the walls (that is excessively retained... ie. moisture not evaporating quickly enough and conditions ripe for mold growth). So now, you need to deal with ventilation... namely moisture ventilation. So while you want appropriate levels of permeability but you need to do this in good building science way, not half ass it. We aren't building a space ship but we need to manage moisture scientifically to do it properly. Proper ventilation... not just mechanical but passively. (such as the permeable). You can't, in a practical manner, seal up historic buildings like you do new construction. You can eliminate excessive draft yet also have permeable materials but sometimes, you can't exactly seal up some building materials because they allow moisture and you can see drywall damage due to moisture infiltration. Where I am, that happens so we have to manage moisture infiltration, evaporation. Sure, it be nice to have absolutely impermiable brick and concrete or wood. Doesn't exist. Here, we have to understand what is meant by "breathe". We want moisture to evaporate and we want as much as possible, dew point to be outside the walls not inside the walls. For human comfort, we do want to control excessive draft that causes discomfort.
I understand what you are getting at. Actually you don't want a building airtight unless you are building a space station. You want to manage air exchange rate. Draftiness is a situation where the conditions are caused by uncontrolled. You want air exchange cycles but you want to be in control of it. You don't want wind pushing through the seams creating concentrated jets of air like you get around doors that caused discomfort. This is also directly related to thermodynamic exchange. Hot air doesn't neccasarily juse rise. More accurately, it hot goes to cold, cold goes to hot. This is how wind is generated in the air. "Stuffy" is when there their is too little air movement and tends to be when people smell breath and body odors. This discomfort is not just the feel through the skin but also the sensory of smell. Now we are talking about ventilation of moisture and air. Refreshing the air with oxygen and cycling out carbon dioxide exhaled. Yes, you can make the building too tight if you don't addressed proper ventilation. This has to be done scientifically. A lot of builders simply should just build what competent design professionals designed and specified because they lack the fundamentals of science with only elementary school level of understanding because that forgot half of what they were taught before they were 13 years old and didn't bother learning throughout their schooling to retain the knowledge. The smart and educated professionals went on to learn more and advance their understanding. Some construction professionals do have that knowledge. However, the uneducated tend to not become architects because of the more rigor required and the exams that tests such knowledge while contractor licensing exam is a joke and a ridiculous attempt at assuring those who are licensed possesses the competency as a construction professional. Sad state of affairs in the U.S. but there is plenty of people who just don't know what they are talking about.
Response to Zenon Tymosko
Zenon,
You accuse Robert Swinburne of "missing the point" and advise him that he should "explain exactly what he thinks 'breathable' means."
I'm sorry, Zenon, but I think that you are missing Robert's point. His point is that "breathable" is not a technical term, and it means different things to different people -- which is why the word is meaningless and should never be used. That's why it drives Robert crazy to hear people say that "walls have to breathe."
Here at GBA, we try to use words that have agreed-upon meanings. If we are talking about vapor permeance, we say, "this material needs to have a high vapor permeance" rather than "this material needs to breathe." If we are talking about air leakage, we say, "this wall has a high rate of air leakage" rather than "this wall breathes."
If anyone doubts that people who talk about walls "breathing" are confused as to whether they are talking about vapor permeance or air leakage, just read Matthew O'Leary's anecdote, recounted in Comment #1.
Finally, you are correct that encapsulating a human being with plastic would kill the human being. But a house is not a human being, which is why the "breathing" analogy fails. A wall doesn't have to breathe. Occupants have to breathe -- so they need a well-designed mechanical ventilation system that brings in fresh outdoor air. A wall needs to be able to dry out in both directions from the layer with the lowest vapor permeability. That's it. The entire wall has no need to be vapor-permeable -- because the wall isn't alive.
Don't just bash it, explain it.
It wasn't me who insisted on the human analogy, it was Jesse Thompson and Robert Swinburne. Of course a wall isn't alive.
This article does absolutely nothing to help homeowners deal with people who use the word "breathable", like in the comment #1 about the open cell foam.
Instead, it makes fun of and ridicules the word "breathable". And by extension, it makes fun of and denigrates people who use the word. Which isn't helpful. It does nothing to enhance or further anyone's understanding of building science around vapor/gas permeability and/or the ability of an assembly to dry out and/or regulate humidity.
A much better article would explain what to do when one hears these words being used. Rather than suggesting that anyone who wants "breathable" components is asking to build a leaky barn.
The entire wall may have no "need" to be vapor/gas permeable, but perhaps it is a desirable characteristic. There are building materials and methods that have survived for centuries with low mold or other air quality risks. Like natural hydraulic lime plasters. Modern energy efficient design doesn't automatically have to mean the opposite of "breathable" or vapor/gas permeable. But this article would make readers run away from designers or contractors who use the word "breathable". Again, without offering any explanation or advancement of knowledge in this area. Except of course to suggest that one can mechanically ventilate.
Response to Zenon Tymosko
Zenon,
You ask of GBA, "Don't just bash it. Explain it."
Fortunately, we've been doing that for years. If you or any other GBA reader is interested in reading articles on vapor permeance and air leakage, I suggest the following articles:
Vapor Retarders and Vapor Barriers
Do I Need a Vapor Retarder?
GBA Product Guide: Vapor Retarders
Vapor Barriers Redux
Forget Vapor Diffusion — Stop the Air Leaks!
When Sunshine Drives Moisture Into Walls
Joseph Lstiburek: Air Barrier or Vapor Barrier?
I don't think that pointing out the problems with the word "breathable" amounts to denigration. GBA encourages builders and designers to learn more about building science, and we also encourage the entire construction community to use accurate vocabulary. I think it's fair to say that the effort is worth it, and there are signs of progress.
Fortunately, use of the word "breathable" is in decline -- and that is to be celebrated.
Don't think of it as an article.
My bog entry was originally written in reaction to yet another builder who railed against the idea of building a tight house. He actually did want air movement through the building envelope to keep the house from getting “stuffy” I suspect he even stuffs fiberglass around windows after installation. I am fairly certain that he has no idea what the difference between a vapor barrier and an air barrier is. “Vapor diffusion” is not in his vocabulary. As an architect I get to work with folks like this on a regular basis. I try to avoid getting technical in my own blogging, instead focusing on the issues I face as a rural New England architect. I leave the more technical aspects of what I do behind the scenes and recommend green Building Advisor as a great resource for anyone interested in building science. There is much information here for anyone interested in such things and I saw no need to cover the subject of "allowing a house to breathe" again. Unfortunately, a lot of people in the building industry are not interested.
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