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Myth: A House Needs to Breathe

 

Have you heard that one before, that you shouldn't seal up your house too tightly because a house needs to breathe? It's a common myth, but that's all it is - a myth. Houses do NOT need to breathe. People do.

I think the origin of this one may lie in the supertight, superinsulated houses of the 1970s, when they hadn't yet figured out how to look at the house as a system. They sealed up the houses to eliminate all the energy wasted on infiltration, but they forgot one key detail. Tight houses need mechanical ventilation.

A house cannot be too tight in my opinion. Yes, a tight house can have problems, but it's generally not because of the air sealing. The problem is the lack of systems thinking. Here are the three main problems that sometimes occur with tight houses:

  • Poor indoor air quality (IAQ)
  • Backdrafting of combustion appliances
  • High humidity, mold growth 

The solution to the first of these problems is mechanical ventilation. We understand this now. Random leaks don't bring in fresh air, so we seal up the house as tight as possible and then intentionally bring in air from a location where we know it will be as fresh as possible (i.e., not off the roof or over the garage). 

Backdrafting combustion appliances can be dangerous. When air is coming down the flue pipe and into the house, the exhaust gases aren't going up the flue pipe. That changes the combustion process, making it more likely to generate carbon monoxide and dumpatmospheric combustion water heater it into the house. Not good.

Atmospheric combustion appliances, like the gas water shown here, use air from the space around them for combustion. The solution here is to isolate them from the living space and give them their own air supply for combustion air. Building codes now require "high-low" vents for combustion air. This isn't for ventilation; it's air for the water heater or furnace to use in combustion, so the room where these combustion appliances are should be air sealed and insulated to isolate it from the living space.

The third problem, humidity, is often solved by proper sizing of the cooling system, a good ventilation system, and materials that don't trap moisture.  An oversized air conditioner doesn't have long enough run times to dehumidify very well. A ventilation system will remove internally generated moisture before it becomes a problem. 

The need for materials that don't trap moisture is true for many houses. Unless you're in a one-way climate, like Minneapolis or Miami, putting plastic in your walls will trap moisture and grow things. Houses don't need to breathe, but they do need to be able to dry out when they get wet.

Here, then, are three rules that we could substitute for this myth about houses needing to breathe:

  • People need to breathe.
  • Don't mix combustion air and people air.
  • Houses need to be able to dry out.

Comments

You're full of it pal - you contadict yourself three times in the first few paragraphs. Misinformation (Like Yours) Hurts people.
Posted @ Tuesday, April 17, 2012 3:02 PM by Jon Davis
Jon D. Thanks for your comment, Jon. Unfortunately, you've said nothing of use here. If I have indeed contradicted myself three times, as you claim, what are those contradictions? If this is indeed misinformation, as you claim, how is that true?  
 
Please tell me, sir. I'd like a chance to respond because I don't think you really have anything substantial.
Posted @ Tuesday, April 17, 2012 3:13 PM by Allison Bailes
I just love it when a commentator lambasts the author but offers no substance to his bombast. Allison clearly gave three components that are to this day still wide open to be debunked by Mr. Davis or anyone else. 
 
I for one find nothing wrong with his three points, but let's look at them anyway: 
 
* People need to breathe - yep. Hard to debunk that one, unless you prefer death to breathing. 
 
* Don't mix combustion air and people air - sure, if you're not fond of breathing in byproducts of combustion, such as carbon monoxide, that's a really good idea. 
 
* Houses need to be able to dry out - nothing wrong with this statement. Elevated interior humidity levels, because people occupying the interior of a house, whether or not it is airtight, create moisture (along with refrigerators, bathrooms, kitchens, and laundry equipment). Leaky houses don't suffer from high indoor humidity levels due to lack of ventilation. Tight homes do. Not only does a house need controlled ventilation and humidity control, doing so also assures wall cavities can dry to the interior in humid summer climates. 
 
Any misinformation in the above? Feel free to point it out, and counter with rational arguments.
Posted @ Sunday, November 04, 2012 3:24 PM by Cameron Taylor
Hi 
I live in a 400 year old house in France. I am from New Zealand and want to spray silicon onto the exposed external stone walls to seal them to stop the moisture getting in. My wife is English and maintains that the walls need to breath. Now I am to slow so I stood and watched the walls but nothing moved. Even after a couple of beers still nothing. So my question is silicon spray or not? 
 
Regards
Posted @ Monday, April 14, 2014 7:26 AM by william
That silicon spray sounds like a bad idea. Aren't you sealing the moisture in? 
Posted @ Sunday, June 08, 2014 2:56 AM by mindbird
Νοt sure what a super tight house is, but from personal experience a house that can open up and allows for an air draft to get through, is in no need for any electronic device (ceiling fan, air-conditioning etc) . Of course location plays a role here as well as the house's orientation, still it is the best way
Posted @ Monday, June 23, 2014 7:19 AM by xrx
william: If you treat the exterior of the stone walls, you not only stop water from getting in, you also stopping it from getting out, thus cutting off a drying channel. Unless you're absolutely certain that no water gets into the walls from the ground, the roof, or from indoors, you're best not doing it. 
 
mindbird: Yep. 
 
xrx: Location not only plays a role, it's the determining factor. If you live in a mild, Mediterranean type climate, that's fine. If you live in a cold climate or a hot climate or a humid climate, leaving the house open will be a problem. How're you going to like that draft when it's -20° C (-4° F) outside? 
 
Posted @ Monday, June 23, 2014 9:48 AM by Allison Bailes
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