They aren’t “airtight”, that would awful. They are well-insulated and designed to take advantage of passive solar heating and air exchange cooling. The way roofs and windows and orientation on the land is usually done for western homes is just terribly inefficient for capturing and releasing heat in the right ways. Just some thick walls, a bank of windows facing the sunrise ,and some proper roof vents that can be opened when it’s hot is all most passive houses really are.
Pfft you’ll never get accepted into journalism school with that attitude
They literally need to meet airtightness requirements to meet the Passive House standard. It’s tested with a blower door test to check the air exchange rate at a prescribed negative pressure. You may be referring to a loose definition of passive house, instead of the standard, though. Airtightness is not “awful” as you suggested - mechanical ventilation provides fresh air
Yes, they certainly have to meet requirements for air exchange. And if you define “airtightness” as that, then yes, the ones that met that definition met that definition. What they are not is the common definition of airtightness, as in a sealed glass jar, steel can, scuba tank, or submarine, which if you look at the comments here was what was confusing a lot of people. I don’t think anyone was contending that there aren’t tests that these houses have to pass, just that the word airtightness, as understood by laypeople, isn’t an accurate term to describe these homes.
I’d bet money that won’t work well here in the southwest USA where it’s been above 110F (43C) for almost 60 days in a row and above 115F (46C) for almost 30 days in a row.
Where in the southwest? I looked at Phoenix for a quick comparison – highs from 108F to 111F for the past week…but lows ranged from 82F to 93F.
What actually comes to mind is Pueblo houses. Isn’t this passive house just an expansion on that concept?
To people who says “they aren’t airtight” are not correct. Living in a country where building houses like this is the norm I can say that they are build to be as airtight as possible to keep in humidity and thereby heat inside. What makes them livable and not a humid moldy plastic bag is a well tuned mechanical ventilation system with a heat regeneration system (air cross flow system, really simple actually) that recovers most of the heat. The ventilation system runs 24/7 and keep the air fresh, more fresh than most conventional houses in fact if it’s tuned correctly that is. But yes the house is as airtight as posible and they pressure test them to ensure they meet the standards. The biggest issue with it is actually cooling them. We have issues here in summer because no method of removing heat is properly implemented yet. But in winter it’s awesome. My heating bill is practically 0.
I moved into one of these buildings about 1.5 years ago and it’s indeed awesome. We also have no gas and tons of solar panels on the roof so last year with the insane energy prices in the whole of Europe I spend €2,83 for all my energy including heating for 8 months, and I’m easily cold so I always have the heating on. The only problem is as you say to get rid of heat in summer, but they opted for smaller windows than is standard so less heat is getting in in the first place. And because of the great insulation you also have pretty much no traffic noise from outside. The only complaint I have is that the mechanical ventilation can get quite loud when it’s windy outside, but the benefits are so overwhelming I can’t be that bothered by it.
So from the article it seems that when the passive air vents are closed the total flow of air is supposed to be less than 10m³/hm². The air flow that occurs during the test is from cracks and leaks in the fixtures and doors. Calling it airtight might be confusing since people assume that would mean zero net flow.
I can see that might being confusing if you are not used to it, but houses are build to be “as airtight as practically posible” of course you could never bild a normal hous as airtight as a spaceship, but if you look at windows doors etc of a passive house you’d see rubber gaskets and seals everywhere. New tech keeps coming up. All houses since early 2000 here are required to have an inner airtight membrane and there are strict requirements about how to apply it. All seams, corners and nail holes etc. must be taped with special membrane tape. In theory the only holes in the house should be the ventilation system. I’m my current apartment even the kitchen hood is connected to the ventilation system so when it runs and an even amount of air is being exhausted and injected back into the house to avoid any pressure differential, minimizing leaks from the inevitable tiny leaks here and there. Airtight is the goal and we are damn close. Many houses are also better than the standards to account for small leaks over time.
Genuine question: if they’re airtight, how do oxygen and CO2 levels remain livable? Spacecraft and submersibles require oxygen supply and CO2 scrubbers to keep occupants alive.
how do oxygen and CO2 levels remain livable?
The ventilation system was explained.
I suppose what trips me up is that my brain sees the concepts of “airtight” and “ventilated” to be in conflict and I am seeking further clarification than what has already been provided.
The idea is that air exchange mostly happens through a heat exchanger, so the air leaving the house warms up the air that is entering the house, for this to actually work all other parts of the place need to be airtight, because otherwise your heat escapes.
I guess this is just a looser interpretation of “airtight” than what I’ve previously experienced in life. In my experience, “airtight” means “zero exchange of air in or out”, but this setup is a controlled process where the only place air exchange occurs is through the heat exchanger. However, from these descriptions, it’s not the same sort of “airtight” as what I’m accustomed to. Not trying to say that anyone is incorrect, just that it’s different from what’s familiar to me and that’s why I was confused.
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At least In NL, what you can do for cooling is to have cold water run through your in-floor heating. Brings things down to about 2-3C under ambient, so not perfect by any means, but a lot more pleasant than without it.
Unfortunately it’s considered an optional upgrade that you can only really get when buying a newly built home and most people skip it in favour of things like a fancier kitchen.
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Airtight isn’t really the best way to describe it. Rather it’s controlled air exchange, this way instead of 1000 tiny leaks all over you have a central controlled means to exchange air.
Passive home typically have ERVs or HRVs (Energy/Heat Recovery Ventilators) to achieve this, they can control the heat/humidity in the air.
Has to be some kind of air exchanger
Sounds more dangerous than it’s worth.
Considering the number of people who have lived safely like this for years, and that some places (Massachusetts, USA) require it for apartment buildings/multi family units, makes me think it’s pretty well understood
Reading through the article suggests that they aren’t completely airtight, rather that the air comes in and out through mostly only through specific paths, with some sort of system that exchanges the heat with air leaving the house, so that the heat (or lack of heat if keeping the building cold) does not leak out much when the air circulates through.
Here is a schematic I found on the Swedish version of this article: https://upload.wikimedia.org/wikipedia/commons/0/00/Passive_House_scheme_1_multilingual.svg
I suspect not all passive houses are built in this except way though.
The WSJ article has a diagram explaining the air stuff
Do the windows not open? Sounds like a good candidate for “sick building syndrome”.
Most passive houses I’ve seen have windows that open, but they are typically double/triple glazed (depending on climate) and are casement style instead of the more typical (and inefficient) double hung. They also typically feature a ventilation system to manage air movement precisely to prevent the issues you’re concerned about.
According to the article the windows do open.
And of course they do. The building is designed to be well insulated, not to make you comfortable.
If the owner wants to let air in or out, of course they should be allowed to do that.
You never know. A lot of modern buildings (at least in the US) do not have windows that open. It’s a pet peeve of mine. Modern public school buildings are particularly poorly designed in this regard.
I live and own a passive house: Feel free to ask questions :)
Can you address any of the intuitive concerns around the air freshness and getting enough O2 and removing enough CO2 ?
How much is the air exchange process a complex active process that you need to monitor and maintain, or is it pretty basic and “just works”?
I would say “Pretty basic just works” it was adjusted during construction of the house and as long as you don’t do any fundamental changes to ventilation system there is no need to readjust.
Do you find yourself having to think about “optimal use” of the house? Or can you just live your life as you would have prior to ownership and reap the benefits of the engineering?
Most of the time I don’t think about it at all. There is have a central ventilation system with a heat exchanger. So I don’t even have to think about opening the windows for fresh air.
Does being airtight mean it’s significantly easier to keep out pests (rodents, insects)?
Ever since I’d first heard of airtight houses (and figured I’d fit nets on all the windows) my arachnophobic ass has been fantasising about a spider-free house…In the ventilation system there is filter for the incoming air and I always find some insect in them but they can’t get through. I the only way for insects to get in is through the front door, for the garden door I have a net.
Thanks for the answer, just makes me want an airtight house even more!
Shame I could never even afford a draughty old dump, let alone anything nice, but a girl can dream lol
As a firefighter, Airtight sounds like a bomb if there’s ever a fire.
If there is a fire in in a air tight room and you close the door and stop the ventilation, wouldn’t the fire die out because of the lack of oxygen?
In an airtight room when there is a fire it consumes the oxygen and becomes ventilation controlled the room gets hotter and hotter and the combustible solids in the room continue to pyrolyze into flammable gasses but can’t burn because there is no oxygen. Then a firefighter opens the door…
There’s actually a vacuum in the room, it sucks fresh air in and all those flammable gasses and smoke ignite and explode.
It’s called a backdraft. It only happens when there is a tightly sealed home/room.
Depending on how air tight it is, couldn’t it make the room explode due to the increased pressure from the hot gasses expanding?
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Just wait until you learn about active houses.
My house was built like that. There is an air intake in the basement and there are ventilation fans that always run on low in bathrooms on the 1st and second floors. They pick up speed when the light is turned on.
I recommend the Livable Low-carbon City podcast for information about building techniques like that.
