Anyone have experience with Airtight homes?

[Kaido]

I've been reading up on stuff like SIP panel & ICF block construction. They give you excellent R-values for insulation & great durability, but they also pretty much require that you use an HRV/ERV mechanical ventilation system due to the airtight nature of the structure to handle fresh air intake, stale air exhaust, and humidity balance.

I'm curious about what happens in the event of a power outage, or if the fresh airflow system has an unmonitored fan failure. For example, in an extreme case, if the power goes out during a -13F day in winter and your generator runs out of fuel, you are now stuck in an airtight home with no method of getting fresh airflow other than opening a window to the cold outside air. I've been doing some reading on it, but there's no clear answer. Seems like kind of a horrible compromise to have to rely on a mechanical system so you don't die in your sleep, haha.

http://www.icfmag.com/articles/features/air_tight_home.html

http://icfmag.com/articles/features/air_exchangers2.html

My buddy installed a bunch of mini-split ductless HVAC systems - Mitsubishi Mr. Slims - which I think are amazing, but I don't know if those could be the only units running in an airtight house, especially if you're not running them 24/7 (each room has an individual Mr. Slim unit, so you just wouldn't turn on the rooms you're not using):

http://www.mitsubishicomfort.com/

High R-value = lose brain cells & asphyxiate? :hmm:

 

[jaedaliu]

Get some plants and full spectrum lighting.

I hear there's this plant that historically was used for rope that grows extremely rapidly and could be your solution for oxygen.

 

[Kaido]

Get some plants and full spectrum lighting.

I hear there's this plant that historically was used for rope that grows extremely rapidly and could be your solution for oxygen.

Hah, was just reading about plants in relation to IAC:

http://en.wikipedia.org/wiki/Indoor_air_quality#Effect_of_indoor_plants

However, my wife hates plants (bugs & maintenance & whatnot). Also planning on using Philips LED lighting, so no full-spectrum stuff. Energy Wise Structures in one of the links in the OP says to have a 10% glass-to-wall ratio to give enough leakage to make up for not using a mechanical system.

I wonder how stuff like Low-E windows with non-wood materials (metals or composites) stack up though, if they allow for air leakage and whatnot. If you get your house too dry, they say that caulking will start peeling, and if it's too wet, you'll start to get mold & condensation.

 

[sdifox]

It is still not airtight. Just less leaky.

 

[Kaido]

It is still not airtight. Just less leaky.

"Airtight" made for a better title than "less leaky" :biggrin:

 

[tortillasoup]

I like how OP thinks it's such a huge deal to open 2 windows (cross ventilation) to get fresh air in the event of a power outage... Like it wouldn't be a big deal that you couldn't heat your house if you had electric furnace/heatpump when there is a power outage.

An airtight, highly insulated house would be definitely better to have in a service outage than a poorly insulated, "free flowing" house. Also if the power load is low enough, you could just have a battery bank of lead acid batteries with backup power.

 

[Kaido]

I like how OP thinks it's such a huge deal to open 2 windows (cross ventilation) to get fresh air in the event of a power outage... Like it wouldn't be a big deal that you couldn't heat your house if you had electric furnace/heatpump when there is a power outage.

An airtight, highly insulated house would be definitely better to have in a service outage than a poorly insulated, "free flowing" house. Also if the power load is low enough, you could just have a battery bank of lead acid batteries with backup power.

In the extreme case example in the OP, if it's snowing outside and really cold, I'd rather not have to open a couple of windows to deal with the air tightness issue. I've had this happen several times - bad storms, power loss for a week or two, gas runs out for generator or generator fails, etc. The fireplace works for heating to keep temperatures bearable, but if the indoor air quality gets messed up, that's the issue I'm concerned about.

I've read mixed things about just how tight & super-insulated new construction materials can be, like interlocking XPS SIPs & integrated ICF blocks, and how doing an appropriate percentage of windows-to-wallspace can mitigate the air quality issue. Part of the reason I'm interested is that I'm a really big fan of the Mitsubishi Mr. Slim system, which doesn't use ducts throughout the house. So you're not getting the common air system in a regular home. Basically there's an outdoor unit and an indoor unit per room (or one outdoor unit to a few indoor units):

http://www.mitsubishicomfort.com/en/consumer/how-it-works/advanced-technology

So the indoor air design approach would be a bit different than a traditional stick house with central air, because it's basically a concrete bunker with a decentralized air system. And yes, with a baby at home and very cold temperatures, it is a big deal to open windows during winter. We've had to leave our home several times due to this situation in just the past couple of years and it's not exactly a pleasant experience.

 

[vi edit]

Is an integrated natural gas generator not an option? In theory it'll never run out of gas (assuming the line from the company is not compromised) and it's an autofailover that will power all primary need devices (vents, heating/cooling/refridgerator, ect). If you are at risk for power failures that often then I'd go no other route with a backup generator.

 

[Kaido]

Is an integrated natural gas generator not an option? In theory it'll never run out of gas (assuming the line from the company is not compromised) and it's an autofailover that will power all primary need devices (vents, heating/cooling/refridgerator, ect). If you are at risk for power failures that often then I'd go no other route with a backup generator.

I do have a Generac in the plans. I'd like to build a starter home within the next couple of years now that I'm close to being done with school (yay night classes) and don't have any huge square footage requirements (or budget :biggrin. I mean, the chances of power loss are low, and a permanent gas generator with an automatic switch isn't a big deal to put in on a new-build project, it's just the idea that you'd have to rely on a mechanical fan to save your life isn't that comforting, especially one that doesn't have a sensor that sounds an alarm or emails you if it fails or has issues. And moreso because I really like the Mr. Slim system, which is not ducted, which means that I'd have to run separate ducts for a fresh air exchange system. So if having more windows would solve the problem, that seems like an easy route to go:

At Energy Wise, our rule of thumb is that if you have at least 10% glass to wall ratio. In other words, if you have 4,000 sq. ft. of wall, you have to have at least 400 sq. ft. of glass—and it’s operable glass not fixed glass—that you have enough natural leakage in the house. Assuming, of course, that you don’t have anything excessive in there, like a commercial dryer or something of the sort. In nearly every case, if you meet the 10% glass-to-wall ratio, you will have enough natural leakage into the house that you don’t need to use an any sort of air-to-air heat exchanger.

I talk to people every day that are concerned about the airtightness of the houses they’re fixin’ to build, and whether or not they’re going to suffocate themselves, and they want to get my advice on whether or not to put in an ERV or HRV system. I have to explain to them that with the way that houses are constructed today, even if we did everything perfect, and got it as tight as humanly possible, there would still be enough leakage through the windows and doors that they would not need, in most cases, an HRV or ERV system.

The reason that happens is because the average house that we see will have somewhere between a 20% to 30% glass-to-wall ratio. And as long as you have that 10% minimum, there’s enough natural leakage in the house that you will not need any kind of additional mechanical ventilation system.

So based on that information, it sounds pretty doable without having to run ducts or a permanent fan system, but there's so much conflicting information out there that it's hard to really nail down the requirements. Energy Wise Systems seems to be pretty on the ball about this stuff, and the information makes sense, so that sounds pretty good to me :thumbsup: I'm hoping someone with some experience can chime in, because I've only met a few people who actually have a concrete or other highly-efficient home. Hard to get solid info on what the right setup is!

 

[jaedaliu]

So based on that information, it sounds pretty doable without having to run ducts or a permanent fan system, but there's so much conflicting information out there that it's hard to really nail down the requirements. Energy Wise Systems seems to be pretty on the ball about this stuff, and the information makes sense, so that sounds pretty good to me :thumbsup:

I was thinking... How much air gets exchanged through paint, plaster, drywall, then again on the other side. Your normal leaky windows will let you breathe.... and die from freezing during an insanely bad snow storm where utilities get cut and you're snowed in for weeks.

 

[Humpy]

I was thinking... How much air gets exchanged through paint, plaster, drywall, then again on the other side. Your normal leaky windows will let you breathe.... and die from freezing during an insanely bad snow storm where utilities get cut and you're snowed in for weeks.

Painted drywall is essentially airtight. It is the basis of one of the best house designs (IMO) where the interior envelope is as airtight as possible and the wall assembly vents to the outside. The combination of the 'Larson Truss' and airtight drywall makes for an extremely energy and cost efficient house in cold climates. In moderate climates the 'Passive House' design is also very airtight, somewhat expensive, but awesome. In the hot south I don't really know. I guess the thermal mass of ICF combined with an excellent AC system would be ideal.

 

[Kaido]

I was thinking... How much air gets exchanged through paint, plaster, drywall, then again on the other side. Your normal leaky windows will let you breathe.... and die from freezing during an insanely bad snow storm where utilities get cut and you're snowed in for weeks.

That's the point - in modern quasi-airtight structures, you have a layer of concrete & foam in addition to the dryer, paint, and exterior finish. Some of the R-values are like R-50 or more, giving it a ridiculous amount of insulation. And if you're doing a new build, you're probably going with Low-E super-insulated windows as well. So I'm curious to see how you can circumvent the mechanical airflow requirement of heavily-insulated homes. The only lead I've gotten so far is to have a 10% glass-to-wall ratio, which makes sense, but I haven't seen much other data to confirm that.

Winter before last, our power got cut for 2 weeks during a bad snowstorm. Got pretty cold. Portable generator had issues & quit working. Had a fireplace, but that's really only good for heating one room, as long as you wake up to add logs during the night. But that's the exception, not the rule. I just don't like the idea of having to rely on something mechanical that requires electricity, as well as ducting, to keep the house livable.

 

[vi edit]

I was thinking... How much air gets exchanged through paint, plaster, drywall, then again on the other side. Your normal leaky windows will let you breathe.... and die from freezing during an insanely bad snow storm where utilities get cut and you're snowed in for weeks.

You also have bathroom vents, dryer vents, hoods over your stove, ect. All of those allow a house to breath to some extent. They should have dampers in them that close off, but it's not completely airtight.

And then as far as health concerns go, if you are seriously that worried, then put in an oxygen alarm that alerts when 02 levels get below a particular point.

But I think most of it is pretty alarmist. You aren't in a bomb shelter waiting out the apocolypse. Yet.

 

[RelaxTheMind]

god help you if your sewage/drain vent ever gets clogged.

 

[Kaido]

Painted drywall is essentially airtight. It is the basis of one of the best house designs (IMO) where the interior envelope is as airtight as possible and the wall assembly vents to the outside. The combination of the 'Larson Truss' and airtight drywall makes for an extremely energy and cost efficient house in cold climates. In moderate climates the 'Passive House' design is also very airtight, somewhat expensive, but awesome. In the hot south I don't really know. I guess the thermal mass of ICF combined with an excellent AC system would be ideal.

Yeah, when I lived in Florida, concrete homes were becoming huge, especially after Hurricane Andrew flattened Miami. I think that's another good application for ductless systems like the Mr. Slim - you only pay for the rooms you want to heat or cool, rather than your whole house + the ductwork.

 

[tortillasoup]

In the extreme case example in the OP, if it's snowing outside and really cold, I'd rather not have to open a couple of windows to deal with the air tightness issue. I've had this happen several times - bad storms, power loss for a week or two, gas runs out for generator or generator fails, etc. The fireplace works for heating to keep temperatures bearable, but if the indoor air quality gets messed up, that's the issue I'm concerned about.

I've read mixed things about just how tight & super-insulated new construction materials can be, like interlocking XPS SIPs & integrated ICF blocks, and how doing an appropriate percentage of windows-to-wallspace can mitigate the air quality issue. Part of the reason I'm interested is that I'm a really big fan of the Mitsubishi Mr. Slim system, which doesn't use ducts throughout the house. So you're not getting the common air system in a regular home. Basically there's an outdoor unit and an indoor unit per room (or one outdoor unit to a few indoor units):

http://www.mitsubishicomfort.com/en/consumer/how-it-works/advanced-technology

So the indoor air design approach would be a bit different than a traditional stick house with central air, because it's basically a concrete bunker with a decentralized air system. And yes, with a baby at home and very cold temperatures, it is a big deal to open windows during winter. We've had to leave our home several times due to this situation in just the past couple of years and it's not exactly a pleasant experience.

This doesn't make any sense... An air tight home vs. a non airtight home, you still cannot run a generator, barbeque or anything to that effect inside of the home anyway. Air tightness is a distraction and is really more of a metric of how well the house is insulated. A house built in the 90s w/o fresh air ventilation (i.e. not opening a window) is unhealthy and so some sort of ventilation has been code for some time. Co2 build up makes the house stuffy so in the event of a power outage, that required ventilation no longer works.

Having a central ventilation system isn't healthier or safer than any other heating method and is more of a convenience thing since most central vent systems don't have fresh air intake.

You don't have to open a window all the way to ventilate the house in the dead of winter, you can just crack the window open a bit and that will provide sufficient ventilation without bringing in a huge cold breeze. Remember, the higher the temperature delta between the inside and outside of the house, the faster the house will ventilate itself.

 

[Kaido]

You aren't in a bomb shelter waiting out the apocolypse. Yet.

Micro-bunker here I come! :biggrin:

 

[Kaido]

God help you if your sewage/drain vent ever gets clogged.

LOL! Hadn't though of that :biggrin:

 

[highland145]

What about air quality? Building materials out gassing into the house and not being able to escape? Carpet, Chinese sheet rock come to mind.

 

[Kaido]

This doesn't make any sense... An air tight home vs. a non airtight home, you still cannot run a generator, barbeque or anything to that effect inside of the home anyway. Air tightness is a distraction and is really more of a metric of how well the house is insulated. A house built in the 90s w/o fresh air ventilation (i.e. not opening a window) is unhealthy and so some sort of ventilation has been code for some time. Co2 build up makes the house stuffy so in the event of a power outage, that required ventilation no longer works.

Having a central ventilation system isn't healthier or safer than any other heating method and is more of a convenience thing since most central vent systems don't have fresh air intake.

You don't have to open a window all the way to ventilate the house in the dead of winter, you can just crack the window open a bit and that will provide sufficient ventilation without bringing in a huge cold breeze. Remember, the higher the temperature delta between the inside and outside of the house, the faster the house will ventilate itself.

I think you're missing the point. The point is, the more airtight a home is, the worse the indoor air quality becomes without some method of ventilation. In extremely insulated homes, most recommendations are to use a mechanical air system (HRV/ERV). In SIP & concrete-based homes, the insulation is very high, which is why this is recommended. Since I'm not a fan of that idea, I'm looking for alternatives that don't rely on an active system (i.e. electricity coming in & a mechanical fan system spinning) and instead can use a more traditional passive system (i.e. window leak).

 

[Kaido]

What about air quality? Building materials out gassing into the house and not being able to escape? Carpet, Chinese sheet rock come to mind.

That's actually why I'm not interested in radiant floor heating. Almost everyone I've talked to say they would always get sore throats after installing it for like a year afterward. I'm not sure if that's due to outgassing or the way the heat works or what.

 

[Kaido]

You also have bathroom vents, dryer vents, hoods over your stove, ect. All of those allow a house to breath to some extent. They should have dampers in them that close off, but it's not completely airtight.

That reminds me, I've been helping my buddy with some remodeling. He just put in the most amazing custom bathroom vent I've ever seen - the best way I can describe it is a high-powered (and silent) attic fan coupled to something like a 12"-diameter insulated exhaust tube going into the filtered vent in the bathroom ceiling. So you flick a switch next to the toilet and it activates an airlock-style oxygen exhaust. It's pretty amazing :biggrin:

 

[bignateyk]

My house is pretty airtight (I've replaced all the doors, weather stripped all the windows, and caulked the hell out of anywhere a draft was coming through). I put a 300cfm energy recover ventilator in that also acts as a radon mitigation system in conjunction with my sub-slab depressurization.

I'm not sure there are any passive systems for ventilation that will recover outgoing heat.

"Natural leakage" described in the 10% glass ratio is no different than opening a window.

 

[vi edit]

That's actually why I'm not interested in radiant floor heating. Almost everyone I've talked to say they would always get sore throats after installing it for like a year afterward. I'm not sure if that's due to outgassing or the way the heat works or what.

Not sure what is up with that. I've got radiant it's one of the most comfortable types of heating I've used. It's much less "drying" than forced air is. And most of the materials it should be used in/under aren't getting that hot anyway. They aren't getting any hotter than what they would in an unconditioned home would hit (or if a window let sun hit it during the summer).

 

[Humpy]

That's actually why I'm not interested in radiant floor heating. Almost everyone I've talked to say they would always get sore throats after installing it for like a year afterward. I'm not sure if that's due to out-gassing or the way the heat works or what.

I guess radiant heat can lead to drier indoor air leading to sore throats in some circumstances. There is nothing inherent with hydronic radiant heating that leads to out-gassing except to increase the rate that it could occur in other material as it heats up. It is best with concrete or tile floor covering anyways.

I put radiant floor and baseboard heating in my house because it doesn't distribute dust and allergens like forced air does. It is the only system I would use.