I have a client whose house was insulated with spray polyurethane foam under the roof sheathing and again on the ceiling after the drywall was installed. His concern is ventilation in the attic. Does this type of attic need vented? If so how much?
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You don't mention what kind of attic this is so it's hard to give an answer, but there are a few consistent features that need to be addressed. The main thing is air flow from the attic space to the soffits and/or a rdige venting system. If the insulation prevents air flow then heat buildup in the roof space will cause problems. If the roof has a ridge vent system then it should be fine, although ideally air should be able to be drawn in through the soffits for complete air exchange.
This attic should not need ventilation unless the house is being run without adequate interior ventilation and maintains high air relative humidities (RH)- say over 40% all winter. Monitor the RH's in the attic all winter.
Did they insulate the gable ends also, if any?
Edited 12/15/2005 7:25 am ET by experienced
>maintains high air relative humidities (RH)- say over 40% all winterAt the same time, he doesn't want low RH all winter. Under 30 and it'll be too dry. If using an air-to-air heat exchanger, be careful to monitor the humidity and air quality, be/c he's bringing in outside moisture/lack of moisture plus any pollutants.http://www.concretenetwork.com/anne_balogh/are_you_overheating.htm
Mr. Rue, in the article you provided the address to, is definitely off base in a number of items. He gets press space because he built a humungous ICF not because he necessarily knows the Indoor Air Quality (IAQ) or the energy efficiency fields. He claims not to put in an HRV due to outdoor humidity or air pollution. There are desiccant heat wheel HRV's that do quite a good job of lowering the RH in incoming air. (they were the first HRV I was installing in 1981 up here in Canada.)
If you have outdoor air pollution in your neighbourhood, why in the hell did you build there in the first place? Simply by not installing an HRV will the air quality be acceptable. The air that's in the house and that exchanges "around the windows" is not going to be clean air- it's from the same neighbourhood!!! At last with an ERV/HRV you 're able to run it through some filters- simple to high tech- to get some of the crap out of it.
At this level, (where at times everyone claims to have the answer- albeit a different one) I find the IAQ and energy efficiency fields are so full of popular misconceptions that I have a growing list of 83 of them!!!
The link came from a guy we all liked who used to be a frequent visitor here. He used Rue on his SIPs house and was very happy with the process and results. As to the article, I agree with its comments on oversizing HVAC equipment. In the designs I've done, which are all for extremely tight houses, the norm is to see the hvac proposal from the contractor include equip sized double or triple what's appropriate. I spend a lot of time then explaining the concepts behind the sizing that is appropriate, and my conversations with HVAC experts and Rue himself have all been consistent on this point. And that's been validated by personal experience.Pollutants aren't just smog. That's often the least of it. It's mold, pollen, street dust, decaying forests, and all that kind of stuff. Whatever method one uses to bring makeup air into the house, filtering that stuff out of the air can only be helpful. Same with controlling humidity. I don't care if one does this with HRV's with filters and humidity controls or some other way (in my house the incoming air is routed through the dehumidifier and its filters)...the goal should be to keep the pollutants outside and to keep the humidity relatively constant. Better for people and better for buildings.What HRV are you most partial to? The ones I see promoted are too often the least expensive without the humidity controls or filters. What should a typical house budget for this? I find it hard enough to get people to _care_ about these issues, let alone budget for them. Better to get a flashy light fixture or countertop, cause that impresses the neighbors!
Edited 12/15/2005 11:49 am ET by CloudHidden
Cloud, you know how interesting I find this stuff. But the outdoor pollutant thing has never made sense to me. Thanks to the Clean Air Act, outside air quality is demonstrably better than at any time during my life. Why are we so afraid to breathe it? Houses often are the source of their own pollution, with formaldehyde, vinyl emissions, and cooking byproducts (not to mention sweaty male teenagers). I think that most houses are more polluted inside than out.
I postulate that the triggers for the current public concern over things such as an increasing rate of asthma and environmental allergies have at least as much to do with the fact that we're all fat and inactive, and that reporting has improved, and that decreased pesticide use has led to an increase in urban cockroach infestations which bring on a spike in urban asthma, than with air pollution.
Also, the ASHRAE ventilation standard is .33 air changes per hour, regardless of the season. If you aren't getting that, which is quite possible in an ICF or SIP house, you're looking for trouble.Andy
Never try to teach a pig to sing. It wastes your time and annoys the pig.
Andy, I was putting the finishing touches on a wonderful post that would have explained everything perfectly and also proven the efficacy of cold fusion and provided a true Middle East peace plan, when the power flicked off and I lost it all. Sorry, I don't remember a word of it anymore. :)I'll try it a different way this version. If you have two identical houses of tight construction...let's say, tight to the standards I design/build. One uses unfiltered makeup air. The other has controls that maintain humidity at 35-45% year round and filters that limit the amt of mold spores, pollen, leaf decay, etc that make their way inside. Which house will be--for wont of better words--more comfortable and better smelling inside?To me, there's no question.I'm not talking about pollution of the Clean Air Act variety, or asthma, or inactivity, or the other things you mention. I'm talking about pollen, and mold, and road dust, and decaying leaves, etc. I'm happier keeping all of that (and excess moisture) outside...and the house smells better, and there's less static, and fewer cracked lips, and there's less dust, and less mold, and less mildew on windows, and fewer sniffles...and all of that is better for people and buildings than the opposite.I've seen this personally, and seen the opposite, and think it's easily demonstrable that controlling humidity and air quality (the way I'm referring to it) makes a positive difference.
Sorry, I didn't pick up on the filtered part of what you were saying. Filtered air is good - It has more space between the molecules to pick up and dilute the indoor pollutants. <G>
Andy
Never try to teach a pig to sing. It wastes your time and annoys the pig.
I'll take my air straight up - neat, thank you;)
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
This attic should not need ventilation unless the house is being run without adequate interior ventilation and maintains high air relative humidities (RH)- say over 40% all winter. Monitor the RH's in the attic all winter.
I got a nifty temperature/ RH guage as a gift recently and have ben keeping an eye out for how its changed in my house over the winter. The RH has been in the 45-50% range so far. You seem to be saying that anything over 40% is high? I did a quick web search and found a nifty chart that looks like a RH of 45-50% would be ideal for health reasons. This chart did not address the health of the building though.... Is there different RH that would be better for the building materials?
Daniel Neuman
Oakland CA
Crazy Home Owner
Wow!!! Second time today that a remnant of one of my past jobs from 1983-1993 is mentioned on a thread. This bar chart was, I believe, developed for the R2000 program as it was in their first revision of the manual about 1987-88 when they were expanding their training in Indoor Air Quality. This R2000 builder training (by the end, I was a site advisor/inspector/trouble shooter/reseacher) eventually led to me being hired by an engineering firm to set up an Indoor Air Quality and air balancing subsidiary for them.
The first remnant was someone running their HRV at 0.5 ACH- the original rate set in R2000 that overdried new homes by January of their first winter and led to many complaints of overventilation, nosebleeds, cracked lips, shocks, etc. (Better to err/air on the side of safety and overventilate)
Back to topic: (by the way, where'd you pick up the chart?)
Yes, 45-50% is the ideal RH for humans but in cooler/colder climes than yours, this is too high and the building may suffer. In the colder weather, these RH's lead to serious condensation on windows and maybe in hidden places like walls and attics. In your climate, you may be able to support 45-50% for most/all of the year with no problems; just keep looking for condensation/ mould to make sure.
We now have the knowledge and technology to run our houses at 45-50% for all of the year. A well executed superinsulated house with R8 windows (w/ warm edge spacer) and a good HVAC and ERV system will do it and save energy as well. There are probably a few out there now that we don't know about but that will be my retirement home!!
Gable ends were also insulated.
They just have to watch interior humidity for the winter so it doesn't lead to condensation/mould growth. If the house is really tight, they may have to invest in an ERV/HRV system or similar (an air cycler with outdoor air duct on the furnace/heat pump/AC return if they have forced air)
I'm with Experienced on this one. Your friend may need a heat-recovery ventilator, but that attic needs ventilation about as much as I need another wife (Love ya, honey).
Andy
Never try to teach a pig to sing. It wastes your time and annoys the pig.
If I understand it right, you have a very unusual application of spray foam.
You said it was on the roof sheathing, then you said it was 'on the ceiling', and you said there is an attic space.
Sounds like redundant weather boundaries. If you vent it, the foam on the sheathing goes to waste. If the attic is not a living space, it can't really be "too tight".
A strange setup indeed, but it should not cause problems.
If the house (as in living areas) is 'too tight', that is another matter, not related to the attic ventilation.
Edited 12/15/2005 9:12 am ET by csnow
Sounds like the foam spray salesman overperformed!
Andy said it best. One wife is enough for any house.
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Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
Well, we likely (despite the diversion into indoor air quality) need to know more about the structure.
Like where is it?
Tucumcari is a different answer than Philly, than Portland, than Mobile than Saskatoon and so on.
I have to wonder if you are seeing a second spray-in installation. Just can't tell which was 'first' <g>.
The ceiling plane is a notoriously hard thing to get a good seal with, what with vents, registers, j-boxes, can lights, etc. all punched through it. That does not mean that a inch or so of foam would not go altogether to waste after filling the rafter bays & covering the exposed rafters (like if I had to buy foam in whole barrels, for instance--not installed thickness).
Give us more info, you may (or may not) get more info.
The house is in northern Arkansas, and yes there was a 2nd spray of foam after the drywall and finish elec. was installed.
Ok, so that's going to be a mixed humid environment, if I remember the zones right.
The attic in question might actually be one well served by some sort of controlled venting by fan. A thermostatic switch might even be a good idea. May take some mulling on.
The air-exchange & house-sealing pros would call for testing the house by blower door, to see where the structure hits on the recommended scale of tight-to-loose. I know Experienced & RayMoore both have some background in this (and know many of the numbers right off the top of their heads, smart about it, too).
So, there's two issues to look at. First is the "normally habitated" portion of the house "too tight." Second is whether the attic, as its own space is "too tight."
How tightly the ceiling/attic floor is sealed will make a difference to the attic. Warm air will be trying to "get through" that ceiling plane all throughout the year. That warm air will take with it whatever is in it (particles, water vapor, etc.) Being in Arkansas, with the bottom of the roof plane insulated, the temperature difference from house to attic will be low (much lower than a conventional ceiling-only situation) in winter. What happens to water vapor "sneaking" into the attic in winter may want addressing--but the "how much" may need finding out.
In the summertime, that sealed-up attic may be better off for not letting hot humid air into the attic where it might heat to 135º during the day and fall to the dew point at night. (Hmm, I may have "logic-ed" my way into not even power venting the attic <darn logic> . . . )Occupational hazard of my occupation not being around (sorry Bubba)
The attic still needs to be vented to let the air mass above the insulated ceiling move out, but I think the thinking may have been that the heat mass in an attic is from the hot roof radiating it's warmth into the attic volume in the first place.
can you give a reason why that air mass needs to be vented out?Wioth everything sealed up there, if the only other means for air to enter the attic is from inside the hosue via the cieling hatch, then venting will create negative pressure in the attic which will draw warm moist air from in the house up into the attic which is not good.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I'm suggesting, since we don't have drawings of what the actual deal is, that the foam was sprayed on the roof sheating to slow transmission of heat from the roof into the attic volume. The lower level insulation at the ceiling level is what's keeping the heated and cooled space insulated. I didn't suggest anyone improperly vent the space.
Ater thinking about the guy's question, I realized what I thought was an oxy-moron at first (insulating a roof -then seperatley a ceiling below) could be a pretty effective idea in reducing radiation from all that hot roof mass in the warm months.
Edited 12/16/2005 2:24 pm ET by byrnsie