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Wow. Well done Talman. To take something as complex as these subjects and break them down like that deserves an award. I agree with most everything there. I would only add that cheap hygrometers shouldn't be taken as literally accurate but can still be very useful in detecting humidity action levels and overall patterns of high and low.
An advantage of having a more permanent hygrometer with convenient display is that its easier to see what's going on down there based on location, season, and seasonal weather. Just because a crawlspace stays "dry enough" for a few years doesn't mean it will always be so. Wetter, weather patterns, failures in outdoor bulk water diversion (gutters, swales, positive slope, foundation drains) or even changes in ground water patterns can all negatively influence a once dry crawlspace.
Having addressed the radon concerns so well, Iam curious what comments can be made on the subject of ductwork in vented crawls. Its definitely a complicating factor when it comes to decisions to encapsulate even if the crawl is deemed "dry". The more ductwork down there, the more it makes sense to go from vented to unvented. Ensuring ductwork is well sealed is important in all cases of course.
noodlecat, radon is still an issue for slabs, especially existing ones. You should probably get a test if you haven't already. I prefer slabs for new construction as its much easier to handle radon issues passively, not requiring an energy vampire fan that runs 24/7. The passive system we use also doubles as extra sub slab drainage. The radon pipe currently required by code is a bare minimum and can be detailed much better than code minimum to avoid active mitigation or adding a 24/7 fan to ensure sub slab depressurization.
Talman20,
It looks like you just joined the forum, so welcome. Your information is very helpful to me and I appreciate it. Can you tell me what field you work in that resulted in so much knowledge? Tell us a little bit about yourself.
Donna
Thanks for all this great info! I wonder if radon is a factor with slab houses as well?
Radon is a factor with any foundation type. One of the things that makes it such an elusive and dangerous health hazard, is that everyone of your neighbors might have no elevated radon levels at all, while your home might. What's more, you could measure it at one point in time, then a month later have a reading that is 5x the previous number (this is why the pros use continuous monitoring equipment to show peaks and drops in readings).
For about $100 you can buy low-end continuous radon monitors with alarm that are not completely accurate but do help give you a good sense of relative amounts and are adequate for determining whether an immediate hazard exists. Sometimes during radon abatement they will throw one of these into the deal if you don't have one already, or you can purchase online. Its a good item to have in the home along with carbon monoxide and smoke detectors. For some reason the slower potential death of long term radiation exposure does not resonate with people like fire or carbon monoxide does. I'd say it's just as evil because it is so easy for it to fall out of sight/out of mind and forget about -- this unfortunately is what most people do, they test when they buy the home without realizing that a one time test is not particularly useful. Monitoring it is an ongoing process just as is monitoring for smoke.
In terms of differences, what differs with foundation types is the actual mitigation method. With a crawlspace you have to seal with a vapor barrier, with a slab or basement you basically create a hole in the slab and vent it out from there. The end result is equally as effective, and to the best of my knowledge the general cost is about the same, just one involves the labor of wrapping piers and the other is concrete work. The actual install of the fan and vent portion takes very little labor and cheap parts and is the easiest part of the job (for example on an older home that already has a system in place, if the fan goes bad you can replace them for a couple of hundred dollars). The cost might vary depending on where the system is placed in the home, how easy that area is to get to in order to work on, the cosmetic results you want to achieve, etc.
Donna and others concerned about radon, DIY kits are widely available from hardware and other stores. Typically you place the kit based on instructions and let them sit for ~48 hrs, seal them up and send it away to a lab for results. I find there is a very large variance in results that you can get depending on how and where you place these kits.
The same exact home can test completely different depending on the room you put it in and how much ventilation is happening. My advice is to test 1x in a worst case scenario like a closet on the lowest level that sees little air circulation. If it tests high, try another kit in a more applicable situation and location like near where you sleep or spend the most time under normal home operating conditions. Lots of things effect this testing. Open windows or ventilation, levels/height off the ground or even different rooms on the same level of the home.
If you hire a contractor, the testing is often more expensive but they leave fancier equipment that you can test more locations and get quicker results with. I use to poo poo radon but its tough to argue with most current research and the importance that the ALA has placed on it. Much of Europe has action levels 2x that of here in the states (~2picocurries instead of 4).
Radon locations are highly variable. My recommendation is to test first, then do encapsulation based on mitigator's and Talman's comments. While radon mitigation can help crawlspace issues, I believe its unlikely to have the same benefits as encapsulation. Afterall, its the open vents that flies in the face of proper building science in our climate. I absolutely agree that each home is different and has its own set of needs depending on the details.
Wow. Well done Talman. To take something as complex as these subjects and break them down like that deserves an award. I agree with most everything there. I would only add that cheap hygrometers shouldn't be taken as literally accurate but can still be very useful in detecting humidity action levels and overall patterns of high and low.
An advantage of having a more permanent hygrometer with convenient display is that its easier to see what's going on down there based on location, season, and seasonal weather. Just because a crawlspace stays "dry enough" for a few years doesn't mean it will always be so. Wetter, weather patterns, failures in outdoor bulk water diversion (gutters, swales, positive slope, foundation drains) or even changes in ground water patterns can all negatively influence a once dry crawlspace.
The type of hygrometer I use (I have a sensor in my crawl and one in my attic) has a remote display that I view from inside the house. I don't think I paid more than $25 for it. I use it more for a "relative number" than something that I expect an exact RH reading from, but I definitely see the cause and effect. On a humid summer day it might read 45%, if I go down and leave the crawl space door open the reading could creep up to 60% fairly quickly.
My own humidity does not fluctuate (as you've correctly pointed out that it can) only because the dehumidifier keeps it at a fairly constant 45% (dehumidifiers have their own hygrometer built in of course, so on mine you basically set an "aggressiveness" setting rather than a number depending on how dry you want to stay. If I set it to a less aggressive number, I can watch the RH rise to 50, 60, etc. it would rise lot more if I turned it off completely.
But yes I agree it should be monitored year round. My number fluctuates between maybe 43-47%, if I suddenly looked at the display and saw 60% I would wonder if I have a plumbing leak, or if the dehumidifier has malfunctioned, or if someone broke into my crawlspace and left the door unlocked (none of which have happened thankfully).
If you have any recommendations on a more permanent hygrometer, I'd be interested. I don't think its something I'd spend hundreds on, but if there is one that records the humidity level at real-time intervals, then the data can be downloaded to computer, that would be useful. That's how the continuous radon monitors the pros use work, they can show the history of where the reading was at any given point in time (but those systems cost thousands). The home/consumer grade devices simply give you a 48 hour average (which is adequate for determining a problem requiring attention).
Quote:
Originally Posted by BrianKnight
Having addressed the radon concerns so well, Iam curious what comments can be made on the subject of ductwork in vented crawls. Its definitely a complicating factor when it comes to decisions to encapsulate even if the crawl is deemed "dry". The more ductwork down there, the more it makes sense to go from vented to unvented. Ensuring ductwork is well sealed is important in all cases of course.
Yes, sealing of duct work is important as you said, and I'm guessing the amount of ductwork in the crawl is directly related to the amount of condensation-related moisture that is generated. There are many factors -- how hot is the weather outside / what's the dew point on any given day, and how cold does the homeowner prefer to run the A/C. In a vented crawl, when the outside air hits the ducts carrying cold air into the house, it condensates, which is why almost every home with duct work in the crawl has a layer of mildew/mold (even if dormant) on the ducts, unless the crawl was sealed at the time the ductwork was installed.
So, in many modern homes in a southern climate there are 3 basic sources of moisture to be concerned with: humidity from the earth itself, humidity from the outside air (hot humid day, rainy day etc), and then the condensation from any ductwork that may be sweating due to hot air hitting cold ducts. Technically we could say there's a 4th source of humidity like plumbing leaks, flooding etc. but of course those need to be solved by methods other than simple humidity solutions.
Talman20,
It looks like you just joined the forum, so welcome. Your information is very helpful to me and I appreciate it. Can you tell me what field you work in that resulted in so much knowledge? Tell us a little bit about yourself.
Donna
I'm actually not in any field that would give me insight on the topic. I just have experience as a homeowner and I'm the type of person that researches matters so deeply that I inevitably end up gaining enough knowledge that relates to my own particular case that I don't have to rely completely on someone else's advice. Maybe a natural curiosity about the subject you could say?
What got me started learning about crawlspace solutions started out as small drywall cracks that would appear and disappear seasonally, then realizing my own crawl was just too wet. So I set out to solve the problem of letting mother nature dictate the condition of my home.
Then of course the insane amount of information online, the ability to read about others' anecdotal experiences and apply them to what I've learned about home ownership in general has a compounding effect I guess?
Overtime I just realized the importance of the stability of humidity in the crawl, and how many problems stabilizing it solves. The radon aspect is just kind of a side-topic, because most crawlspace solutions carry the risk of increasing radon influx into the living area.
I'm actually not in any field that would give me insight on the topic. I just have experience as a homeowner and I'm the type of person that researches matters so deeply that I inevitably end up gaining enough knowledge that relates to my own particular case that I don't have to rely completely on someone else's advice. Maybe a natural curiosity about the subject you could say?
What got me started learning about crawlspace solutions started out as small drywall cracks that would appear and disappear seasonally, then realizing my own crawl was just too wet. So I set out to solve the problem of letting mother nature dictate the condition of my home.
Then of course the insane amount of information online, the ability to read about others' anecdotal experiences and apply them to what I've learned about home ownership in general has a compounding effect I guess?
Overtime I just realized the importance of the stability of humidity in the crawl, and how many problems stabilizing it solves. The radon aspect is just kind of a side-topic, because most crawlspace solutions carry the risk of increasing radon influx into the living area.
Thank you both for sharing your info, Brian and talman. I have bookmarked this thread for future reference. After reading about crawls, I would much prefer having a slab over a crawl or a basement.
My house is on a sloped lot and I think that makes a difference.
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