Addressing humidity in crawlspace

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Old 09-16-16, 12:46 PM
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Addressing humidity in crawlspace

I have a termite inspection every year, and until about 3 years ago, never had an issue with humidity. Around this time, I found that a rat had taken up residence in the crawlspace (and garage). After I had him killed and removed I saw the mess he had made in the insulation - falling down in many places. I didn't do anything at the time to deal with that. The last 2 or 3 years now, I have had pretty bad humidity readings in the crawlspace, high enough that I know I need to do something, soon. I know at the very least, I need to have that old wet insulation pulled down, and a new vapor barrier laid down (the old one is pulled up and is in kind of a disarray in places.)

I have had several companies come out and give me proposals/estimates on addressing this issue. All have tackled it differently, and I just want some opinions on the information I have received. The area of the crawl is 1500 sf.

1) Remove all old insulation in floor joists, do a "crawlspace cleanout", install new R19 insulation, and new 6mil vapor barrier. est$ = $4700

2) Remove all old insulation in floor joists, do a "crawlspace cleanout", install new 6mil vapor barrier, close off vents, install dehumidifier (includes wiring on separate GFI) $7000 (this seems really high)

3) Clean out crawl - remove old poly and insulation, new 10 mil vapor barrier,
block all vents and openings, install dehumidifier (wiring included) $3800

None of these proposals include insulation the crawlspace walls with rigid foam board, which I have read should be done, when the old insulation (the pink stuff) is removed. It is okay to not have ANY insulation down there?

I have one more company coming tomorrow - this is a crawlspace encapsulation company, so I expect it will be pricier. But just wanted to get expert opinions here. I live in SE VA, and it is very humid here, so I need to do something to deal with the crawlspace issue, soon.
 
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Old 09-16-16, 01:14 PM
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I'm from Michigan where it's pretty humid, at least if you live near the lakes. In an old house we actually had a company install a sump pump deep in the ground, lay down some plastic, and replace some of the insulation around it (but not all of it because that can lead to mold and stuff). Maybe try looking into that?
 
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Old 09-16-16, 03:35 PM
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Thanks, but a sump pump is way beyond my needs. There is no standing water to worry about, never has been.
 
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Old 09-16-16, 04:10 PM
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You insulate outside walls and surfaces. If the floor of your home/ceiling of the crawlspace is insulated, you generally do not insulate the walls of the crawlspace. Generally the ceiling is insulated when the space is vented to the outside and sealed from the house air. Wall insulation but not ceiling is when the space is sealed from the outside and open to the conditioned air of the house.
 
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Old 09-16-16, 05:06 PM
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If you encapsulate the crawlspace you then include it in with your conditioned space with air conditioning and heat. As ss said, you would close off the vents and insulate the walls, plus a good vapor barrier on the floor.

With high humidity you don't want to invite that air into a cooler basement. RH (relative humidity) increases as the air is cooled and can easily form condensation.

You said the insulation is wet. It the humidity is that high then you need to close off that space. Let's see what the encapsulation company gives for a quote.

Bud
 
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Old 09-16-16, 11:36 PM
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"You insulate outside walls and surfaces. If the floor of your home/ceiling of the crawlspace is insulated, you generally do not insulate the walls of the crawlspace. Generally the ceiling is insulated when the space is vented to the outside and sealed from the house air. Wall insulation but not ceiling is when the space is sealed from the outside and open to the conditioned air of the house."

Yes, I understand that. My question was, if I have all the old wet insulation removed from the ceiling of the crawlspace, and LEAVE IT OUT - not replacing it with new - is it not necessary to insulate the crawlspace walls? That is what most of these companies are suggesting. (My crawlspace is vented right now, but obviously sealing the vents is now recommended, and most of the companies seem to be suggesting that.)
 
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Old 09-16-16, 11:42 PM
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"If you encapsulate the crawlspace you then include it in with your conditioned space with air conditioning and heat. As ss said, you would close off the vents and insulate the walls, plus a good vapor barrier on the floor."

That why I am asking here. NONE of these companies think it is necessary to insulate the crawlspace walls, after removing the old insulation.

With high humidity you don't want to invite that air into a cooler basement. RH (relative humidity) increases as the air is cooled and can easily form condensation.

You said the insulation is wet. It the humidity is that high then you need to close off that space. Let's see what the encapsulation company gives for a quote."

Not sure if it is actually WET, but definitely some of it is holding moisture, as the moisture readings in the space are above 25 in areas. About half of it is falling down, some down to the vapor barrier.
 
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Old 09-17-16, 01:19 AM
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VA has a range of climates and you said your area is humid. But, 25% RH in a crawlspace is not a problem, need to verify what that number is and what your approximate location is for climate.

Anytime you take a humidity reading also take the temp reading in the same location.
Temperature, Dewpoint, and Relative Humidity Calculator

Here is a link about crawlspaces. Photo #5 is an ideal crawlspace anyone would easily accept as becoming part of their conditioned air space.
https://buildingscience.com/document...es?full_view=1

If you have flat foundation walls that can easily accept rigid insulation, it is much easier to cover them with a VB on the floor than to try to insulate the crawlspace ceiling. It also protects everything down there and seals out that humid outside air. Once the walls are insulated and the floor is covered you will want both supply and return ducts to exchange the air.

Bud
 
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Old 09-26-16, 08:22 AM
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I believe the 25% figure was from the moisture readings of the wood - sorry, I should have clarified that. It used to always be around 14% to 18%.

Thanks for the link. I wish I understood that whole dew point thing...maybe it would make more sense. I don't grast the part about what has changed from "the old days" and how we build houses now (humid crawlspaces did not used to be an issue and now they are)

I had my dates mixed up - the last estimator came this weekend. Pics showed about half of the insulation falling, down to ground - mostly in the center of the house. Also existing plastic was not installed as "overlapping", so wherever the piers are, there is a gap in the ground coverage, that whole length of the house. They proposed 2 options:

1) a minimal "get by" option - remove old insulation and vapor barrier, replace with new, and 12mil barrier, taped to completely cover the ground. $3900

2) minimal encapsulation: Seal off all crawlspace vents; cleanout - removed old insulation and vapor barrier, replace plastic with 12 mil, sealed with waterproof tape and properly staked to ground (existing one used broken-off fiberglass insulation pins stuck in ground...all rusted now) for complete ground coverage, and take barrier up the crawlspace walls. Cover walls with rigid foamboard that has a reflective radiant barrier. Install dehumidifier (Santa Fe) with a remote monitor. Lifetime humidity warranty, 5 year warranty on dehumidifier. $6800. Complete encapsulation would also take the plastic up the piers, but that's about $1800 more so I would not do that.

I'm leaning towards the 2nd option. Right now you'd have to anesthetize me to get me under the house - it's so disgusting under there. It just seems like a good idea to have a "clean dry space" under my house. Anyway...the price seems very good - other companies want to charge nearly the same for just a cleanout and replace.

Thoughts?
 
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Old 09-26-16, 09:26 AM
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The big part that has changed is the amount of natural air flow. Old homes before we start air sealing would replace all of the inside air every 2 hours (on average). As homes became tighter they settled on every 3 hours as a good balance of needed fresh air and affordable energy costs. Tighter than every 3 hours a home will be needing mechanical ventilation to force more replacement air.

Dew point is the temperature at which the air can no longer hold more moisture. If the RH outside is 80% and you bring that air into a cool basement, that RH number increases as the air cools. If you bring that air into a home with heat, that RH number decreases because warm air can hold more moisture. Same air, but varying the temperature varies the RH, however, the dew point remains the same. Use the above calculator to play with different temps and RH.

How thick on the rigid? 2009 energy codes for VA require R-10 as a minimum. Is the reflective barrier approved as the required thermal barrier? Dow Thermax is the only one I know of that meets requirements but still may need local approval. A crawlspace may not have the same requirements so ask local code officials.

Be sure they ventilate the crawlspace while they remove the insulation so that stuff doesn't migrate up to the living space.

Bud
 
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Old 09-26-16, 11:28 AM
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Thanks - that helps me understand.

The rigid foam is R-10. Not sure about the reflective barrier. This company does nothing but crawlspaces, so I'm sure they know about ventilation while working - but I will ask them about that.
 
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Old 10-17-16, 12:29 PM
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"Anytime you take a humidity reading also take the temp reading in the same location.
Temperature, Dewpoint, and Relative Humidity Calculator"


Question: using humidity and temperature (of a crawl space), how can I calculate RH? I don't know the dew point.

Thanks.
 
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Old 10-17-16, 12:35 PM
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The humidity reading is the RH (relative humidity). With temp and RH at any same point you can calculate the dew point.

Bud
 
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Old 10-17-16, 01:48 PM
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Thank you.

Sorry to sound like an idiot, but am I taking temp and humidity from outside or in the crawl space, when using the calculator to figure out dew point? Or am I taking the temp outside and the humidity in the crawl space, to find the dew point in the crawl space?

Thanks again.
 
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Old 10-17-16, 02:47 PM
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You need the temperature reading AND the relative humidity (RH) at the same location.
Example: If your crawlspace is 50 with a RH of 60% then your dew point is 36.6. That means that if walls of the crawlspace (or any surface) cools to 36 or lower there will be condensation forming. Crawlspace air that migrates through fiberglass insulation to a cold exterior wall and forms moisture is a common occurrence.

Bud
 
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Old 10-18-16, 09:10 AM
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Thanks for the info. So in my case, the crawl space last night was 65 degrees and 62% humidity, so a dew point of 51 degrees according to an online calculator.

Is that good, bad, neutral...?
 
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Old 10-18-16, 09:38 AM
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That would not be good for CT. The upper portions of your basement walls may get much colder than 51. You really want the humidity level to be below 50% (I prefer below 45%) and you should insulate the rim and at least the upper (exposed to outside) portion of the foundation. Codes now say to insulate all the way to the floor.

Have you done any air sealing or wall and rim insulating down there?

Bud
 
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Old 10-18-16, 09:38 AM
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Is that good, bad, neutral...?
Not defined that way, those are the parameters around which you have to work.

From Bud's last post:
Example: If your crawlspace is 50 with a RH of 60% then your dew point is 36.6. That means that if walls of the crawlspace (or any surface) cools to 36 or lower there will be condensation forming.
So your example has a higher temperature for the dew point. Hence, you may have more work to do but that's what you're trying to figure out.
 
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