CRAWL SPACE WOES

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jcm71

jcm71

Member
Joined
May 5, 2011
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1,744
Location
Chattanooga, TN
Our annual termite inspection came up positive and Terminex came through and treated the infestation. One cause was excessive humidity and moisture in the crawl space which measures over 3300 sq.ft. They recommended completely incapsulating it with a 12 mil vapor barrier and 8 mil foundation wall liner and installing a dehumidifier, which I agree needs to be done. Terminex quoted me $12,000 to do the job, which would include the installation of a MegaDry dehumidifier plus $150 a year for the annual inspection (rip off).

I figure I can do the job myself for less than half the cost. Hard work, but not technically challenging. My question is do any of you guys have any recommendations on a quality dehumidifier? Thanks for your input.
 
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I installed a product called a Humidex which is a bit different than a dehumidifier. You can look it up on the internet to see how it operates. With this product, you cut two 4x8 inch holes in the living space floor, usually at opposite ends of the house. The Humidex is mounted in the crawlspace and it draws the air down from the house and ventilates it outside. It keeps odors out of the living space and refreshes the air in the house constantly, while pulling moisture out of the crawlspace. I have been using it constantly for the past nine years and been extremely happy with the results.

Jim Smith
 
How much ventilation do you have in there now? i thought all you had to do was circulate enough air so you match outside conditions. A dehumidifier for 3300 sq ft is going to be huge, which equals a big electric bill. I've not heard of conditioning a crawl space, so not much help. sorry.
 
low_48 said:
How much ventilation do you have in there now? i thought all you had to do was circulate enough air so you match outside conditions. A dehumidifier for 3300 sq ft is going to be huge, which equals a big electric bill. I've not heard of conditioning a crawl space, so not much help. sorry.
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Zip ventilation in there now. The newest "theory" is to close off all vents and seal them. Once you seal it off, seal the foundation walls, install a vapor barrier and install a dehumidifier, the electric bill should be small if you did a good seal job. BTW, I could install a 20 mil barrier for less than $2000. My main concern is a quality, reliable dehumidifier rated for at least 3300 sq ft. The dehumidifiers I've researched are all rated in square feet, which IMO is erroneous. They should be rated in cubic feet. My crawl space varies in height from 4.5 ft to 2ft (approx). I estimate my cubic feet at a little less than 11,000. I estimate that a quality dehumidifier would cost up to an additional $2000. Hiring some local help and an electrician to wire it brings my cost to less than $6000.
 
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This is a problem all over the south east. Many air conditioning companies handle this type of thing and would be cheaper than terminex. Drawing air from the homes in some areas can be extremely problematic as the house structure can go to negative pressure. That is never a good thing it can draw moisture into the walls. A local mechanical engineer can also be very helpful as there is a very complex formula to actually determin the size dehumidifier you purchase. Your biggest expense over time will be the electric bill on the dehumidifier. So the smaller the unit the better, but of course it needs to be large enough. The engineer can handle all that for you. The engineer will cost between 250-500 but well worth it. Then if it does screw up he has the insurance you need to repair the damage. You can certainly do the work yourself. Have him inspect it and approve it as you go. They way you over lap the corners actually matters. My more than two cents worth. Lots of luck with this pesky problem. Let us know how it goes.
 
In theory, if you seal up your crawl space correctly you should not need a dehumidifier... if you do, you have other water related issues. Another thing to check into is whether or or not your termite company will let you seal up vents... some wont. In that event, make foam blocks to fit into the vents from the inside and remove them when the termite inspection is due.
 
Not to disagree, there is a weather type zone (for lack of a better term)that runs some what a distance back from the cost that follows the cost line curve mostly. It is special. The national weather map people actually have a US map showing this zone. I can not remember where to find it as we do not have to many homes in Florida with crewel spaces. Starts in Tennessee and runs ll the way down through parts of Florida. Any way it needs to be addressed or the mold that forms under your home will make you very unhappy and cost you a bunch of money. Of course that is if you really have this condition and they are telling you the truth. But it is real get it do. Where there is water or wet surface mold and mildew will form and it never smells good. One other way to solve it is to take the A/C out of your home and vent the crawl space correctly. By the way it's worse if your A/C ducts run in the crewel space. But it can happen other wise also. My more then two cents agin. It has to do with ground water vapor and deferential in temperature in a semi confined space.
 
Buy they way you are wanting to look for grains of moisture removal on the dehumidifier. That is why you need some one in the trade to give you the proper size. Getting a little knowledgeable advice will save you a lot in the long run. Honeywell makes some really nice dehumidifiers that will run for ever. Most likely not the store bought ones. Best place is an A/C supply place. They do make noise and your hear it at night because they do have a compressor in them. So put them far away from any sleeping area. Also put it on a dedicated electric circuit. Do not, do not, use ground fault outlet. Ground fault is not made for continue motor circuits. Side note they produce a lot of water so you have to figure out a drain line. Gravity drains work best but that not be possible in your application.
Also make an access door very near to wear the unit is as they have a filter that needs to be changed. And if you use a condensate pump it will need to be serviced.
Okay I think I am done now.
 
Tom T said:
Not to disagree, there is a weather type zone (for lack of a better term)that runs some what a distance back from the cost that follows the cost line curve mostly. It is special. The national weather map people actually have a US map showing this zone. I can not remember where to find it as we do not have to many homes in Florida with crewel spaces. Starts in Tennessee and runs ll the way down through parts of Florida. Any way it needs to be addressed or the mold that forms under your home will make you very unhappy and cost you a bunch of money. Of course that is if you really have this condition and they are telling you the truth. But it is real get it do. Where there is water or wet surface mold and mildew will form and it never smells good. One other way to solve it is to take the A/C out of your home and vent the crawl space correctly. By the way it's worse if your A/C ducts run in the crewel space. But it can happen other wise also. My more then two cents agin. It has to do with ground water vapor and deferential in temperature in a semi confined space.
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I discounted the possibility of him needing a dehumidifier provided his crawlspace envelope is sealed and there are no water issues due to Chatanooga, TN's average elevation being1790 feet ASL.

I built a lot of homes in the south over the years and never had to put a dehumidifier is any of them.
 
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I have been in many crawl spaces performing water damage mitigation and mold remediation. In the most recent, the homeowner blocked off a couple of outside vents last fall because of cold floors in the bedroom above. Wet spring, gutter issues and poor drainage followed by a humid summer... The high humidity in the crawl space created condensation on the insulation walls and floor. It was soaking wet. We removed wet insulation and found lots of mold and rotten wood. The remediation alone will be over $7000 and that is before any repairs. Not covered by insurance.

Pest control and A/C companies are not the answer. Talk to a water restoration company. They know how to dry out and then control the humidity. The encapsulation process that you mentioned is the best long term solution. Costly up front but cheaper than a full blown mold remediation.

I know a great contractor in your area. I am new to the site and do not know it I am allowed to post it. Contact me and I will post or e-mail it.
 
Donnie,
You are correct. I am not 100% familiar with where the home is or the elevation or ground water pattern. I was at first assuming that the termite company was telling him the truth. I forgot that is not always the case of some, I do not really know who his company is. Or they could be miss informed. That is why I recommended that he contact a local engineer who has no stake in selling a job and is paid only on the bases of his expertise. I was only trying to help a fellow member with an issue. That is why I repeated and still do get. Truly get qualified person to look at it. I am a state certified HVAC contractor in Florida. I have several friends in the Carolina's who have this issue with there customers on a regular bases. We do have this issue in north east Florida as well. it runs the whole cost. I am not sure where our friends house is. But any HVAC contractor or termite company may only want to make a sale. So companies are more truthful than others. I am also not calling any body or company untruthful. I am not their and do not know all the facts. I am thankful that our members are watching the backs of our members. Moisture in a home is a terrible thing if left unchecked. If he really has an issue. Just trying to help. And advise this is not a job to spend money on with out first checking it out with some really local informed person.
Thank you for your informed information on the topic. Hopefully we have both helped our friend.
 
Way more to it than most any one understands including myself, unless you do it every day and really know. I have seen many well intentioned person do a lot of damage with vapor barriers and insulation. Closed cell foam open cell foam. Who knows. A lot of it has to with we're you may unknowing trap water vapor. We have major issues with this in Florida.
I am not an engineer but that is what certain engineers have studied for a long time. As in the prior post the possible damage is crazy high. There is cleaning it up and preventing it. Preventing is way cheaper.
 
I put an exhaust fan at one end of my crawl space, made sure the vents were open, and ran it all summer. My termite inspection guy said it was dry as a bone under there. I live in central TN, so am not a stranger to high humidity.

Jake
 
BURLMAN said:
The dehumidifiers I've researched are all rated in square feet, which IMO is erroneous.
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It makes it easier for the average homeowner to decide on a unit. A homeowner is much more likely to know the square footage of their home than cubics. The companies make an 8' ceiling assumption and go from there. So, if you want to know how many cubic feet/hr they can dry, take their square footage and multiply by 8.
 
Dan Hintz said:
BURLMAN said:
The dehumidifiers I've researched are all rated in square feet, which IMO is erroneous.
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It makes it easier for the average homeowner to decide on a unit. A homeowner is much more likely to know the square footage of their home than cubics. The companies make an 8' ceiling assumption and go from there. So, if you want to know how many cubic feet/hr they can dry, take their square footage and multiply by 8.
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Thanks, Dan. That is good info to know.

John
 
maxwell_smart007 said:
Is closed cell spray foam a viable alternative? When done right, it prevents any condensation occurring due to differential temperatures.
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It is available, but would be way too cost prohibitive and impractical in install in my walls. I would think that would be the way to go for new construction, and not necessarily a 25 yr old house. Thanks for the input.
 
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