I have never lived in NC, but my impression is the summers are not and humid. Is that not true? What are the typical summer highs and humidity levels? Bringing in hot humid air from the outside and then lowering its temperature does not sound like a good solution me.

Am I missing something?

Yes it is hot & humid during the summer. The ventilation theory is that the vents open and the fans run when the heat & humidity drops based on the readings of the meters attached to the fan system allowing the space to breathe and ventilate. So you supposedly are only letting in & circulating drier air than what is in the crawl space. When the meters read out of range, the vents remain closed keeping the hot & humid air out.

The website link may explain it better.

On what is the water condensing? If the ducts, then maybe you have to enclose the ducts to put them into the indoor space. If you are getting condensation on the floor joists or subfloor you probably need seal it in or enclose the crawl.

This is just a start. I know that there is a lot more to read at the LSU web site. There is a lot of information at http://www.buildingscience.com

Here is a link that might be useful: Insulating Raised Floors in Hot, Humid Climates

We have the same problems in our house in Chapel Hill:

Do you have plastic sheeting covering the ground in the crawlspace and are the seams taped?
Is there a drain that takes any standing water out of the crawlspace?
Are the ducts insulated?

There is no simple solution to this. NC code now requires all crawlspaces to be sealed - I'm surprised your crawlspace is not sealed if the house is only 2 years old(?)

If you go the ventilation route, be sure to get a demonstration of the fans first - they can be extremely noisy!

Thanks for the replies. I'll do my best to answer the questions:

The condensation is on the ductwork & air handler (I think that's the right term) under the house. The ductwork is insulated and seams are sealed.

Yes, we have the plastic sheeting down and it is taped. There is no standing water in the crawlspace. We don't have a drainage issue (where the perimeter drains aren't installed correctly or not doing their job adequately). Its just the condensation problem.

We installed the rigid board insulation across the vents, closed the vents and started running the dehumidifiers last summer. They've been running nonstop since then. It no longer rains condensation, but the humidity levels are still too high.

That may be a county code you're talking about. From what I understand, NC goes by International Code and then the counties can further regulate from there. Plenty of homes in Randolph county are still being built & passing code with ventilated crawls.

Thanks for the heads up on the noise level of the fans.

We built our last house too and never had this problem. The only thing we can come up with that's markedly different is that the last house was heavily shaded by surrounding trees and this one is not.

The Atmox ventilation system relies on the fact that the outside air will be dryer than the air in the crawl space. I would think this would not happen very often during the summer in NC. I am skeptical how well this will work.

What is the humidity level in the rest of the basement? What are you using for a dehumidifer?

The Moisture has to be coming from somewhere. Either your crawlspace is not really sealed to the ground, or it is not air-sealed. You have to figure out which in step 1.

In humid environments, the air is a much greater source of water than the ground. Both are infinite in their quantity, but the air can move it onto your house faster. More ventilation can just mean more water to condense. In the olden days raised houses were common but they were not mechanically cooled. Add mechanical cooling to them and you add some condensation problems.

Adding ventilation AND a dehumidifier makes no sense. Adding ventilation makes sense only if the outside air has less ABSOLUTE humidity than the air under the house. Yup, it is cooler under there than out in the sun, so the RH is higher but the absolute humidity is the same. Ventilation will only help dry faster in times of lower humidity after times of high humidity. If the dew point is the same all the time, you gain little or nothing.

You have two choices. You can seal the crawlspace from the outside and make it part of the indoors, or seal the underside of the house, including the ducts, from the crawlspace. If you seal the underside of the house from the crawlspace, you have to be sure that the floor assembly can dry to the inside. IMHO, the first mistake was made putting the ducts outside of the house. I guess that that a third choice might be to move the whole HVAC system inside the house envelope, ducts and mechanicals. You could install mini splits. You have to do the arithmetic. Unfortunately, I don't think that fixing your new house will be inexpensive.

Read up from sources in your climate area. The local land grant universities in your state and ones with similar climate areas are a good source. Buildingscience.com is good too. Universal building codes are sometimes not specific enough and US building practices are often biased to cooler, less humid climates (vented attics). Common building practices change very slowly and are way behind the times when it comes to AC duct location.

You might want to call in a professional to guide you because this is important and it is expensive. I am not there to look at your house and I am not a building professional so I might be missing something obvious. What I do know is that I would not rely on anyone that is selling something to solve a problem like this. Unfortunately expertise of the kind you need might take some digging. Some home inspectors may be able to help ,other not. A lot of energy raters should be qualified, but may not have the experience you need. An engineering consulting firm that does a lot of residential work, including energy ratings and home inspections, might be a good source. I think that you'll have to educate yourself somewhat in order to even choose an expert. Talk to a few and outline your problem and see how they respond before you hire someone.

This post was...

Have to agree with Ionized...but based on La. climate..
great LSU link..loaded with info, although climate specific.

how close to the ground is your house?
how close to the ground are ducts & plenums?
hard pipe ducting, not flex?

there is lots of conflicting information..even among
trades people.
open crawl
vented crawl
semi vented crawl
non-vented crawl.

the only thing that is the same in all of these
scenarios is that the vapor barrier has to be complete,
and sealed to pilars, or walls of crawl.

here where I live in La. we have open crawlspaces...and
houses with ducts in floors that are low to the ground...
like 2'..have wet ducts, plenums, equipment. just not
enough air flow in and around ductwork & equipment.

when you get to 3' crawlspaces the problems lessen...
again because of increased air flow.
4' and higher..usually no problems..some of our
houses were raised 8' due to flooding from hurricanes.

on another forum, I know a guy who's company does
enclosed crawlspaces in NC. great work from the pics he
posts & a very intelligent guy. if you'd like drop me an email
& I'll send you his user name & the website where we are
pro members. while I don't have issue with posting website
here, I don't want to post his user name. so ...email.

best of luck.

For less expensive alternative check out Tjernlund Products, Crawl Space Ventilators

mydreamhome, it honestly sounds like the issues you had with the encapsulation was the company you used to install the system.

To comment on the Atmox system vs an encapsulation, lol honestly you can not compare these 2 products as they are installed to do 2 different things. While they will often be rolled out to compare one against the other, the truth is that it is just a sales gimmick. Encapsulations are installed to control moisture in a crawlspace and as a by-product of the dehumidifier you will get improved air quality (when a proper dehumidifier is used) along with many other things that is topics for different posts I think. Atmox is a air circulation/air quality system that will help with moisture as a by-product. It is not a fair comparison to pit the two against each other.

Atmox in general, this is a system that seems to be taking advantage of the resend crawlspace "boom" if you will. Since around 2006 many studies have been done on crawlspaces and those studies are all saying the same thing. Crawlspace vents do more harm to a crawlspace than they do good. Even with proper air circulation you are still allowing warm moist air into your crawlspace, that warm air will collect on the wood members and allow fungus to grow (mold, mildew and yeast are all types of fungi). I will say that I have ran tests where I have installed 2 power vents in a crawlspace along with 2 fans to add to the air circulation for 3 weeks and what I found is that while the humidity in the air was lowered the wood moisture content did not lower (went from 18.3 to 17.9%). I then replaced those and preformed and encapsulation. In just 2 weeks time the wood moisture content went from 17.9% down to 13.1% in another 3 weeks it went from 13.1 to 9.8% and the levels remained at that range 6 months later.

I would just like to say again, these are 2 different systems that are installed for 2 different reasons, please contact a true professional to find out which will work best for your home. One last note, Atmox is a named brand that uses a rather cleaver way to connect different power sources into one outlet, installing power vents and fans will get the same results if you are a DIY individual but will increase the electrical outlets needed and power consumed (around $10-$50 monthly).

Pelkeytm,

I'm confused. So are you advocating the encapsulation idea and disparaging the Atmox system ? There are two trains of thoughts here in NC, and no one agrees on what is best. Within the crawlspace area, mold remediation companies like the Atmox system, and HVAC companies like the idea of encapsulation within the crawlspace area. That begs the question of what about the metal ducts within the conditioned portion of the house, do they need to be insulted to prevent condensation ? I would so appreciate your thoughts !

I am in S.E. NC and also have humidity problems in my crawl space. I am going to replace the vapor barrier that is in bad shape. My question is what would you think of ducting hot air from the attic in the summer to the crawl space? In my home this would not be that hard to do. Thanks, David

My question is what would you think of ducting hot air from the attic in the summer to the crawl space?

The hot air in the attic would most likely have a higher humidity than the air in the crawlspace. When it cools in the crawlspace, the humidity will condense on all of the cold surfaces. So I'm not sure that would solve your problem.

I'm in SC and I encapsulated and totally sealed my crawlspace and then spray foamed the brick walls. My humidity stays around 30% in winter, 40% in summer. It's made a huge difference, esp with the smells and dust.

Depending on how much of a diy'er you are and how accessible the crawl space is you can do all of this for $1500 (I bought spray foam off of ebay...was skeptical but it was the lowest price and worked great). I bought all of the encapsulation stuff from a company in SC. See link....crawl space company

"what would you think of ducting hot air from the attic in the summer to
the crawl space? In my home this would not be that hard to do."

That would utilize the principle, "Hot air never rises?"When I lived in Charleston the attic air was very humid.. why would you want to put hot humid sir into the crawl space during the summer? Or in the winter, come to think of it?

Have not checked this in a while “sorry” will try to comment on all the posts.

Victoria Dawns, they are absolutely 2 different trains of thoughts and honestly there have not been enough scientific research done on the Atmox system to give you a concrete answer. I will point this out, encapsulations are designed to remove all excess moisture in your crawlspace by not allowing it to enter. Plastic barrier will prevent moisture coming from your hollow block and from the ground from effecting your woodmembers, the dehumidifier will take care of the moisture your home will create naturally. Atmox allows humidity into your crawlspace but claim that the air circulation they are installing will remove the moisture. It’s impor to remember that as air comes in your vents the moisture brought with it goes straight up, it does not get circulated throughout your crawlspace. Most states infact require at least 4 different wood moisture content readings before a contractor can claim that you have a moisture issue. Now that is not checked up on and is something that homeowners are unaware of but humidity ratings in a crawlspace mean nothing, it’s all about the moisture in your wood members. So Atmox is allowing it in and moving it around, where is it going?? Most descent foundation power vents (fans connecting to your vent to remove air) run at 8cfm’s (cubic feet per minute). A tiny 1000sqft house will have around 3000cubic ft of air space in the crawl meaning it will take 6+ hours (if installed perfectly) to cycle through all the air in your crawl. In 6 hours the humidity is already in your wood....

Rich, great for you but remember that homeowners contract out work so they never need to go into their crawlspace so the materials you are using are of a lot less quality than what a contractor would use. I have not check out the link because it reads like an advertisement for what ever company but I can assure readers of this post that the quality is not the same. A $200 dehumidifier will work in a crawlspace for a year but a $1500 will work for 15-20 years, you can do the math.

Dhrockypoint, please do not do that to your home. I think other posters have stated why your shouldn’t.

I will I’ll leave you all with this link, I did not create it but I absolutely love it and refer people to it for their knowledge. http://homeenergypros.org/m/blogpost?id=6069565%3ABlogPost%3A80783

You assess a companies products by simply reading a URL? Good for you.

I went to the companies warehouse to pick up the vapor barrier and their products are USA made and far superior to what the "pro's" and contractors are installing in my neighborhood (Crawlspace medic etc). I have no relationship to this company other than being a very satisfied customer (and lucky they were within an hours drive from me).

As for the math... The OP got an $11,000 quote. I did my own for $1500 (including spray foam). It's labor intensive but if you have the skill to do it you can save a lot of $. It wasn't even really that hard to do compared to the other remodeling I've done. Here's a picture of mine before I spray foamed the walls. Previously this was all just dirt.

Rich, first let me apologize for thinking your post was an add. Now about the job itself, can you tell us what you used? On the site I am seeing 20mm reinforced vapor barrier for $495, not sure how big your crawlspace is but the pic looks like you would need 3 rolls of it. That itself is as much as you claim to have spent on the entire project. Add to the the cost for a Dedicated GFCI outlet that would need to be installed, the dehumidifier (do you have one?), the HVAC contractor (for most Crawlspaces) that would need to come out and inspect your unit then all the little items like seam tape that costs $32 for 50 feet and the list goes on. All the little things that DIY homeowners don’t take into account.

Now then you say that your humidity is at 30% in the summer. As someone who has spent all of his adult life in a crawlspace I can tell you that if that number is accurate then you need more. Encapsulations are (should be) advertised as moisture reduction treatments not elimination. To little moisture in your crawlspace is bad for your wood memebers just like to much is harmful. Now wood/moisture content is what is important, not necessary the humidity. A 30% humidity will take your wood moisture content down to around 6%, this number is way to low, healthy wood need to be 10-14%. Drying wood out to much will make it become brittle over time and with all the weight above it dry rott can do serious damage to your home.

You are absolutely correct on one account, for DIY people, encapsulations are not hard work. Very time consuming and attention to details are key for them. As a professional, I will say that the first step in an encapsulation (after inspections) is completely removing all debris, rock and leveling out the ground. That sir is a lot of hard work, there is a difference between what you shown and what a professional does but it does cost more unfortunately.

Nice job Rich. Your crawlspace is the envy of everyone that has one. As far as moving air through the space goes, we have to think about the dynamic state of the water saturation of the materials. The ABSOLUTE humidity of the AIR in the attic, crawlspace and all of the outdoors will be similar at all times if air circulation is reasonably free. As you blow air in from the attic, if you choose to do that, the RELATIVE humidity of the attic air will be lower than what is in the cool crawlspace. That is not because the air has less water in it, it is because it is warmer, lots warmer.

What that means in a practical sense is that after a damp period, when the underside of the house is cooler than the rest of the environment and thus under condensing conditions, pumping through warm air from the attic will dry it out faster than allowing ambient temperature air to circulate freely through there. The same thing applies to allowing or forcing ambient air through there faster than would otherwise occur. Temporarily sealing the cool space off if the ambient ABSOLUTE humidity increases above condensing conditions down there can also help. All this can contribute to a lower average level of moisture in the building materials bordering the crawl and that might be useful. You are still, however, at the mercy of ambient air and soil moisture levels. The only way to truly seize control is to seal off the crawlspace or seal off the bottom of the house.

Don't forget that both the soil and the air are INFINITE sources of water with respect to our puny homes. The crawlspace side of my house is alike a glass of ice water sitting on a rack over a puddle on a humid day! Where I live in the summer, I don't want my crawl space to warm up. I want it cool and non condensing if it is coupled to the house thermally and hydraulically. The only way to do that is to seal up the crawl coupling it to the moderate-temperature earth while preventing the moisture from the earth from passing through. Note that this open craw was not so much of an issue before we added mechanical cooling.

If I can't thermally couple while hydraulically isolating, the bottom of the house has to be sealed up like a boat bottom and the floor assembly needs to be able to dry to the inside. At that point, the amount of moisture in the ground underneath or in the air flowing through matters not a bit.

The only problem with the boat approach is accessibility of the plumbing and other utilities as well as what happens with the inevitable plumbing problems or large water spills. That is not a minor problem. Just compare the picture of Rich's beautiful bottom, that he shared above, to the view of the underside of a boat while thinking of getting to pipes either in full view or hidden by a beautiful boat bottom.

"Nice job Rich. Your crawlspace is the envy of everyone that has one."

Wow! I'll say. (Much better job than a "Pro" did on my crawl space in Charleston, SC.)

Now where do the vermin and snakes live?

Salti, they are under my house.

With jobs like this, I bet it is not unusual to see great jobs by the homeowner compared to contractors. i am not being negative. It is a simple fact that we can't afford to pay them enough money to spend the amount of time to buff every button as brightly as Rich did.

pelkeytm,

A lot of conflicting details. I was thinking of sealing the crawl space vents but decided not to do this. Radon can build up and trap in sealed vents and nowhere to escape except going to the upper floor of the house which isn't safe. Fral FDK54 Low-Temperature Dehumidifier is installed recently with regular liner plastic on top of the ground. It is not fully encapsulation. HVAC system is installed in the attic. Outside radon is lower than inside house. I was going to install intake and exhaust powered vents and the remaining of the vents to be closed with removable covers. You mentioned that powered vents could bring warm climate in and cause floor joists/broads to grow fungus/mold. Electricity bill seems to be a cheaper option for letting the dehumidifier running in openly automatic vents than spending thousands of dollars to have it fully encapsulation. RH 99 reduced to 50 percent level range shortly when the dehumidifier installed at the beginning. Do you recommend to let the dehumidifier running in openly vents?

Eric, I would absolutely recommend allowing your dehumidifier to run. Crawlspace dehumidifiers will have/should have an internal humidistat meaning that the dehumidifier will only kick in when the humidity reaches a certain level (generally 55%). As for the electric goes, most good dehumidifiers are energy star and run about the same amps as your tv. When you keep in mind that it is not constantly running, only when it needs to the amount your actually spending to keep it going is minimal. Once acclimated to the crawlspace it should only be kicking on once or twice a day for just a minute or so. Opening up the vents will allow more humidity back into your crawlspace so when you do turn on your dehumidifier it has to work harder and longer, both using more electric and wearing down the life span of the unit.

I will not go over the radon aspect, most trusted contractors will tell you that radon treatments are a scam, a way to scare homeowners into spending money. Radon is a naturally occurring substance that you can not get away from, it’s everywhere. You actually intake more radiation (radon) from the food you eat than from within your home.

The service that you had completed we refer to as a closed crawlspace. Seal up the vents, apply a good vapor barrier and install a dehumidifier. This is an excellent choice for most homes and is generally 1/4th the price of a full encapsulation. Very smart move on your end on selecting that route. I have taken anhome with a wood moisture content rateing from 38% down to 9% in less than 3 weeks, it is very effective.

Running a dehumidifier with vents open makes as much sense as running a heater or air conditioner with windows and doors open. There is conflicting information because old, traditional homebuilding techniques are better suited to cool, dry climates and homes with no mechanical cooling. Updating to match new reality is very slow among builders and building code writers. In addition to the ones I posted earlier in this thread here is a helpful paper about crawlspaces. It is pretty simplified, but if anyone needs more background, the site probably has it:

BSI-009: New Light In Crawlspaces Joseph Lstiburek MAY 24, 2010

pelkeytm, you should not have gone over the radon aspect. I've seen radon remediation work. The question is necessity. The biggest problem I see is that with home sales, people are forced to take action after spot checks that are biased to finding a problem. Long term monitoring should be done. You won't be eating radon in your food. It is a very small gas molecule (passes through just about any kind of way of sealing things that you might imagine.) Even if it had a property that made it partition into vegetables and has a pretty short half life, 3.8 days. It decays to a lead isotope that has a half life of 23 years before hitting bottom as a lead isotope via some other less stable atoms.

Radon is not everywhere, only in some areas of our country. Maps are readily available. In areas where it is a problem, it will always be there because it is a product of uranium (long half life) decay. I would think that a radon in crawlspace problem would be easily handled by keeping that space slightly negative pressure relative to the living space and not have any purposeful air connection.

Well this Fral FDK54 Low-Temperature Dehumidifier runs on 500 watts not alike portable heater uses 1500 or more watts, and small window air conditioner runs 1000 watts. I will verify with the bills next several months. It seems that the dehumidifier doesn't run all the time with 16" x 6" opening vents. I can close some of the nine vents and leave two vents open to let the stale out. In 1000 sq ft crawl basement with 3' height of walls.

eric62, That dehumidifier is a typical low efficiency model. What is the humidity level in the crawlspace with that going? Maybe it does not run all the time because its humidistat is defective.

Power venting a crawl space will likely only act to dry it when the humidity is on its way down from high levels, or after a flood under the house. the dynamic situation. It will do nothing to help in a typical situation. Sometimes it will wet it sometimes it will dry it. The dew point of the joists and floor, depending on what kind of insulation you have, will often be low enough to cause condensation.

Go ahead and run your dehumidifier with the vents open. Do you run your oven with the door open and fill your tub with the drain partly open? When you change the oil on your car or lawn mower, do you put the drain plug in tight or leave it loose so oil drips out during the fill?

This dehumidifier will kick in when the humidty gets too high. I had several water standings in several areas at the beginning before the dehumidifier, and afterward, they dried up easily shortly with the vents open with the dehumidifier installed. The remote HR continue reads various 46 to 55 till now. Most of the time it reads around 50 percent, It is not alike for the oven, or the food will not be cooked thoroughly if the door left open and also the car engine will break down with no oil. Pure the dehumidifier runs without trouble if the vents are opened or closed. At least I have some fresh air coming in open vents. I can decide to close the vents when I need to.

I have been researching ATMOX systems for about 7 - months now and there is absolutely nothing in this conversation (thread) about the ATMOX system that you all are having that is correct. I believe that you should not rely on the advice given on this thread about the ATMOX systems. I recommend that you go to their website. I am still undecided about ATMOX even though I just installed their system in my rental house. I encapsulated and installed a dehumidifier in the home last summer but found myself worrying about my tenant being able to afford the power bill. I was also uneasy about the crawlspace not getting any fresh air. So a couple of weeks ago I installed the ATMOX system. Now whenever the air outside is dryer than the air inside the crawlspace the fans will come on. There is a 15-watt, 225-cfm intake fan and a 15-watt, 225-cfm exhaust fan which will give my 2,000cuft crawlspace a complete air exchange every 9 - minutes. There are 4 - 10-watt, 145-cfm deadspace fans that will circulate the dry outside air to the remote corners of the crawlspace. The total wattage of the system is only 70-watts compared to 500 or so watts being used by my Sante-Fe Compacy 70 dehumidifier. I checked the moisture level of the wood throughout the crawlspace and will check again in a few months during the hot muggy North Carolina summers to see if the system is working or not. Also, one other thing, the computer in the ATMOX calculates the dewpoint of the outside air as well as the indoor crawlspace air and when the air outside is drier than inside the crawlspace air fans will come on. There is no other system on the market that I am aware of that can do this. All other crawlspace vent fans just measure humidity which is not what you need. You need a system that compares outside and inside dewpoint and ATMOX has the only license to build this system. I hope that my gamble is right but I wont know until the summertime. Until then I am just as ignorant as everyone else on this thread about the ATMOX system. At least I admit my ignorance.

@HU-563552721, I live in southwest Ohio and purchased a home a few years ago with standing water and moisture/rot issues in the crawlspace requiring professional mold remediation and a whole lot of DIY elbow grease to shore up and replace damaged framing. I also regraded and addressed gutter issues to remove the standing water situation. Since then, I've been operating the foundation vents and dehumidifier manually, switching among three configurations:

1. Winter: vents closed, dehumidifier off

2. Spring and fall: vents open, dehumidifier off

3. Summer: vents closed, dehumidifier on

I do this based on the ambient dewpoint. When the outside temps are doing to dip below 30F, I use configuration #1. When outside temps will stay above 30F and dewpoints are below 55F, I use configuration #2. Once it gets to June-August with dewpoints creeping into the 60s and 70s, I use configuration #3.

In two years, I have not had any return of mold, the crawlspace smells fresh, bugs are few and far between, and radon is drastically reduced in the living space when the vents are open. I get compliments on how dry and nice my crawlspace is, and I haven't insulated or air sealed anything. My home lacks ductwork (has a mini-split instead), so I don't have any HVAC to deal with in the crawl.

The "dehu" costs $40/month to run continuously (and it does, during July and August), so taking advantage of ambient ventilation when the dewpoint is low saves a chunk of money and wear+tear on the dehu; as a side benefit, it cuts indoor radon levels by 4x.

The ATMOX system, from what I can tell from an e-mail exchange with the manufacturer, basically automates my "common sense" approach so that I won't have to fiddle with it myself. I like how it can switch the dehumidifier on when the weather gets really dank. It just makes a lot of sense to me.

My concerns with the system are that a) the banana plug connectors and phone jacks look and ARE cheesy, so I wonder about the rest of their design; and b) last I checked with them, the fans' speeds were not monitored by the controller, so you could have a fan lock up and never know. Will the fans burn up when they lock up and fail? Four-wire fans with tach feedback are cheap, so I don't know why they didn't do this. Otherwise, it's rather appealing.

No connection to ATMOX, just an interested homeowner who hasn't pulled the trigger on a system yet, so I'm very interested in how your installation went and how it works for you in the coming season.

W

I am looking at ATMOX now vs total encapsulation. I am leaning away from total encapsulation for several reasons. I still think the under side of my 100 year old South Alabama home still needs to breath some. And I do not think it is a good idea to encapsulate the older more soft burned brick piers where they remain wet all the time. I believe this can lead to issues with the there condition. They need to be able to dry out some. Just one of several reasons.

I bought this house 25 years ago and have spent many years and $s restoring it. I had Terminex and another company come in this week to assess the condition of the underside after i spent 5 hours under the house this past Saturday myself.

The good news is that it looks like the from testing the wood at around 2-3 pm the past two days in various spots under the house that it ranges from 12- 17 %. I would like it to be lower though. Very little mold or fungs issues. The base of the house has 16 vents and 4 crawl space doors that are also basically large vents as well for open air flow but have expanded metal with screen as do all of the air vets mentioned.

My primary objective is to see if I can reduce the humidity that I would assume is flowing up from the crawlspace into the first floor of the house and we are and have had some humidity issues withe a few pieces of framed artwork and a few clothes as well over the year.

I installed a vapor barrier 20 years ago and it is ready to be replaced as well. I am interested to hear from anyone utilizing a ATMOX now and have they seen it help in the area I am trying to address which is obviously the crawlspace as well as even more importantly the humidity in the living area above.

My house footprint is 3300 sq ft and what is proposed is the Atmox System utilizing 12 volt fans to generate airflow as noted by others above tied into a monitoring system and will have a dehumidifier to help in the most humid hot months of the Summer.

I know some will tell me it won't work. I am not interested in total encapsulation and am not going that route. So please if there is anyone that has an ATMOX System I would like to hear what you think about it either way.

Thank you.

I installed the Atmox system this past January. In June I noticed that the wood humidity went up in some spots from about 14 to 19. I called Atmox and they told me to move their inside crawl space sensor to another location. A few weeks ago I tested it again and noticed that it was creeping back down to about 17. Thus far I cannot give a definitive on whether or not I would recommend this product. If I had to make a decision today I would choose not to use Atmox. It would be nice to hear other peoples' experience with Atmox. I do not believe that the Atmox system has been vetted properly.

On another topic, if you plan to use a dehumidifier inside your crawlspace you will have to encapsulate it otherwise you will be drying your entire neighborhood.

@HU-563552721 Did you block off all unused vents and add a dehumidifier? Where are you located? If ambient dewpoint sits in the 60s Fahrenheit for week after week in the summer, you're going to need a dehumidifier.

I'm in southwest Ohio and have had the ATMOX system on my "someday" list after other repairs to the home. For the time being I adjust my vents and dehumidifier manually, based on the weather. In the peak of summer I run the dehu and close the vents. Opening the vents works great in fall and spring. Once temps fall below freezing at night I close them. They aren't airtight, but they don't have to be. In the winter, ground heat warms the space to keep relative humidity down.

You don't need a total encapsulation job or perfect air sealing to effectively use a dehumidifier. Just make sure the vents are blocked/closed enough during dehu operation so there aren't huge leaks. Around here, the hottest, muggiest summer days have zero breeze, and the cool air sits down in the crawlspace where the Santa Fe Compact2 has no problem capturing the moisture. In autumn, cold fronts bring in drier air from the north, and free ventilation becomes very effective. If the weather forecast calls for rising dewpoints (60s F or above), I revert to the dehumidifier and close the vents again. If the ATMOX system can automate this process, it will ventilate most of the year and run the dehumidifier for 2-3 months when it simply can't find drier air outdoors.

They do have louvers to fit over the fans. What their system lacks (or did lack, when I last spoke with the company) is any use of diagnostic feedback from the fans. They use cheap axial computer fans on custom mounting plates. These fans are commonly available with a speed feedback signal that can be used for failure detection. This is important when the fan is in an area that is difficult to access. Additionally, I would much prefer individual fan control channels so that a failing fan can have its power source cut promptly. They should improve their controller to have a separate port for each fan and allow multple indoor humidity sensors to detect local humidity hotspots and provide redundancy. I also take issue with their use of cheesy banana plug and RJ-11 phone cord connectors on what becomes a critical piece of a home's infrastructure. They should at least have a steel box to enclose the wiring.

I see a lot of potential problems with encapsulation. A lot of companies sell the service without any real industry standard on how it's done or the materials that should be used. The "basement system" type contractors I've encountered wanted to sell me an expensive one-size-fits-all solution, but they don't understand the building science behind what they're selling. Hiring one of these companies is a huge up-front financial commitment with questionable ROI. The rigid foam board on the rim/band joists limits drying potential of the band/rim joists to the inside (which would be a serious problem with this home) and makes a terrific habitat for pests. You're paying $10k or more for a glorified pool liner and a whole bunch of painstaking installation labor in a cramped environment where quality workmanship is difficult. Once installed, that liner will look really sharp until workmen tear it up to replace an HVAC unit or work on your plumbing. Nobody except you will know or appreciate how much money you spent on it. A full encapsulation doesn't address soil gases or "cat urine" fungal smells that find their way around the vapor barrier, nor radon.

Once you encapsulate, you have to exchange air with the crawlspace somehow. My crawlspace is dry, but it's still not a clean space. I can confirm that the cat pee odor phenomenon is real, and I have no interest in exchanging my home's indoor air with the crawlspace... ever. I've put my efforts into air sealing the floor system and controlling the crawlspace humidity without trying to turn it into a clean, hygienic environment that it was never designed to be. Encapsulation may work for some, but I'd rather put the cash toward fixing water issues outside (grading, downspouts, drain tiles) and then put down a cheap 6-mil vapor barrier, lapped up the walls, knowing that it's going to take some abuse over time and won't last forever, and then address humidity with a dehumidifier and/or smart ventilation. My Santa Fe Compact2 costs $40/month to run a few months per year. At $200 per year for electricity (a high estimate) and a new dehumidifier every five years, it would take a long time to break even.

I may see about buying their fan mounting plates and build my own controller with a PLC, so I know exactly how it works and can change the programming.

Not affiliated with ATMOX, just another homeowner who's renovated a home that suffered from decades of crawlspace neglect. If I absolutely had to do a crawlspace in a new build, I would enclose it and pour a concrete floor over the vapor barrier. I'm just not convinced encapsulation makes sense in a retrofit situation.

Thank you for your feedback. I too wish the Atmox System would relay back if there is a problem with a particular fan. The way I understand it is that just notifies that there is a problem with the system and is needs to be checked.

It would be better to have each fan and component feedback directly so you can know what is going on if there is an alarm code. i did talk with them to see if they have an app so you can see what is going on with the system from my phone. They said they are working on it and should have it in 2021.

I live in SE Alabama with lots of humidity. My house is 100 years old and I have been in it for 25 years. My primary reason for looking at doing something is reduce the humidity in the first floor. It can get up to 75% on some days in a 24 hr period and go down to as low as 50% during the same 24 our period. I have hardwood and pine floors (all original) and I have never had a cupping issue.

What the house dose not have (and I am not willing to spend the money to do them) no floor insulation, no wall insulation and it is a wooden house. I do have a vapor barrier and I am in the process of preparing the crawl space to replace it on the 3300 sq feet. My crawl space is around 24" from ground to bottom of joist and to subfloor is about 30"on average.

I have very little mold in the space and on a very hot humid day this week the wood moisture in the joist and subfloor was 13 - 17 %. I have 16 - 8 x 16 vents that are just natural air flow and four roughly 20 x 20 crawl space doors that also act as air vents. They are all open for airflow all year around.

In some repects I am hesitant to do anything different for fear of creating problems I don't already have ( such as doing something that would damage my floors which would be catastrophic).

Back to Atmox, I agree with you that I wish the monitoring system was a little more robust. I worked in my family's robotics company for many years so I am familiar with PLC's and what they can do. A very small one would be great upgrade for the system.

Again, I appreciate your feedback. If I do something different I really need to have a system that will manage things automatically. That is why I was looking at Atmox after my Terminex service mentioned I should look at it if I was considering encapsulation. I am not considering encapsulation after reviewing my specific situation.

I have spoken with Atmox a few times over the past couple of weeks and others that install it in the Carolinas. I am still thinking on it but think the system does have merit. Are you sure about the wall mount fans having closing vents. I thought they told me they do not. To me that seemed like it could be an issue when you are trying to keep humid air from entering the crawl space. I think they said the sensor on that exterior vent would kick on if it detected humid air trying to enter. To me it would be better and more efficient to have closing flaps that would close when needed..

Would love to hear your thoughts.

How many humidity monitors does Atmox utilize on your System? I would hope it would be several. I just purchased a system to monitor the humidity in 4 areas in the crawlspace and it will map it for me so I can see what it is doing before I do anything, It cos me $125 on Ebay. Looks to be pretty nice littel system I just have to finish setting it up.

-Yes, they do in fact have intake and exhaust fans with louvers.

-I have to agree with you that finding someone good to work on your crawlspace and understands the science is quite difficult.

-I did not know that some of those type motors have features that will alert you if they are malfunctioning. It would be nice if Atmox utilized those features.

-My Atmox system uses only 2 - humidity sensors, one indoors and one outdoors. I believe that you want the indoor one to be in the most humid area of the crawlspace.

-FYI, You want your intake fan to be where there is not a chance of a car or appliance emitting fumes that will be sucked into your crawlspace by your intake fan.

-It's been a few weeks since I have checked my wood moisture. I will try to this week and let you know if it is trending in the right direction. It's been dry so the readings should reflect this.

Take care...

Thank you and I look forward to hearing back from you on it. Curious to know how many fans are used on your system - interior fans to move air around, how many exhaust and how many intake or do all of the intake and exhaust fans reverse and push air out and take air in or are they dedicated to one or the other? I can't remember what your sq ft was on the house you installed it under?

I am currently working under the house now with a couple of guys and over the next few weekends to address any mortar joint issues that need patching ,etc., installing a few strings of led lights to leave under there so I can see in the future, shoring up a few weak spots in the floor where they didn't use the correct things to address it before I bought the house 25 yrs ago, checking and redoing some of the duct work, and then we are going to take the 20 plus year vapor barrier out that Terminex put in. It was 6 mill clear and since I have decided not to do a total encapsulation, I am going back with a 10 mil black.

My plan is to over lap by 6-8 inches at the seams and use the metal landscape fabric pins to hold it in place and then place three inch black over them to seal the holes from them some.. Just haven't decide if I should go up the foundation wall a few inches or not and whether I should seam all of the seams. I am curious to know what you did in this area.

Thank you and I appreciate the feedback.

.

Then we are going .

@T Burns I don't have an ATMOX system, but from what I've seen they have one inside and one outside sensor input on their controls. One outdoor should be sufficient, but for a large crawlspace I'd prefer more than one just because humidity CAN be localized if there is bulk water such as a flood or plumbing leak. My home had mold and rot only in certain areas--generally the east (downwind) side.

The ATMOX optional louvers don't appear air-tight but passively flap down over the opening when the fan isn't running, like on a dryer vent. It's probably no worse than a typical sliding crawlspace vent.

Plotting temp and RH over time is a great idea. From there you can obtain dew point and get an idea how often an ATMOX system would be able to run with just fans to keep the RH below 60%. With tight clearance between floor framing and the ground, the joists will track ground temperature by radiant heat exchange unless you have lots of airflow. You can get an idea of what RH will be at the joist surfaces by looking at those temperatures and figure out what max average dew point should be allowed. From there you can look at historical dew points for your area and get an idea of what percentage of the time fans can actually dry the crawlspace. As the ATMOX folks point out in their literature, it takes an extended problem to elevate wood moisture content enough to cause mold. You may be able to get by with a dehumidifier for half the year or less. But I would definitely not install one of these systems without a dehumidifier as backup, integrated into the control logic. If nothing else, it will come in handy if you get a flood or a fan goes bad and you need brute force drying.

There might be some aspects of encapsulation that could benefit your situation, but I'm leery about arbitrarily introducing spray foam, foam board, or plastic-wrapped batts, like the Youtube encapsulation guys do, without really thinking through the moisture transport situation. You could easily end up trapping moisture or hiding rot or termite activity in an old house that wasn't built to modern codes. For example, my home has poly flashing between the rim & band joists and the brick, lacks a brick ledge, and was not built with pressure treated sills. If the brick really gets soaked, the framing gets damp. This is a once-a-year event at most, but it has a way to dry. The last thing I'd want to do is to trap moisture in the lumber. Also, my home's crawlspace vents also admit air to the gap between the brick and sheathing, and blocking those gaps with foam board will reduce ventilation behind the brick. Retrofitting an older home has to be taken case-by-case. I wouldn't trust most one-size-fits-all encapsulation contractors to consider that.

I would probably never be totally satisfied with an ATMOX system, since the control logic isn't arbitrarily customizable, but it's an incremental improvement over full-time passive ventilation that we know doesn't work in summer. Automating the ventilation and combining occasional dehumidifier use may be all you need to banish the mold if there are no drainage issues. Thanks for the tip about the upcoming revision. I'll have to get in touch with them to see if they're adding fan diagnostics.

So I checked the wood moisture and it was 14% which is down from 17% about 4 - weeks ago and 19% about 8 - weeks ago. I am not sure whether this is due to the weather being drier or due to me moving the indoor humidity sensor to the moistest area in the crawlspace. While I was down there I removed the louvers from the intake fan since we are heading into the drier season. @Werhat your two posts are quite helpful. In my other home I have cut off my dehumidifier and opened up all of the crawlspace vents. Also, in my other home I have a really tight crawlspace under a room that is about 16' x 16'. I cannot get the wood moisture down to reasonable levels so I am going to buy 2 - pipe fans from Atmox and run them in there. I will probably use a standard DC power supply instead of buying theirs.

I definitely agree with you that old construction may not be a good fit for encapsulating the walls. Those old bricks do not need any more moisture than they have been subjected to for all of these years.

Thanks

For my other home I ordered some cooling fans and 12v DC power supplies from a company called cooler guys.

https://www.coolerguys.com/products/coolerguys-172mm-7-172x153x51mm-ip67-12v-fan?variant=31800013160544

I plan to run them non-stop in my uber-tight crawlspace area.

My other home does not have an Atmox system but if I ever get one I will be able to use these fans on an Atmox system. Alternatively if I figure out a way to build a plc that calculates dewpoint I may build my own system.

any ideas on how to get rid of the cat pee smell in a fully encapsulated crawlspace? We live in NC and had ours fully encapsulated and all vents sealed about 2 years ago. and now it's gotten to the point where the smell is coming in the house. DryPro now suggests that we replace the vapor barrier and install their plastic waffle underlayment and then reapply a new idential vapor barrier and install atmox exhaust fans in 2 of our vents. the rest of the vents will remain sealed. problem is there is no air coming into the crawl, so i'm not sure what good all this will do

Interesting that they want to install 2 - atmox exhaust fans but no intake fans and no open vents. When they fully encapsulated the crawlspace they should have sealed every opening between the crawlspace and the interior of the home. If they did seal all openings then the air will have to come from vented appliances in the crawlspace which are supposed to vent gases to the outside of the crawlspace. This is very dangerous. You might want to check with your local building department. There are codes in the NC building code book that must be followed. Give them a call and see if you can pay them to take a look at your problem.

Will your atmox system include a controller plus an indoor and an outdoor sensor in order to calculate dewpoint?

What is the highest wood moisture reading in your crawlspace? This will determine what steps you need to take to mitigate moisture and now the cat pee smell.

Did DryPro install a dehumidifier or a supply air inducer? (This attaches to the rigid supply trunk in the crawlspace, thus pumps conditioned air into the crawlspace whenever the HVAC system is running).

Did DryPro prevent all outside water from entering the crawlspace?

@Durbar Biswas The cat pee smell comes from decomposing organic matter under the vapor barrier. I can smell it in certain areas of my crawlspace where air circulation is reduced. This is one reason why I'm not keen on retrofit full encapsulations that fail to account for the moisture, gas, and heat transport in the building. I would not add any air exchange with the living space lest soil gases, smells, and radon spread throughout.

You can add an exhaust fan but need to consider the supply air source. While I have not used ATMOX in my own home, the concept makes sense in that the crawlspace, being separate from the living space, should be independently conditioned with some amount of outside air. Find out if the system can be programmed to a minimum air exchange frequency so you don't end up with weeks of zero air exchange during the summer. The ATMOX rep told me a few years ago they typically use equal number intake and exhaust fans for pressure balance. The little axial fans aren't going to pull extreme negative pressure on the crawlspace, but you'll still need to design an intake into the system.

I installed the atmox system in my crawlspace about a year ago. It does actually run during the summer so it would take care of the cat pee smell year round. Whether or not it is actually helping to prevent moisture buildup in my crawlspace I cannot say for sure. Initially it caused an increase in wood moisture readings and then I relocated the inside sensor to the moistest area of the crawlspace and the last time that I measured wood moisture levels it seemed to be going back to its initial moisture readings from when I initially installed the system. If you do decide to go with the atmox system make sure you design it yourself.

Has anyone removed the encapsulation and had worse smell?

I have to amend my earlier post. I found a second local dealer who was diligent and honest. He set me up with the right people at ATMOX, and they resolved everything without it costing me anything! I am once again a happy ATMOX customer. It sure beats doing an encapsulation.