Why You Should Close Your Foundation Vents

By
Home Inspector with Allen's Pest Inspections
http://actvra.in/48Zg
Putting foundation vents on our homes is an old fashioned idea. We spend lots of money each month heating & cooling our homes & by having a vented dirt crawl space it raises your monthly electric bill 15% (to 25%) every month, and will lead to a bigger expense with mold removal & rotted wood replacement. It's not the standing water that causes the problem in the crawl space it's the water vapor, also called Relative Humidity, that destoryes the home. Understanding relative humidity & where it comes from and how to control it is what everyone needs to no about. Air is a very efficient way to move water. Air, including humid air, moves easily in and out of spaces. Air brings its moisture content with it wherever it goes. When air is heated or cooled, it's relative humidity changes. Crawl spaces are cool, because the earth is around 55 degress year round. So when we bring in warm humid air into the crawl the air is cooled, and the humidity goes up. Having higher relative humidity causes condesation which causes mold, wood rot, lost energy & brings more pest problems to your home. Please learn as much as you can about your home & how to protect it & your family from mold, wood rot & overall health concerns related to wet moldy crawl spaces.  
close

This entry hasn't been re-blogged:

Re-Blogged By Re-Blogged At

Anonymous
Post a Comment
Spam prevention

Accessibility option: listen to a question and answer it!

To submit the form,
drag the lamp to the circle on the side.

Type below the answer to what you hear. Numbers or words, lowercase:

Spam prevention

Accessibility option: listen to a question and answer it!

To submit the form,
drag the balloons to the circle on the side.

Type below the answer to what you hear. Numbers or words, lowercase:

Show All Comments
Anonymous
Anonymous
CyFree

And just to add some more resources to clarify some points concerning vented and unvented crawl spaces, let me offer a couple more links that will help shed some light on the subject.

The website

http://www.crawlspaces.org -

from Advanced Energy, an independent and reputable research organization has a ton of information on crawl space science, including studies performed in conjunction with Habitat for Humanity, on crawl spaces and their impact on home's energy efficiency.

The findings of another important study on crawl spaces and building science fallacies can be found here:

http://www.rlcengineering.com/csfallacies.htm

And more usefull resources can be found here:

http://www.dirt-crawl-spaces.com/

The point is, just because something has been done a certain way for centuries, decades or years, that doesn't mean that it remains being the best way. Things change, science evolves and we should at least keep an open mind, before we quickly dismiss a new concept without thoroughly examining it.

September 29, 2008 11:11 AM #45
Rainer
9,369
jamie allen
Allen's Pest Inspections - Evansville, IN

Most home owners are not sure what size or type of dehumidifier they should use thats why I made the point on not buying the most expensive model out there.

Most dehumidifiers have the ability to add on an extra hose to run into the sump pump pit or well so you don't have to keep dumping the tray as you suggested.

The Energy Star is good but it's only as good as the condition in which you are putting the dehumidifier into. For example if you stick a dehumidifier into an unconditioned crawl space with standing water and no vapor barrier you will never solve the humidity problem. The main thing here is that if you need the biggest unit on the market then use it but for most home owners it will be an overkill without the proper knowledge on crawl space conditioning.

Good luck,

 

October 04, 2008 09:19 PM #46
Anonymous
Anonymous
Ted

There are many theories on crawlspace ventilation. However, good science can prove or disprove a theory, The use of foundation vents to reduce moisture is a poor attempt to ventilate most homes in most areas. The foundation vent theory requires a great quanity of vents, most builders use one vent per 150 square feet of floor space which is a poor choice considering you are dealing with cubic feet of space not square feet.  A 40" tall crawlspace requires more ventilation than a 24" crawlspace. If a suuficient quanity of vents are installed , then you rely on prevailing winds making past other structures, through the shrubs and other landscaping into a vent through the crawlspace and out the other side of the home. This seldom happens! A study of fluid and thermal dynamics shows that temperature void of some means of conveyance will always travel downhill, in other words warm air naturally travels to cooler air. Therefore, warm air at 60% relative humidity is normally drawn into a crawlspace and cools, as the temperature drops, humidity goes up.  I have been told so many times that the HVAC ducts are sweating and causing high moisture in a crawlspace. NO, the high moisture content is causing the ductwork to sweat (even if it is sealed and insulated well). If and only if there are no water infiltration problems, then most homes can benefit from closing and sealing the foundation vents but again this is only if there is not a water issue. When a crawlspace humidity is at or above 60% for any length of time, there is a problem. I tell all customers a few things, gutter your home and discharge the water at least 5 feet from the foundation, plant vegetation near the home that is sturdy and requires little or no irrigation, never allow the irrigation system spray on the home. As they say the proof is in the pudding. I have been resolving moisture issues in crawlspaces for many years. If there is not a water infitration issue most high humidity issues can be resolved by closing the foundation vents. I install reasonably priced Honeywell wireless weather stations with a transmitter in the crawlspace and receiver in the living space and allow the home owner to monitor the conditions. On occaision we do install vapor barriers or encapsulate with a ploy material but this is a worst case senario. Treat the cause not the sympton. Conventional wisdom is not always correct. We used to build cars one way, now we use very little of that technology because is was flawed. A good experienced building analyst can educate most home builders and or inspectors beyond their wildest dreams. Again, theories are just that. The proof is in the results. Don't believe me, than just follow the crowd, right off the cliff.

October 01, 2010 10:45 PM #47
Anonymous
Anonymous
Lee

Not sure if anyone still monitoring this site but I wanted to throw out an issue and see if I can get feedback.

5 years ago, I cleaned out my crawlspace and laid down the thick plastic to pea gravel and up the walls(2005).   There were no visible signs of mold at that time and the home is a 1991 built home here in Indianapolis. 

Just recently I smelled mold in basement and went into the crawlspace to find a moderate size mold bloom near one of the foundation vents.  I cleaned with bleach and mold killer and also pulled the insullation between joists to check there as well.  I notice heavy wind flow into this vent and decided to baffle it some more.

I plan on closing the vents with the vent covers recently purchased , but my main question is did my plastic and renovation 5 years ago cause some preconditions for the mold growth?   My current plan is to cap the vents and then stick a dehumidifier in this crawlspace to drain to nearby sump pump.  Please give me any feedback.

December 13, 2010 05:06 PM #48
Anonymous
Anonymous
Lee

Additional comment to my Dec 13 post ;   I was just mainly curious why there were no signs of mold growth in my crawlspace when I went in and renovated with insullation and the plastic to floor and walls in 2005 (home is 14 years old at this point) versus now see mold issue starting.  Is the plastic itself adding to containing the moister and RH?  And if so, is the capping of vents altogether and then adding a dehumidifier appropriate corrective action?

December 13, 2010 05:12 PM #49
Anonymous
Anonymous
Jamie

Lee,

It sounds like you only did half of the crawl space conditioning in 2005. Once you encapsulated your crawl space with plastic, you must also close your vents and install conditioned air into the crawl space to help with RH.

I see this all the time here in Evansville and it's over looked by most people. You can add a dehumidifier to help reduce the RH, but you also must be sure to close your foundation vents.

Once you clean the mildew and make sure that there are no other leaks or water sources, you should be good to go.

Thanks and good luck.

Jamie,

December 13, 2010 11:06 PM #50
Anonymous
Anonymous
Jamie

Cynthia, you made some good points and suggestions in your comments. I agree with you that most home owners should not try fixing these problems without a expert.

A basic crawl space enclosure is easy to do and it doesn't take rocket science to control moisture & humidity in ones home. There are steps to be taking to make a completed crawl enclosure and most people leave out a couple of the important ones.

Even though your 20mil vapor barrier can help with radon gas, you should not say that this will keep someone from having radon in there home because radon can still enter at the block wall & sill plate and up into the home. It also can enter through water lines and other areas of a home. The barrier can make a big improvement, but it's not a cure all solution.

Thank you,

December 14, 2010 11:29 AM #52
Anonymous
Anonymous
Kenny Vincent

James, I am following along with your statements and I believe that you are correct, my background is being a ridiculously trained automotive technicain, that said, what would I know right. well natural laws, sceince and working on various air condintioning systems, and have had been trained in way to many air conditioning classes, i can just for a short awnser say I am following what you are stateing and believe you are correct, my question is this, could an advantage of keeping vents closed insulate the cool air created by the "ground" or "earth" help or atleast miminize heat gain in a home during hotter months of the year?

August 10, 2011 07:08 PM #53
Anonymous
Anonymous
Kenny Vincent

Ya so just realized this is an old thread... anyway happy crawlspacing to all!

 

August 11, 2011 01:09 AM #54
Rainmaker
18,664
Cynthia Freeney
Basement Systems Inc - Seymour, CT

I stand corrected James, concerning the Radon. I didn't explain myself well and thank you for clarifying. 

What I meant is, the barrier will act as a passive radon barrier, it will keep SOME of the radon, not all of it, from entering the crawl. A opposite to crawl space with closed vents and no air tight sealed vapor barrier, which would allow the Radon in and cause an increase in radon concentration indoors. 

You are 100% correct. Radon can and will enter the home by any openings, and any house with a high radon level, needs a real radon mitigation system.

A crawl space encapsulation system is not, in any way, a replacement for a real Radon Mitigation system, but it can be fitted to work with one.  

August 11, 2011 09:31 AM #55
Rainmaker
18,664
Cynthia Freeney
Basement Systems Inc - Seymour, CT

Answering to Kenny:

Kenny, yes. A conditioned crawl can considerably minimize heat gain during the hot months of the year, as well as heat loss during the cold months of the year.  Even if the encapsulatiod does not include any type of insulation. 

Conditioned crawl spaces prevent thermal losses by significantly slowing down the "stack effect". 

The stack effect refers to the way the air moves in buildings. Heated air rises, escapes though the upper levels (attic and roof). As a result, an area of negative pressure is created in the lower levels of the building. Outside air is thus sucked in from the basement and crawl space.

In fact, the two main components of a "green", energy efficient home are:

  1. properly air sealed and insulated attic.
  2. insulated and air sealed basement or crawl space. 
August 11, 2011 09:44 AM #56
Rainmaker
18,664
Cynthia Freeney
Basement Systems Inc - Seymour, CT

There is a lot of confusion surrounding this matter and by following the wrong advice you can make problems worse.

I work for the company that pioneered the crawl space encapsulation technology, developing the first encapsulation system in the world. So let me try to clarify this matter, based on our 20+ years experience in foundation waterproofing and moisture control. 

First of all, let me explain that sealing the crawl space with a vapor barrier is not the same as conditioning or properly encapsulating it. 

When it comes to controlling moisture in the crawl space, vents are proven to be a scientific fallacy. Vents not only fail to control moisture. They actually contribute to aggravate the problem. 

Closing the crawl space is always a good idea, no matter where you live. The laws of physics apply to any region. Even if you live in an an area with  cold and dry climate year round, and moisture is not a big issue, closing the crawl space is a good idea.

If not for moisture control, for energy efficiency. There are a ton of studies, conducting by reputable organizations, demonstrating that crawl space conditioning effectively controls moisture and make a home more energy efficient by curbing energy losses.

According to Advanced Energy , if you have ducts running through the crawl, the energy losses are so significant that you can literally forfeit all the other energy efficient improvements until you get that fixed.

The benefits of this process are so significant that it is now recommended asBest Practice  by the U.S. Department of Energy, and the U.S. Green Building Council.

That said, it is important to keep in mind that only proper encapsulation will work. That means, completely isolating the crawl space from the two main sources of moisture: the ground and the outside air. That is accomplished by sealing the vents and lining the whole space with a very sturdy vapor barrier. Floors and walls should be covered and the seams, openings and gaps need to be air tight sealed. This process will include the crawl in the building envelope. 

You will then need to condition the crawl space, by means of a crawl space conditioning system (a fan that blows air from the home into the crawl space) or by using a crawl space dehumidifier.  That is because, even with the crawl isolated from the outside, differences in temperature can cause condensation in the crawl, which needs to be addressed with conditioning or dehumidification. 

If the crawl space is not properly sealed, or if it is not conditioned, it will not work. That seems to be the case here, as you didn't mention a dehumidifier or any type of conditioning system. Or perhaps the vapor barrier was not thoroughly sealed, and was still allowing outside air in. 

In other words, if you are not going to provide vapor barrier, don't close the vents, if you're not going to properly seal the vapor barrier, and if you do use it, and seal it properly, you will still need to condition the crawl.

Crawl space encapsulation is hardly a DIY job, although there are a lot of "DIY" kits for sale out there. It can be very dangerous if performed by someone that doesn't have the expertise, specially if the house has combustion appliances running in the crawl, or if it has radon issues. 

A properly installed encapsulation system acts as passive radon barrier, although not a replacement for a real radon mitigation system. In homes with high radon levels, it can also be fitted to work with a professional grade radon mitigation system.

I'd suggest you call a crawl space specialist in your area and have them properly seal and condition the space for you, since it is already lined.

 
August 11, 2011 09:51 AM #57
Anonymous
Anonymous
Kenny

thanks for the input! anything to help the cost of living in the long run is a plus,, and i can see the importance of it being done right!

August 21, 2011 06:32 PM #58
Anonymous
Anonymous
Leif Werner

I have insolated my crawl space walls with thick fiberglass insulation and have no vents...I have an industrial dehumidifier I have had on very sparely ....an hour or so a few times a year avarage....over the 4 years the crawl space have existed now...what I did though was to have the dehumidifier on for about 2 weeks without turning it off when my home was finished in September 2007 to really dry the wood out due to having built my home over the winter 2006-2007....it was wet down there...since then I have seen no problems with moldy, wet or otherwise humid wood or the space being too humid in any way...the climat in the crawl is dry and very stable at 55 F and with about 50-60 % relative humidity and when I turn on the dehumidifier it turns off ....with the automatic on.... at 45 % relative humidity in less than 20 minutes...the crawl is big....1500 SF and almost 4 feet from floor to ceiling       

August 22, 2011 12:10 AM #59
Anonymous
Anonymous
Tony

lol been reading this and maybe I missed something here.... If you block off the vents you better be ready to put a dehu under your home.. Closing the vents is not going to keep the moisture out not the air flow out. It will slow the air movement down, but even if the vents are closed they are still with alot of open gaps... Close vents and you will need a dehu!

January 26, 2012 06:09 PM #60
Anonymous
Anonymous
Torrey Jensen

    Im not getting any answers, just a bunch of arguing...  I live in western Washington, close to Seattle, and would like to know....  To close, or not to close, that is the question???????????????

February 04, 2012 09:04 PM #61
Anonymous
Anonymous
Allen

What if I say both? Opened and closed. I was reading my home repair guide and it says to close all except just the two on the right  in the front, and then just the two on the right in the back. So there would be an invisible diagonal line connecting the 4 open vents so the air comes in one way and out the other; due to pressure. Kind of like when you have one door open at one end of the house and another door opened at the other end creating a "wind tunnel". I am not saying I'm right; just looking to see if I'm wrong. I know all houses are shaped different and the diagram in the book shows it like a box with arrows (air) going through one side and out the other. I not throwing my two cents in and making a point- just because its in a book, I dont really know. Its just a thought and I would appreciate any input on this. Many thanks!

March 31, 2012 12:43 AM #62
Anonymous
Anonymous
Charlie

I live in Georgia and forgot to close my vents after winter. It is so much cooler I decided to just leave them open. I also noticed last summer it was a lot cooler before I closed the vents. About ten degrees. My electric bill dropped about $20.00. The floor is so cold I cannot go without socks or slippers. I'm loving it but after reading everyones opinion on this site, I'm really confused!! I'm going to go under the house and look for what?

May 27, 2012 02:58 PM #63
Anonymous
Anonymous
Donna Jacobs

I have a house that was built in the 40's.  The foundation has concrete block with the holds every several feet.  I do not know why or what to do with them.  Can I block them perminately?  There is plastic down on the ground under my house.  In 2011 I had renters in my house and after a devistateing tornado that distroyed many building within block of this house, the renteres had a terrible rodent problem.  It is cleared up now but I fell that the open blocks incouraged the problem.  Any ideas?

August 04, 2012 06:32 PM #64
Anonymous
Anonymous
Donna Jacobs

I should add that my house is in Alabama.

August 04, 2012 06:51 PM #65
Anonymous
Post a Comment
Spam prevention

Accessibility option: listen to a question and answer it!

To submit the form,
drag the key to the circle on the side.

Type below the answer to what you hear. Numbers or words, lowercase:

Show All Comments
Rainer
9,369

jamie allen

Ask me a question
*
*
*
Spam prevention

Accessibility option: listen to a question and answer it!

To submit the form,
drag the envelope to the circle on the side.

Type below the answer to what you hear. Numbers or words, lowercase: