What Does the EPA Say About Venting Sealed Crawl Spaces

What Does the EPA Say About Venting Sealed Crawl Spaces? Crawl space encapsulation can create issues if not properly ventilated per EPA guidelines. Local building codes vary on this issue but we want to share our thoughts on why you should ventilate a sealed crawl space. The goal of a sealed crawl space is to improve your indoor air quality. Not properly ventilating a sealed crawl space could create odors in your home and expose you to harmful soil gases.

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Exhaust 1 CFM for Every 50 SQ FT

The EPA (Environmental Protection Agency) recommendation for exhausting a sealed crawl space is based on the removal of soil gases before they can reach the living space. As you can see in the image provided by the EPA below, the crawl space contains vapor barrier, insulation, and ventilation. The image also shows the make-up air comes from the living space.

EPA vent sealed crawl space image

Does Code Require Venting a Sealed Crawl Space

We see codes vary from town to town. Some codes enforcement are against venting a sealed crawl space. While others encourage venting a sealed crawl space. You will need to check your local codes requirement in your area. Based on the EPA guidelines, I recommend you encourage the codes agency to allow ventilation of the encapsulated crawl space. Creating a soil gas issue while solving a humidity problem does not seem like a good trade off. Radon sub-membrane mitigation systems can also be installed versus a foundation vent fan to meet ventilation recommendations.

Essential Guide Crawl Space Encapsulation Click Here Image

EPA Indoor AirPLUS Construction Guidelines

If you are looking for more information to help you decide if ventilating your crawl space after encapsulation makes sense. I encourage you to check out the EPA Indoor AirPLUS Construction Specifications.

Here is an excerpt:

1.4 Basement and Crawlspace Insulation and Conditioned Air

Indoor airPLUS Requirements:

  • Seal crawl space and basement perimeter walls to prevent
    outside air infiltration.
  • Insulate crawl space and basement perimeter walls according
    to the prescriptive values determined by local code or R-5,
    whichever is greater.
  • Provide conditioned air at a rate not less than 1 cfm per 50 sq.
    ft. of horizontal floor area. This can be achieved by a dedicated
    supply (2015 IRC section R408.3.2.2) or through crawl space
    exhaust (2015 IRC section R408.3.2.1). However, if radon resistant features are required (see Specification 2.1), do not
    use the crawl space exhaust method.

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20 thoughts on “What Does the EPA Say About Venting Sealed Crawl Spaces”

  1. This post is misleading. If you look at the EPA guidlines 1.4 Exemption states “Additional Exceptions:
     In lieu of perimeter wall insulation and conditioned air, crawlspaces that utilize a capillary break on the floor and that are well-sealed to prevent outside air infiltration are permitted to utilize active dehumidification with sufficient latent capacity to maintain relative humidity (RH) at or below 60 percent. The dehumidifier shall be drained to the outside or to a sump pump.”

    So if a crawlspace is encapsulated, sealed, and has a dehumidifier to maintain humidity under 60% then ventilation is NOT required. You should include this exemption as stated in the EPA guidelines in the article.

    1. Hi Nathaniel, I appreciate you brining this to everyone’s attention. The reason I didn’t include it in the article is I feel the exemption is misleading and further more may cause homeowners to be exposed to soil gases that may cause more damage to their health. None of the items listed in the exemption does anything to ventilate the soil gases out of a crawl space on their own or all installed together. Dehumidifier controls humidity, not ventilates. Insulation will insulate not ventilate, vapor barrier assists in humidity control not ventilate, conditioned air is your HVAC recirculating air in the crawl space where the potential soil gases are located and could bring those gases into the living space more rapidly not ventilate. None of those things will remove soil gases or potentially harmful radon from a crawl space. I am confused as a consumer and crawl space encapsulation professional why the EPA listed these things that do nothing to ventilate the crawl space as acceptable exemptions for ventilating the crawl space. Unless of course, your home tests positive for radon, then the EPA steps up the ventilation with a sub-membrane radon mitigation system, not listed in the exemption. I guess what I am trying to say is I feel the exemptions are misleading and do not solve any issues when it comes to removing soil gases which is why I left it from this article. Thanks for your input.

  2. Im starting to do my own crawl space encapsulation thanks to you and your company! love the videos and how to. halfway done. But im a little confused on where to place the vent fan. does it matter? should it be furthest away from the dehue?

    1. Hi Michael, great question. Yes I like it far away from dehumidifier so it can help draw dry air from the dehumidifier to potentially stagnant or moist areas of the crawl space but I’d also recommend putting under a common area like the kitchen so as not to wake you up just in case you have noise sensitivity. It can be drowned out by the refrigerator under the kitchen. Hope that helps and thank you!

  3. Michael, you have been my guide as I have obsessed of my crawl space for the past four years…thanks for sharing your wealth of knowledge.

    My crawl space is now fully encapsulated and conditioned with an April Air dehume that I purchased from your DIY store. It works great! HOWEVER, the guys who did my encapsulation (we are out of your service area) used a “knock off” brand of plastic with—you know already it—a “cat pee” odor. Now I am needing to do some ventilation to exhaust some of those odors (as well as any radon gas that might be present).

    If I install an exhaust fan without any other openings in the crawl space, will that work? I used to think that the exhaust fan would not be able to pull air out of a “closed container” (i.e. my encapsulated crawl space). However, I seriously doubt that my crawl space is COMPLETELY sealed off from the living space. Therefore, I am now thinking that, if I just put in an exhaust fan without any other open vents, it will simply draw air from the myriad of little cracks, gaps, etc., that no doubt exist between my crawl space and my living space. It will also, thereby, create negative pressure in the crawl space that will result in air movement that is “down and out” from the living space (which would seem good to me).

    Am I thinking correctly?

    Thanks in advance for your help.

    1. Hi Bruce, thank you so much. I am so glad we have been a help to you over the years. That really means a lot to me. Yes, installing a fan should move air out. Even if the crawl space is air tight, the soil is not. We recently received pictures of a crawl space that was so air tight and the plastic so well sealed, the plastic is ballooning of the ground due to air pressure from the soil. If for some reason the foundation vent fan doesn’t take care of all of the cat pee odor, you could perhaps add another fan or a radon mitigation system type setup depending on how potent the odors are. The foundation fan(s) would draw smell from above the plastic and radon system could draw odors from below the plastic Hope that helps.

  4. Hi Michael, reading all your material and find it extremely helpful. Can you recommend anybody at the Jersey shore? Seems like they install the ATMOX system or encapsulation without ventilation. Thanks for sharing all your knowledge. Much appreciated, Bill

  5. If EPA guidelines want 1cfm per 50 dq ft, is more better? Or, is it more beneficial to stay as close to that number as possible?

  6. Hi Mike
    I really appreciated your explanation of why an exhaust fan is needed for removal of harmful gases. However, if the crawl space is encapsulated where does the make up air come from? In the picture you show it coming in around a sewer pipe. Are you indicating it will pull through various gaps in the floor or do I need to create an opening?
    I’m also curious as to why the wall insulation needs to terminate 3” below the sill plate?

    1. Make up air can come from the soil, gap in sill plate, around door or subfloor. The 3 inch termite gap is required by code in TN. GA has a 6 inch termite gap. Hope that helps, thank you.

  7. Hi Michael, I have a new home on the North Carolina coast right on the water. Thanks to your web site I was able to identify some problems with my crawlspace encapsulation and have the subcontractor fix them. I have the heavy duty (no cat pee) plastic that is very thoroughly taped on seams and penetrations, penetrations through floor are sprayed, spray foam on cement block walls with termite gap, and a SeaAire dehumidifier. The rim joist is caulked and the joist bays are sprayed (not done initially, so thank you again). I also have a TempStick sensor down there.

    I have two concerns. First, I see humidity spikes of 1 – 3 % which appear to correspond to storm fronts moving in or heavy rain. I am wondering if this indicates an encapsulation defect somewhere or if this is typical for the location? Second, there is air blowing through the bottom of the access hatch (weather stripping around the other sides) and I am again wondering if this indicates a defect with significant outside air entry or whether this is house air moving downward through nooks and crannies.

    The soil is 100% sand.

    Thanks for your thoughts! Sandy

    1. Sounds like the humidity spike and air movement are within normal ranges. The soil itself will allow moisture and air to infiltrate the crawl space even if everything else is sealed. This is why I like a 50% humidity set point for the dehumidifier to address those storm spikes you are experiencing. Hope that helps and thanks for letting me know the information has helped. That is very kind of you to say.

  8. I appreciate your content! I sealed my crawlspace and encapsulated it. I have a DH providing humidity control. I am torn on providing conditioned air to the space and utilizing a vent fan to exhaust stale air, or installing an ERV system. The ERV seems like to best option would you agree?

  9. I reviewed a lot of instructional data, including yours, prior to encapsulating my crawlspace with a dehumidifier about 2 1/2 years ago. However, this was prior to you publishing this article.The source for my materials for my DIY installation (not you), recommend not ventilating. Due to some health issues my wife is having now, I revisited encapsulation and venting and found your article. FF to current time and subsequent review, I am located in a zone 1 Radon area in North Alabama. I have purchased a couple Radon test kits and am will perform the tests when conditions allow. All this background leads to … Per the EPA guidelines you referenced, if I end up having to add Radon mitigation, I do not need to ventilate the crawlspace … I assume this is because Radon mitigation per EPA guidelines will remove Radon and other soil gasses as well … Is this your interpretation as well?

    1. Yes, that would be my interpretation, sub-membrane radon mitigation system outperforms the fan above the plastic. Glad our information could assist you, please keep us posted as to your radon results.

  10. I used Crawlspace Ninja to encapsulate my crawlspace, with a dehumidifier. A small fan was installed venting to the outside to avoid the potential build up of toxic gases. My question is, where does the air come that the fan pushes outside? Is it coming from the door to the crawlspace (which is sealed well but not perfectly)? Is it coming from the ground / floor and the walls (which has been thoroughly sealed, but may not be 100% airtight? Is it coming from the 3″ termite plate (which has been air sealed but has no vapor barrier)? Or is it drawning air down from the house through various air holes since the ceiling of the crawlspace is not insulated? Or maybe a combination of the four? Second question, is there any value to sealing the ceiling of crawlspace to prevent any air infiltration up or down into or out of the home? thx

    1. It is most likely a combination of all four and yes, I would recommend you air seal any gaps you can seal in the subfloor around HVAC boots, electrical, rim joists, and plumbing. Thank you for choosing us to do this work.

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