Crawl Space Encapsulation Questions

Crawl Space Encapsulation vs Ventilation

Are you a little bit confused about crawl space ventilation and encapsulation?

It’s okay if you are, because if you ask 4 different service providers you are likely to get 4 different answers…

Some companies try to take shortcuts that lead to your crawlspace not being up to code, and not to mention that several other issues can arise from inadequate ventilation. Plus, you could be just throwing your money out the window if you aren’t careful about who you hire for the job.

All of the conflicting information can be very frustrating to dig through and evaluate, so today we are sitting down and answering your most frequently asked questions about crawl space encapsulation and ventilation so you will know the best option for your crawl space, and you will know why we are making the recommendations we do.

If any of the questions you have are not listed or you need further explanation please feel free to Contact Us by sending us a message or give us a call at (865) 659-0390 and we will be happy to answer any questions we can for you.

Does Crawl Space Encapsulation Work?

Before we get started answering some of your most asked questions, take a look at this 18 month update from a crawl space we encapsulated and let’s see how it is holding up with all of the improvements we made.

What is Crawl Space Encapsulation?

Even after doing tons of research you are probably still confused about what exactly crawl space encapsulation is, so we want to give you an answer so you at least know what you are dealing with if you are thinking about having someone encapsulate your crawl space or possibly even doing it yourself.

So right now, your crawl space is most likely filled with dirt or soil and possibly even some washed gravel, and unless you live in the driest part of the desert the ground in your crawl space holds a lot of moisture. You may even notice that your crawl space gets flooded whenever it rains or has a little bit of standing water.

What happens is, that water wants to evaporate by rising back up into the atmosphere which causes water vapor, and the higher the temperatures are the faster this process occurs.

The dangers you face from this evaporation are not only to your health but also to the structure of your home.

Crawl Space Mold

All of the moisture present in  your crawl space can cause mold, mildew, and the release of dangerous gasses that can be harmful when inhaled or when it attaches itself to the structure of your crawlspace.

The mold that is caused by the moisture can do a good deal of structural damage…

What happens is the mold eats away at the wood and it causes your joists to start to sag in places, and in some cases you may have to replace those joists when the damage moves past the point of repair.

Crawl Space Vapor Barrier

What we do when we encapsulate a crawl space is we go in and seal everything off using a 12 mil non-reinforced vapor barrier and a crawl space dehumidifier that prevents moisture problems.

When we install the vapor barrier it stops the moisture from the ground from being able to rise by sealing off the ground and any walls that have a moisture presence. This process eliminates the water vapor, but we also want to install a crawlspace dehumidifier because we want to eliminate any moisture that does make it through the vapor barrier.

Image of Crawl Space Encapsulation After

In addition…we also want to make sure that your crawl space is ventilated to keep the air moving, because there is no such thing as something that is 100% waterproof and there will still be a tiny bit of moisture left even after installing the vapor barrier and dehumidifier, so we don’t want that moisture to be allowed to sit around in your crawl space because we will be back to having a mold problem all over again.

Let’s talk about ventilation for just a second…

What is Crawl Space Ventilation?

When we are talking about crawl space ventilation we are talking about pushing air out of the crawl space. As mentioned you want to keep as much fresh air in the crawl space as possible to prevent moisture build up and mold problems from occurring, and there are a few different ways to do that…

One of the ways that we can ventilate a crawl space is by installing a crawl space ventilation fan that uses ducting and a dryer vent to intake air from the crawl space and then push it through the ducting and dryer vent to the outside of your home.

Crawl Space Vent Fan

We recommend the Panasonic WhisperLine FV-10NLF1E because it has the ability to cycle 120 cubic feet of air per minute and it was built to run maintenance-free and noise-free to continuously provide your crawl space with the ventilation needed.

We also use crawl space vent fans which take the place of your traditional crawl space vents and provide enough ventilation for 5,000 square feet of space, so depending on how large your crawl space is, you will usually only need 1 of these installed for maximum effectiveness.

Should I Insulate My Encapsulated Crawl Space?

As you have probably already discovered, this is one of those questions where there are a variety of answers…but when it all boils down to it, there are only 2 real answers and they depend on whether or not your crawl space is ventilated and whether or not there is already a mold presence.


If your crawl space is ventilated then we would install what is called fiberglass batt insulation under the sub-floor; however, if there is mold present then we will have to go in and remove the insulation that is already there and at that point we would insulate the walls of your crawl space.


If your crawl space is not ventilated then we would install foundation wall insulation to the walls of your crawl space simply because there will be less insulation required than insulating the sub-floor. That is because there is less square footage of space to cover on your walls vs. the square footage of your sub-floor so it saves you money overall and it ensures that your crawl space is insulated so you are not losing heat and air through the flooring of your home.

Should I Install a Dehumidifier?

Every crawl space that we encapsulate we install a crawl space dehumidifier as well because it helps to prevent mold and mildew.

It is important to note that dehumidifier alone will not get rid of mold in the crawl space. The mold will have to be treated properly and removed and once that is done, then a dehumidifier will prevent it from returning.

If you are going to install a dehumidifier yourself we highly recommend the Aprilaire 1800 Series because it is one of the best and most reliable on the market. Coverage varies by model and includes a washable filter that will give you long-lasting mold prevention dehumidifying action.

A craw space dehumidifier is an absolute essential in mold prevention in the crawl space, so you should most definitely install one once your crawl space is encapsulated and ventilated.

Should I Treat The Mold In My Encapsulated Crawl Space?

The first thing you want to do is identify how much mold you have growing in your crawl space. The problem is, you can’t just rely on what you can visibly see, you need to test the areas of your crawl space using a mold test kit that identifies molds that are highly correlated with water damage, high moisture levels, and toxic molds.

This test should then be sent to a lab where the lab will conclude whether you have black mold or toxic mold growing in your crawl space.

Once the test is concluded you will then need to use an effective mold cleaner to eliminate the mold problem all together. If you have a small area that is affected because you caught it early, then you may be able to clean the affected area yourself; however, if the area is larger than about 10 square feet, then you will need to call us in to remove the mold for you.

We will then need to take steps to prevent the mold from returning such as installing a crawl space dehumidifier and ventilating the crawl space.

Should I Ventilate or Encapsulate My Crawl Space?

Some people are under the impression that they should either ventilate or encapsulate their crawl space. And you might not be surprised when we, like our namesake, recommend a sealed encapsulation in most cases. That’s because if you can fully seal the crawlspace, you have a better opportunity to control the conditions of the interior. But there are other options to consider as well. One such option is to first encapsulate, and then close up all of the vents except for one — and install an automated exhaust fan to vent out moist air when the conditions becomes too humid inside. Both ways are completely valid, and give you enough control over the climate of your crawlspace to prevent mold from growing.

If your question was not answered here, feel free to reach out to us via our new Ask A Ninja Feature.

14 thoughts on “Crawl Space Encapsulation Questions”

  1. I currently have an encapsulated crawl space with a dehumidifier. Would adding an exhaust fan at one of the vents help pull moist air out, or would it pull the dry air out?

  2. Does the dryer need to be ventilated to the outside in an encapsulated crawl space or should the duct just hang down into the crawl space

    1. Always ventilate the dryer to the outside. Not only will it throw lots of humidity into crawl space but lint from your clothes. Both of which can feed a mold problem. Great question, hope that helps.

  3. Hi! I am in the process of encapsulating my crawl space and when checking the insulation around the duct work, it is completely soaked. Do I need to replace the insulation over the duct work or can I remove all duct work and leave the ducts non-insulated?

    1. I am not a fan of no insulation on duct-work. Many times when you lower humidity with a dehumidifier the insulation will dry out. If you remove insulation from ducts, its a great time to air seal them but I would re-insulate after. Here is a video about that. Thanks for the question, I hope that helps.

  4. I am in the process of encapsulating my crawl space and I have a question. I have my furnace in the crawl space and I am wondering if I have to put in a pipe to provide combustion air. I have heard of putting in a 1 1/2 ” PVC pipe to the outside with a trap at the furnace for the cold air. Is this necessary, or will the air in the crawl space be sufficient ? I appreciate any advice you can give me. Thanks

    P.S. I really enjoyed the videos, they were very helpful .

    1. Hi Tom, thank you so much. I would like to defer you to a licensed HVAC pro for that. I suspect the furnace had exhaust already installed if it is gas. If you are unsure, please have an AC contractor out to take a look. I would still install a foundation vent fan per EPA guidelines after you encapsulate. Here is a video we did on crawl space ventilation. I hope that helps.

  5. Hi there,
    I just bought a new house that has a fully encapsulated crawl space (floor, walls AND ceiling). Would you know the best way to inspect this area? Thanks so much!

  6. Hi! My crawl space is only about 2 feet high. Would it even be possible to encapsulate it? You can barely move under there as it is! What about a dehumidifier?

  7. Hi, I had my crawl space encapsulated a while back, followed your videos for guidance on finding the righ contractor located near me for the job. They did great work and installed a aprilair dehumidifier. My question is that my crawl space has a bad like stagnant air Oder down there. The dehumidifier is set to 53% humidity. And the crawl space is about 3.5 feet deep 1200 square feet. And I have installed a 100cfm exhaust fan vented to the outside to try and help, does a little bit not much. Any ideas on how to help my situation? Thank you

    1. Hi Jacob, did they remove the subfloor insulation and perform proper mold removal by removing molds and applying a mold cleaner liquid or disinfectant? Also did they remove debris and old vapor barrier prior to installing new one? I see these being the main reasons crawl spaces still have odors after encapsulation even with proper ventilation. Hope that helps and thank you!

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