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Why Does Crawl Space Humidity Spike After Encapsulation

Why Does Humidity Spike After Encapsulation? Before I can answer that I need to let you know what we consider crawls pace encapsulation. For the purpose of this article we are saying the crawl space has vapor barrier installed on walls, floor and pillars. The plastic is overlapped and taped. The vents are insulated and air sealed and a dehumidifier is installed.

Wet Wood Raises Humidity

As the dehumidifier dries out the crawl space, keep in mind the wood may be wet. Different types of wood hold more or less moisture than others. When we inspect a crawl space we always check the wood moisture level. Even if visible mold is not present, high wood moisture levels can support microscopic mold growth. Microscopic mold or wood rot fungus will eventually become visible if the wood moisture level is high. As the dehumidifier dries out the wood, the humidity spikes.

Encapsulation After Picture

Humidity Spike from Ground Water

Many homeowners assure us their crawl space has never flooded but it is a good idea to check for signs of moisture during the inspection. If you encapsulate the crawl space and standing water happens after heavy rains, this can cause humidity spikes. Signs of past flooding include muddy vapor barrier, efflorescence on cinder blocks, concrete, stone and bricks. Other signs of flooding is plastic that has shifted away from the foundation wall.

Mold Remediation in Crawl Space

Many companies use liquid mold cleaners to address crawl space mold problems. The crawl space should always be dried before mold remediation. If the crawl space is dry and chemicals are applied, this can also create a humidity spike in the crawl space.

Do you need crawl space encapsulation? If so, please contact Crawl Space Ninja and we will be glad to help. Also, let us know in the comments below if you have noticed other foundation issues we did not mention in this article.

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About Michael Church

Michael Church has been involved with indoor air quality since 2005 and feels the unhealthy crawl space is one of the major problems causing poor indoor air quality.


  1. James on November 4, 2020 at 1:06 pm

    Do you encapsulate then dry and remove mold or dry, remove mold then encapsulate?

    • Michael Church on November 18, 2020 at 12:33 pm

      You should always dry first. Here is a video that may help “Crawl Space Mold Removal – What NOT To Do! Crawl Space Mold Treatment | Crawl Space Mold Mistakes” https://youtu.be/DdknHGFEKH8. Thank you.

  2. Ron on October 22, 2022 at 8:30 pm

    I’d like to ask you a question question about my crawl space encapsulating. Crawl space ninja.

  3. Joanna Leifeld on November 15, 2022 at 9:26 am

    I have bought some Ninja products and started my DIY encapsulation. I have a new sump pump, mold test showed a common fungus no dangerous mold, I added a crawl space dehumidifier, but have now halted the project as I have an open combustion gas water heater that sits in the center of my crawl space. I believe Michael suggested on a video contacting a professional. We actually had a well-known water proofing company quote the job, and there was no mention of the appliance being an issue. You can actually stand upright in a large portion and upright on knees in the rest so maybe air is not a problem.
    My question is about two areas above grade that have a musty smell. Both are exterior walls and limited to certain rooms. Other rooms along wall do not smell. The smell in in the hardwood floor along the edge of the flooring. I removed the baseboards and the smell was definitely stronger, but this smell is not in my crawl space. Neither room has plumbing near it. Moisture meter is elevated in the wood, but air humidity level is normal. The humidity does raise with the temperatures. I’m in GA. Everything I’ve read points to moisture being trapped without proper ventilation. I find that so confusing as I am wondering if encapsulation will make it worse. No signs of moisture damage on the crawl space side of subfloor either. I am thinking this is coming in with the exterior air and getting trapped. Any thoughts are appreciated!

    • Michael Church on November 22, 2022 at 6:09 pm

      Hi Joanna, exterior walls can 1. condensate due to temperature changes between the crawl space and the outside or 2. perhaps you have water penetration from the outside in (possibly even a small penetration can cause damage) or 3. the moisture from the crawl space could have gone up that wall and become trapped in the wall. The outside to inside leak should be investigated and corrected if needed. The crawl space encapsulation could fix the moisture trapped either no matter what as long as the source is addressed. If you have huge swings in the temperature outside vs inside crawl space, I’d recommend rim joist insulation and dehumidification to prevent condensation. I’d have a plumber verify the water heater is vented properly, just to be safe. Hope that helps and thank you!

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