My buddy has a subfloor/crawlspace and there is no insulation in the floor. He has humidity issues and his flooring swells up, but no leaks or water intrusion that I can see. We live in Florida, and I just don’t think that is correct, I feel like there should be insulation installed in between floor joists. Anybody know for sure?
Insulation will not solve a moisture issue! Refer to an expert!!
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I agree, the insulation will hold moisture and rot out the floor system,
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Is there a proper vapor barrier on the ground? Is there adequate cross ventilation? Are building components adding moisture such as plumbing leaks or HVAC condensation?
These are just a few possibilities. I see you are a CPI. This is a great learning opportunity, and I would suit up and start crawling. Meanwhile, have your friend hire a specialist.
That can come from more than one source. Crawl is a great place to start.
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Insulating the floor system is not a problem down south if the moisture in the crawlspace is managed.
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If you install insulation between the floor joist, it will trap the moisture and cause bigger problems. I see it all the time.
I would start with a vapor barrier as mentioned by @bcawhern1, but the best fix IMO, albeit the most expensive, is to encapsulate and condition the crawl.
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A dehumidifier in a vented crawlspace (especially in FL) will continually run and never make substantial changes in humidity levels.
@kleonard, in my experience, moisture trapped between the craft paper and the underside of the floor is typically not a problem in GA/FL. However, insulation falling because of damp conditions is common in a vented crawlspace in my area.
This is GA energy code. I do not know what FL requires. So, to your point, encapsulated-conditioned crawls are great.
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Here’s a good article on the subject.
BA-0401: Conditioned Crawlspace Construction, Performance and Codes | buildingscience.com
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In actually, it brings in more moisture through the foundation and building envelope.
Lower the vapor pressure and more will come in as fast as you can take it out.
This BS was adopted as Code, outside of Nashville. Had some serious pissing contests with the AHJ. My partner at the time was an air quality control engineer. We documented mold patterns that showed directional mold growth from the opposite end of the crawlspace to the dehumidifier.
Explain this AHJ.
To remedy the issue, they changed their code to making the crawlspace a conditioned space and had direct connection from the CS to the interior. Had a client walk into a new construction, “what is that smell”?! I pulled up an HVAC register and showed them the crawlspace.
What happens when you lower the CS with HVAC?
Pools of water on top of that pool liner they installed with floating mold…
I hear Agents tell their clients to open the CS Vents on the foundation in the summer and open in the winter. The house is air-conditioned, with the coldest air at the floor. Allow the summer moisture in and it rains.
Insulation in the floor, if properly installed, slows down the heat flow and subsequent condensation.
Vapor barrier up or down?
Where is the moisture when it is at its highest levels in the summer?
Another Code argument if you’re up to it…
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I do not see that as a reasonable option here in the South. I have yet to see one in the wild. I have spoken with a few Canadian inspectors, and that configuration is common. These are homes way up north and are not air conditioned, only heat 
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I hope I can be of help.
Building Code Requirements
International Residential Code (IRC):
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IRC R408 - Under-Floor Space (Crawl Space): This section of the IRC provides guidelines for ventilation and insulation of crawl spaces.
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Insulation:
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In Florida, insulating the crawl space floor is less common due to the warm climate, but it is important to insulate the crawl space walls. This approach helps to create a conditioned space that can be more effectively controlled for humidity and temperature.
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If insulating between floor joists, use insulation with a vapor barrier facing up towards the subfloor to reduce moisture transfer from the crawl space to the floor above.
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Vapor Barrier:
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A vapor barrier (usually 6-mil polyethylene plastic) should be installed on the ground of the crawl space to prevent ground moisture from rising into the crawl space. This is crucial in humid climates like Florida.
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The vapor barrier should be overlapped and sealed at the seams and extended up the walls, sealed to the foundation walls.
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Ventilation:
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According to IRC R408.2, crawl spaces must be ventilated. However, in humid climates, venting a crawl space can sometimes introduce more moisture. An alternative approach is to seal the crawl space vents and use a dehumidifier to control humidity levels.
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If the crawl space is vented, ensure proper ventilation with vents placed on opposite walls to allow cross-ventilation.
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Dehumidification:
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Installing a dehumidifier in the crawl space can help control humidity levels. This is particularly important in Florida, where high humidity is common.
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