Can I effectively reduce humidity in my crawl space by laying down plastic myself, considering the high cost of professional services?
Asked by Nishitha Rao 
4 months ago
Last Updated: June 4, 2024
Hey, so my crawl space is at 70% humidity, which is not good. The quote I got from the company to fix it is way too expensive for me. Do you think I could just put down some plastic myself to help with the moisture issue?
Why not try to get to the space if you can?
Ensure you take the time to thoroughly research the task
Sure. That’s unfortunate… lol
Yes, you definitely can do that
Of course, you can start using a dehumidifier right away.
I enclosed my crawl space with plastic and used duct mastic to attach it to the walls and columns. Then I taped the seams. I covered the vents with covers and run a dehumidifier during the summer. I’m in the Southeast and summers are really humid. The air quality inside my home has significantly improved since I sealed my crawl space. Now I discovered that my neighbor has a radon problem, so I’m conducting tests inside my house to check the levels. The first reading in the basement was 3.4, but I always keep the windows cracked, so I need to test with them open.
I had the same experience as . Having an Airthings monitor made a significant improvement in the indoor air quality of my home.
By the way, I purchased an Airthings monitor. My yearly average radon level is 1.2, but I do see some readings of 3 to 3.4 occasionally, especially in late fall or early winter.
I’ve thought about getting one myself, but the reviews are quite mixed.
I have the model that monitors pm2.5, voc, radon, humidity, temperature, and barometric pressure. I’ve had it for over 2 years now and I really love it. There are probably some newer, more affordable options available though.
How much did it cost?
This is one I purchased. It sometimes goes on sale. I noticed they now have several other models available as well.
Airthings 2960 View Plus – Battery Operated Radon & Air Quality Monitor (PM, CO2, VOC, Humidity, Temp, Pressure) https://a.co/d/dRFKeMc
First step is to crawl around and check for any water sources causing running water under your house. It’s important to address that issue first. Make sure to use plastic sheeting that is at least 6 ml thick, which is the minimum code requirement. Consult your local code enforcement office for specifications. Opt for clear plastic rolls that are 12′ wide to minimize seams and allow visibility under the plastic over time. Avoid black plastic, as it offers no visibility according to my installer, Terminix. The width and total square footage of the rolls are indicated on the label, as the rolls are not 12′ long when packaged – they are usually around 3 or 4 feet and need to be spread out. Remember to overlap at least 12 inches and use recommended stakes at seams and perimeters with spacing recommended by the code. Let the plastic loosely meet the foundation block to allow moisture to wick away from the foundation. Do not cover the foundation completely. This is a vapor barrier, not encapsulation, which is a more intricate process and should be handled by professionals. You can find tutorials on YouTube to learn how to install a vapor barrier. I used to work in sales for home building supplies.
It’s pretty simple to do some home improvement projects. Personally, I recommend getting knee guards and a good headlamp. I usually lay down plastic sheeting and then dimple underlayment. ‘t forget a few rolls of red sheathing tape!
Yeah, I’m with you. I did mine on my own. Just use the wide Gorilla tape for the seams
Absolutely! Use thick plastic to cover the entire floor. Make sure to tape all seams and wear an n-95 mask and gloves.
Consider getting your house spray insulated underneath and adding a vapor barrier. With so many companies out there, it’s worth getting a few quotes to find the best price. Currently, rates are sky-high, so don’t be afraid to ask for the bottom line rate. If a company needs the business, they will likely negotiate. For example, we were quoted $1200 for a garage door opener repair but ended up paying only $300. So definitely shop around!
That’s included in my to-do list for my schoolhouse. I’ll have to work with only about 15″ of space to get it done, so I might begin by manually removing some dirt, lying on my stomach.
Having 70% humidity inside your home usually points to another issue. We often come across homes where the HVAC ductwork runs beneath the house, leading to compromised return ducts that draw in humid air. For instance, in a townhouse plan, we identified 10 units experiencing this problem, all with high humidity levels and some running dehumidifiers constantly. Another common crawl space issue is fiberglass batting falling down, exposing the floor. This is a prevalent problem in the southeastern US, resulting in mold growth beneath the floor and excess moisture causing hardwood floors to buckle. Someone mentioned spray foam. That’s our main focus, providing a nearly impenetrable seal to the subfloor that’s resistant to moisture, vapor, insects, and critters, but it does come at a higher cost.
There’s a new product called thermal barrier that’s available now. It’s a lightweight blanket for crawl space walls that you can find on Amazon. The rolls are 4’x25′ with grommets on one side to make it easier to hang and tape. If your crawl space is shorter than 4 feet, you can let it drape onto the ground and then cover the rest of the floor with 10 mil plastic. We’re planning to install ours after Christmas. For now, we’ve just sealed off the vents to the outside. Instead of using a dehumidifier, we’ll circulate air through our HVAC vents.
I suggest not blocking the vents
Hey Aaron! I know you have the option to leave the vents open for insulating the underside of your floors, but we chose to treat the crawlspace as an extension of the basement. We insulated the walls, put a vapor barrier on the floor, and have the HVAC system circulating air to maintain a consistent temperature. Leaving the vents open would let freezing air in, especially considering how hot and cold it gets in Michigan.
Hey there, I’m the insulation guy. Putting down a vapor barrier is pretty straightforward. Just ensure it’s 5 mil or more. You can use landscape fabric anchors to secure it in place. And definitely wear a mask.
You really need to address the humidity issue as soon as possible! Have you received a quote from a company for the work? What is the condition of your crawl space? Is it concrete, sand, gravel, or soil? Is it wet down there?
Before installing the vapor barrier, double check that no water is seeping into the crawl space.
I had a major issue where the vapor barrier would have trapped water on top, so I had to remove it all and address drainage problems around my home, as well as fix plumbing leaks and condensation issues.
Take into account the size of the air space when considering the installation of the vapor barrier, as a smaller crawl space may present a more challenging situation and higher costs depending on who is completing the work.
Good luck with your project!