When asked “How do I get rid of that smell in my basement”? Sometimes the answer is to remove the people making the “smells”, however more often than not, the source of the smells the house itself. There are several sources of smells in basements and crawlspaces. Here are some of the common ones that we encounter and how to address them. This post is meant to cover the basics and I have linked to external site or other posts to go into detail the building science behind the explanations. Most smells are a result of Water + Indoor Air Pollution.
Moisture:
There are 2 types of moisture that you may have to deal with in a crawlspace or basement. The first type is bulk moisture- this is water that you can see in it’s liquid form. This is NOT something that you can deal by plugging in a dehumidifier alone. Water needs to first be addressed from the exterior and if that does not work interior management systems can be installed to capture and remove the water coming through the walls or floors in your below grade spaces.
While bulk water infiltration is a big deal, I am only going to focus on the second type of moisture and that is water vapor. This is water in a gas state and for the most part you cannot see it indoors. If you are outside the house, you see fog and clouds and this is a visible form of water vapor.
To control water vapor you first must seal up the source of the water coming into the house. If it is a vented crawlspace the water vapor is coming in through the vents and through the soil. This combination causes unpleasant odors to come into your house because the moisture content in your crawlspace is too high. This process of sealing up the space in a crawl space is called “crawlspace encapsulation.”
Most of the encapsulation systems use at least a 6 mil plastic over the exposed dirt. We recommend at least 6 mil plastic and if the budget allows, encapsulating with concrete as well over the plastic. This can help keep critters from tearing through the plastic.
Once the sources of the water have been addressed, you still need to deal with moisture that is in the air. We prefer a stand alone dehumidifier that is designed to address the size of the space that it is dehumidifying. I’ll create a list of brands that we have used and recommend after doing a little more research to see what products are still on the market. Picking up one from your local hardware store should do the trick if the space is not too large. If you are trying to dehumidify several thousand feet, then you should consult with your HVAC company to see what options they might have access to.
DO NOT use a dehumidifier in your crawlspace or basement if it the vents to the exterior are still open. This is equivalent to running the AC in your house and leaving the door open. I know your parents asked you “Do you live in a barn? Close the door…” This the same with the spaces that you are dehumidifying. The moisture from the outside will be transported into your basement or crawl through “air transportation.” If it high relative humidity outside (high RH is above 60% RH), then that humidity is brought into the foundation vents and into your structure through transportation and diffusion.
Bottom line- reducing the relative humidity in the space will help the smells and help control microbial growth in addition to helping with the comfort (I’ll write another article on this later). Aim to keep the air in the space between 40-60% RH. Personally, 48% is most comfortable for me an my family.
Indoor Air Pollution:
Indoor Air Pollution can be split up into several categories: Biological, Chemical and Toxic Materials.
Some examples of biological pollutants are bacteria, animal and human dander, mold, viruses, dust mites, cockroaches and pollen just to name a few.
Chemical pollutants can also adversely affect indoor air quality. Pollutants such as cigarette smoke, ozone carbon monoxide, Radon, VOCs and pesticides are all examples of chemical pollutants that can be found in your breathable air.
Anything labeled toxic sounds bad and it is bad. Lead, Asbestos and Arsenic are toxic materials that can be found around your home.
Just like moisture, these indoor air pollutants must be controlled at the source first. Many are easy to control if not outright avoidable.
Here are some examples:
Mold can be controlled by controlling moisture that comes in contact with organic materials.
Cigarette smoke can be controlled by not smoking indoors.
Lead and Asbestos are toxic, however if they are not disturbed they do not affect you. For instance asbestos that is disturbed and is friable can enter into the air supply. It is not NOT disturbed OR friable then you will be harmed by it. Some thing with lead- do not disturb areas of your house that contain lead such as paint and you will not breath lead dust. There are methods for containing both of these during the renovation process.
Volatile Organic Compounds aka VOCs- many household chemicals and building products may contain VOCs which are not good for humans or animals to breath is their gas state. These should be avoided or allowed to off gas before installation if possible.
Solutions
If you need help with encapsulation or bulk water management, there are lots of companies in the Atlanta market and I don’t mind sharing my preferred list with you if you contact us.
I am not making any particular recommendation for dehumidifiers at that is time until I can test a few out. Here is an article and list from another site.
If you need help filtering out some of the air pollution in the air AFTER to stop or reduce the sources, there are many stand alone versions that can work. Make sure you buy according to what it can filter and the size of the space that it was designed to filter. Here are several guides that I found that have useful information on air filters. I have not tested any of these out (yet) so this is not an endorsement of any particular product. If you have used one and have a recommendation feel free to share it with us in the comments section.
Current Case study (and inspiration for this post):
I have a client that is complaining about smells coming from their basement. Here are some of the sources that I smelled and solutions for each:
Musty– even though the crawlspace was encapsulated, the air in the crawlspace which is shared with the mechanical room is stale since there is not any mechanical ventilation. Since the area is small, we recommended a stand alone dehumidifier to help bring the moisture down in that area which will help reduce the old house musty smell. We also found some gaps in the plastic that need to be sealed so will address that.
VOC smells– they recently installed a rubber floor in their storage room. The product and adhesive used to install the project is still “off-gassing” the VOCs. Our recommendation is to get an air filter that can help filter out this indoor air pollution. We also recommend allowing the space to get some fresh air from the outside when they humidity it not too high. Opening doors and windows allows for the some of the VOCs to escape and reduce the smells.
Dust Control– I also noticed dust in the fans of some of the media equipment that they just purchased. I checked the air filter on the HVAC system and it was doing its job. The stand alone air filter used for the VOCs can also help with dust control in a storage room. Since that space does not get much air flow, the dehumidifier and separate air filter will help keep the smells and dust under control.
In this case, the crawlspace and basement are already well sealed so the dehumidifier and separate air filter will make a large improvement in controlling the smells in the storage area. I would get an air filter that is large enough to address the main part of the basement as well since there are other products that are still off gassing.
Update:
This is what our client ended up buying for the air filter.
Bottom line:
Indoor air quality can be tricky and the proper holistic solution must be designed for your particular scenario. If you need help renovating your basement or building a new home with a strong focus on indoor air quality we have decades of experience with this building science. Contact us today for assistance on your project.
