Yes, you read that right, some basements (and crawlspaces) are dirt!
This is much more common in homes built a hundred years ago, but can be found in newer homes as well. I have successfully mitigated homes with dirt basements and dirt crawl spaces in and around Calgary and Crowsnest Pass. A dirt basement adds a number of challenges and requires some additional work in order to install an efficient and effective radon mitigation system.
The most common method for radon mitigation is through Active Sub-slab Depressurization (ASD) where suction is applied below the basement floor, the radon gas is collected at a suction point, and exhausted to the atmosphere. I wrote a blog article on this entitled “How Does a Radon Mitigation System Work?” which goes into ASD in detail.
How do you apply suction to a dirt basement if you don’t have a floor? Good question! You need to create an airway (usually with perforated drain pipe called weeping tile) and an airtight barrier between the living space of the house and the dirt. There are two main ways of doing this depending on a number of factors including budget.
The first, and most common, method is to install a membrane over the dirt floor and up the walls to an area where it can be sealed. This is certainly easier said than done as it is crucial to have a perfectly sealed membrane around the entire perimeter as well as any penetrations through the membrane such as plumbing or posts, and the suction point of the radon mitigation system. The membrane selected should be durable enough that it will not be easily punctured during installation or through the use of that space by the homeowner. If the area is used for storage or regularly accessed then it is recommended to use a thicker membrane, whereas if the are is never accessed, a thinner membrane may be acceptable. Membranes for this application usually range from a thickness of 6 mil through 10 mil polyethylene sheeting, however thicker membranes are also available. Thin membranes are easier to work with, however the risk of puncture is greater. Great care must be taken to ensure a good perimeter seal and to mechanically fasten the membrane to the sidewalls. Any membrane overlaps are required to be well sealed using specific caulking and/or tape with manufacturer-specified overlap amounts.
Prior to installing the membrane, a loop of weeping tile should be laid around the basement and secured to the ground. This will be what the radon mitigation system is attached to and will act as a radon collector once the fan is activated. Consider also laying a cushioning layer over the dirt, but under the membrane, such as old carpet, underlay, or moving blankets to reduce the risk of membrane puncture.
There are a few methods for checking the integrity of the membrane install, and it is recommended to use more than one method. The most basic method is to block the penetration where the radon system will attach to the weeping tile loop and leave the membrane alone for a few hours. Upon return, the membrane should be puffed up with soil gas compared to when you left showing that the seal is good. Unblocking the suction point and attaching a radon fan is the next step. Once the radon fan is activated, the membrane should suck down to the ground and look like a vacuum sealed package.
The next method for checking membrane seal integrity is with chemical smoke. This can also be done in two ways. The first method is to go around all overlaps, penetrations, and the entire perimeter with a smoke gun looking for the smoke to be drawn in to any of these areas indicating a poor seal. This must be done with the radon system (or a least a radon fan) active. The second method is to flip the radon fan upside down and pump chemical smoke under the membrane and look for leaks where the smoke is coming out. Leaks should be sealed as they are discovered before moving on.
Contracting a spray foam company to spray foam the entire dirt basement or crawlspace is the second way to form a soil gas barrier to apply suction under. There are certainly pros and cons to this approach, however results with this method have proven to be fantastic. The main con to this approach is the cost. The application of spray foam and then the required fire-retardant spray over top can become quite expensive. The second con to spray foam is that it isn’t overly durable and therefore provisions must be made if that area will be used or accessed. Walking paths must have addition protection over top of them such as foam tiles or carpet scraps and underlay. The pros to this are improvements to the insulation factor and energy efficiency of the home and the change in smell of the basement from what is usually a musty dirt scent to something much more neutral (once the fire-retardant has off-gassed).
Prior to the application of spray foam, a loop of weeping tile must be laid as described above, with the radon mitigation system attached to it. The spray foam contractor will recommend if any material should be laid down first before the application to allow the spray foam to adhere better. Once the spray foam and fire-retardant applications are complete, the integrity of the seal (especially around the perimeter) must be checked. The same methods using chemical smoke described above will work well for this. Caution must be taken when moving over the spray foam so as not to damage it. Leaks can be sealed using canned spray foam and/or polyurethane sealant. There should not be many leaks at all if the spray foam was applied with care and with enough thickness. I recommend requesting at least 4 inches of thickness, with more being better.
Please feel free to contact me with other questions regarding radon mitigation systems with dirt basements are crawlspaces. I am happy to provide free, no-obligation quotes for all types of radon mitigation systems. Please click on “Request A FREE Quote” in the menu bar.
