A vapor barrier is a polyethylene sheeting system installed on the ground and walls of a crawl space or basement to block ground moisture from migrating into the structural environment above. Understanding what a proper vapor barrier consists of, however, goes well beyond simply laying plastic on the floor.
Standard 6-mil poly sheeting has a relatively high vapor permeance rating, meaning it allows some moisture vapor to pass through over time, particularly as it ages and develops micro-perforations from foot traffic and environmental factors. For most homes in Northbrook, IL, we recommend a minimum 10-mil product for general installation and a 20-mil product for spaces with high moisture loads or frequent access requirements.
Overlapping sheets by 12 inches or more at seams and securing them with butyl tape creates a continuous, mechanically bonded membrane that resists separation as the sheeting settles and moves over time. A perfectly spec'd 20-mil liner installed with poorly treated seams performs no better than a budget barrier at preventing moisture migration.
Covering only the floor and stopping the barrier at the wall-floor junction leaves the porous block or concrete foundation walls as an open pathway for moisture to enter the crawl space environment. The combination of floor coverage, properly lapped and taped seams, and full wall coverage to the sill plate creates a complete moisture envelope that dramatically reduces crawl space humidity and protects the wood framing above.
High crawl space humidity leads to wood rot in floor joists and sill plates, a process that progresses silently over years before structural symptoms appear. A well-installed vapor barrier is also a prerequisite for effective dehumidifier integration in crawl spaces where mechanical moisture extraction is warranted.
Our installers are trained on manufacturer specifications for every product we use.
The materials we install in Northbrook are built to last decades, not years.
Full perimeter coverage is non-negotiable in our installation standard.
You receive documentation of your warranty before we leave the property.
The result is a continuous moisture envelope that protects your floor framing from ground vapor for years to come.
Older thin-mil or damaged vapor barriers in Northbrook, IL homes are common and leave crawl spaces with inadequate moisture protection.
The installation includes full seaming, perimeter taping, and wall coverage to the base of the finished wall or sill plate.
This combination approach addresses both vapor diffusion and water management in a single installation.
Adding a properly sized dehumidifier completes the moisture management system and ensures consistent relative humidity control regardless of outdoor conditions.
We offer post-installation inspections for vapor barriers installed by other contractors, as well as for our own older installations, to assess barrier condition, seam integrity, and wall coverage completeness.
We measure the space, assess existing moisture conditions, document any existing barrier or mold, and identify all penetrations that will need to be addressed in the installation
Based on site conditions, we specify the appropriate mil rating, calculate material quantities, and plan the seaming layout for maximum coverage and minimum waste
Sheeting is laid, overlapped at 12 inches minimum, taped with butyl tape at all seams, and extended up all walls with mechanical fastening at the top edge
We walk through the completed installation with you, confirm all seams and coverages are complete, and provide written warranty documentation before leaving
"We had a previous vapor barrier installation that was barely 6-mil and had separated seams throughout. The humidity in our crawl space was unacceptable and we were starting to see mold on the floor joists. JCB Waterproofing and Construction completely replaced the barrier with a 20-mil system properly taped and sealed wall-to-wall. The difference in our indoor air quality was noticeable within a week."
"Very professional team that explained the difference between the grades of vapor barrier sheeting before recommending anything. The 20-mil they installed is rock solid and the seams are all properly taped. We can already see the humidity meter reading dropping consistently."
"The crew extended the barrier all the way up the walls to the sill plate, which the contractor who did our original installation did not do. We had been missing that wall coverage and did not even know it. Great work from a team that clearly knows what they are doing."
Our certified team is ready to assess your crawl space and provide a clear, honest recommendation
