Vapor Barrier for Foundations: Purpose, Cost & Installation Guide
What is a Vapor Barrier? A vapor barrier is a protective layer designed to prevent moisture from seeping through the foundation and into the building structure. Vapor barriers are made of polyethylene sheeting or specialized membranes, it acts as a moisture resistant shield beneath concrete slabs or crawl spaces. Vapor barriers help prevent mold growth, reduce structural damage caused by excess moisture, and improve indoor air quality. They also enhance energy efficiency by minimizing humidity related issues in homes.
In Aqviz we have dealt with all the water problems mentioned above in the foundation. Most of them could be minimized if the vapor barrier is installed under the foundation slab. So, we highly encourage you to install a vapor barrier in your foundation slab during foundation construction.
What is the Main Purpose of Using a Vapor Barrier Under a Foundation?
Vapor barriers are installed under the foundation due to these purposes such as,
- Moisture control in the foundation: Vapor barriers block ground moisture from seeping into concrete slabs, reducing dampness and preventing water damage in basements and crawl spaces.
- Prevent foundation mold and mildew: Vapor barriers inhibit the growth of mold and mildew in the foundation by keeping low humidity levels and maintaining high air quality.
- Increase foundation structural integrity: A vapor barrier preserves the foundation’s durability.
- Increase energy efficiency: Reducing moisture infiltration in the foundation helps to maintain stable indoor temperatures, lowering energy costs for heating and cooling.
- Improved indoor air quality: Vapor barriers contribute to a healthier home environment by preventing moisture related issues like musty odors and allergens in the basement.
What You Should Consider Before Choosing a Vapor Barrier for Foundation
Choosing the right vapor barrier is crucial for long term foundation protection. At Aqviz Waterproofing, we’ve encountered many projects where the wrong selection led to moisture issues and costly repairs.
So these things you should check with recommended values when you choose the right vapor barrier for the foundations.
Permeability rating of the vapor barrier: The permeability rating (perm rating) measures how much moisture can pass through the vapor barrier material when it is installed under the foundation. The lower the perm rating, the better it resists moisture.
Recommended value: A vapor barrier should have a perm rating of ≤0.1 perms, meaning it’s classified as a true vapor barrier under ASTM E96 standards.
Puncture resistance of the vapor barrier: Puncture resistance refers to the barrier’s ability to withstand tears and punctures during installation or over time due to soil movement in the foundation.
Recommended value: Look for materials with a minimum puncture resistance of 2000 grams according to ASTM D1709 to ensure durability against construction activities.
Tensile strength (strength class): Tensile strength determines how well the vapor barrier resists stretching and tearing when under stress in the foundation.
Recommended value: A high-quality barrier should have a tensile strength of at least 45 lbf/in (pounds per inch) per ASTM D882 to withstand environmental and structural pressures.
Thickness of the vapor barrier: Thickness impacts the overall effectiveness and durability of the vapor barrier in the foundation slab. Obviously, the thicker materials generally provide better protection.
Recommended value: The recommended thickness is 10 to 20 mil (1 mil = 0.001 inches), with 15 mil or higher preferred for high-moisture areas or heavy-duty applications.
Seam sealing method of the vapor barrier: Seam sealing prevents moisture from leaking through gaps where sheets overlap in the foundation slab.
Recommended method: Use taped or heat-welded seams rather than just overlapping. Butyl or polyethylene tape is commonly used to achieve a secure, long-lasting seal.
Durability of the vapor barrier: Durability refers to the barrier’s ability to maintain effectiveness over time, resisting wear, chemical exposure, and environmental factors when it is use for foundation salbs.
Recommended features: Choose UV-resistant, chemically stable materials with long-term performance warranties (25+ years) to ensure lasting protection.
How to Install a Vapor Barrier Under a Foundation
Proper installation of a vapor barrier for the foundation is critical to ensuring effective moisture protection. At Aqviz Waterproofing, we follow ASTM E1643 standards for installation, ensuring long-term durability and performance. Follow these steps for a successful vapor barrier installation:
1. Unroll and Position the Vapor Barrier
Unroll the vapor barrier with the longest dimension aligned with the direction of the foundation concrete placement. Face the lap seams away from the expected concrete flow to prevent displacement during pouring.
2. Extend to the Perimeter and Seal
Extend the vapor barrier to the foundation’s perimeter. If possible, terminate it at the top of the slab. Otherwise, seal it to the foundation wall, grade beam, or slab edge.
3. Overlap and Seal Joints
Overlap all vapor barrier joints by at least 6 inches and seal them using the manufacturer’s seam tape. Apply tape only to a clean and dry surface to ensure strong adhesion.
4. Seal All Penetrations
Seal around pipes, conduits, and other penetrations per the manufacturer’s instructions to prevent moisture leakage. Proper sealing is key to maintaining an uninterrupted barrier.
5. Minimize Punctures During Interior Forming
Minimize the punctures when you install it on the foundation. You should be careful and minimize using sharp edges, and tools keeping on the vapour barrier. If vapor barrier is damaged repair holes as per the manufacturer’s recommendations. As well as ensure that reinforcement bar supports have base sections designed to minimize puncturing the vapor barrier.
7. Repair Any Damage Immediately
If the vapor barrier gets damaged, patch it using material of similar or better permeance, puncture resistance, and tensile strength to maintain moisture protection.
8. Use Vapor Barrier-Safe Concrete Screeding
After the vapor barrier is installed properly pour the concrete on the foundation slab carefully. Do not let the barrier to damaged during the concrete pouring.
Read more: How to Waterproof Foundation?
How much will it Cost for the Foundation Vapor Barrier?
The cost of the vapor barrier under the foundation may vary with the material quality, thickness, and labor cost.
Material costs: Basic polyethylene plastic sheeting (6-mil thickness) ranges from $0.05 to $0.20 per square foot (approximately $0.54 to $2.15 per square meter). For a 1,500-square-foot area, this equates to $75 to $300.
Thicker Material cost: Higher-quality vapor barriers (8-mil to 20-mil thickness) cost between $0.25 and $1.50 per square foot (about $2.70 to $16.15 per square meter). For the same 1,500-square-foot space, expect costs of $375 to $2,250.
Installation Costs: Professional installation, including materials and labor, typically ranges from $2 to $4 per square foot (approximately $21.50 to $43 per square meter). Therefore, a 1,500-square-foot area might cost between $3,000 and $6,000.
More than that, vapor barrier installation costs can be varied with the area size, labor rate, and site accessibility. So we recommend you to have a site inspection before starting the project. Contact Aqviz, we will help you today!
How Long Can a Vapour Barrier Last?
A well-installed and maintained vapor barrier can last over ten years under the foundation slab. But its lifespan depends on the material quality and how well it’s installed, environmental impacts, building settlements, water table, thermal expansion, and ground forces changes.
What If a Vapor Barrier Is Not Installed Under a Foundation Slab?
If a vapor barrier is not installed under the foundation slab, it may cause these 6 severe moisture related problems.
- Moisture intrusion into the foundation
- Mold and mildew growth
- Foundation deterioration
- Reduced energy efficiency
- Increase unpleasant odors
- Damage to the foundation fixtures
If you see any of these water damage signs in the foundation, you should install a waterproofing membrane. Our experts have prepared a guide for foundation waterproofing. It includes all the details from starting to end.
So Aqviz motivates you to install a vapor barrier under the foundation slab to prevent future water related damages.
How to Damage a Vapor Barrier?
A vapor barrier can be damaged as follows ehn it is installed in the foundation
- Puncturing during construction
- Exposed to UV light
- Improper seam sealing
- Tearing from foot traffic
- Using low-quality material
- Ignoring repairs
