Waterproofing Below-Grade Insulated Concrete Forms

Waterproofing Below Grade Insulated Concrete Forms

Above and below-grade walls of a building or home can use insulated concrete forms (ICFs) in their construction. Both above and below-grade ICF walls are durable, sound reducing, energy-efficient, and disaster-resistant. However, because of soil conditions, below-grade walls require added waterproofing steps, unlike above-grade walls. In fact, both the 2018 International Residential Code(IRC) R703.1 and the 2018 International Building Code (IBC) 1404.2 require a weather- or water-resistive-barrier on a solid monolithic concrete wall, like Fox Blocks, when placed below-grade.

While both above and below-grade walls can utilize ICF, only below-grade walls require an additional application of a waterproofing membrane.

Waterproofing Below-Grade ICF Walls


Below-grade ICF walls require a waterproofing membrane and depending on soil conditions a reliable drainage system to reduce the possibility of moisture intrusion from soil and water. Self-adhered or peel-and-stick waterproofing membranes are common below-grade waterproofing systems used for ICF foundation walls. In addition, application of dimple drainage board over the membrane provides protection and hydrostatic pressure relief and is used in many areas and by many contractors.

There are nine steps Fox Blocks recommends for concrete waterproofing below-grade ICF walls.

  1. The ICF below-grade wall sits directly on a footing or slab.
  2. Follow manufacturer specifications for the application of the self-adhered waterproofing membrane.
  3. For some soil conditions it is good practice to encapsulate the entire underside of the slab with a poly vapor barrier.
  4. Place or adhere the waterproofing membrane on the ICF wall to create a complete envelope per the manufacturers specifications.
  5. Apply the entire below-grade portion of the ICF foundation wall following the waterproofing membrane manufacturer’s instructions.
  6. Place the dimple drainage board outboard of the self-adhered waterproofing membrane.
  7. Install French drain or weeping system to ensure the final drainage of water away from the wall.
  8. Around the drain tile and near the bottom of footing and ICF foundation wall, place gravel fill.
  9. Finally, cover the rocks with filter fabric.

Proper installation of a waterproofing system over below-grade ICF walls will create a waterproof wall. The waterproofing system ensures that moisture in the soil adjacent to the wall will filter through the fabric, then down the dimple board and the drain board, and finally into the drain tile. A quality ICF waterproofing system can eliminate Below-grade water issues.

Water-Resistant Above-Grade Fox Block ICF Walls


Above-grade ICF Walls are Air- and Moisture-Resistant

Above-grade Fox Block ICF walls resist thermal convection and therefore do not need an air and moisture barrier. Thermal convection is the process where heat moves by the flow of liquid or air molecules from the warm to the cooler side of a wall.

For example, above-grade Fox Blocks create a solid continuous monolithic above-grade concrete wall that provides continuous insulation with an R-value of 23. Ultimately, Fox Blocks create an airtight building envelope that limits thermal convection and moisture intrusion through the above-grade walls.

ICF Walls are Vapor-Resistant

ICF walls act as vapor retardants; therefore, ICF walls do not need vapor barriers. ICF’s have insulation on the exterior and interior of the walls separated by a thermal mass of concrete. The insulation stabilizes the temperature and prevents condensation within the concrete walls. For example, on a humid and hot summer day, when it is cool and dry inside a building, the temperature within the ICF wall system remains uniform and above the dew point, which prevents condensation.

What is Condensation?

Condensation is when water vapor (moisture in the air) changes into liquid water. Condensation occurs when the temperature drops to the dew point. The dew point is the temperature when the air becomes saturated with water vapor. Below the dew point, the vapor turns to liquid water. Furthermore, when the air temperature drops below its dew point through contact with a colder surface (like a wall system) water will condense and accumulate on the surface.

ICF Walls Inhibit Condensation and are Permeable


An ICF wall system maintains a steady temperature above the dew point; therefore, preventing condensation. Also, ICFs, like Fox Blocks, act as a vapor retarder with a perm rating of less than 1.0. So, even though water vapor can get through the Fox Block foam, the Blocks control moisture accumulation. Stopping the accumulation of moisture is essential to preventing the growth of mold within the wall system. ICF walls resist moisture accumulation because they are permeable and stop condensation.

ICFs are used to construct above and below-grade walls of a building or home. However, only below-grade ICF walls require waterproofing and proper drainage systems. Notability, though, if the designer and owner want a “belts and suspenders insurance” concerning moisture issues, they can apply a spray on WRB that is compatible with EPS foam to the above-grade walls. Please visit Fox Blocks for more information on ICF waterproofing.