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ICF Waterproofing: How to Waterproof Below Grade Insulated Concrete Form Homes

Insulated Concrete Forms, or ICFs, are quickly becoming one of the most popular and effective means of building new homes, replacing the traditional standard of stick-built construction.

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However, ICF construction has yet to become the main standard, owing mostly to some of the limitations of its design. In particular, waterproofing insulated concrete forms built below grade—that is, for basement floors—is a fairly tricky challenge compared to building with concrete blocks or stick-built frames. 

In this article, we will be exploring a few of these waterproofing options for below grade ICFs to help you decide on a method that would work best for your new home. 

What is an Insulated Concrete Form?

An insulated concrete form is a wall structure that is made of rigid foam insulating panels that are held together by an internal frame of metal rebar. Once the ICF modules have been constructed to form the house layout, concrete is then poured into the space between the insulating panels to form the final wall. 

There are many variations of the insulated concrete form in modern-day usage, but all of them generally provide a number of benefits compared to other methods like stick-built construction and concrete block construction. A few examples include:

  • Higher strength
  • Built-in thermal insulation
  • Built-in fireproofing (depending on the foam material used)
  • Improved soundproofing
  • Improved energy efficiency (from improved insulation and less air leakage)
  • Easier setup for electrical wiring and plumbing

But as we mentioned earlier, the primary challenge of ICF construction is managing humidity, especially when building below-grade structures as the ground tends to have a lower temperature and little to no ventilation. For this reason, waterproofing measures must be implemented to ensure the longevity of the ICF structure. 

Waterproofing Your ICF

It is important to note that the foam panels used as the exterior panels of the ICF construction are particularly vulnerable to damage from water and moisture.

The materials that are commonly used to make these foam panels are also susceptible to harm from solvents and acids, which means that when compared to other building methods, the possibilities for waterproofing are even more limited for builders. 

Thankfully, there are a variety of materials and methods used today as waterproofing measures for ICFs.

Waterproofing Membranes

Applying waterproofing membranes to the whole outside surface area of an ICF building is one of the most popular techniques of waterproofing below-grade concrete structures, and it’s also one of the most effective.

As you might expect, there are various different types of waterproofing membranes available, each with their own set of advantages and disadvantages. We’ve split them down into the following categories: 

  • Peel and stick membranes are, as the name suggests, waterproofing membranes that adhere to the surface of the ICF’s external foam, blocking out water droplets and vapour from passing through to the inside. These membranes are typically made out of asphalt or plastic sheets, and are typically stuck on with the use of a water-based primer. 
  • Air gap membranes give the ICF a barrier against water through the use of a small but significant air gap that provides just enough clearance to prevent water transfer onto the wall. The air gap is achieved through the membrane’s unique design which incorporates bumps or dimples that are adhered to the ICF. 
  • Spray-on membranes are another fairly effective waterproofing method for ICF structures, and is applied to the foam panels through a pressurized spray that helps ensure an even coat of the waterproofing compound. However, contractors must take care to choose the right spray-on membrane if they decide to use it, as the foam panels of the ICF can degrade from solvents. 

Concrete Additives

Alternatively, it is also possible to waterproof the ICF through the use of additives that are mixed into the concrete before it is poured into the ICF mold.

Concrete additives for waterproofing typically use of silica-based compounds that combine with the mixture and become part of the concrete form. Under normal circumstances, the silica compounds remain completely inert; however, they activate in the presence of excess moisture or water that enters the ICF. 

At this point, the silica compounds grow towards the source of the water as they absorb the moisture, expanding as they go. Multiply this by several million silica particles, and the result is a perfectly-sealed concrete pour that has had its tiny cracks and crevices filled in by these silica compounds. 

Other Considerations

Besides the waterproofing measures we have discussed above, there are a few other considerations that builders must take into account to ensure that these measures actually remain effective for the expected lifespan of the home. 

ICF Construction

One of the major factors that affect the effectiveness of ICF waterproofing measures is the construction of the ICF itself. While insulated concrete forms aren’t exactly made with very low tolerances, construction of the forms themselves must, at the very least, be done correctly.

For instance, gaps between the insulating foam panels must be minimized to prevent air and water leaks. The same is also expected of the concrete filling, which is typically solved by pouring the concrete into the forms in layers (this approach allows even curing). 

Drainage Control

Beyond the ICF, in order for the below grade waterproofing to work effectively, water coming in from above ground must also be controlled to minimize contact with the ICFs built underground. 

The most common measure implemented above grade is a properly-designed system of ducts and drains that lead water into the ground. Drainage planes—water control devices that move water away from the wall—could also be installed throughout the house structure. 

Moisture Control

Finally, homeowners must also be aware of potential issues with humidity in the ICF structures below grade given its typically cold and damp conditions that we touched on earlier. 

One of the ways that humidity can be controlled below grade is through proper backfilling and compacting of the soil around the ICFs below grade. It is important to ensure that the backfilled soil is fine enough for solid compaction without any rocks or sticks that could create air gaps or damage the waterproofing layers. 

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