Build Stem Walls or Frost Walls

Every building requires a stable foundation, starting with footings and a foundation wall capable of supporting the load of the building plus resisting environmental forces. Some homes in the southern climate zones, where frost is not an issue, may be built as a slab-on-grade. In colder regions, frost depth becomes a significant consideration. Footings and walls are designed to protect the foundation against frost heave, or movement from the ground due to cold weather. The depth of footings and frost walls is defined by local codes and the International Residential Code frost requirements (https://codes.iccsafe.org/content/IRC2018/chapter-4-foundations).

As the climatic requirements change, so do the designs for frost walls, stem walls, crawl space foundations, and full basements. This has led to renewed evaluation of foundation technologies for improved thermal performance, reduced installation risk, and enhancements for long-term durability.

All exterior foundation walls are load bearing walls, designed to support the structure, which must remain structurally sound and resilient for the life of the building. Frost walls are typically backfilled on both sides. Stem walls and basement walls retain earth on one side only but have a partial section of the wall exposed above grade. Conventional construction methods use concrete block (CMU) or formwork for poured concrete to build these walls. Recently, these conventional wall types have been showing issues with some sort of failure due to:

• pressure from floods and high water table
• soil expansion from expansive clay and cold weather frost heave
• cracking, allowing for water intrusion and deterioration of the materials
• deterioration from exposure to changing climate conditions

Ongoing code changes address some of these issues with waterproofing and insulation, but the basic design, materials, and installation quality may still promote some of these evaluation failures.

In today’s environment, there is a unique market for specific retrofit contractors that address repairs on conventional CMU and poured concrete foundations that have failed through cracking, spalling, and water intrusion. The big issues may be the creation of mold and mildew or possibly safety due to structural damage to the building.
Load-bearing frost walls are in direct contact with the outside environment and bear the load of the building. In addition to the vertical load, frost walls are designed to withstand pressure from the soils around the home caused by the freezing and thawing cycles (expanding and contracting soils), which apply a great deal of stress on the foundation that can ultimately cause serious problems over time.

The original concept of ICF was to build a better foundation with an insulated, reinforced concrete wall assembly. The concept has worked exceptionally well over the last 60+ years. With the current labor shortage, scheduling for either masons or formwork contractors to be on-site to build a frost wall has become a major issue. Building your own formwork for a frost wall incurs material and labor costs. Plus, new code requirements address protection from thermal transfer at the foundation wall and under the slab, which requires insulation and moisture protection.

Insulated concrete forms provide the best solution for stem walls and frost walls. Even though these walls are short in height (generally one block at 16 inches, two blocks at 32 inches, three blocks at 48 inches, or a cut block to achieve the required height), the application has many benefits:

• Fast and efficient to install with a minimum crew
• Material available on demand and installed according to your schedule
• No formwork installation or stripping
• Can be installed in cold weather, year-round
• Continuous insulation on both sides of the wall
• EPS on the inside face may be exposed to backfill with no deterioration over time
• Insulation protects the concrete to eliminate cracking due to exposure
• Superior thermal and moisture performance
• Predictable scheduling, as the contractor or your forces install the ICF to eliminate subcontractors
• Easy to install with manufacturer’s instruction and training
• Straight and plumb foundation walls

In the design aspect, frost walls and stem wall foundations earn their keep when the site is working against you rather than cooperating:

• On a sloped lot, a short perimeter wall bridges between high and low points so the floor stays level while the footing follows the contour of the ground. ICFs are easily adapted for step footings and may be designed as retaining walls.
• In flood-prone areas or where drainage is poor, an ICF foundation will not absorb water and will withstand the pressures of flood waters.
• In cold climates with significant frost depth, placing a reinforced wall above a footing set below the frost line helps the structure resist heaving and seasonal movement, while keeping framing safely above the snow and ice zone.
• The same logic applies to sites with expansive soils, shallow bedrock, or variable fill, where the priority is controlling movement at the perimeter instead of fighting it later with repairs. ICFs may be installed directly on bedrock with the blocks scribed to the rock elevations.
• In some applications, a short stem wall may be installed as a monopour with the footer and/or the slab. This expedites the installation but does require expertise in concrete installations.

The engineering for an ICF foundation allows for a 6-inch reinforced concrete core. At the floor connection point, a taper top block may be used to expand the bearing point of the above-grade wall and floor system. Utilizing a 6-inch core provides a cost saving over an 8-inch poured concrete or 10-inch CMU.

Modern climate conditions, labor shortages, and evolving code requirements have exposed significant limitations in conventional CMU and poured concrete foundation systems. ICFs are quickly becoming recognized as the “go to” material and application for foundations, either frost walls, stem walls, crawl spaces, or full basements.

The advantages for any trade or general contractor installing ICFs foundation systems create the opportunity to control that specific part of the build, expedite timelines, and build a stable, high-performance foundation with the confidence that it will endure for years to come. For renovation or residential contractors, having the ability to use ICFs for any type of foundation expands your capabilities to handle the whole project and eliminate dependency on other contractors. The other big plus is that ICFs provide plumb and straight foundation walls.