One Best Practice for Energy Efficiency & Strength
Originally published by: Construction Canada — June 26, 2019
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One of the smartest decisions a home owner can make is to use Insulated Concrete Forms (ICF) as an innovative building envelope alternative to traditional light-wood frame or light-gauge steel. Consider structures that survived the wrath of Hurricane Katrina. Several ICF buildings not only withstood the tremendous wind gusts, but also the force of the storm surge. But, ironically, most builders or home owners don’t choose ICF systems for their disaster resiliency. The bigger draw is the well-known energy efficiencies of insulated concrete forms.
An insulated concrete form (ICF) system offers the best of both worlds: the strength and durability of reinforced concrete and the energy efficiency of expanded polystyrene (EPS) rigid insulation. It is clearly a synergistic partnership, producing a combined effect that is greater than the sum of the separate benefits of each building product.
The ICF system serves as a permanent interior and exterior substrate for walls, floors and roofs. To construct an ICF wall, two layers of rigid insulation are separated with recycled polypropylene webs to create an ICF block. These hollow blocks are interlocked (in dry-stack fashion) and the webs locate and hold reinforcing steel (rebar) before the cavities are filled with concrete. The end-result is a reinforced concrete wall in the center, encased in barrier insulation on each side. The materials work as a team, with the concrete and rebar providing an ideal load-bearing wall that carries vertical loads and resists lateral loads from wind and seismic motions. The entire ICF wall assembly with all the layers combined creates a secure air tight envelope with good acoustic properties.
In the case of ICF roof and floor systems, the EPS functions as a one-sided insulating form on the bottom surface. EPS panels up to 30 feet in span are placed between concrete walls, then fitted with reinforced steel and filled with concrete. Since ICF walls are concrete bearing walls, any traditional flooring or roofing system can be used in conjunction with ICF wall systems, including precast hollow-core plank, reinforced concrete slabs, metal deck/steel joists,cold-formed joists or wood joists.
ICF WALL CONSTRUCTION
Step 1: Stack
Place corner blocks, they lay straight blocks toward the center of each wall segment.
Step 2: Brace
Install alignment bracing around the entire wall of the structure to ensure that the walls are straight and plumb, as well as to enable alignment adjustment.
Step 3: Pour
Pour the concrete into the walls using a boom pump.
Best Practices for a Successful ICF Install
- Hire a qualified installer – The installer on your project should be trained and certified in the particular ICF system specified. Some product manufacturers offer site visits at several points throughout the install.
- Account for wall thickness – Although ICF walls are thicker, the amount of “lost” space is only noticeable in a situation where the builder changes from ICF wall to wood framed construction in a knee wall scenario.
- Avoid inefficient wall sizes/shapes – Walls with bump-ins or bump-outs result in shorter walls (i.e., less useful living spaces) or shifting of window placement if these features are used around corners. Whenever possible, straighten bump-ins and bump-outs. This will not only add construction efficiency and living space, but reduce the need for more costly corner/ specialty blocks. If a bump-in/bump-out is a stylistic preference, check manufacturer recommended coursing charts—or accomplish the effect with a façade built of light guage steel, brick, block or lumber.
- Be aware of the right attachments – When securing items to the ICF, use the method recommended by the ICF supplier.
- Work efficiently with wall lengths – Your strategy for combining multiple ICF blocks and working with cuts/seams will have a major impact on project speed and quality. Select even-inch increments for wall lengths whenever possible since the connection pattern repeats every inch, thereby making stacking far easier. Work with block’s web spacing increments to ensure that all embedded attachment points are vertically aligned, allowing for smooth application of finishes. Do not take pains to achieve zero cuts in an ICF block—use of a common seam often eliminates layout problems, speeds up the process, and ensures the majority of plastic webs are aligned.
- Brace from the inside – Proper bracing is the key to ensuring that walls are straight and plumb, which is critical to structural integrity and accuracy for sub-contract finishing work. The higher the wall, the harder it is to reach the exterior with bracing, so brace from the inside. Rather than creating your own bracing system, go with the ICF manufacturer-recommended (OSHA approved) scaffolding/ bracing system that works best with their products.
- Strategically place a vertical or stack joint – In applications where a vertical or stack joint is required, place the joint over a door or window opening to minimize the required length of the joint and associated labor. Just be sure to properly brace and strap the joint at this critical juncture. Most importantly, maintain proper horizontal dimensions above and below openings.
- Don’t compromise the thermal envelope – Maintain continuity of insulation and avoid cantilevered concrete floors or exposed slab edges to prevent thermal breaks.
- Avoid heavy vibrating during concrete pour – ICF walls should be vibrated to remove voids in the concrete. Consider substituting with a small-diameter mechanical vibrator to allow concrete to spread evenly and maintain integrity.
- Make sure the concrete completely fills the form – To avoid holes and gaps in the concrete pour, be familiar with the structural requirements and the design of the webs. It is highly recommended for the structural engineer to be familiar with the ICF block to optimize the placement of rebar in webs in order to avoid voids and expedite stacking.
Choose the proper mechanical system – Because ICF is so energy-efficient, mechanical engineers need to factor this in as they calculate HVAC requirements. In fact, if a unit is oversized, it can actually create humidity/moisture issues in the interior. The energy efficiency comes in two parts: added thermal resistance which reduce cooling/heating loads therefor allowing for reduction in the heating/cooling equipment and increased air tightness of the building due to the ICF construction. The increased air tightness usually requires for a dedicated fresh air intake to be present and properly sized. In the past, due to poor construction, the fresh air would enter via uncontrolled air leaks through the building envelope.
“Resilience” is an integrative strategy that promotes sustainable building decisions that encompass disaster-mitigation, durability and environmental protection. While energy efficiency has been a huge motivator for selecting ICF materials to date, a building’s disaster mitigation capacities and durability are just as important as any LEED-certified standard in achieving a sustainable design.
In fact, all three priorities are so interlinked that a decision made in one sustainability arena positively impacts the others. For instance, making the decision to select a robust system like insulated concrete forms heightens a building’s durability and longevity in the face of normal wear and tear. If disaster does strike, these durable qualities minimize structural damage, which in turn conserves energy and reduces the need for additional natural resources during the recovery phase.
Adopting a resilient building strategy is not just the responsible thing to do, it is the most sustainable investment which will pay for itself many times over during the short-term build and long-term occupancy phases of a project.
When you make the decision to install insulated concrete forms as the basis for your building’s structural system, you and your client will reap the rewards during the short-term construction and long-term occupancy phases of a build. These benefits influence virtually every facet of project decision-making, including construction cost/efficiency and building maintenance, durability and sustainability—in terms of both “green” building and disaster resilience.