For a new ICF installer there is considerable information from the ICF manufacturers about how to lay the blocks, but one of the main questions being asked on social media is about the construction sequencing or phasing — how many courses to install and when to place concrete. Naturally, the build sequence applies to the size of the building and some major structural principles, but generally, ICF construction sequencing is similar to conventional construction: footings, foundation walls, main floor and main floor exterior walls, second floor and exterior walls, roof. For ICF applications, there are two major technical/structural terms that every installer must be cognizant of and follow — lateral support and cold joint.
Lateral Support – These walls are basically designed to be laterally supported at the top and bottom, meaning that the walls are physically connected to a footing, slab, floor, or roof system, preventing and securing the walls from moving inward or outwards from any lateral pressure. Walls not only support the vertical or point loads of the building but are subjected to a continuous live load, laterally/horizontally, which may cause walls to move or shear from soil pressure, wind pressure, or earthquakes.
Cold Joints – Cold joints are horizontal when the placement of concrete is interrupted or delayed, allowing the first level of concrete to set (harden) before the next level is placed. This creates a cold joint or a physical seam in the wall. Cold joints are allowed in the construction of above-grade concrete walls but must be designed with overlapping rebar dowels and located at an appropriate spot in the wall assembly. Cold joints are NOT allowed in below-grade foundation walls that will be retaining backfill. Cold joints create a rough horizontal seam in the wall that must be installed with rebar dowels to structurally tie the two layers of the concrete wall together through the joint. Cold joints are commonly installed in above-grade walls between the concrete placement per floor level. Note that in some larger projects, due to time allocation versus volume of concrete to be placed, a vertical cold joint may be required. Similar principles apply, but it is recommended that an engineer design the detailing and location for these.
In the review of the installation sequencing, it is very important to understand the technical principles and applications of lateral supports and cold joints.
The type and size of ICF structures relates to the sequencing of the installation. In all applications, and in all ICF core sizes, the bottom of the ICF wall is connected and laterally supported at the footing or slab with reinforcement dowels. This is a basic overview of the “‘how to” for each:
ICF Frost Wall – Frost walls are a few courses of ICF block in the ground with backfill on both sides. These small walls are typically poured as continuous monolithic walls from bottom to top. The backfill may be slightly uneven on the wall being laterally supported at the top by a slab or floor assembly.
ICF Crawl Space – A crawl space is typically a two- to three-course short wall assembly, which may have minimum backfill pressure. Build this wall to full height and place concrete monolithically to the full height. Cold joints are not recommended. The wall is laterally supported at the bottom by footing dowels and by the floor system bearing on the ICF concrete core at the top. The top of the wall is connected, either with anchor bolts or metal straps cast into the concrete.
ICF Foundation – A below-grade foundation or basement wall could be six, seven, or more courses high, with an above-grade wood frame structure bearing on top of the ICF wall. The foundation will retain backfill and must be constructed to full height. No cold joints are allowed in foundation walls. Concrete is placed in the top of the full-height ICF wall, with continuous lifts (layers) of concrete, approximately 4 feet in height, and each lift is consolidated or mixed into each other. Wet set anchor bolts or metal straps into the concrete at the top of the wall for the floor sill plate. Backfill only when the foundation walls are laterally supported at the top by the floor framing.
Slab on Grade One Story ICF Above Grade – ICF walls constructed over a slab on grade could be any number of courses. The wall is laterally supported at the bottom with dowels into the slab and laterally supported at the top by embedded anchors or straps set into the concrete for the roof system. As an above-grade wall, this wall may have a cold joint but, if possible, try for full-height concrete placement. Build the wall full height, place concrete continuously in 4-foot lifts, and consolidate each lift.
ICF Foundation and One ICF Story – The sequencing here is to build the foundation walls first, place concrete, and then build the above-grade walls second. Typically, once the concrete in the foundation wall has set, install the floor system and work off the sub-floor to install the above-grade ICF walls. For ICF walls, the floor system is typically fastened to the side of the ICF wall with embedded anchor bolts or ICF ledger connectors and
As a planning example — assume the building has an 8-foot ceiling height in the basement and first floor. Calculate that from top of footing to top of the ICF for the roof sill plate requires 13 courses of block. For this build, the foundation wall should be built with eight courses, or 10 feet 8 inches high. This will allow the concrete to adequately cover (3 to 4 inches at a minimum) and support the floor connectors embedded in the wall. The concrete should be placed to about half the height of the eighth block or top block, leaving the top cross-tie in this block exposed so the next layer of block can be connected with a clip or tie wire. Total height of the concrete in the foundation wall would be 10 feet 3 inches ± as a cold joint. This will be a rough cold joint with 4- or 5-foot-long dowels inserted half-way into the concrete, at a minimum spacing of 4 feet on center. The dowels must follow
the criteria for reinforcement overlap lengths – 40 or 60 times (24 inches or 30 inches) the diameter of the rebar. As an option to eliminate dowels, the vertical rebar in the foundation can be installed with the extra overlap length through the cold joint.
Once the first floor is installed, work off the sub-floor to install the next five courses of ICFs for the main floor walls.
Multi-Story ICF Above Grade – Follow the same techniques as for a one-story. Install the ICF block above each floor level to ensure the concrete is slightly above the finished floor level to provide structural coverage of the floor connectors. Install a rough cold joint at each floor level with reinforcement dowels through the joint. The ICF wall is laterally supported at footing with dowels, at each floor connection and the roof connection.
Tall Walls – For the construction of taller above-grade walls for warehouses, garages, retail spaces, etc. in the range of 12 to 16 feet, these above-grade walls may include either a cold joint or be monolithically poured in lifts. Taller bracing systems are required, and concrete may be placed continuously and consolidated in 4-foot lifts around the perimeter. Taller walls require more attention to detail and specialized equipment. It is recommended to have an experienced installer for concrete placement in tall walls.
Pre-plan the block installation sequencing for heights and connections for every project. Considerations on the placement of concrete may be based on a number of factors — availability, maximum supply per day, weather, and delivery distance. There is also the ability of the crew in how much they can comfortably handle per day.
Break down each level to ensure the right amount of concrete is ordered and estimate the time required for placement. Ensure dowels and embedments are ready for placement in wet concrete. The best scenario is for placement of concrete to be continuous for each level. Concrete must have adequate coverage over the floor connections by locating cold joints correctly, installing reinforcement dowels to maintain the structural integrity of
It is very important to plan and have the whole crew understand this sequencing of the build, the mechanics, rebar placement, concrete placement heights and consolidation. Once the concrete and pump truck are on-site, it is go time.
Tom Patton had a 30-year architectural design background prior to joining the ICF industry in 2001 with the technical support department at ARXX. Over the last 20 years, Tom has worked with major ICF companies developing technical documentation, application details, and training programs, as well as consulting and promoting ICFs with various associations including the ICFMA, NRMCA, and codes and standards committees. Currently, Tom is Corporate Brand Ambassador for Fox Blocks and co-developer of the Fox Blocks Integrated Learning Center.