Code Compliance with Insulated Concrete Form Foundations

Transcription

1 Code Compliance with Insulated Concrete Form Foundations Insulated Concrete Forms (ICFs) are increasingly being used as foundations in commercial and residential projects. Part of the reason is that ICFs naturally help comply with increasingly strict energy codes. While many are familiar with ICFs for above-grade walls, their benefits transfer to foundations as well. Energy code compliance, quicker more efficient construction, and safer site conditions are present in ICF construction, whether above or below grade. However, it is the need for improved energy performance in foundations that is really driving the use of ICFs below grade. ICFs offer a stay-in-place, double-insulated, steel-reinforced concrete forming system. It is for these reasons many designers and contractors are choosing ICF walls. Insulated Concrete Forms are increasingly being used as foundation walls.

2 Building Codes and Energy Efficiency Energy codes have been changing rapidly. Designers and builders must keep up with and be compliant with these changes. Changes include stricter requirements for continuous insulation, higher R-Values and tighter building envelopes. These requirements are now changing the landscape of exterior wall assemblies. Insulated concrete form (ICF) wall systems inherently meet the new building code requirements. Designers, contractors, and owners can comply knowing that the ICF wall has an exterior and interior continuous insulation panel of typically 2-5/8 in. thick expanded polystyrene (EPS) continuous insulation on every project. Combined, the two layers of insulation meet and exceed today s energy code standards, even in the most stringent climate zones. A typical straight ICF block segment. The applicable energy standards referenced by the International Residential Code (IRC) and International Building Code (IBC) include ASHRAE 90.1 and the International Energy Conservation Code (IECC). These documents establish the requirements for continuous insulation and R-Value requirements. Chapter 11 of the 2015 IRC defines the energy efficiency requirements for residential construction. The map in Figure 1 depicts the location of the different climate zones and corresponds to IRC tables providing county-by-county

3 listings of climate zones and R-Value requirements for both above grade and foundation walls. This information is duplicated in the IECC, whereas Chapter 13 of the IBC refers the user directly to the IECC IRC Climate Zone Map The IECC divides the United States into eight climate zones, each with specific requirements for the type, placement and amount of insulating materials both cavity and continuous in the wall assembly. Several versions of the IECC are currently in effect across the country (visit iccsafe.org for look-up), making it vital to be aware of which version has been adopted by the state or local jurisdiction in which a project is located.

4 R-Value Requirements from 2009 and 2012 IECC Each update of ASHRAE Standard 90.1 and IECC adoption has increased the amount of continuous insulation required in commercial buildings (see Figure 2). The latest ASHRAE Standard 189.1, Standard for the Design of High Performance Green Buildings adds the requirement for an air barrier as well as requiring and increasing the thickness of C.I. in ALL climate zones (1-8). ICF walls typically provide continuous insulation layers totaling an R-22+ as well as a continuous air barrier found in the solid, monolithic continuous concrete core. This core also qualifies the building envelope component as a mass wall by building codes. Mass walls typically require less R-Value insulation than non-mass or cavity walls. The most stringent climate zone requires an R-19 for a mass wall, which is less than the typical ICF. Therefore, these new energy code requirements have not affected the ICF wall assembly price or speed of construction in order to meet the new code requirements. Other wall systems, including masonry walls and traditionally formed concrete walls, have had to make a more concerted effort to

5 meet the new energy code requirements. These efforts have significantly affected both the cost and scheduling of these systems. Prior to the increased energy code standards, these wall system types were not typically as energy efficient as an ICF wall. Even with the new continuous insulation and energy requirements, the traditional systems still do not match the natural ICF energy performance, which in many instances exceed code requirements. ICF corner block segment Whereas previous codes only alluded to general air sealing of the building envelope, the 2015 IECC changed to a mandatory requirement for air barrier performance. This includes specific, mandatory provisions for air barriers in climate zones 4-8. The requirements may be met through the use of approved materials, approved assemblies, or whole building air leakage testing (ASTM E779). As more states adopt this code, these provisions will become mandatory for designers of commercial buildings in those jurisdictions. The energy code requirements of today have forced some building systems to need additional continuous insulation as

6 part of their assembly. Installing these additional layers has added material and labor costs. It has also impacted the construction scheduling and construction time for some systems. There is little doubt that future codes will be even more stringent when pertaining to energy efficiency. Building Code Requirements Insulated concrete form building systems have an ASTM standard, ASTM E2634 adopted by both the IRC and the IBC. This standard provides the minimum requirements for certifying any ICF system. In the IRC, insulating concrete forms are provisioned in Sections R404 and R608 and can also be found addressed in the referenced concrete code, ACI 332, which is an optional requirement code for residential concrete design. Benefitting the Construction Process Because colder climates translate to higher insulation requirements, concrete and concrete placement into the ICF formwork is protected by the double-insulated, stay-in-place concrete formwork. Concrete work and the ICF walls can continue in colder weather where masonry and traditional concrete wall construction may be shut down or require expensive heating and sheltering to continue in the cold weather. In addition to the newer energy code requirements that are driving more designs towards ICF construction, there are also many advantages that contractors are enjoying. ICF is often referred to as a 5-in-1 construction. This means the ICF wall assembly consists of 1) a structural concrete wall, 2) a double-sided continuous insulation, 3) furring or studs on both sides of the concrete wall for interior and exterior attachment, 4) an air barrier, and 5) a vapor retarder. Any

7 other wall system requires multiple steps to add layers to the assembly in order to achieve the same result. The net result of this 5-in-1 construction is reduced construction costs and schedules, largely due to a reduction in the number of trades involved in the wall construction. Time is saved completing the building shell sooner as other sub-trades such as electricians, plumbers, and drywallers can begin work earlier as well. ICFs Provide a 5-in-1 Construction Assembly While larger capital investments, maintenance, handling and storage for reusable formwork is eliminated, contractors also discover that ICF formwork is easy and light to work with, positively impacting the physical health of the workforce and improving job site safety by reducing job site incidents. While the building codes are driving toward tighter building envelopes and less energy consumption, ultimately, there are many reasons ICFs are increasingly used in residential and commercial construction. When added up, it comes down to meeting codes while saving time and money.

8 About the Author Kelvin Doerr, P.E. is a registered professional engineer with a Bachelor of Science in Civil Engineering from the University of Nebraska-Lincoln and a MBA degree from University of Nebraska-Omaha. He has 19 years of experience working in the insulating concrete form (ICF) industry with Fox Blocks. He has been involved with several different industry technical committees through the years. Was on the committee to create and write the ASTM E2634 standard for flat wall ICFs. The ACI 332 and ACI 560 technical committees. The EPS-IA technical committee. Has a designed and a patent on a couple of ICF ancillary products. Out of Plumb May Not Mean Damaged and Unsafe As published in Concrete Contractor Magazine. Question: The foundation for my new home has one wall showing two vertical cracks and the top of the wall is not even with

9 the base of the wall. I m concerned the backfilling has pushed the wall in and the building inspector wants an engineer to certify the wall before the builder can proceed. What should I do? Home Owner (Wisconsin). Answer: The process of building a foundation for a home inevitably leads to the two most common issues that have been raised by this inquiry. First of all, any homeowner who begins inspecting the concrete work performed will have concerns when cracks present. While the two truths of concrete are quite well known in the construction industry; 1) concrete gets hard, and 2) concrete cracks, the owner is not prepared to consider this an acceptable explanation. Cracking, by itself, should never be an immediate cause for concern. There are distinct characteristics of cracking that determine rather quickly whether the crack is problematic or simply a result of the drying and shrinkage process. More information on cracking can be obtained from our website in a free public download ( However, in the case of this inquiry, another common concern that presents during the final stages of the foundation work, and unfortunately all to often before the beginning stages of the above-grade structure work, has been identified. That is, the wall is out of plumb and backfilling has been completed. It must first be noted that the primary code references for residential foundation walls both state limitations for the backfilling operation. For a practical interpretation of the backfill process, the CFA provides a tech note on backfilling, TN The International Residential Code (2015) states: R Backfill placement. Backfill shall not be placed against the wall until the wall has sufficient strength and has been anchored to the floor above, or has been sufficiently braced to prevent damage by the backfill. 2

10 Furthermore, ACI 332, which provides a broad set of minimum prescriptive code requirements and the performance based design for a majority of the residential foundations, echoes the position of the IRC by stating: Lateral restraint The equivalent fluid pressure of the backfill shall be determined, but in no case shall be taken as less than 30 psf/ft. The foundation walls shall be restrained top and bottom against lateral movement. The top and bottom restraint for the foundation wall shall be in place before the introduction of backfill against the foundation wall. Temporary lateral restraint shall be permitted. 3 Both code references call attention to the same design assumption for foundation walls, a positive top and bottom connection exist so that the concrete wall performs like a beam and not a cantilever. The difference in performance or applied force can be quite substantial. While it is true there are likely hundreds of thousands of successful constructions where a top connection (the first floor framing) or bracing was not installed prior to backfill, there are enough cases where problems have been created from backfilling with no top connection to validate this code position. When a concern for movement in a foundation wall exists, however, caution should still be taken to not assume backfilling has cracked or pushed the wall inward. Some basic questions must still be asked. The first is whether horizontal reinforcement was placed continuous in the wall and does it meet the minimum code requirements? The purpose of the required horizontal reinforcement is to reduce the number and width of cracks resulting from shrinkage. The second question is whether the wall is bowed out of plane or leaning out of plane. This is an important condition to note. In order to determine the answer to this condition, a string line is the best method to test the position of the

11 wall. A string should be drawn taught from bottom corner to bottom corner and from top corner to top corner. The string should be pulled taught as it approaches the wall so it can be determined if it touches a point near the center of the wall before getting to the corners. There are three potential outcomes from this test. 1. String line is true at base of wall; string line at top of wall shows a bow. This is the case most likely to be of concern to an engineer and is the one to be sure to engage the parties on the project. With no bow at the base of the wall, the forms were set up true and it may be assumed that the top of the wall corresponded to the base, since forms are rigid. It should be noted that insulated concrete form walls may vary from this concern if they are plank or block style. The bow evidenced by the string is more likely to be a result of the backfill operation and stability of the wall is the next condition to investigate. An engineer should be involved at this stage. 2. String line is bowed at base of wall; string line at top of wall shows a bow. This condition is a bit trickier and may still require an engineer s assessment. Variation in the bow may still indicate influence in the wall structure by the backfilling operation. However, the bow in both the bottom and top of wall may also indicate a forming tolerance issue and forms that may not have be set completely straight. This I particular so given that the footing connection provides restraint against bowing or movement, further indicating that the wall was likely formed to that shape. 3. String line is true at base of wall; string line is true at top of wall. A true string line should be the first indication that a forming tolerance is at hand. Walls that are loaded dynamically and moved from their cast position will evidence stress. Stress is not applied uniformly and movement does not result uniformly. The

12 wall is confined at the corners where it has a much higher capacity and therefore movement results in a bowing along a longer section or cracking at or near the corners. In the case of the project at hand, the contractor engaged the owner and demonstrated that a string line was true at both the top and bottom of the wall. The two cracks were spaced relatively evenly across the wall and were located on form joints, which further indicates a pattern of shrinkage cracking. Yet, the top of the wall was out of plumb inward by 1.5 inches, indicating an issue for tolerances. It is proper to enter into any project with expectations of perfection and yet construction is a series of processes that require the allowance for tolerance of conditions that are less than perfect. The CFA Standard 4 offers the following when considering tolerances: 8.3 Foundation Tolerances - The wall should be considered within tolerance if the following conditions are met: 1. The deviations did not cause the building to become structurally unstable. 2. The deviations did not encroach on areas reserved for other work. 3. The deviations did not severely impede other trades from doing their work. 4. The deviations did not put the building out of compliance from the governing building code. 5. The deviation or blemish did not contradict the specified class of architectural finish (unspecified class assumes unfinished. )

13 The project presents the case that the foundation wall was completed with a deviation along this particular wall. It was the only wall with such a remarked deviation. A dialog of acceptable tolerance is the next consideration. There are three references that influence this discussion as the jurisdictional codes do not address tolerances. Those references are 2010 CFA Standard, ACI 117 5, and Residential Construction Performance Guidelines of the National Association of Homebuilders (NAHB). The particular tolerance in question for out of plumb of a vertical plane varies greatly across these three industry references. The NAHB reference is the most directly applicable reference specific to both residential construction and the nature of something being acceptable or not. This reference states: 2-13 Concrete walls shall not be out of plumb by more than 1.5 in 8 feet when measured from the base to the top of the wall. 6 Applying this reference and consideration of the full conditions for this project. The homeowner, builder and contractor should be having a conversation about how to complete the space for effective finishing of the basement. Concern for structural stability does not seem warranted, despite the builder proceeding with backfill ahead of top connection or temporary bracing. Jim Baty is the Executive Director for the Concrete Foundations Association after having served as Technical Director since He is currently chair of ACI 332 and a voting member for ACI 306 with priorities of establishing better guidance and structure for residential concrete construction. For more information on this topic, contact Jim Baty at jbaty@cfawalls.org. Find out more at References: 1 Backfilling Foundation Walls (TN-002) published by

14 the Concrete Foundations Association, st Street NW, Mount Vernon, IA Phone: International Residential Code For One- and Two-Family Dwellings published by the International Code Council, Inc., 4051 West Flossmoor Road, Country Club Hills, IL Phone: Residential Code Requirements for Structural Concrete (ACI ) and Commentary published by the American Concrete Institute, Country Club Drive, Farmington Hills, MI Phone: CFA Standard published by the Concrete Foundations Association, st Street NW, Mount Vernon, IA Phone: Specification for Tolerances for Concrete Construction and Materials (ACI ) and Commentary published by the American Concrete Institute, Country Club Drive, Farmington Hills, MI Phone: Residential Construction Performance Guidelines for Professional Builders & Remodelers published by the National Association of Home Builders, National Housing Center, th Street NW, Washington, DC Oil on Rebar by JAMES R. BATY II

15 As published by Concrete Contractor Magazine. Created: August 21, 2013 The Concrete Foundations Association explains the code reference and common misconceptions regarding oil on rebar for residential concrete. Question: On several of our most recent residential projects, the inspector in our area has been complicating our pour schedule when finding form oil over-sprayed on the rebar in our walls. Is it our misunderstanding that form oil on rebar shouldn t pose a problem to the wall performance or the acceptance of our pre-pour inspection? Concrete Contractor (Ohio) Answer: Your question addresses a common problem across the construction industry that is created as codes are modified over time. Regardless of the comparison of residential to commercial work, code edition after code edition presents challenges to professionals throughout the industry to remain current with the latest acceptable practices and minimum requirements.

16 In its Overall Grand Prize winning project in the 2013 Concrete Foundations Association Project of the Year Awards, Ekedal Concrete utilized 191 tons of steel in the foundations and footings of an 11,000-square-foot, seaside home. For the complete article, visit the article at For more information on the codes affecting this issue or the research, contact Jim Baty, CFA Managing Director. American Concrete Institute Announces New Publications Farmington Hills, Michigan (July 9, 2008) The American Concrete Institute (ACI) announces the availability of five new publications to educate and inform industry professionals

17 on the newest concrete-related information and technology. As always, ACI members receive a special discount (up to 40 percent) on all publications. Publications can be ordered by calling or online at : Code Requirements for Residential Concrete and Commentary The code portion of this document covers the design and construction of cast-in-place concrete one- and two-family dwellings and multiple single-family dwellings (townhouses) and their accessory structures. Topics include the design and construction requirements for plain and reinforced concrete footings, foundation walls, and slabs-on-ground, and requirements for concrete, reinforcement, forms, and other related materials. Also available in PDF form. Publisher: American Concrete Institute Publishing date: June 2008 ISBN: Number of pages: 27 Price: $55.50 (ACI members $34) 209.2R-08: Guide for Modeling and Calculating Shrinkage and Creep in Hardened Concrete This guide is intended for the prediction of shrinkage and creep in compression in hardened concrete. It outlines the problems and limitations in developing prediction equations for shrinkage and compressive creep of hardened concrete. It also presents and compares the prediction capabilities of four different numerical methods. This document is addressed to designers who wish to predict shrinkage and creep in concrete without testing. Also available in PDF form. Publisher: American Concrete Institute Publishing date: May 2008 ISBN: Number of pages: 45 Price: $68.50 (ACI members $42) 330R-08: Guide for the Design and Construction of Concrete

18 Parking Lots Concrete parking lots serve many kinds of public facilities, commercial developments, businesses, and multifamily housing projects. They primarily accommodate parked vehicles, but may also provide maneuvering areas and access for delivery vehicles. A full appreciation of the differences and the modification of design and construction procedures to take these differences into account can result in economical concrete parking lots that will provide satisfactory service for many years with little maintenance. This guide includes information on site investigation, thickness determination, design of joints and other details, durability considerations, paving operations, and quality-assurance procedures during construction. Maintenance and repair are also discussed. Also available in PDF form. Publisher: American Concrete Institute Publishing date: June 2008 ISBN: Number of pages: 36 Price: $62.50 (ACI members $48) 201.2R-08: Guide to Durable Concrete This guide describes specific types of concrete deterioration. Each chapter contains a discussion of the mechanisms involved and the recommended requirements for individual components of concrete, quality considerations for concrete mixtures, construction procedures, and influences of the exposure environment, which are all important considerations to ensure concrete durability. Also available in PDF form. Publisher: American Concrete Institute Publishing date: June 2008 ISBN: Number of pages: 49 Price: $70.50 (ACI members $43) 421.1R-08: Guide to Shear Reinforcement for Slabs Tests have established that punching shear in slabs can be

19 effectively resisted by reinforcement consisting of vertical rods mechanically anchored at the top and bottom of slabs. ACI 318 sets out the principles of design for slab shear reinforcement and makes specific reference to stirrups, headed studs, and shearheads. This guide reviews other available types and makes recommendations for their design. The application of these recommendations is illustrated through numerical examples. Also available in PDF form. Publisher: American Concrete Institute Publishing date: June 2008 ISBN: Number of pages: 23 Price: $52.50 (ACI members $32) For more information, contact: Sara Steptoe Marketing Communications Specialist Advancing Concrete Knowledge Founded in 1904 and headquartered in Farmington Hills, Mich., USA, members of the American Concrete Institute advance concrete knowledge by producing consensus, concrete-related codes, specifications, guides, and reports; creating and administering certification programs that support individuals in the concrete industry; delivering seminars and distance learning opportunities; publishing Concrete International magazine; and producing two peer-reviewed technical journals. For additional information, visit New membership benefits are available. Get More than ever before!