CFA Tech Talk
By: Ed Sauter
Editor's note: As part of our partnership with the Concrete Foundations Association (CFA), the following article by Ed Sauter, executive director of the CFA, is the sixth in a yearlong series on the basics of concrete foundation construction. For more information, visit www.cfawalls.org or call 319-895-6940.
With new regulations and industry standards changing at a rapid pace, concrete professionals need a reliable source for information, as well as a voice to ensure their interests are represented with the code bodies. The Concrete Foundations Association (CFA) has stepped in to fill this role on two very important issues that will affect most concrete homeowners - pressure treated wood and stepped footings.
Pressure treated wood
For decades, residential contractors have been using pressure treated wood in the construction of homes and decks. According to the Simpson Strong-Tie Web site, "Pressure treatment is a process that forces preservatives into the wood. Wood is placed inside a closed cylinder then vacuum and pressure are applied to force the preservatives into the wood. The preservatives help protect the wood from attack by termites, other insects and fungal decay."
Until recently, the most common chemical used in the pressure treatment of wood was Chromated Copper Arsenate (CCA-C). Effective Dec. 31, 2003, the treated wood products industry voluntarily agreed to cease the production of CCA-C wood for residential and consumer use. This action responded to concerns about the arsenic levels in the wood. As such, the primary type of pressure treated wood now available is Alkaline Copper Quat (ACQ). Testing conducted by Simpson Strong-Tie has shown that ACQ is more corrosive to steel than CCA-C.
According to Bryan Herboldsheimer, president of H & B Foundations in Elizabeth, Colo. and chairperson of the CFA's Technical Committee, the more corrosive wood required a change in the type of sill plate anchors that many foundation contractors were using. "When the testing revealed that corrosion occurred at a faster rate with ACQ lumber, building officials called for a switch to double hot-dipped galvanized or stainless steel anchors."
An important element in concrete foundation construction, the anchor bolt or strap connects the sill plate to the top of the concrete wall. If the incorrect anchor bolt is used, corrosion occurs at an accelerated pace, leading to deficiencies in the connection between the foundation and the sill plate. The remedy necessitated by the chemical change involves using double hot-dipped galvanized or stainless steel bolts or straps. Herboldsheimer notes that if you use a plain steel bolt, it must be at least a full half-inch in diameter and must be solid - it cannot be hollow.
Jim Baty, technical director of the CFA, says this topic has become one of the most significant issues facing the industry. The change in connection type increases the unit costs on the project, Baty says, and the result is often a conflict between the foundation contractor and builder. Further, he says, although this issue is not readily apparent to the home buyer, it is a significant example of the rising costs of residential construction.
Residential foundation construction is increasing in complexity each year as homeowners seek more unique and dramatic structures. Innovative contractors are responding by adapting their forming systems and foundation designs to develop cost-effective and efficient solutions for meeting these challenges. Some of these processes have been used for many years and are extremely effective in solving complex design challenges and maximizing concrete performance. However, these proven solutions are occasionally questioned by local building departments. One such example of this scenario is the use of stepped, discontinuous footings in foundation construction.
As mentioned in a previous column, footings are located below nearly every residential foundation and serve two distinct functions. Footings distribute the building loads to the ground and they provide a platform for constructing the foundation wall. During foundation construction, it is advantageous and quite common to cast the basement area, garage and all attached portions at the same time. Because basements are a predominant feature of homes in the vast majority of the country, the main foundation walls are deeper than those typically required for the garage walls. Main foundation walls are 8 to 9 feet tall and garage foundation walls only need to extend below the required frost depth.
The common solution for this challenge is a section of the continuous wall that spans from the higher garage footing to the lower basement footing. This section is reinforced to act as a beam, transferring the building loads across a span controlled for maximum allowable distance.
Occasionally, this design is questioned by code officials interpreting a building code to require the footing be continuous from the main foundation all the way through the garage foundations. This scenario is very challenging for contractors, because of the additional costs involved. In a stepped footing, the foundation wall is designed to serve as the beam for transferring loads across the discontinuation of the actual footings. Although this condition is not addressed in the International Residential Code (IRC), it is used daily in the industry and has a proven performance.
When building and code officials challenge the practice of stepped footings, contractors are forced to seek support for this construction technique. Recognizing the importance of arming members with information that helps them address these concerns, CFA developed the Concrete Foundation Standard.
The CFA Standard presents evidence to show that continuous footings are not only uneconomical and difficult to provide, but they are also impractical and do not contribute structurally at those points. Further, Baty states that the current CFA standard affirms when a subgrade changes elevation, the footing may be discontinuous for a length of 6 feet, if the footings are on a minimum of 4 feet of undisturbed soil, on both sides of the discontinuous section.
Working for you
Industry associations such as CFA are an invaluable resource. CFA works on behalf of all our members and the entire industry to develop, support and influence code bodies. CFA also represents the interests of our members on several code and regulatory bodies, including the American Concrete Institute's (ACI) code for residential concrete (ACI-332) and cold-weather concrete standards. Our goal is to also teach our members how to interact with code officials. As such, we offer educational seminars and counsel on how to affect local code bodies and processes.
Established in 1974 for the purpose of improving the quality and acceptance of cast-in-place concrete foundations, the CFA has a variety of resources on this topic. In addition to providing promotional materials, educational seminars, opportunities for networking and a telephone network that places members in one-on-one contact with an experienced contractor for assistance in resolving a variety of issues, the CFA represents the interests of its members and the industry on several code and regulatory bodies, such as the American Concrete Institute's committee responsible for the creation of the "Residential Concrete Standard." Once complete, this standard will likely be adopted by the UBC, CABO and other building codes. The CFA has several of its members on the ACI committee responsible for this document and will endeavor to ensure that the interests of the foundation contractors are considered. CH
For more information about CFA, call Sauter at 319-895-6940 or see www.cfawalls.org.