Insulated Forms Make Warmer Concrete Walls
Note: This is the first of a two-part article about insulated concrete form systems. The second part will focus on installation procedures and thermal considerations.
By Steve Andrews
Flip through any building magazine and you'll find manufacturers of insulated concrete form systems spending a bundle on advertisements extolling the virtues of their products. And they're expanding dealer networks nationwide, so no matter where you build, you can probably buy one of these products.
Most builders use insulated form systems to replace poured concrete or concrete block basements. However, the systems work above grade, too. They can be used for any concrete wall or foundation, but their greatest benefits apply to insulated walls.
As a group, foam forming systems have several advantages: high strength, good insulating value and low sound transmission. The systems also replace much of the wood framing needed for the typical house. That puts less pressure on a declining timber resource and less stress on the building budget.
Builders who have used foam forms note some quality advantages. They say they like the finished results and plan to keep using them. They also admit foundations and walls built with foam forms tend to cost more and involve a learning curve.
Foam forming systems were introduced more than two decades ago in both Europe and the U.S. Yet the first major marketing efforts didn't start until the 1990's. Foam forms have a good foothold in several areas, such as Iowa, Minnesota and parts of the Southwest. However, these systems are still new to most contractors and building officials.
Working with Foam Forms
Foam forms are easy to work with. Unlike lumber, each one is the same size and shape. And they don't shrink. Compared to concrete blocks, they are light and easy to handle.
Builders who use these systems feel the forms save them some time, though probably not much on standard foundation walls. On insulated walls--above and below grade--the foam forms are faster because they eliminate several steps: sheathing, insulating and vapor sealing. Eliminating subcontractor scheduling can be a big benefit for small builders.
The blocks cost anywhere from $2.00 to more than $3.00 per square foot. However, comparing material prices for blocks is misleading. You need to look at the entire system. That system cost can range from $5.50 to $7.50 per square foot. In areas where many builders have adopted the system, competition drives the prices to the lower end of the range. Some builders get a good price by becoming the local distributor for the product.
There have been no widely publicized reports of insect problems with these foam form products. However, foam makes a great nesting ground. And there have been reports of structural foam core panels being infested.
Since the foam isn't structural, termites and carpenter ants pose only a moderate threat to the concrete forms. The threat is much greater for the traditional wood-frame home. In both cases, precautions should be taken to treat against insects. One option is to purchase treated foam from AFM Corporation, which recently introduced Perform Guard, an EPS foam treated with a borate based wood preservative that fends off insects. It can be used with some of the sheet products.
Codes and Inspections
Sheet foam systems provide a relatively conventional concrete wall, so they seem to be consistently and readily accepted by code officials. Code questions with the block systems seem to vary more by jurisdiction than between products. Some building officials are interested, even enthusiastic. Others are skeptical and require documentation or extra engineering.
As block manufacturers gain more widespread code approvals, some builders find the requirements for special engineering drop away. For example, EnerGCorp has been acknowledged by the International Council of Building Officials because their product passed the required structural tests.
One Way to Find Out
Just about every builder is thinking about alternatives to wood-frame construction. Insulated concrete forms deserve a close look.
--Steve Andrews is a residential energy consultant based in Denver, Colo. This article first appeared in the Journal of Light Construction.
Most foam forming products on the market today fall into three categories: molded stackable blocks, larger cored molds and sheet foam panels.
Stackable blocks come in a variety of shapes and sizes. Most are made of expanded polystyrene and include teeth, grooves, or knobby attachments that interlock. The foam sidewalls--2 to 3 inches thick--are held apart by molded foam cross members or braces made of plastic or metal. During lay-up, the blocks are laced with vertical and horizontal rebar. Then they are braced before the pour. Stackable blocks are about half air, making them bulky and somewhat expensive to ship long distances. One manufacturer recently introduced a collapsable product to cut shipping volume by 50 percent.
Large-core blocks are a type of stackable block. They use more foam and more steel, but less concrete than other blocks or sheet systems. Once filled with concrete, they create a post-and-beam structural system.
Sheet foam systems require assembly by the contractor on site or by the dealer before delivery. Sheets come in two sizes: 8 inch x 4 foot or 4 foot x 8 foot. Plastic spacers connect the two sheets. You can choose 8 or 10 in. connectors, depending on the wall thickness you want. The results looks similar to traditional forms made of plywood.
Assembly is easy work, but it takes time. Once assembled the forms are placed on footers, reinforced with rebar, braced, and filled with concrete. The Quick-Strip system from Lite-Form allows one side of the foam to be stripped off and used on the next job. This reduces the R-value by half.
This article appeared in Energy Source Builder #32 April 1994