Ask the Expert: What are the benefits of Insulated Concrete Form?
A popular green building material is Insulating Concrete Form (ICF). ICF is a system of formwork for concrete that works as insulation for energy-efficient, cast-in-place concrete walls, floors and roofs. The forms for ICF are interlocking modular unit that are stacked without mortar and filled with concrete, similar to Lego bricks.
We wanted to know more about ICF, so we asked our Approved Contributing Experts, also known as ACE's, to respond to our question on the pros and cons of ICF.
Chris Conway, president of Conway Construction:
What is an insulating concrete form anyway? Most people have heard builders throw around the term ICF and you have probably been wondering what they are and what the benefits are, with great reason. ICF is basically reinforced concrete forms which allow for tight insulation, great thermal breaks and have been around for quite some time. Below are some of my favorite reasons for using them:
- The great insulation and thermal mass they allow is great because they are created as hollow forms and pack a mean punch when it comes to insulation.
- The amazing sound dampening ability which is wonderful in cities and between floors.
- The very minimal mold potential. There are not any cavities for mold to grow in, and this is a great thing for people who suffer from allergies, but also just for longevity of the building.
You can't go wrong with a product like this.
Joe Bowling, president of Energy Wise Solutions:
I recently read an article of an experiment in Home Energy magazine. They built three homes in the same area, orientation, and floor plan — one with ICF, one with Structural Insulated Panel (SIP) and one with 2 inches by 6 inches spray-foam insulation. They conditioned each to the same temperature and shut the HVAC off at 12 noon. They monitored each to see how long it took for each to rise to a designated temperature. The ICF lasted the longest, the SIP came in second (reaching its temperature a couple hours before), and the 2 inches by 6 inches inch spray-foam home reached the designated temperature first.
ICF has thermal storage characteristics because of the concrete. This can be of greater benefit to regions that experience cool nights and warm days. The warmth collected during the day will radiate at night and vice versa.
The strength, sound resistance and fire resistance are higher with ICF over stick frame.
Chad Cornette, architect and founder of Cantilever Studio:
- If you are going to finish the entire basement area, they can be cost effective.
- If used above grade, is a very durable building shell.
- Nice insulating qualities and air-tight.
- Must sheetrock and tape/mud seams in space that would otherwise be unfinished; thereby, increasing costs of construction.
- Difficult to work with if foundation footing is not level and flat.
- You could get same effect by attaching rigid foam to interior concrete after the pour since concrete forms are usually metal last forever these days (then recycled).
- In the past forms were temporary plywood and wasteful.
- Running wiring and plumbing can be an issue unless you furr the wall.
- Attaching finishes to the ICF channels are sometimes difficult because there is not a uniform system (vertical or horizontal) that is standard.
- Any special architectural features require special engineering, so it's expensive once you get away from building bombshells without wasting lots of insulation form material.
Scott Flynn, founder of Flynner Building Co.:
ICF is easy to install and provides excellent R-factors for conditioned crawls.
They fit together like Legos making assembly a breeze. The R-30+ of the ICF system provides the needed insulation for a tight conditioned crawl space.
I do have to add this though, there are drawbacks. Currently we do not use ICF because of costs. It is less expensive to pour a standard foundation wall, then spray-foam the joist cavities, foundation wall and the footing (with ICFs spray-foam is still required in the joist cavities and footing).
Ted Clifton, founder of Zero-Energy Plans LLC, and CVH Inc.:
The first advantage is the structural strength inherent in a reinforced concrete wall. In one simple operation, you have the structural qualities of concrete, with the air-sealing and insulation qualities of a SIPS wall...sometimes.
The ICF wall has half of its insulation on each side of the thermal mass. This means that when the heat energy gets just half way through the insulation, it gets to the concrete, which transfers a large amount of that energy to the ground through the footings. This can be a very good thing in a hot climate, where you do not want the heat to get into the dwelling. This can be a very bad thing in a cold climate, where you do not want the heat to leave the interior of the dwelling.
If I were building along the Gulf Coast, or in the Southwestern desert, I would use ICFs almost exclusively. In the rest of the country, not so much, except for closed crawlspace designs, and daylight basement homes.
Waffle style ICFs will use up to 10 percent less concrete than straight form ICFs, and even the straight form blocks can often develop more strength in 6 inches of concrete than a traditionally formed wall can develop in an 8-inch wall, saving up to 25 percent of your concrete cost and placement cost. (Pumper trucks are expensive!) The reason the ICF wall will develop more strength is because the concrete is left in the form forever, holding the moisture in the wall, assisting the curing process. Walls that are exposed after just 24 hours are significantly compromised. Unfortunately, this is the norm in the concrete industry today, and the engineers know it, so they will often require a thicker wall than might otherwise be necessary.
I often use ICFs in conjunction with SIPS walls, where I need an especially strong sheer wall, for example. We are in seismic zone D-1, so we often need the structural strength of a concrete wall where lots of glass is desired to take advantage of a spectacular view. The ICFs can provide the same air-sealing ability, with nearly the same effective U-value as SIPS, which I then use for the rest of the walls and roof.
Wiring and plumbing are not a problem, the foam is thick enough that it can be grooved out, the wires or pipes inserted, and then spray-foam used to cover the tracks.
The speed with which ICFs can be set, and the elimination of time spent stripping and cleaning forms will usually offset the extra cost of the ICFs, once the alternative insulation method is factored in.
To summarize, there is no one building method that is right for all situations. An astute builder will evaluate all methods for each project to determine which is right for that time and place.
Teena Hammond Teena Hammond has published more than 2,000 articles in People and W magazines, Women's Wear Daily, and in dozens of newspapers and books. She also wrote a home improvement, remodeling and decor column that ran in Gannett newspapers nationwide. She's interested in all things green and would love to hear from you with your story ideas.