Ryan Davis, Assoc. DBIA, ADMG
The title of this article is not misleading in the least. They really do look like giant foam Legos. Insulated Concrete Forms, or ICFs, have been around for a long time. Originally developed in post WW II Europe as an inexpensive and durable way to rebuild, the ICF has evolved over the years. The ICF has really come into prominence in today’s “green building” era and has been used as a successful building component in many modern day structures.
A better understanding of their capabilities, inclusion in most modern building codes, and more choices in manufacturers has contributed to their rising popularity since the 1970’s. However, classifying them as a sustainable building method/material is widely contested. Also debatable is their cost effectiveness, practicality, and suitability. This article aims to explore some of the pros and cons of ICFs as well as explain why there may be no single correct answer.
The ICF is a modular, structural building material much like a concrete masonry unit, the most popular size being 12”-18” high and 48”-96” long. The thickness varies anywhere from 4”-over 20” depending on concrete fill width and layers/thickness of foam. The most popular type of ICF is made from polystyrene foam (extruded or expanded), though other materials are available. Think of a dixie cup, only thicker, and you have the idea. The blocks are hollow to allow for a solid concrete fill and have webbing inside that provides for a consistent shape and rigidity, while also allowing for the attachment of reinforcing bars and finishes. The foam is not stripped like traditional concrete forms and remains in place as an assembly component after the concrete is placed inside.
Pros of ICFs
- They speed up construction in the early phases and can be placed and manipulated much easier than traditional formwork. They are very easy to handle and transport.
- The foam increase insulation value or R value. Polystyrene is far superior to traditional fiberglass type batt insulation in this regard. The building envelope is also much tighter than traditional framing thus reducing heat loss/gain.
- Concrete as a building material creates extremely strong, quiet, mold/fire resistant structures that can last hundreds of years.
- As stated above the use of concrete is superior in areas with earthquake and hurricane concerns.
- The thermal mass of concrete, or ability to retain and dissipate heat, is much better than in wood or steel. This is a major factor in sustainable “passive design.” Simplified: not using fuels for heating and cooling comfort.
- Depending on the ICF used you can greatly reduce the comparable amount of concrete needed in a standard poured-in-place monolithic wall.
- Plumbing and electrical can be done at almost any time in the construction schedule and not just while walls are open. This may also make remodeling easier.
Cons of ICFs
- Polystyrene is made up of many different chemicals (mostly petrochemicals) that have a high toxicity level. The fire retardant coating HBDC (hexabromocyclododecane) used on polystyrene has been deemed by the EUs REACH program as chemical of “very high concern.”
- The thickness of the walls means that on very tight sites (even some not so tight) you are losing interior square footage (and paying for it anyway) by virtue of the walls being thicker than typical 2×6 or 2×4 construction.
- Embodied energy, or the energy needed to extract, produce, transport, maintain, dispose of and/or replace a given material. Mining concrete aggregates, transporting concrete and manufacturing foam all consume a lot of energy. Thus the higher the embodied energy the higher the carbon footprint.
- There is an argument that the significance of the thermal mass benefits of concrete, when sandwiched between foam, is negligible or not fully realized (see pros above).
- The recyclability of a reinforced concrete and foam assembly is much less than that of a wood framed assembly.
- The construction costs for ICF walls as compared to conventional framing can be double in most cases. The argument is that you make this money back through energy savings or through intangibles such as better overall occupant comfort.
- Plumbing and electrical costs may increase because of the unconventional way it is installed (see pros above).
As you can see from the above pros and cons there is a big split among experts as to the usefulness and practicality of using ICFs. The product is most often marketed today as a sustainable building alternative. This claim is based on the fact that over the building’s lifecycle there is a huge saving in energy costs due to the reduced need for mechanical heating and cooling. However, green building experts (and pundits) point to the fact that ICFS still have a large carbon footprint by virtue of their embodied energy and also contain harmful chemicals. How “green” can this really be? Not to mention there are many other methods of creating a reduced need for fuel consuming mechanical systems. Using passive design or better conventional building materials and technologies (and craftsmanship) are just some of the ways.
If you take the sustainability factor out of the equation and look at ICFs from a practical standpoint there is still no clear winner. It comes down to one of the basic tenants of architecture and that is, the design, material and methods must be appropriate to the site and the end user. You can debate all day as to the virtues and evils of ICFs but the fact is they are useful in CERTAIN circumstances. They have been proven to greatly increase energy savings, withstand earthquakes, tornadoes, and hurricanes, and without a doubt create a structurally sound and quiet living environment that can last a very long time.
Consulting a professional is the first step in any good building design. Contractors tend to build with what they are comfortable with and make them money and manufacturers, of course, want to sell their products. A good architect’s highest priority should be that of protecting the owner’s best interests and designing in a responsible effective manner. This priority would definitely include deciding whether using ICFs is appropriate for you and your next project!