People are talking about a new way to build homes. They talk about the advantages ICF homes have over traditional building methods, and it’s not just the typical excitement of adding something new to the ways of building homes that we’ve used for millennia.
ICF stands for insulated concrete form, and the three words describe it perfectly. But there’s more…
Table of Contents
- What is ICF (Insulated Concrete Form) Construction?
- What Are The Advantages of ICF Construction?
- What Are The Disadvantages of ICF Construction?
- Does ICF Construction Cost More?
- Is ICF Construction Insect-Resistent?
- What Interior Finishes Can You Use?
- What Exterior Finishes Can You Use?
What is ICF (Insulated Concrete Form) Construction?
An ICF (insulated concrete form) is two sheets of expanded polystyrene foam board (EPS) held a distance apart by rigid plastic ties. These interlocking forms stack and connect to create a hollow wall, given that they are filled with reinforcing bars and then concrete. You can get ICFs to create insulated reinforced concrete walls of any desired dimension and shape.
You install reinforcing iron bars in the space between the plastic boards and fill it with concrete to produce a strong, monolithic, insulated concrete wall. You can use supplementary cement-like materials like fly ash in the mixture to reduce the amount of carbon-intensive cement needed, which produces more environmentally-friendly concrete.
The ICFs are available with different thicknesses of EPS for different insulation values. Various distances between the foam walls are available to provide different thicknesses of concrete; 4” to 12” separations are available. 6” is typically used for exterior walls; 6” or 8” is typical for foundation walls.
What Are The Advantages of ICF Construction?
ICF construction has many advantages over traditional methods of construction, especially wood-framed buildings.
Buildings usually leak at joints between the various building components, and walls tend to have a lot of such joints. But an ICF structure has an integral wall structure that doesn’t allow air or moisture infiltration. Having intact air and moisture barriers is an essential prerequisite of modern energy-efficient construction, and the ICF system automatically creates them.
Since the air and vapor barriers are already built into the construction, you don’t have to worry about them. It can be difficult in conventional construction to make sure they are leak-free. And they are essential to a high-performing, healthy building.
As a result of this tight construction, the air inside can be much cleaner than in a traditional building. In addition, because there are no unwanted and unintended openings, less outside noise penetrates the walls.
Comfort and quiet were two of the top four features ICF homeowners most appreciated about their homes. Peace of mind was another benefit mentioned.
ICF buildings are better insulated than wood-frame buildings. ICFs have continuous foam insulation, usually with an R-22 or R-26 value, while typical wood construction may have R-13 or R-19 fiberglass insulation in the walls. But the wood structure, which has an R-value less than 5, accounts for 20% or 25% of the wall, reducing the “whole wall” insulation value.
Because ICF structures are so much better insulated, they are more comfortable. In addition, the mass of insulation and concrete makes for a very quiet interior. Only about one-eighth as much noise gets through the ICF walls as through wood-frame building walls.
Also, the uniform insulation reduces the chances of having drafts or having uneven temperature distribution between rooms due to exterior conditions like exposure to sunlight.
Because the concrete walls have a lot of mass and are insulated to slow heat transfer, they absorb heat slowly and release it slowly. This so-called “thermal mass” improves the temperature stability inside the structure, increasing comfort.
In a test at a low exterior temperature (-31°), a wood-frame structure required 158% more energy to reach an equilibrium temperature. After that, the ICF wall needed 58% less energy to maintain that temperature. This energy-saving behavior is due to the thermal mass of the ICF wall.
Since ICF buildings are reinforced concrete, they can last for a century or more. The plastic insulation does not degrade or settle over time. As a result, the building shell itself does not lose any of its strength or efficiency.
ICF buildings are fire-resistant and can better withstand natural disasters. Because of this, insurance costs tend to be lower. In disaster-prone areas, where insurance may not be available at all, insurance costs are very much lower. Because the strength of this reinforced concrete construction is much greater than the strength of a wood-frame structure, it can survive disasters. There are ICF structures still standing in disaster-devastated neighborhoods to prove it.
In high heat, the foam can melt, but it will not burn and will not add any fuel to the fire.
An ICF structure with a 6” concrete core has been tested to withstand 200+ mph winds and flying debris and have a 4-hour fire-resistance rating. By contrast, the door between your garage and your house needs to have only a 20-minute fire rating by code, although many house fires start in the garage.
You can make the house more disaster-resistant by adding a roof that is fireproof and well-anchored to the structure, along with impact-resistant windows and metal shutters where appropriate.
Because there is little air interchange with the exterior, ICF buildings are very energy-efficient. The buildings are free from drafts that can plague conventional construction, increasing comfort. Heating and cooling cost significantly less than in traditional construction, giving ICF construction a significant financial advantage.
Energy costs are generally about 50% lower in ICF construction because the buildings are so tight and well insulated. You can get additional energy cost reductions by installing good attic insulation, air-sealing the attic, and using energy-efficient windows and doors.
Also, the EPS foam insulation is continuous both inside and out, with virtually no defects to compromise its function. Gaps in the typical batt insulation in wood-framed structures disproportionately reduce its effectiveness. Insulation even in newer wood-framed systems is not likely to be installed carefully enough to achieve its rated efficiency, in the writer’s experience.
ICF Construction Cost Savings
Twenty years ago, HUD estimated in this paper that ICF construction was 5% to 10% more expensive than wood frame construction. This situation has changed.
Given an experienced contractor, ICF construction generally costs less upfront than conventional construction and has lower operating costs. See “DOES ICF CONSTRUCTION COST MORE?” below.
Operating Cost Savings
The ownership costs over time are always less than with conventional construction because of lower relative operating expenses. ICF buildings need much less maintenance during their long lives. Owners usually add energy-efficient windows and water heaters, etc., to complement the structural energy efficiency, further lowering energy costs.
Mortgage originators recognize that both insurance and energy usage costs are significantly less. As a result, many are prepared to increase the loan size since the buyer will have more disposable income to service the loan. The debt service payments may be a little higher, but the utility and insurance payments are lower. Breakeven is usually five years or less, after which the owner is saving money each month.
Also, $1 savings on operating a home can increase the value of a home by $20. So if you save a typical $250/month on energy and insurance, your home is worth $60,000 more than comps without the lower operating costs.
Longer clear spans for large rooms are easier to design because the concrete walls can easily carry the loads of the steel beams these designs require. Designing wood frame construction with these features can be tricky, and large rooms are currently in demand.
Exterior finishes on conventional construction generally require vapor barriers. But the vapor barrier is already built-in to ICF walls, so no additional work is usually necessary. Adding exterior finishes to unusual shapes is easier.
One company is offering ICF components for building pools. These include curved ICFs as well as the plaster coatings used to finish the pool interior.
These pools are much more energy-efficient than the other types of pools whose walls are in direct contact with the ground; they retain heat well because of the insulation. Extensive contact with the earth can suck the heat out of the water.
What Are The Disadvantages of ICF Construction?
An obvious disadvantage is that ICF construction is different from traditional construction, so relatively fewer contractors have a lot of experience with it.
And although it is conceptually simple, it can be challenging to get all the conjoined forms in proper alignment—plumb, level, and straight—and keep them there as you add heavy concrete.
An extensive bracing system is necessary to keep the walls in alignment before and during the concrete pour. Aligning and bracing the ICF forms usually takes more time than assembling the IFC blocks, sometimes much more time. The systems can be complicated, especially for multi-story buildings.
Since ICF buildings are so tight, unhealthy indoor air quality can develop. Carbon dioxide and radon, as well as dust, pollen, and mold spores brought in by occupants, can accumulate without enough fresh air exchange. So you will need to add provisions for adequate ventilation to keep your indoor air healthy.
ICF construction is most suitable for warm climates and less suitable for cold climates. Concrete is in contact with the ground at the bottoms of the walls. So the heat that makes it through the interior insulation dissipates into the soil instead of staying inside the house. This is desirable in warm climates, not in cold ones.
One potential problem is that organic solvents, and organic solvent-based products, cannot be used with ICFs because they dissolve the EPS foam. So products used with the construction, like coatings, foams used to seal penetrations, and adhesives used for wall coverings, must be carefully evaluated for compatibility.
Although best practices have been developed through testing, ICF construction does not have a 50-year track record of what works and what doesn’t. So, for instance, techniques for interfacing ICF construction with other materials and with window and door systems haven’t stood the test of time.
Does ICF Construction Cost More?
ICF construction used to be somewhat more expensive than traditional construction, especially with taller buildings. This mistaken perception persists.
Currently, the initial construction costs of ICF homes are usually comparable to or less than conventional construction. Often any higher costs are due to shortages of qualified labor at a particular time in a particular area. But contractors have become efficient with experience.
Building with ICFs takes less time and costs less if you have an experienced contractor. Some of the time-consuming functions of working with concrete, necessary with at least the foundations of virtually every home, are absent when working with ICFs.
You don’t have wooden or metal forms for the concrete that must be removed and cleaned once the concrete sets, which saves on labor costs, too.
Other factors can reduce the initial construction costs. The building usually requires downsized heating and air conditioning system equipment because of the increased energy efficiency. Fewer photovoltaic cells are needed. Air and moisture barriers are not needed.
Is ICF Construction Insect-Resistent?
Termites are the bane of buildings in most of the country, from California to New England, and especially the southeastern states. They attack wood and cause considerable damage every year. The subterranean termites are the worst problem.
Your first thought would be that ICFs are plastic and concrete, neither of which give termites anything to eat. But they are determined little pests and will bore through the plastic underground, looking for wood. The concrete will stop them, but they will try to go around it. They can burrow inside the plastic until they are either blocked or find food.
Building codes in various jurisdictions regulate ICF use below grade since the termites can burrow under the ICF to reach wood within the foundation, the floors, or even the attics.
One solution is to strip the insulation from the exterior of the ICF blocks used below grade, producing a standard concrete foundation with insulation on the interior of the foundation walls. Another solution is to create a barrier of some sort to prevent the termites from even reaching the ICF on the exterior.
A couple of products have come on the market that contain an additive in the EPS that stops the termites so they will not bore into it.
In any event, you should be aware of the potential threat posed by termites even to ICF structures and make sure you deal with them appropriately and follow local requirements.
What Interior Finishes Can You Use?
Your interior finishes can be whatever you want. The foam sheets have anchor strips 8” apart on both sides, from the rigid ties used to hold the sheets apart. These are intended for the screws to attach material like drywall, stucco lath, or furring strips that can support various finish materials.
For heavier components, like cabinets, you use longer screws that extend into the concrete to provide a solid anchor. You just have to drill into the concrete first.
It is just as easy to install drywall on the interior walls of an ICF structure as in a wood-framed building. And one contractor finds she has 15% less drywall waste with ICF.
Wood paneling is another interior finish that is easily attached to furring strips screwed onto the plastic walls. Or you can apply an acrylic plaster or stucco finish to give a particular look.
What Exterior Finishes Can You Use?
The most important thing about the exterior finish is that it has to protect the EPS plastic from sunlight, which will degrade it. Since most exterior claddings provide this kind of protection, you’re not much limited in your choice of finish. The structure can look just like any other.
Stucco is a common choice in many areas for its durability. It is applied in the usual way, by attaching a screen to the EPS and using three coats of stucco.
Brick or stone facing can be glued directly onto the EPS. So can prefinished concrete panels to give it a modernistic look.
Some may prefer wood or vinyl siding, although these may require more maintenance or even replacement several times during the life of the supporting structure.
Some textured acrylic finishes have been developed specifically for the EPS plastic exterior. These have improved impact resistance and are “greener” than other finishes. These spray-applied finishes are available in quite a variety of colors and textures, and experts can make them look like granite, antique brick, or limestone blocks.
ICF construction is superior in many ways to conventional wood-frame construction. You’ll get increased comfort and much better energy efficiency. Reduced operating costs can more than offset initial costs that could be slightly higher. And the buildings are much better able to withstand natural disasters.
Should you use it? You should definitely consider using it, given all the advantages it offers.