ICF Construction Guide: Pros, Cons, and Costs
Insulated Concrete Forms (ICF) are a system for pouring concrete walls. The exterior and interior faces are rigid foam boards held together by webs of plastic ties. The insulation and ties remain in place after the concrete cures to provide thermal insulation and hold the layers together.
In the past, builders used ICF construction to pour foundation walls. Now they can use ICF systems to build multi-story houses, saving time and improving the structure’s energy efficiency.
What is ICF Made Of?
Insulated concrete form walls consist of 2 ¾” thick rigid foam, which may include any of the following materials:
- Polystyrene Rigid Foam. Expanded or extruded. Most common product.
- Polyurethane Rigid Foam. Better R-value. More expensive.
- Cement Bonded Wood Fiber or Polystyrene Beads.
- Cellular Concrete.
Polypropylene ties hold the forms together and provide support for the placement of rebar, which are steel bars that increase overall and flexural strength. Manufacturers use different-sized ties to make forms for 4”, 6”, 8”, 10”, and 12” walls.
These sizes represent the concrete portion of the wall only. Builders use different sizes in different locations to satisfy load-bearing requirements. Four-inch interior walls act as roof-bearing walls, and eight-inch concrete acts as standard concrete foundation walls. The foam faces of the wall system are not load-bearing.
The blocks fit and lock together like a giant Lego building system.
ICF Construction Costs
The average 2,000-square-foot ICF-constructed house costs between $260,000 and $400,000. The average ICF cost per square foot of floor space is $130-$200.
Insulated Concrete Form Specifications
The International Residential Code (IRC) section R611 addresses ICF construction. ICF is acceptable for most residential housing applications and for buildings up to four stories high, but these buildings often require an engineer’s approval. Some other ICF specs include:
- High R-value. Type II closed cell foam. Up to R-4.0 with expanded polystyrene foam (EPS). Up to R-5.0 with extruded polystyrene foam (XPS).
- Moisture Resistant. Non-absorbent.
- Mold Resistant. Doesn’t rot or provide a growing medium for mold spores.
- Infused with Flame Retardant. Smoke is non-toxic.
- Recyclable.
Insulated Concrete Forms – Pros and Cons
I.C.F. construction has many benefits along with some disadvantages. Here are some of the more convincing arguments for – and against – using these forms when building.
ICF Construction Benefits
In addition to the advantages listed below, there are a few others that usually are not top of mind during planning and construction. They include:
- Year-Round Building. Many contractors will not pour concrete when temperatures are below freezing because concrete that freezes before it cures is weaker. I.C.F. forms are insulated and will prevent frozen concrete.
- Lower Insurance Premiums. I.C.F. homes withstand hurricanes and floods better than traditional construction.
- Net Zero Building. If fitted with solar panels, an insulated concrete form house can meet the World Green Building Council’s definition of net zero.
Faster Build Times
Insulated concrete forms save weeks or months of construction time. There is very little waiting for the weather since the walls are insulated before the builders erect and pour them. Also, the exterior foam doesn’t absorb moisture and sheds water, making it unnecessary to waterproof the exterior.
Contractors cut plumbing and electrical channels into the form and seal them with spray foam insulation.
Save on Long-Term Costs
In the beginning, I.C.F. construction is 5% – 10% more than conventional stick-framing, working out to about 2% – 4% additional cost for the entire project. The 4% increase is negligible when considering the long-term energy savings, reduced insurance costs, and construction savings like exterior waterproofing and sheathing. It will also result in a more draft-free and comfortable home.
As with most construction-related projects, I.C.F. costs vary. Insulation thickness, concrete thickness, and climate zones influence price.
The R-value of I.C.F. walls may not meet the recommendations for cold climate energy-efficient buildings. In this case, custom forms with thicker or better insulation will add to the cost.
Energy Efficiency
The uninterrupted blankets of insulation inside and outside of the concrete provide a consistent R-value of R-23.0. The R-value of most stick-framed houses varies from about R-9.0 – R-15.0 because of thermal bridging and inconsistent batting. Plumbing, wiring, and bracing make it difficult to keep batt insulation to a consistent R-20.0 blanket.
Better Soundproofing
Not only are I.C.F.s warmer, but they’re also more comfortable since they are quieter. Standard stick-framed houses have a Sound Transmission Class (STC) rating of about 33 – 38. I.C.F. houses have consistent STC ratings between 46 and 72 depending on wall and insulation thickness, mass, and how air-tight the walls are.
| STC | What can be heard |
|---|---|
| 25 | Normal speech can be understood |
| 30 | Loud speech can be understood |
| 35 | Loud speech audible but not intelligible |
| 40 | Loud speech audible as a murmur |
| 45 | Loud speech heard but not audible |
| 50 | Loud sounds faintly heard |
| 60+ | Good soundproofing; most sounds do not disturb neighboring residents. |
Better Air Quality
Insulated concrete forms are non-toxic and contain no formaldehyde, asbestos, fiberglass, or Volatile Organic Compounds (VOC). They also don’t off-gas. They provide a tight draft-free building envelope–reducing air infiltration by up to 75%.
- Eliminates dust mites.
- Eliminates mold.
- Reduces dust and pollen in the house, reducing asthma and allergy attacks.
ICF Construction Disadvantages
Insulated concrete form construction presents a few challenges. Most are easy to overcome, but you should consider them when planning a new home.
I.C.F.s Require Bracing During Construction
ICF forms are easy to put together, but for various reasons, may not be plumb. Builders have to brace the forms to keep the wall straight. The forms also require bracing to prevent blow-outs while pouring concrete.
To make ICFs, builders pour concrete in lifts between one foot and four feet high–giving it a little time to settle. Pouring eight or nine feet of concrete at one time is hard on foam forms and can result in concrete leaking through the horizontal and vertical joints. Builders have to chip the dried leaks off before drywall and/or siding can be installed.
Humidity Problems
One of the downsides of reduced airflow is increased humidity–especially during and for a short time after construction. Curing concrete, drywall taping, and drying wood–like flooring–produce a surprising amount of moisture. Some insulated concrete houses require a dehumidifier and a good HVAC system.
Remodeling Problems
Adding a window, moving a doorway, or taking out a wall in a standard wood-framed home is challenging. Doing the same job when faced with inches of concrete is even more daunting. Having a concrete coring company cut out concrete is wet, messy, heavy, and expensive. Try to consider all needs during the design phase.
Loss of Floor Space
I.C.F. walls are thicker than stick-framed walls. If planned for, the size difference is insignificant. If not planned, there could be problems with built-in furniture. For instance, reducing the floor space of a 10’ x 10’ room by 2” on all four sides reduces floor area by about 6.7%.
Lack of Qualified I.C.F. Contractors
Insulated concrete form construction is still rare. Depending on location, finding enough qualified contractors to bid on a job may be difficult and increase the costs–due to lack of competition and/or increased travel.