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5 things you didn't know about insulated concrete form construction

July 27, 2015

 

As building codes demand homes with tighter building envelopes and continuous insulation, home builders and consumers are looking for building strategies that deliver that performance without paying a premium.

That’s why homes built with insulated concrete forms (ICFs) are becoming a popular choice in many climates.

Insulated concrete forms (ICFs) are cast-in-place concrete walls that are sandwiched between two layers of insulation material, usually expanded polystyrene (EPS) foam insulation forms. The foam blocks are stacked as interlocking blocks, connected with steel reinforcing rods. They offer well-insulated, airtight, energy-efficient building enclosures. Also, ICFs are a great fit for regions prone to severe weather because of their strong impact resistance.

In ICF construction, two insulating faces of a foam block are separated by a connector or web and concrete is poured into the cavity. The foam blocks are left in place to provide insulation throughout the life of the home. Any traditional finish from wood to brick to siding can be applied to interior and exterior faces. On the inside and outside an ICF home can display any architectural style.

1. ICF homes outperform many other building techniques

One of the biggest benefits of using ICF is the continuous insulation on both sides of the wall that virtually eliminates thermal bridging and energy loss. An ICF home can cut energy bills in half and can achieve a HERS index in the 40-50 range, which means they are outperforming existing building codes by 50 to 60 percent.

According to the U.S. Department of Housing and Urban Development report "Costs and Benefits of Insulating Concrete Forms for Residential Construction," field comparisons of similar ICF and wood-frame house constructions found that ICF wall construction can provide a 20 to 25 percent savings in annual heating and cooling costs

To achieve a similar level of energy performance, a typical wood-frame home would require an “energy upgrade” that adds about $2,640 to an average home cost of $200,000 (or about $1.32 per square foot of living area). This amount is equivalent to about one-third of the cost difference between ICF and typical wood- frame house construction.

According to the HUD report, many ICF homeowners who are willing to pay a little extra on the front end for downstream energy cost savings, not to mention the benefits of added safety and comfort.

2. ICF construction doesn't have to cost more

The short answer to the question, "How much does it cost to build an ICF home?" is, it depends. It depends on the local market in terms of costs of material and labor, and experience of the contractors involved.

But that's also the case with a wood-framed home as well.

After several studies of ICF construction costs, HUD determined that using ICF wall construction generally adds about 3 to 5 percent to the total purchase price of a typical wood-frame home and land (about 5 to 10 percent of the house construction cost). "In other words, the added cost is about $2 to $4 per square foot of the floor area of a typical home. For a typical 2,500 square foot, two-story home and lot (sale price of $180,000), the additional cost amounts to about $7,000. The additional first cost of ICF construction should be weighed against longer-term benefits," according to the HUD report.

3. ICF construction reduces costs in the rest of the home

Construction costs are only part of the big picture of the total cost of construction and ownership. Because ICF houses are more energy efficient, the heating and cooling equipment can be smaller than in a frame house. This can cut the cost of the final house by an estimated $.75 per square foot. So the net extra cost is about $.25-$3.25, according to the EPS Industry Alliance, a concrete forms trade organization. Additional costs may come from wall thickness adding costs to window and door installation, as well as indirect cost impacts to plumbing, HVAC and electrical installations. The EPS-IA says that it's safe to assume that a home will cost about $2.00 more per square foot to build with ICFs on average, and particular architectural features or site issues could have an impact as well.

4. ICFs don't have to stop at window and door openings

For many ICF systems, one weak point has been door and window bucks. Often the ICF construction required using dimensional lumber, vinyl or steel to create a nailing surface to mount doors and windows, and to seal the blocks where they form an opening.

Now ICF makers like Fox Blocks have developed foam bucks in the system for a continuous insulated surface. When an ICF wall is constructed without a buck system, builders typically use dimensional lumber or vinyl to frame the openings for doors and windows. That means there’s a gap between the framing and the ICF wall construction. That could allow air leakage around the framing, leading to energy loss and drafty conditions. A gap could also open the envelope to moisture penetration as well, leading to degradation of the wood framing, mold and other problems. A non-foam buck also leads to a drop in R-Value because the wood or vinyl doesn’t insulate as well as the EPS foam. Wood and metal allow for thermal bridging, or transfer of heat through the material itself. Dimensional lumber may also warp, leading to problems fitting the door or window in the frame.

An ICF system with a foam buck offers fully integrated, continuous insulation around the opening. That means there’s a barrier against air and moisture penetration. It also provides a continuous concrete barrier around the opening for maximum strength.

Most of the moisture intrusion in a home can be traced to a very small surface area, usually at connection points near doors, windows, roofs and floors.

To achieve the full benefits of ICF construction, look for a system that offers a fully integrated buck system that maintains insulation and air sealing capabilities around every door and window opening.

5. ICFs can stand up to storms

In addition to energy efficiency, ICFs also offer resilient buildings that withstand severe weather events like hurricanes and floods better than stick-built construction. Many new ICF homes include a safe room designed for emergency situations.

Here are a few areas where ICF construction makes a difference:

  • Fire Resistance: Insurance companies recognize concrete homes as being fire resistant and offer premiums to reflect that fact.
  • Wind Resistance: ICF homes are designed to withstand high winds and can exceed building codes for areas prone to hurricanes and tornadoes
  • Impact Resistance: In storm much of the damage comes from flying debris hitting the home. Concrete walls and roofs can withstand the impact of debris from extreme winds with little or no structural damage.
  • Seismic Resistance: Steel reinforcement and concrete can minimize the risk of damage from earthquakes.

If you live in an area prone to severe events, you don't have to build a new house to be safe. You can build a storm shelter with insulated concrete forms to provide safety in an emergency. Fox Blocks offers storm shelter kits that provide the insulated concrete forms and a steel storm door rated by the Federal Emergency Management Agency to stand up to severe storms.

Read more about insulated concrete form construction.


Topics: Building Green, Foundations, Insulated Concrete Forms - ICF, Insulation, Proud Green Building, Thermal Envelope

Companies: Fox Blocks


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