Closeup on the inner composotion of an ICF block wall before the concrete is poured

Insulated Concrete Forms are gaining popularity in the home building industry. They are generally made of polystyrene foam blocks with space to pour a concrete wall.

Previously ICF was solely used for foundation walls; however, several homebuilders are now going a step further and using this construction technique for above-grade walls of one, two, and three-story homes.

This article will answer all your questions regarding ICF block building. 

So, continue reading for everything you ever wanted to know about ICFs.

Table of Contents

What Are Insulated Concrete Forms?

ICF is a system of expanded polystyrene rigid insulation blocks partitioned by plastic webbing. ICF blocks are available in interlocking sections, allowing a fall system to fit tightly together. The concrete is poured into the space after the blocks are set in place.

The finishes are then attached to fastener strips lodged in the insulation. A contractor can quickly complete many steps of the construction process since the insulation and fastener strips come with the ICF blocks. 

What Are ICF Blocks Made Of?

ICF blocks are made using incredibly lightweight expanded polystyrene (EPS) and are hollow in the center. In addition, the blocks feature an interlocking grid that allows easy stacking, similar to Lego.

This mechanism reduces a significant chunk of construction time compared to a conventional building style, as the builder can assemble them quickly. 

Can I Build My Own ICF House?

Yes, you can build your own ICF house. However, we recommend that you only consider it if you have a significant amount of essential construction experience and the project is a simple, uncomplicated design such as a rectangle. 

Are ICF Walls Good Insulators?

The simple answer is yes. However, you need to use a more holistic approach if you wish to build a high-performance, sustainable house. 

ICF construction offers two critical advantages regarding the building’s energy performance.

Firstly, it seals exceptionally well, preventing air leakage via the walls. Secondly, it has two continuous layers of insulation, one outside and one inside, without any thermal bridges, which minimizes heat loss. 

What Is the Highest R-Value of ICF Walls?

ICF walls comprise a center cavity to maintain concrete between two layers of EPS, offering two continuous insulation layers rated R-22 and above. 

Nevertheless, a regular off-the-shelf ICF system isn’t thick enough when constructing a high-performance home, such as a Passive House. Plus, it might fail to meet insulation standards in a cold climate such as the northern US or Canada.

Thankfully, certain manufacturers, such as Nudura, have developed ICF products with an R-value up to R-48 to cater to colder regions. 

Moreover, you can use additional on the exterior, particularly for a foundation. Using extra insulation on the interior compared to the exterior can be a better option for above-grade walls.

Certain brands now offer ICF options with thicker insulation to simplify things. BuildBlock Building System is one example that sells one-inch or two-inch inserts that attach to the inside of the wall, creating an insulation value of nearly R-4.2/inch. 

How Thick Must ICF Walls Be?

You can figure out the thickness of ICF walls through the soil condition and the level of support that the overlying elements of a structure need. For example, typical residential walls will use 6″ or 8″ ICF blocks. 

A closeup on the end grain of some ICF blocks

You cannot use the 4″ form below grade as a foundation wall. These blocks are generally only used for non-loadbearing applications such as demising walls in hotels, dormitories, or apartments. 

How Big Are ICF Blocks?

ICF wall blocks are available in thicknesses of 4″, 6″, 8″, 10″ and 12″. However, some manufacturers offer even thicker blocks. The 4″, 6″,  and 8″ blocks are 16″ high, whereas the 10″ and 12″ blocks are 24″ tall. 

Dimensions of ICF Blocks

The dimensions of an ICF block primarily depend on its thickness. Generally, a 6″ standard block is 16″ high,  11.25″ wide, and 48″ long. On the other hand, an 8″ block is 16″,  13.25″ wide, and 48″ long.

What Is the Maximum ICF Wall Height?

You can use ICF blocks for single-story residential and commercial buildings and high-rise projects. In fact, ICF blocks have been used for walls surpassing 40 feet of unsupported height. Presently, the tallest ICF structure is a 23-story building in Waterloo, Ontario. 

Can You Pour ICF in Stages?

The answer to this question depends on whether you are pouring ICF foundations or ICF walls.

When it comes to foundations, the majority of ICF versions are poured using a two-stage method. However, combining a unique fabric form with adjustable supports makes it possible to pour simultaneously level and square footings, as in the first few courses.

A buiild site where an ICF foundation is partially-laid
Courtesy of Logix

Apart from eliminating a cold joint, this method helps save time and reduces one of the pumper’s visits to the construction site. 

On the other hand, most bracing manufacturers recommend that a total ICF wall height of no more than 16 feet be poured at a single time. 

Can You Use ICF for Footings?

Correctly built footings are imperative to a building’s durability and strength. The ICF footings can effectively distribute all the loads from the building to the ground. 

Generally speaking, you cannot use ICF for footings. However, you can use certain ICF blocks such as Nudura forms on basic strip footings, slab-on-grade, and grade beams connected to piles. 

If your project requires building on bedrock, Nudura forms are easily scribed to the rock profile—a nearly impossible process with concrete block or conventional forming. Make sure to speak to your site engineer if you have any footings questions or concerns. 

Can ICF Be Used as a Retaining Wall?

ICF works just as well for retaining walls as foundations and walls. Using ICF as a retaining wall for a retaining wall produces a more flexible, economical, durable, and attractive option over using structural insulated panels and concrete masonry units. 

Can ICF Be Used Below Grade?

You can use ICF to build below-grade walls of a home or building. However, these walls require waterproofing and proper drainage systems. 

How Long Can ICF Be Exposed?

If you shade the ICF blocks or cover or paint them with an appropriate material to bear the brunt of the sun exposure, they should be fine for as long as you like. However, vendors generally recommend that you don’t leave ICF blocks uncovered and exposed to sunlight for more than three months.

If you do, you might notice a light dusting on the surface and a yellowing discoloration of the forms. Fortunately, this doesn’t indicate any adverse effects on the ICF blocks. 

Can ICF Be Recycled?

ICF blocks are made of lightweight expanded polystyrene (EPS), which can be recycled and put back to use again. Many facilities that manufacture EPS foam in Canada and the US recycle 100% of the foam. In fact, most are zero-landfill facilities. 

The corner of a wall built with recycled ICF blocks
A wall using recycled EPS ICF blocks. Courtesy of ICF Builder

Recycling EPS foam starts by putting the material into a shredding machine through a conveyor belt. Once the shredding is complete, the foam goes into a plastic extruder, where pressure and heat are applied to the foam to melt it. This process is known as densification.

Next, the melted EPS foam emerges through a small outlet situated at the end of the extruder and hardens into a spongy continuous form. The dense material is then packed and transported back to a bean manufacturer to be used in new products.

The EPS can then be transported to factories to be remolded into new EPS products. 

After several cycles, when the EPS is no longer recyclable for use as EPS beads, the material is densified again and sold to manufacturers for other goods like trash bags, etc. 

Can ICF Be Used for Interior Walls?

Many builders use ICF for interior walls. ICF walls are between six and 12 inches thick. The wall thickness usually depends on the soil condition and the level of support required by the building’s overlying parts. 

The good news is there are several benefits of using ICF for interior walls.

Firstly, ICF blocks offer excellent thermal insulation and can effectively eliminate the need for conventional thermal insulation. 

Second, ICF walls are incredibly durable. They are resistant to moisture, insect infestation, rot, and other elements that can compromise the structural integrity of your property. ICF walls can even stand up quite well to seismic activity and inclement weather conditions such as strong winds. 

Finally, ICF blocks create extraordinarily thick and solid walls that do not allow noise. They are commonly used in commercial structures such as movie theaters, where soundproofing is vital to the primary function of the building.

How Much Does ICF Cost Per Square Foot?

ICF home construction generally costs around $150-$160 for every square foot. It is similar to the cost of a concrete home, if not the same.

Certain contractors use ICF interchangeably with poured and removable forms. We strongly suggest you speak to your builder to see which approach they recommend. 

A laid ICF foundation at a build site

How Much Does an ICF House Cost?

On average, you will have to pay between $300,000-$320,000 for a 2,000-square foot insulated form house. Unless you reside in a region with a warmer climate, many home builders use ICF for all concrete construction. 

Is ICF Cheaper Than Wood?

Insulated concrete forms cost approximately $150 per square foot. This figure means it’s 2-7% higher than traditional wood frame construction. All in all, you will probably spend nearly 5-10% more on building costs than you would for a typical wood-frame house. 

However, remember that concrete prices can fluctuate, and the price of your house is also dependent on the local construction labor costs, design, and extra factors. 

Nevertheless, there are cost savings in other areas that will help offset some of these initial costs. For example, opting to construct with insulated concrete forms will considerably improve daily operational expenses and environmental impacts. 

Are Insulated Concrete Forms Better than Wood?

Insulated concrete forms last longer than traditional wood-frame houses. Thus, the natural resources are utilized to their maximum potential.

ICF construction also significantly minimizes construction waste compared to timber-framed houses. Almost 60% of the ICF block’s weight is made up of recycled materials. 

Moreover, insulated concrete wall systems contribute 20 points to LEED ratings. 

How Long Does It Take to Build an ICF Home?

In most cases, the formwork for a four-room ground floor can be constructed in only a couple of days.

Your builders would then spend a couple of days bracing the walls and any structural openings. Finally, the concrete for an entire story can generally be poured in less than a day. 

a picture of two ICF forms, with white styrofoam on each side of the picture showing connecting rods in the middle with a big gap to pour concrete in

Nevertheless, it’s vital to remember that the amount of time needed to acquire all necessary permits for an ICF house will probably take longer than a traditional home.

Since ICF construction isn’t the standard in the residential construction industry, the permitting process can be a little more arduous. However, an experienced and licensed builder can make the process smoother and hopefully quicker. 

How Long Will an ICF House Last?

ICF houses have more than 100 years of lifespan, with minimal maintenance needed as the foam isn’t going to degrade.

It’s also important to remember that ICF houses can add additional protection during natural disasters. Such homes perform well in flooding; thus, they are suitable for coastal areas. 

Moreover, reinforced concrete also makes them suitable for highly seismic zones. Some home builders also ensure up to a four-hour fire rating. An ICF house could give you peace of mind if you reside in an area susceptible to natural disasters. 

How Much Money Does an ICF Home Help You Save?

An ICF house’s payback and savings depend primarily on what you’re comparing to and the construction quality. If you have an ICF home with a very tight building envelope, you will probably experience higher savings.

Even though you may pay 5-10% more upfront for an ICF home, your energy bills will be lower monthly than if you construct a wood-frame house to traditional standards.

According to industry leaders, if you compare the initial cost of an ICF home to the overall cost savings, it costs the same as a wood-frame house. However, this again depends on several factors. 

Are ICF Blocks Toxic?

ICF doesn’t contain any formaldehyde, asbestos, HCFC, or fiberglass and doesn’t suffer from off-gassing. Moreover, no dangerous CFCs (chlorofluorocarbons) are used in their manufacture.

All in all, ICF is made of non-toxic materials, thus creating a healthier environment for you and your family. 

Are ICF Homes Tornado Proof?

ICF walls are resistant to tornadoes. A study conducted by Texas Tech University revealed that ICF walls could resist damage from flying debris moving at over 100 mph. In contrast, regular framed walls cannot prevent the penetration of airborne hazards. 

Therefore, ICF walls are the best protection from wind-blown debris to a house and its residents during a tornado event. 

Are ICF Homes Hurricane Proof?

Insulated concrete forms use expanded polystyrene foam panels reinforced with steel cables and rebar and filled with concrete, which makes a house extremely strong.

a close up of ICF blocks with rebar in the middle, showing the internal construction of the IFC foundation

Thus, ICF construction offers an easy way to attain hurricane-resistant wall systems that shield against flying debris, flooding, and wind.

Unlike wood, ICF homes don’t collapse under hurricane-force winds. In fact, some manufacturers such as Logix ICF engineer their ICF wall blocks to be wind-rated at over 300 miles per hour. 

Are ICF Homes Fireproof?

Buildings and homes constructed with ICF offer excellent protection from the flames. The concrete core prevents fire by slowing down heat conduction from one side of the wall to the other. 

Steel and concrete ICF walls have a four-hour fire rating compared to fifteen minutes for a similar wood-framed wall. Insulated concrete form walls have been tested up to 2,000°F for up to four hours in fire conditions.

Wood-framed walls generally collapsed within an hour, whereas ICF walls didn’t experience any structural damage. 

Do ICF Walls Crack?

It is essential to keep in mind that all cast concrete is vulnerable to shrinkage cracks. However, there are some steps the builder can take to reduce the number of cracks and prevent them from spreading.

Nevertheless, eventually they will occur in ICF walls. 

Do ICF Blocks Off-Gas?

The expanded polystyrene foam used to manufacture ICF blocks does not produce any off-gassing as it is inert and inorganic. The low expanding foams and adhesives used to assemble ICF blocks are equally harmless, as is the concrete mass.

Does ICF Need a Vapor Barrier?

ICF walls work as vapor retardants; thus, ICF walls don’t need vapor barriers. Instead, ICF blocks have insulation on the walls’ interior and exterior, separated by a thermal mass of concrete. 

The insulation stabilizes the temperature and prevents condensation within the concrete walls.

For instance, on a hot and humid summer day, the temperature within the insulated concrete form wall system stays uniform and above the dew point, helping it stay dry and cool inside a building. 

This feature helps to prevent condensation. 

Does ICF Need House Wrap?

ICF walls don’t need a house wrap, but they might be necessary on framed portions, such as dormers, window walls, and gables. 

Conversely, flashing is used in several areas of an ICF installation and aims to direct water flow away from moisture-sensitive materials and the home’s interior. It should always extend past the layer below it, much like shingles in a roof continuously overlap.

Door and window flashing performs the dual role of flashing against air and moisture infiltration. 

AN exterior window on a home with flashing extending past the edges of ICF block
Courtesy of ENERSTRUCTA

Does ICF Need to Be Waterproofed?

Securing a building from moisture is essential to any construction, particularly below-grade walls.

There are two levels defined by building codes to safeguard a structure from water. Dampproofing secures a basement and other enclosed spaces from moisture in the soil around a house. 

How Do You Waterproof ICF Blocks?

The main waterproofing techniques include liquid systems that are rolled, sprayed, or applied with a trowel, peel and stick membranes, and dimpled drainage mats attached to the walls. 

There are several waterproofing systems that you can choose. 

Specific methods are popularly used with outcomes you can depend on, whereas others are more innovative techniques to save material and labor costs. Therefore, you must research your available options and results before selecting one. 

Some standard waterproofing options entail:

  • A self-adhesive membrane like the PolyWall Homestretch – you can even use this along with a dimpled membrane like PolyWall Arroyo Drain Board to secure the waterproofing from the backfill and offer extra hydrostatic pressure relief. 
An icf wall under construction with waterproofing attached
An ICF self-adhesive waterproofing membrane. Courtesy of ICF Builder.
  • A spray-on membrane that is compatible with ICF – (word of warning: don’t use a petroleum-based primer or paint as these products are going to dissolve the EPS foam)
  • A single-step mat type protection (like DMX-AG, SuperSeal) – this plastic mat offers an air gap between the insulated concrete form wall and the surrounding earth. 
    As hydrostatic pressure rises, it will displace the air, allow the pressure to be released, and avoid attempting to pass through the wall. It works in several locations with soils that drain or perk well. However, it might need a membrane in certain areas. 

Does ICF Need to Be Covered?

It is not necessary to cover ICF blocks. However, you should protect them from sunlight and impacts through coverings such as stone, brick, siding, EIFS, stucco, etc.

Building wraps by DuPont™, Tyvek®, and other house wrap products are aimed to shed bulk water like heavy, wind-blown rain.

Does ICF Need Rebar?

Yes, the concrete poured into the spaces in the ICF blocks is generally strengthened using rebar. However, you can use other products like Helix micro-rebar. Such reinforcements can be inserted in various areas throughout the wall to offer extra strength. 

For below-grade basement applications with a backfill on a single side, the rebar is typically placed on the tension side of the wall. This application results in higher strength from the pressure of the backfill on the wall. Make sure to follow local codes or site-specific engineering to allow for proper and adequate reinforcement placement. 

On the other hand, in above-grade applications, rebar is usually placed in the center of the walls, making it more robust and allowing it to resist seismic and wind forces that can swing both ways. 

How Is Rebar Placed?

Builders must install horizontal rebar before pouring in the foundation or footing. You should use rebar chairs or other techniques to ensure that you have spaced them appropriately.

The vertical dowels need to go above the top of the footing by around 20-25 inches. The amount might depend more on the lap requirements and wind and seismic load ratings. 

Since ICF walls are stacked, the horizontal rebar needs to be inserted in the forms as instructed by the manufacturer. Vertical rebar needs to be inserted after the wall if fully stacked or before placing the final course.

However, you should always do it before pouring in the concrete. 

What Finishes Can You Use for ICF Walls?

Constructing an ICF house or building allows you to choose from several exterior finishes: stucco, masonry veneers, wood or vinyl siding, fiber cement boards, and panel siding.

The rule is if you can install the finish on a conventional wood-frame structure, you can use it on an ICF wall. 

An ICF wall section with masonry veneer finish
Courtesy of ICF Builder

However, you must consider that applying exterior finishes to the solid substrate of an ICF wall offers higher durability and strength than when applied to a wood frame. 

ICFs generally offer fastening points for exterior finishes at eight inches on the center and extra fastener points at the corner. The flexibility of ICF sidings enables you to attain the structure’s aesthetic and design objectives.

All in all, the exterior finish selection boils down to your budget, local styles, and personal decision. 

Can You Use Stucco Over ICF?

You can apply stucco directly over an ICF wall without a membrane above grade. However, below-grade requires waterproofing.

Certain contractors will use house wrap or paper behind the stucco, which is unnecessary. For conventional stucco, a mechanical attachment is needed (metal lath screwed to the wall through the plastic webs or a similar application). 

Should You Use Stucco Cladding Over Insulated Concrete Forms?

Stucco offers a visually appealing and weather-resistant exterior finish for ICF walls. Other benefits of stucco finish include fire, rust, and rot resistance. 

Stucco cladding is available in three different kinds: traditional stucco, thin-coat acrylic stucco, and exterior insulation and finish systems (EIFS). Builders prefer the thin-coat stucco technique as it allows for less costly and quicker installation than EIFS and traditional stucco. 

Can You Use Stucco Cladding Directly Over ICFs?

The EPS used in ICF blocks allows you to apply thin-coat acrylic stucco directly. This way, you don’t have to install an extra layer of EPS over the wall assembly. 

You can directly apply traditional stucco to the ICF walls using a metal lath secured into the ICF fastening strips. 

Rendering of a Sto ICF stucco coating system
Courtesy of Sto Corp

The success of stucco application depends on correct installation, including transitions, wall cladding edges, and opening details. In addition, you can enhance the exterior architectural detailing with the extra EPS window trim, trim, molding, etc. 

Can You Nail into ICF?

This question does not have a straightforward answer. The truth is that while you can use ring shank nails to hang the siding onto the ICF, it is better to use screws. 

Many ICF manufacturers, such as FoxBlock, recommend installing finish materials using screws as they offer the highest holding capacity into the ICF’s fastening strips or plastic webs.  

Can You Screw into ICF Walls?

It is okay to screw into ICF block walls. Certain manufacturers recommend specific ICF screws for their blocks. 

For instance, BuildBlock recommends using ICF screws by ClearCo Fasteners. These screws feature a loose washer design and are available in 2-inch and 3-inch. 

All the screws are hardened and galvanized for added strength. Moreover, coarse threads offer maximum attachment to the plastic webs. 

Do ICF Walls Need Drywall?

You might need to install drywall on your ICF wall’s interior face to comply with your local building code’s thermal and ignition barrier provisions.

That said, municipalities might waive this requirement in several jurisdictions across the US as long as the foam thickness and occupancy requirements are met. 

What Size Drywall Screws are Needed?

You can attach wall covering to the webs or ties in your ICF system using #6 or #8 Type W (coarse thread) drywall screws. Make sure the screws are corrosion resistant and are sufficiently long to penetrate the web or plastic tie a minimum of 6.4mm or ¼”.

Can You Paint ICF Blocks?

ICF walls can be painted after you have taken the appropriate steps to make them paint-ready. Generally, the best way to go is to apply a single coat of PlasterMax base coat troweled or sprayed directly onto the foam with a minimum thickness of 3/8″.

This makes your ICF walls code-approved, fire-rated, and paint-ready. Moreover, the PlasterMax base coat is ten times stronger than conventional drywall with a compressive strength of 4,000 psi, as opposed to the 400 psi compressive strength of ½ inch drywall. 

Can You Plaster Over ICF?

You can plaster over ICF walls; however, you must make sure you choose a plaster suited for ICF blocks.

Perhaps, one of the best plaster options is PlasterMax-ICF by GigaCrete, which offers ICF builders a superior and long-sought alternative to gypsum-board finish. It is a fire-rated, rock-hard interior finish that you can trowel or spray directly over the EPS foam without installing a reinforcing mesh or drywall. 

You can apply PlasterMax using several different methods, depending on the labor cost and the desired performance of the finish. Nevertheless, the most economical route is to spray or trowel a single coat directly onto the foam with a minimum thickness of 3/8″. 

Apart from PlasterMax, you can also use Earth Clay plasters, such as those made by American Clay. Like PlasterMax, they can be applied over drywall or directly to the foam. If you choose to skip the drywall, you must use a sanded base coat or “browncoat” first. 

Can ICF Be Used for Pool Construction?

Insulating Concrete Forms used initially for wall, basement, and foundation construction are currently used to build high-quality, energy-efficient, durable, low-maintenance, durable pools. 

Homeowners pour and shape concrete in a backyard DIY ICF pool

ICF pool construction offers multiple benefits to consumers, architects, and builders over traditional pool construction methods, including precast, shotcrete, and cast-in-place concrete. 

For instance, builders prefer ICF pool construction as it’s faster and easier than concrete pool construction. These advantages help save money and time.

In addition, designers and architects appreciate ICF pool construction because of its flexible and versatile design options. 

Are ICF Pools Energy-Efficient?

ICF pools aren’t just easier, quicker, and more budget-friendly to build, but the highly-insulating EPS foam prevents more than 60% of the heat loss in the pool.

Higher energy efficiency means it is relatively cheap to heat your pool. In addition, ICF blocks stabilize a pool’s temperature. Thus, the length of the pool season can be increased over conventional fiberglass or concrete pools. 

Is It Expensive to Construct ICF Pools?

ICF pools don’t require precise excavations compared to the concrete pool wall system. This helps to keep construction costs low.

If the excavation of an ICF pool is overdue, the only additional cost is to backfill the walls after they are in place. Moreover, ICF is reasonably lightweight, so building an ICF pool requires fewer crew members than traditional pool construction, which can considerably minimize labor costs. 

Is It Difficult to Install Electric Connections in ICF Walls?

Installing electrical wires, audio-video cables, or telephone jacks in ICF walls is less challenging than many assume. This is because there’s not a lot of work tied up in the exterior walls of a home—generally, only a light and a couple of outlet boxes. 

The two standard methods are to insert conduit in the wall’s concrete core or cut chases into the foam after pouring the wall. 

The most straightforward technique is pouring the wall and then returning and cutting in the chases. The cleanest and quickest method is renting or purchasing an electric hot knife for this task and placing the wires.

Once the electrical wires are in place, they can be held with expanding foam glue. Some choose to fill the complete chase to restore the walls insulating properties. 

Last Few Words

ICF is revolutionizing the construction industry. It offers an easy and quick way to build energy-efficient homes and structures, allowing you to benefit from significant cost savings.

Hopefully, this list of FAQs cleared up any uncertainties you had about ICF construction, and you can now begin your ICF undertaking.

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