Every builder who uses removable concrete forming (RCF) systems does not build in the same way. Some use concrete throughout the home-for the exterior and interior walls and for the decks that form the floors and ceilings; others use concrete for the shell and build interior walls and floors of wood; others still use RCFs to build the basement and first level only. Some may use Lite-Deck forming systems for floors and some may use insulating concrete forms (ICFs) for curved walls. One builder even designed his own forming system to make it easier to include concrete decks (floors/ceilings) in concrete homes.

Removable concrete forms typically use aluminum panels on an aluminum frame that are set into place by crane. When building with RCFs all the electrical work, plumbing, and the window and door blockouts are planned and positioned in advance of concrete placement. Usually, the concrete for an entire level is placed with a concrete pump in one lift using a flowable mix. The thickness of the concrete wall and its reinforcement and the use of expanded polystyrene (EPS) insulation all vary according to the engineering, the climate, and the builder's preference. Builders like RCF construction because it's fast: the forms can be stripped and set into position the next day to build another home or to construct another story of the building. They also like the energy efficiency and thermal advantage of removable form construction, the protection from bad weather events and from the invasion of mold and insects-all bonus points for building with concrete.

A New Concrete Deck System

Van Smith, Smith Bros. Concrete, Wallkill, N.Y., invented a patent pending removable concrete forming system for cast-in-place concrete decks that he is confident will change how decks are cast. Smith's RCF deck system uses forms that are 1/8-inch-thick aluminum manufactured in an inverted "U" shape. The lightweight forms slide into one another increasing or decreasing the length to accommodate different floor shapes and dimensions without requiring filler. The forms stack into each other like cupcake papers for easy storage, transport, and jobsite handling. The underside of the form leaves a 16x14-inch canal to accommodate mechanicals-including the electrical, plumbing, and heating and air conditioning ducts.

Smith recently used this deck system when converting a standard wood-frame house into a RCF concrete home. All the decks are 2-inch-thick concrete with two #6 rebars at the bottom of the profile. The 2-inch-thick lift of concrete covered the deck and filled the perpindicular voids every 16 inches giving the floor strength. The 2-inch surface reduced the slab weight-a 53x129-foot floor carries 135,000 pounds of concrete. A 16-inch thickened edge around the perimeter connects the floor to the wall. The flexibility of the system accommodated cutouts such as the stairwell opening for each floor, and the smaller above-garage attic space.

The 4013-square-foot house includes a basement and two stories with all the walls and decks built of concrete. The attic sits on the top deck, or ceiling of the second story, and is framed to accommodate a traditional roof. At each level, the windows and door openings were framed and wall penetrations placed inside forms and in the floors for the electrical and plumbing. Reusable aluminum forms were erected to form 8-foot-tall concrete walls that are 8 inches thick. The 10-foot lengths of rebar emerge at the top of each level to tie-in successive stories of walls and decks. Beginning with the basement foundation, workers form the walls, pump concrete into place, remove the forms, and repeat ... setting forms for the walls and deck of the next level of the house, placing reinforcement, and assembling the shoring for the concrete placement. All the walls are wrapped with 2-inch-thick EPS for a thermal barrier.This new RCF deck forming system is named Van Deck and is available through Western Forms, Kansas City, Mo. "It's fillerless; it can fit any size floor pour and it even accommodates recessed lighting," says Smith who is understandably enthusiastic.

Only The Exterior Walls Are Concrete

Mike Hancock, president of Hancock Building and Design and Basement Contractors, Oklahoma City, prefers to use RCF construction for a home's exterior walls and to build the interior walls of wood framing finished with drywall. Hancock's philosophy is to produce what is most economical for the client. He appreciates the speed of removable form construction, as well as its weather protection and thermal advantage, but feels that the price tag scares customers away. He works at pricing a concrete home within 2% of a wood-frame home.

"I do a tremendous amount of mixing-considering what is functional and structural to build but economical for the customer to buy," says Hancock. "The greatest concrete gain is in the exterior walls for the weather, fire, and mold protection. But the economics of interior concrete walls and floors is hard for me to justify in a residential application." Hancock will use a wood joist floor unless the client wants a decorative concrete floor finish, then he will use the Lite-Deck forming system to make a concrete deck. "My subcontractors know how to work faster building traditional wood-frame interior walls and floors and that knowledge saves time and dollars for the customer," says Hancock.Hancock believes in insulating concrete walls inside and out. "It stores energy in the walls and transfers it to the interior as it cools down outside and absorbs it as it warms up. Placing insulation on the inside and the outside maintains the thermal mass of the concrete wall longer, slowing the energy transfer resulting in more consistent temperature. Also, concrete walls diminish outdoor sounds heard inside the home, but interior insulation adds a bonus, it reduces interior sounds too," says Hancock.

The typical wall profile of one of Hancock's homes includes a 5½-inch engineered concrete wall. There are 2 inches of EPS foam on the outside of the 5½-inch-thick wall and 2½ inches of foam on the inside. The foam on the inside makes vent pipes and electrical box placement easier. The top of the concrete form is kept 1½ inches lower than the standard form height to run a treated 2x10 board as a top plate for placement of rafters with anchor bolts. Hancock embeds hangers into the concrete to attach the rim for the floor joist placement. He uses Simpson Strong-Tie hardware to attach the wood floor to the wall.

Matt Eckman, describes himself as a home improvement enthusiast interested in homebuilding. He owns American Video Transfer, Brighton, Mich., and with co-builder and good friend, Mark Markovich, Dependant Foundations, Brighton, Mich., used RCF construction to build his own concrete home in Hartland, Mich. Eckman was the general contractor and Markovich did the concrete forming.

The four-bedroom, three-bath home is 6160 square feet including the garage and basement. The basement exterior walls are 6-inch-thick concrete with 2-inch EPS insulation. The above ground walls are 4-inch concrete with 4 inches of insulation. A flowable 18- to 24-inch slump, self-consolidating concrete was pumped into the forms. It saved labor time by eliminating the need to vibrate the concrete and it produced void-free walls. The footings and basement floor were poured together, followed by the first floor and basement walls and then the attic floor and first floor walls-completing the entire home in three placements. To construct the walls, 9-foot wall panels formed the outside of the walls with a 1-foot cap. The concrete interior walls used a 9-foot form with a 6-inch ledger form that attached to the top of the wall. This produced a 9-foot 6-inch ceiling height, with a 6-inch concrete deck.

Some unique features of the home include a first floor 30x24-foot family room and a similarly sized bonus room in the basement. The large walkout basement made space for a four-room apartment with a "day room" to the outside. An engineered 26-foot beam designed by Brent Anderson, Brent Anderson Associates, Fridley, Minn., permitted long spans of concrete in the basement and first floor without the use of pipe-column supports. The interior walls of the home are concrete except in two bathrooms where interior walls are wood frame. The attic also is constructed with a traditional wood frame for the dimensional asphalt shingled roof. The interior walls of the house were finished with drywall compound applied directly to the concrete. The 6-inch-thick concrete floors include radiant heat in the basement and second floor deck. Wall-Ties and Forms, Shawnee, Kan., acted as the architect for the home and offered building counsel throughout the construction. The house is finished with vinyl siding.

RCF Four-Plex Uses Sandwiched Insulation

Ray Brooks, owner of Brooks Construction Services, Sioux Falls, S.D., used RCF construction with EPS foam sandwiched into the forms to build a four-unit apartment building with two units on the first floor and two on the second. "It can take 41 trees to build a house. The only wood I used was where the plumbing is installed," says Brooks.

The building shell has 10-inch-thick exterior walls-3 inches of concrete on each side of a 4-inch high-density foam layer. Sandwich wall trusses placed 1 foot apart provide reinforcement horizontally and #3 rebar placed every 2 feet through the two stories reinforce vertically. The wall trusses, manufactured by Western Forms, lock the foam into place permitting both sides of the concrete wall to be cast together. All the foam insulation is precut to fit the form. The walls are joined to the main floor composed of an 8-inch-thick Lite-Deck insulating system and a 4-inch concrete layer. The flat roof is formed with Lite-Deck with a 1/8-inch-per-foot pitch. There is no basement.

Inside the building are 4.5-inch thick engineered concrete walls. The concrete walls are tied to the Lite-Deck with #5 rebar bent to the joist. The center wall dividing the units has 2-inch-thick EPS foam sandwiched in the center of the 8-inch concrete. The additional foam diminishes the transfer of heat and cold, and reduces sound transmission. The interior walls are completed after the forms are stripped with a portland concrete "rub" that evens the color and fills any small air bubbles. Brooks sheetrocks the ceilings to cover the exposed EPS foam Lite-Deck forms. The only wood wall construction is where plumbing is installed.

Brooks likes the speed of construction with RCFs. After the foundation was placed, the ground level floor was poured. Then the first floor walls and the deck were formed and poured simultaneously. The first floor forms were stripped and the second floor walls and roof were formed and cast. All portions were formed using interlocking Lite-Deck for a monolithic structure.

What Builders Think

The builders interviewed all agree that the benefits of building with concrete far outweigh a stick-built structure and they all choose aluminum form technology because of the increased efficiency and forming speed. The advantages of building with the RCF system include:

  • the walls are straighter and stronger
  • there are no blowouts
  • the fire safety is increased with interior concrete walls
  • there is a better thermal heat sink for radiant heat floors
  • the energy required to heat and cool is reduced
  • for investors or renters there is nothing to fix-no wall damage or missing shingles
  • the soundproofing advantage is superior Without exception these builders believe concrete homes have a bright future, and their goal is to house people economically and safely in concrete homes.

The typical wall profile of one of Hancock's homes includes a 5½-inch engineered concrete wall. There are 2 inches of EPS foam on the outside of the 5½-inch-thick wall and 2½ inches of foam on the inside. The foam on the inside makes vent pipes and electrical box placement easier. The top of the concrete form is kept 1½ inches lower than the standard form height to run a treated 2x10 board as a top plate for placement of rafters with anchor bolts. Hancock embeds hangers into the concrete to attach the rim for the floor joist placement. He uses Simpson Strong-Tie hardware to attach the wood floor to the wall.