Building Back Better: The Removable Form System

The entire ground level floor of this house is formed with aluminum form panels and is ready for concrete placement. Credit: Joe Nasvik

Today, there are several systems available for building concrete homes. Originally, wall forms were handmade on site by carpenters. Later, manufactures introduced steel or aluminum form panels in order to increase efficiency and accuracy. While steel forms were heavy and required on-site equipment to erect them, aluminum forms could be hand set by small teams because they were light.

Other concrete building systems include precasting wall panels at off-site facilities and transporting them to location, or casting “tilt-up” wall panels horizontally on site and then lifting them into place with a crane. This process is typically used for industrial and large-scale projects.

A third type of concrete construction involves laying up insulating concrete forms (ICF) like blocks to form a wall. The blocks are made with plastic foam materials, providing insulation for the structure as well as forms. Afterward, the voids in the center of the blocks are filled with concrete. Building walls with concrete blocks is another common method. These voids are also filled with concrete, and rebar is added to both ICF and block walls for tensile strength.

Modular pre-designed form panels were introduced in the early 1950’s. They were originally made of plywood,and in the early 1960s,the plywood was attached to modular steel frames. Modular forms made of aluminum were also introduced in the early 1960s and have since become the system of choice for most contractors in the residential foundation business.

Of all the systems, removable concrete forms are the most basic method in the U.S. for building foundation walls for home construction. Those same forms can also be set above grade to construct the walls for a home. They are less labor intensive, save time and expensive and produce better looking results.

After forming the walls, workers are installing deck panels so that concrete can be placed in the walls and on the ceiling at the same time. Credit: Joe Nasvik

Aluminum forms

Western Forms, located in Kansas City, MO, is the oldest—and arguably the largest—manufacturer of aluminum forms in the U.S. They started doing this 70 years ago and today ship their forms internationally. Their specialty is building form panel packages that serve the residential home building industry.

Aluminum forms have advantages: they are lightweight and can be moved and erected by hand without the use of measuring devices. The smooth surfaces and tight interlocking frames create concrete walls that are flat and smooth. Ron Ward, chairman of Western Forms, explains that the easy interlock system to join panels and the insertion of steel bridging (called form ties) streamlines the assembly process. Furthermore, setting an aluminum forming system in place doesn’t require highly skilled workers.

In 1983, Western Forms added deck forming to their wall forming systems. As Ward tells the story “One of our long-time customers asked if it would be possible to join wall and deck forms together so that walls and elevated floor panels could be joined and cast together. We jumped at the opportunity.” The result, from an engineering point of view, is a much stronger structure, one that easily resists natural forces such as hurricanes, tornadoes, and seismic events. Superplasticizer admixtures also became available at this time, making concrete very easy to place and consolidate. An entire floor level&mddash;walls and ceilings—could easily be cast in one placement.

How the process works

The first step is to cast a spread footing to distribute the structure's weight evenly across load-bearing soil. If the house has a basement, the footings are formed and placed separately from any walls. If a house is constructed “slab-on-grade” in climates without freeze/thaw cycles, the footings and floor slab can be cast together in one placement.

Next, crews set a pair of aluminum form panels directly onto the footings over rebar pins, tying walls and foundation together. Typically, one side of a wall is set in place first and then rebar reinforcement is set in the middle of the wall according to engineers’ design calculations. It is also possible, at this time, to add electrical conduit and plumbing lines in the forms as necessary. Once that side is complete, workers place form panels for the other side of the wall and lock the two sets together with the form ties. Concrete placement is next.

Wall thickness is determined by factors such as soil load-bearing capacity, wall height, and the engineer’s design—all of which must comply with local building codes. While walls can be as thin as 4 inches, they are rarely thicker than 8 inches, even though there’s little to prevent greater thickness if needed.

If an elevated slab is included, contractors embed connections between the tops of wall forms and the deck. The deck panels are set in place and clipped together, supported by shoring braces, and rebar is placed to support the ceiling/floor. For long spans, beams may be cast into the slab to provide additional support.

View from the top of a deck with steel reinforcement in place. You can see the opening for a wall below the deck. Credit: Joe Nasvik

Reinforcement

Rebar placement and size must be designed by a structural engineer. Rebar provides concrete with the tensile strength it needs to carry loads and resist natural forces such as earthquakes, straight-line winds, hurricanes, and tornadoes. Concrete is strong in compression and reinforcing steel is strong in tension. More recently, the advent of structural steel fibers and reinforcing made from composite materials such as basalt and fiberglass allows for some replacement of steel rebar. This can help reduce costs.

Placing concrete

Concrete contractors typically use concrete pumps with booms to place concrete. As mentioned earlier, superplasticizing admixtures are typically used to increase the placing slump, while also increasing the concrete's strength. Plasticized concrete flows easily into the wall cavities, under window openings, and around reinforcement to form the walls. The top of the deck is struck off and the floor surface is finished in the normal way.

A concrete pump with a boom is used to place the concrete and in the background a truss-screed is finished striking the surface of the fresh concrete. Credit: Joe Nasvik

Insulation

The walls of concrete houses can have insulation panels (typically Styrofoam or polystyrene-type foams) placed on the outside or inside of a wall. Insulation panels are typically placed inside removable form walls so that concrete bonds to the insulation. Insulation can also be placed in the middle of a wall so that it is encapsulated by concrete on both sides. Special grommets hold the foam in position during concrete placement. Concrete stores energy, so designers position insulation where it takes best advantage of concrete properties in the context of local ambient temperature conditions.

Concrete walls are extremely air-tight, and openings such as windows and doors can be constructed that way also. There is never any air movement through a wall, and it is easy to install windows and doors in perfectly square openings, resulting in reduced heating and cooling costs over time.

Interior walls

While it’s possible to cast all interior walls in a home with concrete, most builders use concrete only for the exterior walls or party walls in townhomes. Usually, the interior walls are built with either standard wood or steel stud walls covered by drywall. Ward says he prefers interior walls to be steel frame in order to further reduce the amount of combustible material. Framed interior walls also make interior remodeling easier.

Roofs

In the U.S., most homeowners tend to favor pitched roofs, so for homes constructed with concrete, it’s common for roof construction to be wood trusses with standard sheathing and asphalt shingles. But that defeats one of the main purposes of building with concrete: fire resistance. More recently, homes are being designed with flat roofs that can be placed with concrete. Ward says his company also makes forms allowing for low-slope concrete roof construction. Flat, structurally reinforced roofs are easily accommodated using concrete that can be insulated with foam panels (which are either flat or pitched to drains) and topped with waterproof membranes.

Cost

Construction companies that specialize in building concrete homes can deliver prices that are well below companies that build just a few because they are much better organized. Some experienced contractors even claim they can beat the cost of wood construction. But uncontrollable conditions also influence cost. Currently there are high tariffs on construction lumber and portland cement from outside the U.S. (the U.S. currently imports 25% of its cement need).

Many building professionals see concrete as a more expensive alternative to wood-frame shell construction, but that is because they only consider first cost. If you live in a concrete house, you know it is less expensive to heat and cool, easier to maintain, cheaper to insure, and more comfortable to live in than any other type of construction. If you experience a disaster such as a fire or earthquake, there is a strong chance your home won’t be destroyed.

Considering build time, Ward says forms for an average 1500 sq.ft ground level floor home can be assembled in as little as two days, and the concrete can be cast in one day. If a ceiling is included, shoring to support the ceiling will be kept in place for a couple weeks after concrete placement, but other trades can perform their work during this time. Also, there is much less construction trash to haul to a landfill.

Removable-form concrete houses can be built for every income level, including the Frank Lloyd Wright home built alongside a lake with a 28-foot cantilevered floor. Photo Credit: Sua Sponte. Photo Credit: Joe Nasvik

Closing thoughts

Removable-form concrete shell construction is the oldest method for building with concrete. It is also the method that allows for the most structural stability and resilience. Lightweight forming systems have increased efficiency, reduced construction costs, and can create more pleasing results. A concrete house can look like any other house on the block or it can be used to create some of the most beautiful homes in the world that celebrate the finished look of the concrete; homes designed by Tadao Ando and Frank Lloyd Wright, for example.

About Joe Nasvik
Joe Nasvik has been a prominent figure in the concrete industry for over four decades. Before transitioning to editorial roles, he owned and operated a concrete construction company for nearly 20 years. In his editorial career, Nasvik served as a senior editor for Concrete Construction magazine, contributing extensively to the field through articles and insights.