Article No: 51

2006-05-01 10:10:43
Affordable concrete housing
By: Larry Storer


The 10th annual concrete show home at the International Home Builders Show was designed to demonstrate the affordability of a concrete home, according to Jim Niehoff, residential program manager for the Portland Cement Association (PCA).

"What many builders think about when they consider a concrete home are the many beautiful luxury homes that have been the hallmark of the industry in recent years," Niehoff said while conducting a tour of the Count on Concrete precast concrete home erected in the parking lot at the Las Vegas Convention Center parking lot for display at the International Home Builders Show and the World of Concrete.

 

"And certainly, some of the most beautiful homes in the country have been constructed from concrete," he said. "But this year PCA with its 'Team Concrete' initiative and The Dow Chemical Co. wanted to build a demonstration home that would show the face of affordable concrete housing."

The 1,237-square-foot-house used the current floor plan built by the Las Vegas Habitat for Humanity chapter for a three-bedroom, two-bath ranch-style with a single car garage. It also featured cement-based construction materials such as roof tiles, siding and trim, and decorative concrete flooring.

Niehoff said the primary purpose of the show home project was to educate those attending the shows about the benefits of exterior concrete wall construction for residential homebuilding. "But a secondary purpose was to spotlight PCA's Team Concrete initiative, which encourages the cement and concrete industries to work with their local communities to build energy-efficient, high-quality concrete homes for the affordable housing sector," he said.

The pre-cast panels were built offsite and transported to the Convention Center site four days before the Builders Show. At the conclusion of the World of Concrete, the home was dismantled in 18 hours and relocated to a lot owned by Habitat for Humanity in nearby Henderson, Nev. to ultimately become a new home for Rosa Bonilla and her son, Edgar.

"Habitat for Humanity likes concrete housing not just because of its durability, quietness and lower insurance rates," he said. "They like it because it is energy efficient. Sadly, what some Habitat families discovered once they got into their traditional homes was that they couldn't afford the utility bills. Energy savings takes stress off the family budget, saving as much as 44 percent to heat and 32 percent less energy to cool."

The interior of the show home had various exhibits that demonstrated the different concrete wall systems — removable forms, concrete masonry, insulating concrete forms and precast concrete. Also available for examination was the Styrofoam TMass technology from Dow Chemical Co., a system that combines the energy efficiency of Styrofoam extruded polystyrene insulation and concrete for foundations and above-grade walls.

For this precast house, Niehoff said the large panels for the walls were poured horizontally in a carefully controlled environment. Openings for walls, doors, and electrical and plumbing lines are selected in advance. Once completed and poured, the panels were delivered to the Convention Center by truck and lifted into place with a crane and fastened together. Roofing trusses were also pre-engineered and delivered to the site.

Why the concrete house saves energy

Think of the walls of the Count on Concrete show home as a sandwich — an insulated concrete sandwich wall system constructed with Styrofoam T-Mass technology from Dow Chemical Co. that uses the thermal mass effect of concrete to create an equivalent wall performance R-value several times greater that what is estimated by a traditional R-value calculation.

In fact, on this particular house in the Las Vegas-area climate, the results of testing by the Oak Ridge National Laboratory (ORNL) were dramatic, according to Brian Goodmiller, national marketing director for the Precast/Prestressed Concrete Institute, a precast evangelist on-hand in the house during the shows.

He said that the ORNL had researched the thermal performance of the wall technology, with the results tabulated to show comparative R-values that would be needed in conventional wood frame construction to produce the same loads as insulated sandwich walls using the Styrofoam T-Mass technology. Six climates were tested, with the most dramatic difference being in Phoenix where a comparable Rvalue of conventional wood frame exterior wall would need to be 2.9 times higher than the steady state R-value of an insulated T-Mass wall to produce the same loads.

With a climate similar to Phoenix, the house that was moved from the Convention Center parking lot to Henderson, Nev., for a Habitat for Humanity home, could expect similar results. A comparative wood frame wall R-value should be R- 31 to achieve the same effect as an insulated sandwich wall using the T-Mass technology.

Goodmiller explained that the resistance to the flow of heat is measured in Rvalue. The higher the R-value, the harder it is for heat to get through. Styrofoam extruded polystyrene insulation is rated at an R-value of 5.0 per inch at 75° F. A wall using Styrofoam T-Mass technology with a 2-inch exterior layer and a 4-inch interior layer of concrete, along with a 2-inch layer of Styrofoam extruded polystyrene insulation, would result in a material R-value of about 11.33.

All materials have intrinsic mass based on their specific heat capacity. By designing a wall to have a significant layer of concrete adjacent to the interior space and a thinner concrete layer exposed to the climate, the wall behaves with a dynamic performance that is several times greater than what can be estimated by the material Rvalue. This feature is referred to as the mass performance R-value or the equivalent wall performance R-value due to the utilization of concrete's thermal mass.

Goodmiller said that by placing a layer of Styrofoam extruded polystyrene insulation between the two concrete layers, the interior temperature will warm the interior layer of concrete. Once this layer hits its maximum capacity to store this energy, it will release it, transferring it back into the interior of the building.

He explained that the effect on the heating and cooling system is substantial because there is a shifting of heating and cooling loads to off-peak hours when electricity is cheaper. The economic benefit is the same or better than increasing the insulation. The performance can actually be better than additional insulation in that the mass of the concrete allows for a natural energy load shift that insulation cannot provide.

Walking all over beauty

The concrete demonstration home constructed on the Las Vegas Convention Center parking lot was the face of affordable concrete housing — an entry-level home that emphasized function over form. It was designed to first be an educational exhibit touting the benefits of building with concrete, and after the show a house for Habitat for Humanity.

The flooring in the house could have just as easily come out of a luxury home.

Master Builders Inc. and the L.M. Scofield Co. co-sponsored the PCA home, providing materials and supervision for all interior floors, constructed using concrete integrally colored with Chromix L Admixtures from Master Builders. Lithochrome stains and color hardeners from L.M. Scofield were used to create the distinctive decorative look throughout.

Kelly Mawby from Master Builders was on hand during the show to explain the color system used to create floors. Flooring within the house was a compelling variegated shading of rich brown and earth tones.The garage had a beautiful imprinted design that was a work of art.

Mawby said the flooring was achieved with the Chromix Admixtures that demonstrated alternatives to traditional building materials such as brick, flagstone, granite, marble, slate, tile and wood.

"The new Chromix liquid coloring admixtures from Master Builders have been engineered specifically for use in ready mix and precast concrete applications to produce enduring, structurally sound colored architectural concrete," she said.

Mawby said Master Builders was excited about the residential market for color-conditioned concrete. She said color combinations, textures, imprinted patterns and design motifs can also be used outdoors to create driveways , walkways, patios and pool decks that can withstand heavy use and add to the appeal of the property.