Concrete Masonry Design, By David Holzel


The word most often associated with North Carolina’s Triangle region is wood—wood furniture, plywood and, naturally, wood-framed homes. So a builder who uses a load bearing concrete masonry frame sys- tem for his homes is definitely going against the grain.

Yet nearing completion in the picturesque small town environment of Morrisville is a unique two-story home with 5,000 square feet (464.5 m2) of finished space, a cement stucco veneer and masonry framing. In fact, concrete masonry is key to meeting the owner’s primary expectations for the finished product. “We want a structurally sound, well insulated house,” says the owner, Gopal Muppirala.

That’s exactly what custom home builder Rex Bost, president of Bost Construction Co. in nearby Gary, is giving Muppirala and his family. The concrete block home is sturdy and stable, and its superior insulation will shield him and his family from fluctuations in outside temperature and the sounds of passing trains and aircraft.

Visitors to the home won’t initially be aware of the structural advantages that block delivers. Their first impression will be of the home’s signature design element: a 16-foot (4.8-meter) circular staircase rising from the entirely open first floor to the second floor. And that’s just fine with the homeowner. “We wanted that to be the focal point,” says Muppirala, who admits to being ‘fascinated’ with spiral staircases. “When someone walks into the house, that’s what they’ll see.”

As he, his wife, Krishna, and Bost sat down in February2001 with a blank sheet of paper to design the home, they quickly decided there was no way to go other than with block.

The Muppiralas’ home is the second Bost has built using concrete masonry framing. But in his 15 years as a homebuilder, he has used block extensively as a way to provide customers with a superior stucco facade, a style that is popular in the Triangle. Bost says he switched to 4-inch (102-mm) block veneer covered by cement stucco after finding problems with the more widely used stucco surrogate exterior insulating finishing system, or EIFS.

“We were finding moisture problems with EIFS,” he says. ”It was detrimental to the homes’ value. So I stopped using it.” The block and cement stucco combination is “a way to build a more secure home and to bring stucco into our marketplace,” he adds.

Bost believes concrete block brings some economic stability even to North Carolina’s lumber heartland. “We’re in a softwood area. It’s a cheap, renewable resource, that’s the only reason it’s used. But our lumber prices are so erratic. And most of our lumber actually comes from Canada and it’s subject to a tariff.”



At $135 per square foot ($12.50/m2), the Muppiralas are paying slightly more for their concrete masonry-frame home than they would have if it had been stick built. But, they were never interested in that option to begin with, Gopal Muppirala says.

“My wife was reading about steel framing, so we decided to go with that. Nobody in this area had a steel-frame house,” says Muppirala.

The Muppiralas quickly learned why. “No one in this area has the expertise to build steel frame,” he says. After meeting with Bost and emphasizing their top priorities, “we felt that a concrete blockhouse would be a better choice.”

By the time he began working with the Muppiralas, Bost had learned a lot from building his first concrete masonry-frame home, his Parade of Homes entry for 1999. The first attempt at concrete masonry framing was “a little cumbersome,” he says.

As he adapted techniques used in south Florida and the Southwest, Bost needed to keep in mind the needs and norms of homes in central North Carolina—namely, two-to-three story construction over

crawl spaces and basements, and increased insulation requirements.

Bost began that first house by building its foundation walls using 12-inch (305-mm)concrete masonry units (CMUs), and { framed the floor system to sit on the inner 4 inches (102 mm) of the foundation. “We erected the concrete masonry walls up to the first-floor ceiling line using 8-inch-wide (203-mm) block,” Bost says.

After the first-floor walls went up, the framers returned to frame the first-story interior walls and second-story floor system. This time, the floor system rested on the inside 2 inches (51 mm) of the 8- inch (203-mm) block wall.

The masons came back to the site and put up the second-story walls using 6-inch-wide (152- mm) block. When they were finished, the framers returned again and built the second-floor interior walls and the third-story floor system, which rested on the inside 2 inches (51mm) of the 6-inch (152- mm) block walls.

“At this point we erected the roof, which was supported by the concrete masonry itself.”

“You basically end up with a concrete-and-steel post-and-beam support system,” he continues. “Vertical columns were grouted solid and reinforced with rebar under all point loads, on either side of all openings, and at 4-foot (12.2-rn) centers, which supports a perimeter bond-beam (U-shaped block filled with concrete and steel), at each floorline. The rafters were attached to a pressure-treated plate bolted to the top bond-beam. The bands of each floor system were also bolted to the bond beams. All the remaining open cores were filled with expanding foam insulation.”

To finish the inside of the block walls, Bost used an unconventional method. Instead of putting down furring strips, we ran 1-by-4s (25 mm by102 mm) horizontally, 48inches (1219 mm) on center, and attached them to the block walls. “We put on 2-by-2s(50 mm by 50 mm) vertically,16 inches (406 cm) on center, on top of the 1-by-4s. That gave us an easy cavity to slide the wiring behind and enabled us to plane out the walls.”

Bost placed fiberglass insulation into the 2-1/2- inch (63.5-mm) cavity, even though the block alone provided insulation that went beyond building code requirements.

The result was a strong, quiet and efficient structure that has proved to be substantially more stable than stick-built homes. “We had very little settling, almost no sheetrock cracks, hardwood floor separations or door adjustments after two years,” Bost says. “But the shuffling of contractors made the process somewhat inefficient.”

“We found we had difficulties getting the openings of the windows and the doors exactly right. That’s one of the reasons I decided to change the technique the second time around.”

The change in technique Bost made when he began to build the Muppiralas home was fundamental.

“This time we actually stood up a temporary wood frame of 2-by-4 (51-mmby 102-mm) walls along the exterior perimeter while we built the floors and until we could transfer the load to the concrete masonry system,” he explains. “The 2-by-4walls just became partition walls to hold the pipes and wiring. I had to convince my engineers that this made more sense.”

This time, he says, the process went much more smoothly. Like the first home, the foundation walls were built using12-inch (305 mm) block, with the floor system built on the inner 4 inches. The framers set up the 2-by-4walls, 16 inches (406 mm) on center.

“All our beams in the floor system cantilevered out 7inches (178 mm),” Bost says. “We didn’t use vertical supports to carry the loads. Just enough to temporarily support the beams until the loads could be transferred to the block work.”

Workers constructed the framing for the entire house, placed the roof rafters on knee walls so that the overhang would allow for the 8-inch(202-mm) veneer, and set windows and doors in the frames. Except for the fact that the house wasn’t sheathed in plywood, a visitor might think a conventional wood-frame structure was being built.

At that point, the masons returned to lay 8-inch block, pouring concrete and laying bond beams as they went. The 2nd- and 3rd-floor systems were attached to bond beams with bolts.

As reinforcement, vertical columns stand on the sides of each window and door opening, under all point loads, at each corner of the house, and at 4 feet(1.2 m) on center, using two No. 5 rebars running vertically.

The 8-inch by 8-inch by 16-inch (203-mm by 203-mm by 406-mm) block is insulated with foam pumped into the block cavity. In addition, fiberglass insulation was installed between the studs of the 2- inch by 4-inch (51-mm by 102 mm) interior stud walls with sheetrock.

The complicated roof system, including four copper-barreled roof areas, contributed to the nine-month construction time, which began in August 2001.

“We applied real stucco with some unique patterns,” Bost says. “It almost looks like cast limestone.”

“There’s that spiral staircase. (A second, smaller staircase near the kitchen leads to a room above the garage.) With the exception of the laundry and powder rooms, there are no interior walls on the first floor,” he says. “There are four columns around the spiral staircase with steel beams that point load on those columns.”


There are plenty of advantages to a house built this way, Bost says strength, thermal efficiency and sound-dampening qualities, as well as resistance to termites and fire, are characteristics that can reduce insurance premiums and lower the cost of the home in the long run.

“I wanted to use this technique for two reasons,” he adds. “Number one, I was raised in masonry. And number two, this maximizes the trades [subcontractors] that we have in place.”

Bost’s third concrete masonry home is just off the drawing board. It will be his Parade of Homes entry for 2002. “We’re going to put stone and cedar shakes on the exterior walls to show it doesn’t have to be just block or stucco. You can put anything [on the face] you usually put on a house.”

With 4,000 square feet (371.6 m2) on two floors, the house will feature a first-floor master suite, an open family room, a screened porch and a deck. The design includes unfinished space in the basement and third floor.

“It’s certainly different for a masonry-framed house,” Bost says.

“It looks magnificent. It looks unique,” owner Gopal Muppirala says of his own home. “Almost all the houses in the development are brick face. The neighbors said, ‘This is what we need for the development.’”

More people in Rex Bost’s area are thinking about the advantages of a concrete masonry-frame home. Whether it’s the strength and stability concrete block offers, or its superiority as the backbone of someone’s architectural fantasy, block is likely to delight more residents of the Triangle in the years to come.

“We’re starting to get more and more calls from people who want to meet me about concrete masonry homes,” Bost says. “I tell them it’s 4 percent more than a brick home. But you get so much more home.”