Article No: 169

2006-05-03 09:31:42
Building in the face of hurricanes
By: Concrete Homes


 

The catastrophic damage caused by Hurricane Katrina has driven home the vulnerability of residential construction in the onslaught of a natural disaster. But in Florida, where hurricanes are more commonplace, building codes dramatically changed in 2001 after the massive destruction caused by Hurricane Andrew. Since then, the use of concrete masonry block as the primary structural component in residential homes is on the rise.

Concrete masonry's high mass gives it a better ability to withstand rain and the impact of flying debris. When reinforced, it can also withstand high-force winds because it allows exterior walls to flex, reducing structural shifting.

The proof of indomitable concrete masonry can be seen firsthand at two homes that have been under construction over the past year on Florida's coast. While the buildings were going up, one tropical storm (Arlene) and three hurricanes (Ivan, Dennis and Katrina) have come through.

Builder Paul Hartzog, owner of Silver Sands Development and Decks N Such Marine Inc., has been building a 22,000-square-foot, reinforced concrete masonry home, the Adams residence, on a peninsula that juts out into Choctawhatchee Bay in Destin, Florida. Each time the weather prediction called for a hurricane, he has prepared for the worst--scaffolding was disassembled and removed, materials were tied down or removed and equipment was put under cover. But as for the house itself, it was never a worry.

"There were no problems with the house during the hurricanes. The first time--Hurricane Ivan--the block was just coming up on the foundation. The second time--Hurricane Dennis--we were dried in and just about to put the tile roof on. This last time--Hurricane Katrina--we were about 90 percent complete," says Hartzog, adding that the house has come through all three storms without damage.

"We talked a lot about sustainable materials with the biggest threat being hurricanes," says architect Dennis Chavez, principal of Dougherty + Chavez Architects, who designed the Adams residence. "When you design a building or structure on a body of water, you have to take into account the phenomenon of high winds and storm surge."

The foundation of the Adams home began by hammering pilings into the ground. "In this particular design," says Chavez, "we have a footing that is constructed with 14-foot-long timber piles about every 10 feet on-center around the perimeter of the house. That was an extra precaution to resist scour--the wave action taking away dirt, trying to undermine the foundation."

The foundation was completed using standard 8-by-8-by-16-inch CMUs, laid in horizontal courses to bring the foundation up to 11.33 feet above sea level. Every block course was reinforced with No. 5 steel that runs vertically through it and every cell was filled with concrete, forming the entire exterior envelope of the house. The only wood in the exterior of the house is on the second floor where a few parts of the walls are 2-by-6-inch CMUs.

In terms of design, Chavez says that they have never been limited by the choice to use concrete masonry in construction. "In some ways, it is actually better because you have certain design parameters you want to achieve with block and you can do a lot of interesting things," he says.

The Adams residence is anything but square, with many curves and turns throughout the design. Some of the features achieved with block masonry construction in the house include a colonnade wall with columns, four fireplaces, a full vault ceiling, a safe room, a 90-by-60-foot zero-entry pool and a grotto with waterfalls.

"We also have a sitting room with a dome that we did out of 8-inch block in a perfect radius with windows all the way around," says Hartzog. The exterior block was finished in stucco with soffits and corbels done in solid cypress.

The story of the Wilson house on Stallworth Plantation in Walton County, Florida, reads much the same way as the Adams house, withstanding three hurricanes and a tropical storm while under construction. "It is usually not even a question about the type of material directly on the Gulf--we build in concrete masonry because it can withstand anything," says Greg Tankersley, one of the principals of McAlpine Tankersley Architecture in Montgomery, Alabama, who designed the 6,700-square-foot (of heated space) house.

The Wilson house sits on 118 concrete pilings. The entire exterior is standard 8-by-8-by-16-inch concrete masonry block.

According to builder Tommy Norred of William T. Norred Construction, who has been working on the house for two years, there have been no issues with the house during or after the hurricanes, not even water penetrations.

"This house is built like a fort," he says. "All the concrete blocks are solid poured. All the 16-inch on-center have 5/8-inch rebar vertically from bottom to top. So there is one in every concrete block, and all those blocks are filled with concrete. Then, all around, there are two courses of lentils with 5/8 rebar every 6 feet vertically. So you have a belt in steel all around the house."

Tankersley says the choice to use concrete masonry block was simply the history of common sense. "You go down to Florida and parts of the Panhandle where there are some structures that have been there forever and they are concrete masonry houses," he says. "So you look at what has been around and is still standing and that is concrete, so we are not trying to reinvent the wheel."

Tankersley also says that using concrete masonry never limits his design capabilities. "The Wilson house, which is far from a box house, is on a fairly small footprint and made up of a bunch of outer buildings. Using standard block material does not limit the design at all." The house is composed of three separate structures--the main house, a separate two-bedroom apartment and then a two-car garage with a bedroom on top.

Like Hartzog, Norred has had to prepare the site each time a hurricane is forecast, policing the area to make sure everything has been picked up, having the dumpster removed and putting up plywood over the windows. He says they usually store a lot of the materials and equipment inside the house "because we know it will be safe there."

"As soon as we see it coming," says Norred, "we treat it like it is coming right here. Unfortunately, we have been right too many times. I just have had no concern about the structure of this building. My only concern is erosion. There is nothing we can do about rising water, but in the wind rating, it would survive a class four or five hurricane."

Norred and Tankersley both are pleased with the masonry aspect of the home and how it has withstood the onslaught of hurricane-force winds. So far, it has gone virtually unscathed. "It is a more a matter of trying to aesthetically keep it from being beat up, but not blown away," says Tankersley.

Natural disasters are probably the ultimate barometer of a building's mettle because they represent some of the most extreme conditions to which a structure will be subjected. But as hurricanes continue to ravage the U.S. coastline, more and more homebuyers are choosing concrete masonry construction. "A lot of these houses are really high-end custom homes, and people are spending a lot of money to buy a sliver of Gulf front, so if you are building in such a place with such a high property value, it does not make sense to skimp on building a house not only for hurricane winds but durability over the years," says Tankersley.

"I have had more people asking me about concrete construction after these storms," says Hartzog. "I think it depends on where you are building and the type of structure you are building as to what material they like. As for me, I would much rather build out of block."

Tankersley relates the story of a home he designed in Rosemary Beach, Florida. "It was much farther inland and the client wanted a wood-frame/wood-sided house. We designed the house and then the owners decided to sell and move somewhere else. They had a ton of people look at the lot and the house, but every sale fell through because it was not concrete. They would have sold it five times over if it had been a concrete design."

This article and photography is reprinted with permission from the National Concrete Masonry Association.