Article No: 56

2006-05-01 10:31:46
North Carolina TopSail Beach townhomes stand confidently in face of Atlantic hurricanes
By: Larry Storer


It's summer and most outdoor enthusiasts who love the beach are probably stretched out soaking up some sun. Despite disappearing beachfront property, many still want to build a part of their version of paradise as close to the water as possible.

But when a buyer invests in an oceanfront home, he wants to be sure that the house will still be there after each storm passes. Coastal building technology has developed into a wind and water science, but regardless of code requirements, concrete construction has an inherent superiority over other building methods and materials.

 

"The number one concern of homebuyers considering a coastal purchase is 'Can this house survive most hurricanes and weather events?'" David Pfanmiller, partner of Security Building Building Group LLC (SBG) of Raleigh, N.C. said. "The best answer available anywhere is: 'Yes it will.' Not only will your house be standing tall season after season, but you will save money along the way. You can't find a more comfortable, secure, money-saving residential investment than one of our cast-in-place concrete homes."

Pfanmiller is a cast-in-place concrete evangelist who has taken his message to TopSail Island on North Carolina's Treasure Coast where he has built six, two-story all concrete steel-reinforced concrete duplex townhomes right on the beach.

Functional, fun and beautiful
The 1,533-square-foot townhomes all have three-bedrooms, 2.5 baths, kitchen, living room and dining room. The first and second floors have an awesome view of the ocean with 12-foot by 20-foot private, covered concrete.

When you drive up, there's a covered parking area and an 8-foot by 15-foot entryway. You enter the structure on the ground level and immediately go up steps to a wide-open living area on the first floor that's approximately 19-foot-8 by 36-foot. The kitchen is in the front, an open dining area is in the middle and the end facing the ocean is the family room.

Within the L-shaped kitchen area, there is a laundry closet that holds a stacked washer and dryer, and an adjacent powder room. There's an island with a cooktop and a bar or counter area. Even through the home is compact, the dining area can hold a table for six, and four more can eat on barstools at the island. Outside the family room, there's a 12-foot by 20-foot deck with a 4-foot wide walkway that goes out and joins with one from the unit next door and continues toward the ocean, over the dune and down onto the beach. The deck has potential to be enclosed for a sun room, plant room or some other expansion.

Upstairs are three bedrooms and two baths. On the ocean side is a 20-foot by 17-foot master bedroom with a three-quarter bath. The master bedroom has a door leading onto a 12-foot by 20-foot private deck with a panoramic view of the ocean. The hall bath has a tub and serves the other two bedrooms.
All the mechanical equipment is in the attic, which is accessed by pull-down stars from the upstairs hall. The second floor ceiling height is 8.5 feet and the first floor ceiling height is 9.5 feet, but Pfanmiller has lowered the dining room ceiling to 8 feet. All duck work comes down through chases and on the first floor level, the air conditioning is blown out of the false ceiling in the dining area.

How it is finished inside is a market-driven issue for Pfanmiller. Direct glued sheet rock or a texture finish are common.

"We feel it is just as easy to skim coat it and leave that surface as smooth as possible so as not to slow down that transfer. At the beach, things are casual so we are doing it with what I call a knockdown texture on it. In some of the big houses we've done here in Raleigh, they added a couple more coats and sanded it down and basically put a high quality sheetrock-type finish on the face of the concrete."

The exterior is a synthetic stucco colored finish over a cementious hard coat, which is also the moisture barrier, accented with Bahama shutters that are both functional and attractive.

"What we're trying to do is complement the durability and long life with a maintenance-free exterior," Pfanmiller said. Our wall system allows us to do that because we don't have any of the negatives associated with stucco construction of the last few years: no cavities to grow mold or mildew, no wood and nothing to rot.

There's an architectural roof to create the gables for the look Pfanmiller said he wanted. To achieve the "Fortified" certifiction (See sidebar article), he had to build the roof structure to the Institute for Business & Home Safety specifications, which are basically Dade County Florida-type code requirements standing up to at least 130 mph winds, and using 5/8th-inch roofing plywood instead of .5-inch.

Out the back and off the lower deck location, there is a dune crossing, a 4-foot deck walkway that comes straight out the back of the house and high enough to go the 40 feet over the dune. Steps lead down from the dune crossing to the beach. A sand dune is a natural barrier between the actual surf and the building lot.

Hurricanes: a fact of beach life
In an average year, 10 tropical storms develop over the Atlantic Ocean, Caribbean Sea and the Gulf of Mexico. Many remain over the ocean, but six will probably develop into hurricanes. In an average three-year period, roughly five hurricanes will strike the U.S. coast between Texas and Maine - two are typically intense or major hurricanes. North Carolina has survived a number of major hurricanes in recent years, including Hugo in 1989, Bertha and Fran in 1996, and the largest of all, Floyd in 1999 with billions in damage and the loss of 52 lives.

So building on the beach is serious business. Construction considerations include winds, flooding, vertical erosion and scour, the erosion of soil and sediment that provide support for the supporting piers.

From a design standpoint, as far as wind loading is concerned, you got a rigid connection between the top of the column and the 8-inch slab. That connection, working with the rectangular shape of the column, creates the lateral stiffness that's required for the structure. Then as far as shear uplift, honestly there is none. The big difference between wind loading on the cast-in-place concrete structure and a frame structure is that the concrete townhouse weighs a million pounds. So in the structural analysis, horizontal wind loading and uplift is not even an issue because of the dead weight of the structure.

Flooding is an issue
"From ground up, we drilled 28 12-inch auger-cast piles 45 feet into the ground," Pfanmiller said. "On top of the auger cast piles, we formed up a structural grade beam that was around 20 inches square and it had a case of steel much like a bridge beam that spans from piling to piling. Then on top of the grade beam, we constructed a 12-inch by 30-inch structural column that has two gauges of steel in each column. We went with a rectangular shape because we wanted the shape of the column to also create the rigidity we needed so we wouldn't have to cross brace it with a bunch of ugly cumbersome cross bracing typically seen out of wood frames.

"On top of the 12-by-30 structural column, we've got what I've always called the elevated slab. The elevated slab - the first slab on the first living floor — is elevated 10 feet above existing grade because of the flood elevation of that particular section of the beach. So we elevate the first floor slab and it is an 8-inch structural slab that's got 4 inches of rigid foam attached to the bottom of it to create our thermal envelope on the bottom of that first-floor level. Then on top of the 8-inch structural slab are the two housing lifts.

"Worst case scenario in a catastrophic storm is that you could possibly lose the roof, I guess," Pfanmiller said. "But even if you did, you would still have your sealed structure intact."

Storm surge is water that is pushed toward the shore by the by the force of winds swirling around the storm. The advancing surge combines with the normal tides to create the hurricane storm tide, which can increase the mean water level 15 feet or more. In addition, wind-driven waves are superimposed on the storm tide

"In the particular flood zone that we're in down there, the house was designed for the wave and wind action to work simultaneously. And there are safety factors built into the depth of our pilings for wave scour around the bottom."

You're only as strong as your legs
Each of the 28 pilings is rated for 50,000 pounds. Pfanmiller said the 8-by-8 timber that's put in conventionally the way the local builders do for frame beach homes, is rated at only 12,000 pounds.

The auger cast pile, also known as a continuous flight auger, is a giant drill bit that is fluted all 45 feet so that the entire thing looks like a giant drill bit. It sits in a big crane rig and has a hydraulic drill head on top, a drill bit in the bottom of it and a hollow shaft.

"You can't pull the auger out and leave the hole there because the loose sand will fall back in. So what they do is drill down to the depth the soil engineer requires, then hook up a concrete pump to it and pump in a high strength grout mixture. Actually, as they withdraw the auger they're pumping grout into the void they create right below the auger. And they continue to pump as they pull the auger out and the soil engineer knows how much void is created per foot as they pull the auger out and he knows how many cubic feet per surge is in the concrete pump so he literally counts it and makes sure that you put in more concrete than void that you create and that's how you are assured of a continuous concrete pour."

These are friction piles, not end-loaded piles where all the weight is on the tip of the pile. Basically the friction is created between the sides of the piling and the adjacent sand.

"Sand erosion is only going to happen during the storm surge of a heavy storm, and that's the purpose of the dune between the house and the ocean. It's got to eat the whole dune away before it ever gets to the face of the structure. Even if it does, there's a safety factor in there of five to seven feet of scour (where the wave and water action would actually scour the sand away from the piling) that we can survive without worrying about any structural integrity."

Cost factor
The cost difference between Pfanmiller's beach homes and a comparable wooden structure would be about 12-15 percent higher. Most of that difference is for the pilings and grade beams that will keep the heavier concrete home in place.

"If we could take that building off the ocean front and put it on the mainland, but close to the coast in the same wind load and put it on straight footings, our costs are probably only 8 percent more than conventional construction. "But the pilings are expensive," he said. "They charged me $9,500 just to move their equipment onto the site to drill these piles.

Energy efficiency
The townhouses are extremely energy efficiency. With the monolithic pour, there are no cracks or joints, so there is little air filitration. This is a tremendously strong box-shell with the potential for a tremendously energy-efficient shell..

"We built a similar size duplex in Raleigh two years ago and had tests done on it, and the building science people who came out and performed the tests said it was the tightest structure they had ever tested from an air infiltration standpoint.

"In each of the units we've built so far, we've put an energy recovery ventilator in them to maintain indoor air quality because we don't have the air exchange that we need to keep the air fresh. What we did at the beach is we put a pickup for the ventilator in the kitchen and laundry room downstairs and one in the upstairs bathrooms to pick up the humidity."
The pickups lead into the energy recover ventilator, which is set up to take the latent energy out of the air as it dehumidifies and exchanges the humid, stale for fresh outdoor air.

"The building we did in Raleigh was an Energy Star-rated building. We went through the process to get it tested and rated. And every structure that I know of in the country that has been built with this technology has achieved the Energy Star rating with no problem. The Energy Star is based on a 30 percent improvement over the model in code, and he said it's been his experience that the people who have lived in our buildings are actually seeing upwards of 50 percent improvement over what their neighbors are paying.

Pfanmiller said that from the standpoint of the builder, energy efficiency is also a marketing issue, and it is difficult to sell energy alone. At the beach, he doesn't press the energy issue as much as he would if he was building inland.

"To me, that's the beauty of our concept. I can list you 10 or12 benefits of our construction method, and depending on my market, I can just re-prioritize the list and come up with a list that would trip your trigger whether you are an investor looking at durability, lifecycle costs, .low operating costs; or whether you want to build on the oceanfront and your paramount interest is the storm resistance.

"The end-run for us in this technology is that we've got a product that can slide the scale and fit into a variety of different markets including commercial. CH

For more information about SBG, call 919-782-6789 or e-mail Pfanmiller at noSpam("SBG9118", "aol.com"); SBG9118@aol.comSBG9118 at aol.com.

Cast-in-place moves 'above grade'
Security Building Group (SBG) uses cast-in-place removable aluminum form concrete construction technology that enables crews to form the walls and the floor at the same time, pouring the concrete monolithically. The result is a tightly integrated concrete envelope that's not going anywhere in a storm.

The aluminum panels are 2 feet wide and range from 7-foot-10 to 9-foot-high. SBG Partner David Pfanmiller's crew stands two panels up opposite each other, and use a flat metal spreader that holds the two panels in position opposite each other to create the desired wall thickness. Then inside the panel they put two inches of rigid foam on the outside face, held in place by a retainer clip that holds the foam against the outside face of the wall. Concrete is then poured in the 4-inch void between the foam and the inside panel.

When the form is stripped away on the inside, there is a raw concrete wall; on the outside, it looks much like an ICF because of the foam surface with the face of the retainer exposed on the outside that works as a catching point for whatever siding is to go on the house.

He said there are two big differences between what he does and what IFCs do. "Structurally our forming system allows us to form the walls and the floor at the same time. So when we pour, we pour everything monolithically - the walls and the floor of that level all go at one time. Then we literally strip those panels out, move them up a level, reset them and then we pour the walls and, in this case, it is the attic floor that would get poured. So we have a 4-inch structural wall out of concrete and then typically we have a 6-inch thick concrete floor slab between the floors and also the attic floor.

Pfanmiller said the other big difference between what he does and what ICF builders do is that he doesn't want foam on the inside. "We want the mass of concrete to be able to absorb and store the thermal energy and then radiate it back out into the room. So we prefer to just put a thin veneer plaster or some specially fortified dry wall compounds that will stick directly to concrete without any problem. So we want that hardened finish primarily to not inhibit the thermal transfer of energy from the mass."
The connectors Pfanmiller uses are rebar. When each floor is completed, the crew comes back with an epoxy rebar to tie in the structural reinforcing form one floor to the next.

Two pieces of patented technology has opened up the above-grade market for SBG's removable aluminum forming system. "The panels themselves are very similar to what we have always used in our basement construction," Pfanmiller said. "They are 2 feet wide instead of 3 feet, they're stiffer and give us a flatter finish than what our basement panels do. Basically it gives us more of an architectural finish."

SBG has been instrumental in developing some of the ideas and technology with Wall-Ties & Forms, their panel manufacturers.

One is the flat metal spreader, about an 1/8th inch thick and 6 to 10 inches long with holes in the end of it. The panels are literally pinned together with a pin and a wedge. Traditionally when you strip them out, a little tab of that spreader still sticks out of the wall.

"It was set up to break right at the base of the wall," he said. "That's fine unless you are trying to build a thermal structure and in that case it created a perfect avenue for heat and cool to slip through that metal spreader. What Wall-Ties came up with is what they called a break-back spreader, which was designed in our case to break off 2.25 inches behind the face of the wall so that it literally breaks behind the face of the concrete and behind the foam. On the inside it breaks back about a quarter-inch inside the face of the concrete. So when we come back and pour our finish on the outside, it seals it and we don't have that thermal transfer.

The other patented piece is the retainer assembly — the retainer clip that holds the foam in place.

"People have been trying to pour sandwich walls and put Styrofoam in concrete for years. The problem is that it wants to float and move around and this retainer doesn't allow that to happen. CH

'Fortified for Safer Living'
SBG partnered with the Institute for Business & Home Safety (IBHS) to add even more disaster-resistant materials and techniques to these beach townhomes, as part of IBHS's award-winning "Fortified…for Safer Living" program.

The IBHS, a national nonprofit disaster safety group with headquarters in Tampa, Fla., launched the "Fortified" program in Florida in 2000, according to Chuck Vance, IBHS Fortified program manager.

"Fortified" features added protection against windblown debris for windows and doors. And through the program's inspection process, the home is certified upon completion as a "Fortified…for Safer Living" home. The following "Fortified" features are part of the TopSail Island homes:

  •  Reinforced continuous piles that elevate the home and critical utilities a minimum of two feet above the Base Flood Elevation (BFE) and ground level walls and stairs that can break away from the main structure.

  • From the peak of the roof to the foot of the reinforced piles, the home is connected to form a continuous load path capable of withstanding at least 130 mph winds.

  • The windows, doors and other openings are protected by tested products that can withstand the impact of windblown debris without penetration of wind and water.

  •  An engineered roof truss system with an enhanced minimum 110 mph wind rated covering and a secondary moisture barrier; plus, twice the required underlayment, and a thicker plywood deck sheathing with a stronger holding nail and nailing pattern.

  •  Verification by a certified inspector that all required "Fortified" products and materials are installed correctly in accordance with manufacturer's specifications or "Fortified…for Safer Living" requirements.

  •  The home and property is also verified to be a low-risk hazard for exposure to wildfire.