The first challenge, when building in a flood zone, is to allow rising water to pass underneath the building without damaging the structure or its contents. Here we are building a house in a High Velocity V Zone (elevation 17). In very simple terms, this means that the structure will have to withstand direct wave action in addition to rising water and must be elevated above a base flood elevation of 17 feet above sea level.
A second challenge, when building in a high wind zone, is to strengthen the building so that it won’t blow over or be damaged in hurricane force winds. We are building in a High Wind Zone (120 mph). This means that the building must withstand a base wind of 120 mph with gusts of 138 mph. No three little pigs huffing and puffing and blowing this house down!
We are using a Helical Pile and Grade Beam Foundation which will allow us to anchor our building into the ground and elevate it above the flood zone. Helical Piles are essentially big screws that are turned into the earth until refusal.
In the picture to the right the helical piles are set in sleeves which go down into the earth. Rods in the hydraulic drive attachment snap when the piles are met with a specified level of resistance – in this case 4,000 pounds of torque.
The helical piles we are driving went into the ground between 20 and 27 feet. A steel plate attached to the top of the pile connects the helical pile to the grade beam. Rebar reinforces the connection and extends up into what will be the columns.
Forming and pouring the helical piles and grade beams is an exacting job. The anchor provided by the helical pile is what will allow us to build in a Flood Zone. The top elevation of the grade beams establishes the grade and sets the elevations for the surrounding landscape and the stormwater management plan.
We are working in a very small waterfront lot and are extremely mindful of the environmental impact of our construction. Not a single drop of rain that lands on the house or driveway can go into the salt pond or onto the road or adjacent lot. We have designed a stormwater management plan that uses rain gardens and bio-retention. Establishing the finished grades is critical and setting the grade beams is the first step.
Once the grade beams are poured the next step is to form the columns. Here the top of the finished columns will be approximately 12.5′ above grade. This is 18′ above sea level, giving us 1′ of freeboard above the flood plain. Building and Zoning Code allows for a maximum building height of 35′ above grade. The architectural design, the site plan and stormwater management plan, the septic system, and the landscape design all have to work with the existing grades, flood plain and zoning restrictions.
The rebar is extended to go the full height of the columns. The columns are formed and leveled and then filled with concrete.
Finally the forms are stripped, the water and septic lines run underground, and the grade beams backfilled.
We are now ready to build!