Un-reinforced Cement Block Walls
In many coastal U.S. and Caribbean communities you find residential structures built with cement block walls. These wall are often unfilled or selectively filled with concrete or a mix of concrete, sand and water called grout. Most of these un-reinforced wall are made with smaller size 4″ or 6″ deep blocks and limited or no rebar reinforcement. The roofs are generally of conventional wood construction. Older structures will have rafters ranging from true 2″ X 6″ to 4″ X 4″ dimensions arranged at 3ft to 4ft horizontal spacing intervals. These designs do not reliably stand up to hurricane winds over category 2. The roof surface in these structures are often wood planking that while substantial in strength is attached with old fashion nails. These are smooth shank nails and over time loose their grip as the rafters age. In the Caribbean the roofs may be made only corrogated metal panels nailed on to the rafters with no wood sheathing at all. These older structures also lack the newer hurricane straps mandated by recent building codes. This combination of circumstances can result in catastrophic failures in hurricane conditions especially above category 2 in severity. Even with hurricane shutters installed the wind can grab the soffet overhang, pick up the edge of the roof and allow the wind pressure to enter the home. Once this happens the entire roof comes off in one violent event exposing people to the full deadly force of the storm.
Concrete block homes often lack any insulation making them expensive to heat and cool. People with homes of this type can take steps to improve the survivability of their home by increasing the roof structure. Improving the attachment to the walls. Using deck screws or ring nails to attach roof sheathing as part of the re-roof and making sure the home has hurricane rated shutters on all the windows and multiple bolts at the corners of the doors.
Even with these improvements people should evacuate these structures if there is potential for storms to reach strengths above category 2.