What Went Wrong?
- November 28th, 2017
- in PROPERTY
It was tragic news to learn that “70 percent of our buildings,” were damaged or completely lost in Irma. Nevertheless, as the BVI’s leader, Premier and Minister of Finance Dr the Honourable D. Orlando Smith, OBE added in his press announcement on September 25, 2017, “this now gives us an opportunity to build smarter and stronger.”
In this pursuit for the BVI’s improvement, it is prudent to ask the question—what went wrong? Or, perhaps more productively and progressively phrased, ask: what can we do ‘right’ to aid ourselves for the future?
During Irma, although there was an element of luck involved in where properties were positioned geographically, there were many properties that did not adhere to the expert advice of structural engineers, for example, those residences not reinforced with steel or filled block.
VIPY spoke to several members of the property industry—all in different sectors—to gain a collaborative concept of moving forward.
TigerQi Architecture’s Principal Lavina Liburd has nearly 20 years’ experience in architecture. Rufred Forbes and Associates Construction Managing Director Cortez Forbes has over 40 years’ proficiency in the construction industry (passed down by Rufred Forbes). Interior Designer (NCIDQ) and Artist Debi Carson holds 20 years’ expertise in all matters integral and related to interior design. And aTec Managing Director Dana Miller holds 10 years’ experience in the field of alternative energy resources. All have kindly offered their expert advice on advancing from the unexpected.
What went wrong with roofs and structures during Irma?
Lavina: By international building codes, there is a minimum amount of vertical reinforcement necessary for concrete block walls to resist lateral forces. This requirement usually becomes critical when considering earthquake resistance. However, wind is in itself a lateral force, and hurricane force winds can exert pressure on walls equal to that of horizontal movement in an earthquake. It is important to fill and reinforce the block work on both sides of windows and doors. With regards to roofs, the number one reason for roof failure in framed roofs was the use of incorrect or insufficient fastening at each layer.
Cortez: After visiting many of the houses after the storm to do insurance assessments, it was evident that most of the damage structures sustained during hurricane Irma were caused by structural elements that were not used. The hollow block walls that were visible in most of the older houses and newer structures did not hold up. Some of the rafter sizes were too small for the span, rafters were not poured into concrete, and some roof structures lacked the proper Simpson straps and screws as well as screw sizes needed to secure the structure together.
Debi: We witnessed walls that were not reinforced with appropriate structural support, e.g. not using the correct steel in the structure, unfilled blocks, or blocks that were too small for exterior wind and loads. Failing with wood structures came with those not fabricated of structural timber, those incorrectly sized, i.e. using 4”x 4” when the components should have been 6”x 6”, hurricane clips or fasteners that were spaced incorrectly—too wide of spans—installations of roof and decking materials with incorrect fastening i.e. nailed when it should have been screwed. It’s not only the quality of the fastener, but the installation method that is key.
Dana: Old roofs and roofs that were not constructed with enough consideration for huge winds suffered. Second story roofs also suffered more damage. Unenclosed roof spaces like porch roofs can be seen as sacrificial unless they are reinforced somehow. Straps and wire turnbuckle systems saw some success.
What buildings survived?
Lavina: Buildings which used properly installed high velocity hurricane zone rated window and door assemblies were often able to maintain a sealed envelope even where wind and debris shattered the glass. This prevented uplift pressure on the roofs and protected interior walls and contents. This is important as in many cases the wind ripped away hurricane shutters and then smashed through the ordinary windows behind.
Cortez: Buildings that were structurally designed by certified structural engineers and built by certified general contractors. These homes were properly inspected to insure all material components and installation were done to the specifications of each design.
Debi: I saw that many homes designed by Alan Smith survived. Hendo’s on Jost Van Dyke which is a timber structure, but well designed and built to the structural engineer’s specifications is an example of a structure that stands when others around it failed.
Dana: We noticed that buildings with rafters that were closer together survived better. 16” on centre rafters or less fared better. Concrete buildings survived better too. Wooden homes tended to suffer more damage. Buildings that were well boarded with plywood survived well. Everyone should be prepared to board up completely in addition to hurricane shutters. When installed properly, the plywood adds an additional barrier that will save your doors and windows.
Why did these buildings survive?
Lavina: I think I covered that pretty well in my answers earlier. In addition, some older (even wood framed) buildings with steep hipped roofs did well as this roof form tends to break the force of the wind, and the more vertical slopes resist suction pressure much better than shallower sloped roofs.
Cortez: Again, buildings survived because they were properly designed and built.
Debi: In some cases, buildings survived through ‘luck.’ In cases where buildings survived that were well constructed, we saw that it was due to following structural engineer designs, specifications, and manufacture instructions as to installation methods. Structural engineers and product engineers do mathematical calculations to ensure the ratings for sustainability against wind loads.
Dana: If your roof survives then your home will be liveable after the storm. This is critical. Make sure your roof is very strong.
Concluding, what should buildings look like in the future to withstand category five hurricanes?
Lavina: Many jurisdictions adopt a proven building code such as the International Building Code and where necessary introduce modifications or enhancements for local conditions. A combination of properly built traditional framed roofs along with flat concrete roof areas over living spaces can provide ‘safe-zones’ and divide the framed roofs into smaller areas which resist uplift more easily. For example, we can use hipped roofs to accent living rooms and master bedrooms, while using concrete roofs for kitchens, bathrooms, secondary bedrooms etc.
Cortez: Buildings can be architecturally designed to suit the taste and personality of the home owners. It is then placed in to the hands of the certified structural engineer to strengthen that design to withstand the forces of ‘Mother Nature,’ whether it be category five storms or earthquakes. The concept is then placed in the hands of a certified contractor to bring it to life.
Debi: Buildings should be constructed and inspected by licensed structural engineers.
Dana: Make sure to have a single level concrete bunker with sacrificial external components.