OBMI’s Managing Director provides his professional view on progressing in 2018 following September 2017’s Irma
Hurricane Irma was the largest and most powerful hurricane to form and make landfall in the Atlantic Ocean. Sustained winds of 185 mph and gusts upward of 215 mph created a perfect storm, of the likes we have never experienced.
Progressing with the rebuilding process and having reviewed where structures failed, we’ve uncovered some commonalities as to what things attributed to the mass destruction.
Nails served as weak points in a roof’s installation
The most common contributing factor to roof failures was the prevalent use of nails as a fastener for roofing materials. Unfortunately, this far too common construction material resulted in significant failures stemming in thousands of damaged roofs.
A proper roof structure should utilise screws to attach the heavy timber wood, framing members together. As the weakest point in the roof’s structure, the fascia requires additional reinforcement with multiple screws directly connecting the fascia to the heavy timber battens and galvanising roof cladding.
Improperly installing roofs with nails, diminishes the strength needed to resist hurricane force winds.
Wind finds weaknesses through compromised openings
For homes where roofs appeared to have been lifted off, it was frequently due to the wind finding entrance into the home through compromised openings, like windows or doors that were cracked or not airtight.
In many cases, the hurricane pried open windows and doors that did have shutters. Once the wind and rain entered the structure, they created a tornado-like effect, thus causing the pressure within the home to build to the point where the only escape was through the weakest structure, the roof, doors and windows.
Impact-resistant Miami-Dade approved windows performed better than others. Two 1/4” thick panes of glass should be sandwiched together with a clear laminated sheet. This creates a bond so that if a wind-borne object were to hit it, the glass may crack, but not shatter and disintegrate. How the entire window is attached to the concrete opening is also very important.
A strong BVI roof should have a combined concrete, wood, and steel reinforced assembly. This means that wood rafters leading to the primary roof structure are cast into reinforced concrete ring beams along with both vertically and horizontally connected reinforcement-bars tied together.
A monolithic concrete pour will sufficiently lock these elements into place. Try to avoid making multiple pours to achieve this connection. This hooking effect secures the roof and gives it a far better chance of surviving a hurricane, and resists the uplift created from the hurricane force winds.
The survivors
With category five hurricanes come a myriad of other environmental challenges including tidal surge, heavy rainfall, and tornadic activity.
Although safeguards can be made to reduce tidal surge and flood damage, tornadoes are indiscriminate and wreak havoc on everything in their path.
This was seen throughout the BVI where one structure was left untouched when a neighbouring property was severely damaged. It’s a widely held belief that hurricane Irma spawned dozens of tornadoes which resulted in a great deal more damage than attributed to any other cause. Some buildings in the BVI that were spared substantial damage include:
- Commerce House
- Fireproof Building (now hurricane proof as well)
- Ritter House
- Peebles Hospital
- OBMI designed residences: Bayhouse Villa, Tonic Waters, and Nora Hazel Point, as well as Nanny Cay Condominiums
Why did these buildings survive?
- Location was a huge factor; some buildings weren’t directly battling the winds as the storm approached the BVI. This could have been due to a protected hill side or valley
- The direction the winds were moving before and after the eye passed was also a factor
- An elevated structure on an open slab reduced the risk of damage from flooding and storm-driven water
- A home with a square floor plan (or better a hexagonal or octagonal plan) with a multiple-panel roof (four or more panels) was found to have reduced wind loads
- Roofs with multiple slopes such as a hip roof (four slopes) perform better under wind forces than gable roofs (two slopes)
The future?
OBMI is working with AIA Miami to review the 2017 hurricane season and identify what design, engineering, and built structures fared better than others, and what commonalities are shared in those structures that sustained major damage.
The team is not just reviewing what design and engineering features are critical to a building’s strength, but also how code regulations and enforcement play a role in maintaining a structure’s integrity.
Following hurricane Andrew, much of the northern hemisphere has adopted the stronger building codes of Miami-Dade County (Florida), which require buildings to be able to withstand winds of 130 mph.
It is clear given this year’s unprecedented storms and devastation that building codes need to be not just implemented, but continually reviewed and strengthened for the safety of BVI citizens and security of our structures. As teams of professionals identify island-wide best practices, there are things that individuals can do during the building and rebuilding stages to help strengthen their property to mitigate against storms of the future.
Self-sufficiency amenities
As we experienced in the BVI, although a major hurricane has passed, the process of getting life back to normal takes much longer. Natural disasters frequently damage and weaken public infrastructure including electricity, water flow, and roadways.
As we rebuild our island, it’s important to keep self-sufficiency features in our plans from underground water cisterns to solar panels and back-up generators; these amenities can improve quality of life during times of natural disasters. Discuss these features with your architect as you rebuild, as these self-sufficient amenities can add value to your home and peace-of-mind when needed.
Investing in secure building materials
Investing in hurricane windows and doors and installing storm shutters over all exposed windows and glass surfaces are easy and effective ways to prevent debris from entering a building. Hurricane windows and shutters also aid in the prevention of your roof being lifted off by not allowing airflow to penetrate the home through blown out windows and doors.
Identifying opportunities to minimising damage due to large shade canopies
One of the things that makes island-living unique and the homes and architecture distinct for the Caribbean is the use of large overhangs.
Functionally, they provide shade and allow a home to receive ventilation from the trade-winds. However, in times of extreme weather, these overhangs can capture the wind and cause damage to the connecting roof structures. In light of this year’s hurricanes, OBMI has a team of architects assessing damage to roofs with these large overhangs and are looking into potential design alternatives that would prevent substantial roof damage due to these overhangs.
Concepts currently being reviewed include designs that incorporate a natural breaking point between the overhang and roof structures, allowing for the sacrificial overhang to be lost in the event of severe weather, while minimising or eliminating damage to the primary roof structure.
A design concept that OBMI has utilised for years is the use of a continuous concrete gutter that hides the eave and fascia. This concept shields what is considered to be the weakest point in a roof and by design, the wind is naturally directed above it.
Utilise alternative roof styles
Choosing the right type of roof for a structure is more difficult than most people imagine and some clients simply allow the designer or contractor do it, however, being informed during the building and rebuilding process can add to your home’s value.
Roofs do a lot more than provide shelter. They also define a structure’s look, as well as a level of security during a hurricane. As you embark in building or rebuilding, review options for roofs with your architect to determine the alternative styles that are traditionally stronger in the tropics. In the immediate aftermath of the hurricane, the concept of a concrete roof was discussed often—consulting a structural engineer prior to making that decision is most important because the home needs to be structurally designed for it.
Hip roofs have slopes on all four sides and assuming the aforementioned factors outlined are accommodated in the design, the inward slopes make it more sturdy and durable.
Flat roofs are typical in the Caribbean as they are cost-effective and provide a surface to install solar panels or have an elevated living space. Flat roofs can also be turned into green roofs, which use the space to add vegetation providing another layer of insulation and beauty to a structure.
Photography courtesy of OBMI
Marvin E Flax
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