Stormproof your roof
Published:Monday | July 22, 2024 | 12:08 AMSashana Small/Staff Reporter
With the damage inflicted on the island’s housing infrastructure by Hurricane Beryl, two local architects are urging Jamaicans to embrace better design choices as they rebuild, even on a limited budget, so their roofs can withstand storms.
The Category 4 storm pummelled the island two weeks ago, causing extensive damage to properties and infrastructure, especially in the southwestern section of the island.
And with hurricanes expected to become more intense due to the impact of climate change, Richard Picart, director of strategic project development at the Urban Development Corporation, believes builders must apply improved standards, especially to roofing, to minimise devastation.
Speaking with The Gleaner, Picart said that an upgraded design standard should take into account an optimal roof angle of 30 degrees for wind resistance and water runoff. Very flat roofs, he noted, are prone to uplift, while very steep roofs are subjected to increased wind force and structural stress.
When it comes to spans – the distance across the roof and measured to the outer edges of the wall plates – Picart advised that it is best to have multiple roofs with smaller spans instead of one large roof with no contingency.
“If there is a failure, all is lost. Typically, when building a large span roof, the roof angle is flattened because you would end up with a way taller ridge and use way more material,” he said.
It is also crucial to ensure that roofs are adequately anchored to prevent lifting.
Hurricane straps could be useful in ensuring they remain in place.
Additionally, Picart noted that wall plates could be displaced if roof anchors are insufficient or if J-bolts are not properly distributed.
Picart emphasised that when designing for functionality, shorter overhangs help reduce wind uplift. He also noted that incorporating boxed eaves and adding a soffit creates a smooth surface, which reduces friction caused by wind on exposed rafters.
While acknowledging the drawbacks of concrete roofs, such as heat retention in a tropical climate like Jamaica’s, Picart argues that they should not be dismissed entirely. He suggests that incorporating a concrete slab in at least one service area could be a prudent measure, providing a designated panic zone where people can seek shelter if all other options fail during a storm.
UPKEEP KEY
Maintenance is another key thing to consider to ensure roofs can withstand severe weather systems. He advised homeowners to have an expert come in periodically to inspect the roof for weathering, wear, rot, rust and termites.
“By prioritising these design choices and allocating resources effectively, it’s possible to build roofs that can withstand strong winds and heavy rainfall, even on a limited budget,” he said.
David Cuthbert, principal architect at CutWorks Architecture, acknowledged that people are often reluctant to embrace new standards as they believe it will incur more cost, but said this is often not the case.
He argued that even in such an instance, the extra investment would be worth it.
“Where the cost is coming in ... , unfortunately, it’s now the cost to repair it. Old people always tell you, ‘Do it good now or it’s going to cost you a fortune later’,” he said.
In his evaluation of the damage in southern St Elizabeth, which bore the brunt of the hurricane, Cuthbert observed that the buildings that remained intact were generally more modest, while the more elaborate structures sustained significant damage.
He argued that a lack of knowledge, rather than cost, is a greater obstacle to people rebuilding with these improved standards.
The experienced architect believes it will take collaboration among the municipalities, training institutes, and professionals like himself, who are willing to provide guidance and share their expertise, to enable a culture shift towards more resilient structures.
“Collectively, we need to upgrade our standards, much like we learnt lessons from Gilbert, ... we’re close to 40 years since Gilbert and again we’re now having to see what are the other lessons that we have to learn and what are the other things that we need to put forward,” he said.
He noted that there were standards implemented after Hurricane Gilbert, a Category 4 system that wrought havoc in Jamaica in 1988, that warrant revisiting.
Although he stated that there is a building code, he stressed that presenting this information in a simplified format will make it easier for people to digest and abide by.
Jamaica’s new building codes will require that buildings are constructed to withstand Category 5 hurricanes – the fiercest storms on the scale.
“It might be helpful that we take some of those things and [create] diagrams that the layperson can read and understand and can implement the things that are there, and that become part of what we as professionals can begin to offer,” Cuthbert said.
Building resilient roofs
(tips by Richard Picart)
1. Optimal Roof Angle
• 30 degrees is optimal for wind resistance and water runoff.
• Very flat roofs (less than 20 degrees) prone to uplift
• Very steep roofs (over 35 degrees) subject to increased wind force and structural stress
2. Roof spans
• Consider having multiple roofs with smaller spans instead of one large roof with no contingency.
3. Roof lifting and wall plate failure
• Roofs may lift off, though intact, due to inadequate anchoring or anchor weakness
• Wall plates may be pulled through inadequate/alternate roof anchors or inadequate distribution of J-bolts
4. Rafter and batten spacing
• Avoid large spacing with undersized rafters and battens that compromise structural integrity. Depending on the design, 18-24” (450-600mm) rafter spacing should be used and no rafter less than 2x6” (50x150mm)
• Inadequate fixing, hurricane straps, or screwing instead of nailing can increase resistance to wind loading
5. Sarking and undersupport
• Absence of sarking (plywood or tongue-and-groove boards) reduces structural rigidity
• Sarking provides additional support, allows for increased fixings, helps to reduce fluttering vibrations in the metal sheets arising from gusts and creates an additional membrane so if sheets are dislodged your living space is still not fully open to the elements.
6. Ridge and end caps
• Flimsy ridge and end caps comprise the first line of defence against wind and water intrusion
• Thicker gauge capping and reduced screw spacing is recommended for improved durability
7. Zinc sheeting and wall plates
• Thin zinc sheeting and large rafter/batten spacing increase vulnerability to wind and rain
• Increase screwing/fixing points of sheeting at eaves, especially when using thinner gauge sheeting, to save construction costs
• Wooden wall plates require regular inspection (every 10 years) to prevent moisture-related deterioration or termite attack
8. Overhangs and design functionality
• Shorter overhangs reduce wind uplift and boxed eaves, adding a soffit, create a smooth surface, thereby lessens friction from wind on exposed rafters
9. Use slab
• Use slab in at least one service area to serve as a panic zone. If all else fails in a storm, there is a place to shelter.
10. Maintenance
• Maintenance is important. Have someone come in periodically to inspect your roof for weathering, wear, rot, rust, and termites.