The Functioning of Concrete Roofs

Tornadoes and hurricanes have the potential to cause massive destruction, with their high-speed winds tearing through towns and businesses, and relentless rainfall soaking everything. Amid the storm's debris and destroyed buildings, you’re bound to find homes with their roofs completely torn off. Hurricanes often damage thousands of roofs, which raises the question: if the storms aren’t getting any weaker, can we at least strengthen our roofs?

Roofs are one of the oldest innovations in human history. At some point, humans decided to upgrade from caves and tree cover, and since then, we’ve continued to evolve our housing designs. Roofing technologies have advanced for millennia, from primitive thatched roofs to modern steel and glass domes. Despite all these advances, the fundamental principles of shelter have remained close to the basic designs of trees and caves. Stone and wood have remained essential building materials, and even methods of waterproofing continue to reflect these ancient roots of sheltering against the elements.

There are two main ways to prevent water from entering a building: you can make the roof a solid, impermeable surface (as in a solid roof or a membrane-coated barrier) or cover it with multiple overlapping, waterproof tiles or shingles that guide water away from the gaps. In both cases, you’re effectively using either a solid shield or a series of armored scales to protect against rain.

For centuries, humans have built vaulted stone ceilings, but the high costs of such architecture have made it unattainable for most residential homes. Instead, we've lived beneath flat and sloped wooden roofs, sealed with tar, vegetation, and various types of tiles and shingles to protect us from the elements.

Thanks to modern concrete technology, homeowners now have the chance to reinforce their roofs with stone while still maintaining traditional roofing styles. In this article, we’ll explore how concrete roofs and concrete roofing tiles have enhanced both flat and sloped roofing designs.

Building a Concrete Roof

When thinking about the possibility of a concrete roof to shield against storm winds, it’s hard not to recall "The Three Little Pigs." This classic fairytale narrates the adventures of three pig homeowners trying to protect themselves from a wolf with hurricane-force breath. While the straw and wooden houses fall to the wolf’s huffing, the brick house remains standing strong.

More and more builders are following the example of the third pig, using concrete in larger quantities for home construction. While wood may endure under normal conditions, it can quickly fail under the strain of added weight or the forces of strong winds—whether from a wolf or other sources.

A concrete roof is precisely what it sounds like: a sturdy slab of concrete placed atop your home. While the exact thickness can vary, most concrete roofs are several inches thick. For instance, Hurricane Proof Systems in Florida offers a 7-inch (18-centimeter) concrete slab in three layers.

To install a concrete roof, a crew first constructs a framework for the roof. These frames may consist of removable concrete forms or stay-in-place insulating concrete forms, which are integrated into the finished roof. Next, a concrete mixture is poured into the frame, spread evenly, and reinforced with steel bars to act as a skeleton for the concrete as it hardens. Flat roofs are the simplest to create using concrete, but sloped roofs are also achievable, though they require more engineering and design work. Concrete roofs can be finished with tiles or shingles to match any style of home.

A concrete roof demands more structural support than a wooden one. Due to its weight, the outer walls must be strong enough to hold up the heavy slab. Interior support beams can assist, but the ideal scenario is when the concrete walls, floors, and roof form a cohesive shell. Adding a concrete roof to a wooden-framed house requires significant structural modifications. If not properly supported, the concrete roof could collapse under additional stresses such as earthquakes or snow accumulation. A solid concrete structure, however, moves less under stress and is known to withstand category 5 hurricane winds of over 155 miles per hour (249 kilometers per hour) [source: Shepard].

Concrete roofs also reduce the risk of damage from fire, termites, fungi, and water. While floodwaters can warp or lift a wooden home, a well-built concrete home will remain stable. This makes the structure more likely to survive in the worst-case scenario. In many regions, concrete roof construction can help buildings bypass certain codes and may also lower insurance premiums.

The final cost of a concrete roof for a home is typically high, often two to four times more expensive than a traditional wooden roof [source: Vanderwerf]. However, it's possible to construct a more affordable concrete roof. In the hurricane-prone Caribbean islands and parts of the developing world, simple concrete roofs are common. These homes often consist of small cinderblock structures with steel beams and blocks, all covered in a layer of concrete.

There are multiple ways to incorporate concrete protection into your roof. On the following page, we’ll explore concrete roofing tiles.

Concrete Roofing Tiles

Even if a large concrete roof isn't a practical option for your home, you can still add some stonelike durability. Instead of using asphalt shingles or clay tiles, some homeowners opt for tiles made from concrete to enhance their roof's resilience.

Concrete tiles were first created in the 1840s by Adolph Kroher, a German cement manufacturer who invented a machine to press out the tiles. This technique quickly gained popularity in Bavaria, and many roofs installed during Kroher’s era remain intact and functional to this day.

Though concrete tiles don't offer the same solid strength as a full concrete roof, they do provide protection against class 3 hail and winds up to 125 miles per hour (201 kilometers per hour) [source: Portland Cement Association]. Unlike shingles made from petroleum, concrete tiles are non-flammable.

Concrete roofing tiles are typically more expensive than some other tile and shingle options, but they tend to last longer. Advances in modern concrete mixing have also enabled tiles to be made in a variety of styles and colors. Rather than looking like dull gray slabs, concrete tiles can even resemble fine ceramic materials.

Even though concrete tiles are durable, they still require maintenance and may need to be replaced over time. Harsh weather, earthquakes, or falling debris can cause the tiles to crack or become dislodged. Over time, moss and algae may also grow on the tiles, requiring pressure washing or chemical treatments to remove them.