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Wind and Hail Effects on Flat Roofs

Commercial Flat Roof Repair May be Needed

Commercial Flat Roofs are actually built so they provide about 1/8 to 1/4 inch per foot of water drainage.  Flat roofing systems are built differently than steep-slope roofs and are usually watertight rather than water-shedding systems.

The most commonly constructed commercial roof coverings are single-ply membranes, multi-ply asphalt systems, and metal panels. Single-ply membranes include TPO (thermoplastic polyolefin), PVC (polyvinyl chloride), and EPDM (ethylene propylene diene monomer).  TPO and PVC are both thermoplastic membranes, usually white, while EPDM is constructed of a more traditional black rubber material.  Asphalt-based roof systems, including modified bitumen and built-up (BU) asphalt roofing, are the most commonly used flat roof systems on smaller commercial buildings.

Damage From High Wind

High winds from a storm affect all of the low-slope roof systems in the same way. Wind pressure from uplift are a function of the speed of the wind and how high above ground the roof is. The uplifting pressure that results is strongest at the corners and along the perimeter edges of a building. Wind damage is usually found first at the edges of the roof.  Once the flat roof system is damaged, a larger, more catastrophic failure can happen. Roof coverings that have lifted and peeled up from the edges is the usual sign of wind damage.

When a single-ply roof systems is damaged by wind, you’ll find loose and wrinkled materials at the surface, while metal panels can be kinked and folded sharply in sections.  When high winds hit a flat roof system, you’ll usually find other collateral damage. Things like satellite dishes, antennas, and other roof-top items can be blown off the roof or relocated before wind reaches a speed that will damage a solid roof covering.

Damage form Hail

Wind damage is similar for most roof coverings, but hail damage to commercial roofing is depends on the materials that have been used. The size of hailstones that will cause damage to different kinds of commercial roofing can vary from ½ inch to over 2 ½ inches in diameter.

Denting is what usually happens to metal roofing panels. While it doesn’t look great, dents from hail don’t usually affect the watertightness of the roof panels.  If the finish on the metal panel gets cracked or chipped, it can rust, which would shorten its lifespan. But, unless the panel is split or fractured, the dents are more cosmetic than anything.

Commercial Flat Roof Repair ContractorsPVC and TPO can withstand hail up to 1 ¾ inches in diameter if the roof system is in good shape.  As they get older, plastics in the material can leach out of the membrane, which leaves it more prone to be damaged.  In some cases, hail as small as ½ inch in diameter can fractures a substandard thermoplastic roof membrane. When hail damages a membrane, cracks or concentric semicircle patterns will show. To improve resistance to hail impact, you can have rigid cover boards installed below the membrane.

EPDM systems are more flexible than most thermoplastic materials.  A solid EPDM roof covering can withstand impact by hail thats as large as 2 ½ inches. When EPDM roofing systems are damaged, cracks can happen similar to thermoplastic membranes. Hail can puncture the EPDM if the substrate underneath is soft or malleable.  Most single-ply membranes are supported firmly in the field of the roof, but could be stretched over the surface around the perimeter or along any rooftop equipment.  These areas are easily damaged by incoming hail and will usually take on damage before the central roof areas.

Modified bitumen and built-up asphalt roof (BUR) systems are more resistant to hail based on their installation materials.  Built-up asphalt roof systems commonly use gravel on their surfaces. The gravel protects the underlying roof membrane from human traffic, ultraviolet (UV) light exposure, and hail.  BUR systems can also be installed in a smooth-surfaced way, but they are more vulnerable and will be damaged from smaller hailstones as small as 1 ½ inch in diameter.

Modified bitumen systems are usually installed in two plies – a base sheet and a cap sheet. The material is made from asphalt blended with rubber or plastics, providing a more flexible and longer lasting roof covering.  The longest lasting modified bitumen roofing systems have granules on their surface, kind of like an asphalt shingle.  Modified bitumen roof coverings that are in good shape can withstand the impact from hail thats 1 ½ inches or larger. Hail will spread the granules or break the underlying reinforcement of the system. When blisters or ridges are found in BUR or modified bitumen membranes, the affected area will be more prone to be damaged from incoming hail.

Trusted Commercial Flat Roof Repair Contractors

As with most building materials, the age and condition of the flat commercial roof coverings will have a big impact on their ability to withstand wind and hail.  Properly installed roof membranes will withstand severe wind, but an improperly installed membrane can be blown from the roof during relatively moderate wind gusts.  In that same vein, most commercial roof coverings withstand hail impact well.  As the materials they’re constructed of age and break down they quickly become more prone to damage.

Armadillo Roofing & Exteriors, (512) 333-7663, has been providing commercial flat roof repair and commercial flat roof installation services to Austin, Texas and the surrounding communities for over 15 years. When you need an experienced, professional commercial roofing company to assess your commercial flat roof, give us a call.

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