Types of Flat Roofing and Factors Affecting its Deterioration

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If you want a new flat roof but you’re having trouble deciding what kind to get, our roofing experts at Kauffman Roofing in Jamesport can explain the available types of flat roofing and factors affecting its deterioration, so you can find the one that best fits your needs.

A U.S. General Services Administration article lays out information about the two types of flat roofs, the built-up roof (BUR) membrane and the elastomeric/plastomeric roof membrane. Let’s take a look at both types.

Built-Up Roof Membrane (BUR)

The built-up roof membrane is assembled in place, using multiple layers of asphalt-impregnated felt bedded in bitumen. Hot asphalt or coal-tar is applied, allowing it to merge with the saturant bitumens in the felt and form a single-piece membrane.

The felt is laminated in overlapping layers which helps form a membrane that is two to four plies thick. A layer of aggregate is then applied to protect the membrane from sunlight and deterioration. The layer of aggregate may be crushed stone or other mineral granules embedded in the surface ply.

Elastomeric/Plastomeric Roof Membrane

This roof membrane consists of a single layer of sheet material applied to the roof. It requires less on-site labor than built-up roofing and is usually more elastic, which means it’s also less prone to ripping and cracking.

The elastomeric/plastomeric membrane may be fixed to the roof by adhesive, by the weight of a gravel ballast, by fasteners buried in the seams between sheets, or by using mechanical fasteners that don’t penetrate the roof’s membrane.

Elastomeric/plastomeric roof membrane comes in various types, including: neoprene, EPDM, PVC, chlorinated polyethylene and chlorosulfonated polyethylene sheets, polymer-modified bitumens, and fluid-applied roof membrane. Let’s explain those a bit further:

1.  Neoprene (polychloroprene) - A neoprene membrane is a high-performance synthetic rubber compound that is applied in sheets and joined together at the seams with an adhesive. These sheets range from 0.030 to 0.120 inches thick and should be adhered to the roof deck with aggregate ballast to prevent wind uplift. This membrane is susceptible to damage by the sun’s ultraviolet light, so it is usually coated with a protective layer of chlorosulfonated polyethylene. It’s also susceptible to aromatic solvents and strong oxidizing chemicals.

2.  EPDM (ethylene propylene diene monomer) - The most widely used material for single-ply roof membranes, EPDM is a synthetic rubber that is manufactured in sheets ranging from 0.030 to 0.060 inches thick. These sheets are joined at the seams with an adhesive. It may be fully or partially adhered, or used in a protected membrane roof. As for downsides, EPDM  is vulnerable to petroleum products and plastic roofing cement.

3.  PVC (polyvinyl chloride) - The PVC membrane is a thermoplastic compound best known as vinyl. It may be fully or partially adhered, or used as a protected membrane. PVC is a relatively low-cost material and for this type of roofing application, it comes in sheets ranging from 0.032 to 0.060 inches thick. These sheets are joined at the seams either by solvent welding or hot air welding. PVC is most vulnerable to ultraviolet radiation, petroleum products, and coal tar.

4.  Chlorinated Polyethylene and Chlorosulfonated Polyethylene Sheets - When aggregate ballasting isn’t an option due to a sharply sloped roof or style preferences,  chlorinated polyethylene and chlorosulfonated polyethylene sheets are a great alternative. While not compatible with PVC and vulnerable to petroleum products, this type of membrane is highly resistant to ultraviolet deterioration and comes in light, heat-reflective colors.

5.  Polymer-Modified Bitumens - The polymer-modified bitumens are formed into composite sheets. When installed, some sheets are put down loosely while others are adhered to the roof deck or insulation. Like other types of elastomeric/plastomeric roof membranes, this material is vulnerable to petroleum products. It’s also susceptible to hydro-carbons and certain chemicals.

6.  Fluid-Applied Roof Membrane - For more complex jobs and roof shapes, like domes or vaults, a fluid-applied roof membrane is an effective, yet less traditional option. Using a roller or spray gun, it is applied in several coats and forms a rubbery membrane when it cures.

Factors Contributing to Flat Roof Deterioration

When choosing a flat roof, it’s important to look at factors such as sun, water, wind, temperature changes, settlement, and outside interference. Depending on your climate, these factors might be more or less important considerations. At Kauffman Roofing in Jamesport, we can certainly point you in the right direction when it comes to types of flat roofing and factors affecting its deterioration.

Sun

The hot sun beating down on a roof causes the chemical components of tar or asphalt to evaporate. The asphalt oxidizes and then becomes brittle. And the roofing mat slowly loses its elasticity. If the surface coating becomes checked and flakes off, the felt underneath will be exposed.

Water

Water is tough to combat and can find its way into a dry roof through any cracks and trigger a leak. This moisture can turn to ice in freezing temperatures and can cause the roof to tear or heave.

Wind

A strong wind can push rain into defective joints in the mat or parapet and can cause the roof to tear at loose seams. This can cause the roof structure to sway.

Temperature Changes

Expansion and contraction strain the roof structure, the deck and the walls, as well as the flashings. These strains can cause the roofing mat to tear and mortar in coping joints to crack, which allows water to get in.

Settlement

As walls settle, extra strains may be exerted on flashings or the roof may settle below the level of the drain pipe. This will either cause a backup of flood water, or a leak through the crack around the drain.

Outside Interference

Roof mats can’t handle signs and electric wires, or foot traffic. Anchorage planks are spiked or lagged to the deck, piercing both the mat and the deck, causing serious damage. Coatings and ballast coverings can give some protection from pollutants, acids, and saturated animal fats, which can damage the roofing membrane.

There are a lot of things to consider when deciding on what kind of flat roof you want.  Our roofing experts at Kauffman Roofing in Jamesport understand the types of flat roofing and factors affecting its deterioration, so we can help you choose the right one. Feel free to call or contact us today for more information and to get started on your roof project.

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