Roofing materials used for flat roofs

Flat-Roof

What is the best roofing material for a flat roof? This is a question that pops into the minds of many homebuilders looking to undertake their first roofing project.

Flat roofs, which are loved for their flexibility in terms of designs, are not flat per se but have a slight pitch of between 1/4″ to 1/2″ per foot – enough to drain water if fitted properly.

However, due to the widespread notion that flat roofs are a recipe for leaks and endless repairs, many builders hesitate to install flat roofs on their houses.

This should not scare you since the marketplace has enough roofing materials designed to increase the dependability of flat roofing systems.

Here are various types of roofing materials for flat roofs:

Built-up roof (BUR) membranes

Commonly known as BUR, built-up roof membranes have been in use for more than a century. These materials are mostly made up of several alternating layers of bitumen and reinforcing fabrics (roofing felts, or ply sheets) that form a roof membrane.

The bitumen mostly used in built-up roof systems is asphalt, cold-applied adhesive, or coal tar.

The hot-applied tar mixes with the bitumen saturated reinforcing fabric to create a monolithic roof membrane. The roofing felt is applied in overlapping layers until the assembly is two or four plies thick.

BUR systems are considered to be totally adhered if applied directly to roof decks or insulation.

Surfacings for built-up roofs include mineral surfaced cap sheets, aggregate, hot asphalt mopped over the entire surface, elastomeric coatings, aluminium coatings, or glass-fibre.

Modified bitumen roofing

Modified bitumen roofing is asphalt-based sheet roofing that was developed in Europe in mid 1960s as a replacement for the built-up roofing. The material is designed for buildings with low-slope roof structures.

It is designed using the built-up roofing technology, with manufacturers adding polymer reinforced roof wear layers or cap sheets to give builders a wider array of options compared to the BUR systems.

Modified bitumen roofing may be fitted using the torch-application method, or “hot-mopped” like built-up roofing, or installed with “cold-process” adhesives.

Thanks to recent innovation, the material comes with a self-adhering sheet. Using polymers to modify the bottom of the modified bitumen sheet, manufacturers deliver rolls that are fitted with release papers.

Once the installer removes the release paper, the sheet rolls out and adheres itself to the substrate – thereby eliminating the risks that come with the usage of hot asphalt, and torches.

In addition to the ease of application, the modified bitumen sheet is free of VOC (volatile organic chemicals) gases during and after application.

Single-layer membrane roofing

Technically known as plastomeric or elastomeric roof membrane, single-layer roof is the latest roofing technology and the material of choice for commercial buildings – most of which are fitted with flat roofs.

As the name suggests, single-layer roofs (also branded as single-ply roofs) are designed to be installed in one layer. They are generally categorised into two clusters: ​ thermoplastics and thermosets.

Thermoplastic membranes are generally designed to include a reinforcement layer, normally polyester or fiberglass that offers supplementary strength and stability. They are ideal for large roof areas since their manufacturing size is optimised for reducing or minimizing seams.

On the other hand, thermoset membranes are made from synthetic rubber polymers, and the most frequently used polymers are EPDM, CSPE, and Neoprene.​​​​

Both thermoplastics and thermosets membranes are very flexible and resistant to ultraviolet radiation.

Single-layer membrane roofs are installed as thin sheets – 30mm to 60mm – thick and are applied to the roof in a single layer – just as the name suggests. These roofs are flexible and can withstand temperature changes better than built-up roofs.

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