Simple-Ply membrane vs. built-up roofing: which is best for-commercial roofs?

Posted September 8th, 2019 in Commercial Roofing

The following article explores the differences between single-ply membrane and built-uproofing systems to provide people all necessary information they need in choosing rooffor their facility.

INSTALLATION

Single-Ply Membrane Roofing

Initiation of installation process is similar between EPDM and TPO single-ply membraneroofing systems.
After the existing substrate is prepared, either by removing or cleaning existing roof,insulation is installed. There are a few kinds of insulation options that facilitymanager/owner can choose from Extruded Polystyrene (XPS), Expanded Polystyrene(EPS), Polyisocyanurate (Polyiso). Insulation layers are cover board. There are threeways to attach membrane to cover board: ballasted, mechanically fastened or with anadhesive.
Basic difference between EPDM and TPO comes when it is time to adhere membraneseams together. EPDM is joined together with seam tape. TPO uses a hot-air gun to meltdown the membrane at the seams and fuse them together.

Built-Up Roofing
The first layer can be adhered directly to roof substrate. If needed, a base sheet can befastened to roof to create a flat and safe work space. A built-up roofing system is installedby alternating layers of reinforced fabric and bitumen. Property managers can selectthree, four or five ply roofs to meet their budgets and needs.
Last layer is rock or stone, this layer protects the underlying layers from extreme heat orcold, UV rays, and wind damage. A layer of gravel can be added to be more aestheticallyappealing.

BASICS

Single-Ply Membrane Roofing
Single-Ply Membranes are sheets of synthetics and rubber that can be chemically adheredto ballasted or insulation creating a layer of protection on commercial facility.There are two main kinds of single-ply membrane commercial roofing: EthylenePropylene Diene Terpolymer (EPDM) and Thermoplastic Polyolefin (TPO). They differin their chemical makeup, how they are installed and the energy efficiency.

Built-Up Roofing
For over 100 years, Built-Up Roofing Systems have been in use in the U.S. These roofsare commonly known as “tar and gravel” roofs. Built-up systems are installed byalternating plies of tar or asphalt and supporting fabrics directly onto the roof. People canchoose the number of layers (or plies) that are installed. Final pile of a built-up roofing
system consists of gravel or stone.

COST

Single-Ply Membrane Roofing
For a common 20,000 sq. foot commercial roof, it will normally cost between$3.50 to$6.50 per square footfor TPO and$3.50 to $7.50 per square footfor EPDM, includinglabor warranty and materials.

Built-Up Roofing
For a common commercial roof, it will generally cost between per $5.50 – $8.50 squarefootin labor and materials to install a typical built-up roofing system. This cost range canchange depending on the materials people choose.

ADVANTAGES

Single-Ply Membrane Roofing
A commercial single-ply membrane roof can last 30 years if properly installed andmaintained. There are a few other advantages of single-ply membrane roofing systems:

  • Proven Track Record– For over six decades, EPDM roofing has been used forcommercial flat roofing. This time period on the market has allowed various fieldand laboratory studies to be performed and tracked.
  • Class A Fire-Rated –EPDM and TPO membranes can obtain UnderwritersLaboratories (UL) Class A fire resistance listings by adding fire retardantchemicals during the manufacturing process.
  • Reflective or Retentive –TPO is usually white and highly reflective. EPDM isoften known as “Black Roofs,” because of the natural dark color of themembrane.

Built-Up Roofing
A commercial built-up roof can last 40 years if properly installed and maintained. Thereare quite a few other advantages of built-up roofing systems:

  • Seamless and Waterproof– Continuous solid surface does not need seams orjoints, eliminating the most vulnerable area for leaking.
  • Reflects UV Rays– offers ultra-violet protection.
  • Low- maintenance– Minimal upkeep needed after installation.

DISADVANTAGES

Single-Ply Membrane Roofing
While advantages of a single-ply membrane roofing system outweigh its disadvantages,there are a few things people should keep in mind. Here are disadvantages of single-plymembrane roofing systems:

  • Seams –Although these seams are sealed either with melting adhesives ormechanically, they are still areas that are more vulnerable to leaks than otherroofing systems.
  • UV Rays –UV rays can degrade the adhesives quickly over time.

Built-Up Roofing
Built-up roofing systems have been around for decades; their longevity can only beobtained if the roof is maintained properly. Here are other disadvantages of built-uproofing systems:

  • Time– Slower installation time frame
  • Safety– Hazardous fumes and vapors when installing it
  • Costs– Installation costs
  • UV Rays– Without the gravel top layer, UV rays can break down the membranequickly

Both Single-Ply Membrane and Built-Up Roofing Systems have their pros and cons.Selecting which one is best comes down to a customer-by-customer basis.

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