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A cutaway view of an installed IRMA system.


Inverted Roof Membrane Assembly

An IRMA system is the most common type of roof used on modern high-rises today. IRMA can be referred to as an Insulated Roof Membrane Assembly. Some references may use the term Protected Membrane Roof or (PMR) system. More generically, others may categorize an IRMA, or PMR system as "Built-up-Roof" system, or (BUR).

Roofing Systems

When selecting a roof system, the bottom line is often top of mind particularly in today’s challenging economic environment. Consider these figures:

  • 16 years – Average life of a roof system in North America
  • 50 billion pounds (annually) - 5 percent of waste in registered landfills in the United States comes from the roofing industry
  • 39 years – Depreciation period for a commercial roof in the United States [1]

Description of Layers

Layers composing an IRMA system.

An IRMA system is typically used on commercial and large scale residential structures with flat roofs. It consists of many layers.

The 'waterproofing' membrane is usually adhered directly to the roof structure, typically the concrete roof.

In order to protect the membrane from atmospheric degredation such as sun, wind, and rain, and from foot traffic, the protective moisture resistant insulation layer is laid on top of the membrane outside the structure.

An optional layer of fine mesh may then be laid as a filter for debris. The insulation layer is then held down with a form of ballast, such as gravel wooden decking or paving stones.

Drainage is directed to roof drains from a slight camber, or slope, of the roof created during construction or from a professional installer.

IRMA Lifespan

Michigan State University Campus

One of the many benefits of installing IRMA roofs is their extended lifespan. IRMA roofs are designed to have a minimum 40 year life cycle.

In 1960 Michigan State University (MSU) became among the first to have this technology incorporated into their roofing systems. The IRMA roof has performed flawlessly for 50 years in a climate that sees snow, sun and everything in between.

MSU has since installed the IRMA roof on 160 of their buildings.

Green Roofs

A view of the layers of a garden roof.

An IRMA system is ideally suited for roof gardens and other vegetation. This is becoming a more and more popular roofing application among architects, builders and for condominium owners. Now flat spaces on building tops can become pleasant green spaces for residents who may not have access to parks nearby.

Roof gardens can take many forms. Here are a few examples:


  1. DOW Chemical Company

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