IRMA stands for Insulated Roof Membrane Assembly.
Irma roof systems are typically used on commercial and large scale residential structures with flat roofs. They have the insulation ontop of the roof membrane, not below it. The insulation is weighted down by ballast, ie: gravel and/or paving stones.
Since the added weight of the gravel is so heavy it is really not used in wood frame construction, especially when you can insulate between the rafters, or in the ceiling.
The Pro's of the system are that the roof membrane is protected from ultra violet degradation by the insulation and ballast, and its also is protected from thermal shock by the insulation. The roof is also protected from pedestrian traffic by the ballast. This supposedly extends the life of the roof system. These roofs can be installed with single ply as well multiple ply roofing membranes.
In our experience these roofs typically do not have a greater usefull life than a more tradition flat roof system, usually from poor installation details. Since the membrane is covered, it is very dificult to track down and repair leaks. Because of the weight of the ballast the roof structure has to be stronger and therefore more expensive.
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.The IRMA (insulated roof membrane assembly) is the ideal <a href="http://www.wildwoodroof.com/roofing-services-st-louis/">roof system</a> for USA over other green roof systems because it is the only system able to cope with extreme climatic conditions in flat, concrete, and metal deck roof construction.