Commercial, Mixed-Use and Strata Roof Maintenance in Vancouver, B.C.

IMRA Or PMRA Roof Membrane: What Is It, Pros, Cons, And More! (Inverted Roof)

IMRA Or PMRA Roof Membrane: What Is It, Pros, Cons, And More! (Inverted Roof)

What comes in front of your eyes when I say the word inverted roof. If it’s an upside-down roof then I’m sure you have never heard about IMRA or PMRA roof membranes.

An inverted roof is a roof that had a waterproofing membrane placed below the insulation layer, reversing the ordinary layering of the roofing system.  

In this article, we will see what are IMRA or PMRA roof membranes and how they play an important role in an inverted roofing system. Along with some pros and cons of this particular roofing system, and some more details about it.

What Do You Mean By IMRA Or PMRA Roof Membrane? 

Unlike a traditional roof where the insulation layer is placed below the waterproofing membrane, an inverted roof is a roofing system where the insulation layer is placed above the waterproofing layer.

In this design, the waterproofing membrane is typically covered by a layer of ballast, such as gravel or pavers, which helps to hold the insulation in place and protect it.

One type of waterproofing membrane used in inverted roofing systems is a PMRA or IMRA roof membrane. PMRA stands for Polymer-Modified Root-Resistant Asphalt, while IMRA stands for Insulated Modified Roofing Asphalt.

These roof membranes are made with a blend of asphalt and synthetic polymers. It provides increased strength, flexibility, and resistance to damage from animals, plant infestations, and other environmental factors.

Overall, an inverted roof system with a PMRA or IMRA roofing membrane can provide excellent protection to a building’s roof and insulation. They ensure that the building remains watertight and energy-efficient for many years.

What Are The Advantages Of IMRA Or PMRA Membrane?


IMRA and PMRA membranes are designed to withstand exposure to the elements, including rain, snow, and ultraviolet light. They also resist punctures, tears, and other damage.

Making them long-lasting and an excellent waterproofing solution for flat and low-sloped roofs.

Compatibility With Existing Systems 

IMRA and PMRA membranes can be integrated with existing systems, making it easier to retrofit them into industrial processes. This saves time, money, and resources that would have been required to replace the entire system.


IMRA and PMRA roofing membranes are available in a range of materials, colors, and thicknesses. This allows for greater customization and flexibility in the roof’s design to suit the building’s specific needs.


IMRA and PMRA roofing systems can contribute to the effort made toward achieving sustainability, by reducing the amount of waste generated during the installation and maintenance of the roof.

These systems typically use limited materials and generate less debris than traditional roofing systems, without compromising on the roof’s durability.

Energy Efficiency 

IMRA and PMRA membranes can also improve the energy efficiency of a building by reducing heat loss and improving the insulation performance of the roof. This can result in lower energy costs and a more comfortable indoor environment.

What Are The Disadvantages Of IMRA Or PMRA Membrane?

While there are many advantages to using IMRA or PMRA roofing membranes, there are also some potential disadvantages to be aware of. Here are a few of the most significant:


One of the main disadvantages of IMRA and PMRA roofing membranes is that they can be more expensive than traditional roofing systems.

This is because of the high-grade materials used, as well as the specialized installation cost.


Another potential disadvantage of IMRA and PMRA roofing membranes is that they can be more difficult to install than traditional roofing systems.

Which means an ordinary roofing contractor may not be able to install it correctly.

IMRA and PMRA require a specific set of skills and expertise to ensure that they are installed properly, which can make the installation process more time-consuming and complex.


While an inverted roof system can be easier to maintain than a traditional roof system, there are still some maintenance requirements to be aware of.

To take care of these requirements it is necessary to conduct regular roofing maintenance.


Another potential disadvantage of IMRA and PMRA roofing membranes is that they can be quite heavy. This is particularly true with IMRA membranes, which are made from modified bitumen making them quite dense.

As a result, these systems may not be suitable for all buildings or structures, particularly those with weight restrictions.

If you wish to install an inverted roof it’s important to make sure your building is structurally sound to handle its weight. If not, measures could be taken to make sure your building is able to support these roofing systems.

Limited Availability

IMRA and PMRA membranes are relatively new technologies, and there are limited manufacturers and suppliers in the market. This can make it challenging to find the right membrane for a particular application or to obtain replacements when necessary.

It can also limit the availability of technical support and resources to help with the installation and maintenance of the membranes.

While there are some potential disadvantages to using IMRA and PMRA roofing membranes, the benefits of these systems often outweigh the drawbacks. By providing a durable, waterproof barrier and extending the lifespan of the insulation, these systems can be a valuable investment for many commercial and industrial buildings.

How To Know Which Is Better For Your Roofing System, IMRA/ PMRA Or Traditional Roof Layering?

To determine which roofing system is better for your building, it is important to consider several factors, such as:


The climate in your area can affect the performance of your roofing system to a large extent. For example, if your building is located in an area with a high risk of water damage, such as a coastal region or a place with high snowfall, an IMRA or PMRA roofing system may be a better option due to its better waterproofing capabilities.

If you live in a dry or a region with low precipitation a traditional roof would be a better alternative.

The Slope Of The Roof

The slope of your roof is an important factor to consider when choosing a roofing system. Traditional roof layering may be more practical and cost-effective for buildings with steeply sloped roofs, while IMRA/PMRA systems are designed for flat or low-sloped roofs.


Last but not the least, we have established above that IMRA/ PMRA roofing membranes could be expensive. So, your budget plays a critical role in picking from traditional roofing systems and IMRA/ PMRA roofing systems.

By considering these factors, you can decide whether IMRA/PMRA or traditional roof layering is better suited for your roofing system.

What Is The Lifespan Of An Inverted Roof?

An inverted roof can last up to 25-30 years with proper care and regular maintenance. It can outlive most flat roofing systems.


We hope with this article we could convey the meaning of an inverted roof with its benefits and shortcomings. If you have any more questions regarding the IMRA or PMRA roofing membrane, feel free to drop your comment in the comment section below.

Also, if you need a roofing professional to take a look at your roof connect with us today!

Leak-Stop is a one-stop destination to meet your roofing-related requirements. We offer roof repair, replacement, maintenance and inspection services all over GVRD (Greater Vancouver Regional District).

We offer a free inspection to first-time clients. Connect with us TODAY at 1 866 777 0084 for immediate assistance!

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