TPO: Fully Adhered or Mechanically Fasten?

Generally, roofs are fixed to buildings in one of these two most popular ways: fully adhered or mechanically fastened. Roofs that are set through either one of those methods rest on top of an insulation layer that sits between a metal deck and the roof, which is attached to the structure below it. It’s important to know this tidbit; failing to match the construction of your roof with the actual needs of it may mean you’re spending money on something you have no use for.

In today’s post, we’ll discuss TPO roofs and which method is best to install it. We’ll also tackle TPO roof repair, maintenance, and other necessary information you need to know to have a lasting, durable roof.

FA or MF?

TPO (Thermoplastic Polyolefin) is a roofing membrane made of single-ply reflective. It consists of ethylene-propylene rubber and polypropylene that are polymerized together. While both roof installation methods (mechanically fastened and fully adhered) are completely warrantied, the subject of which one is better for TPO roof often comes up among roofers. We’ll take a look at the pros and cons of each method, and see which one is better for TPO roofs.

We’ll give you an overview of MF and FA using the standard components of assembling roofs, which are membrane and insulation. Remember that typical assemblies also incorporate other factors such as substrate board or fire rating, vapor barrier, and a coverboard or protection from traffic or hail.

Mechanically Fastened (MF)

Mechanically Fastened is more commonly practiced than the Fully Adhered method. It’s also the cheaper of the two, which is most likely what contributes to its popularity. A standard MF assembly often incorporates multiple layers of a 4’x8’ rigid board insulation. The base layer is installed loosely, while the top layer is secured with screws and plates that are inserted through the two layers of insulation all the way into the deck.

Screws and plates are used to fasten the bottom sheet mechanically. The fasteners are concealed with hot air welded below them, stopping the next layer from overlapping. The hot air that’s welded makes a solid layer that is tightly sealed. Many contractors prefer this method and guarantee its effectivity, praising its affordability and easy installation.

Even though the MF assembly is more economical than FA, it does come with its own issues. For example, when there are strong winds, the uplift may lead to the membrane roofing system fluttering or even billowing – depending on how strong the winds are. This can cause problems since conditioned interior air coming from below is pulled upwards the roofing installation, which can lead to condensation, specifically in the colder months. This likelihood is often exaggerated if the air-vapor barrier is not part of the installation.

Another potential issue that comes with the MF assembly is leak tracing. If the membrane is damaged, the water will flow between the membrane, insulation, and deck before you see it on the floors. These leaks are typically more challenging to locate, which can cause more costly TPO roof repair.

Fully Adhered (FA)

Similar to the MF assembly, a standard FA installation includes many layers of the rigid board that serves as insulation. The bottom layer is installed loosely, and the top layer is secured with screws and plates.

FA insulation is assembled over concrete decks. They are installed using low rise foam adhesive as opposed to mechanical fasteners; with LRF, you wouldn’t have to pre-drill the concrete before securing the roof.

Once the insulation is completed, the roof membrane is laid out, coinciding at the seam and wholly attached to the insulation using a bonding adhesive that is solvent based. Once the membrane adheres, hot air weld is used at the seams to put a solid sheet all over the roof completely.

Even though the FA assembly method is more expensive and takes a longer time to install than MF, there are claims that the benefits are worth the cost. FA roofing systems are more visually pleasing since there are no wrinkles; it’s also more resistant to strong winds, so there wouldn’t be a significant need for a TPO roof repair.