Installing TPO over a Metal Roof:  Increasing Energy Efficiency

We have recently completed a metal reroof project. As with most older metal buildings, the metal roof panels had expanded and contracted over time, causing the roof to leak. Our goal was to provide a water tight roofing system, by installing a TPO roofing system, and increase the R-value of the roof by installing a EPS flute filler and iso roof insulation.

Due to the configuration of the metal roof panels it is first necessary to install an EPS (expanded polystyrene) insulation in-between the metal ribs of the roof panels to create a smooth surface to support the 1 1/2" iso (polyisocyanurate) roof insulation over which the 60mil white TPO roofing membrane is installed.

The EPS has an approximate R-value of 4 and the iso has an R-value of 9, giving the owners an added R-value of 13.

With the reflective value of the white TPO membrane, the building will be much cooler in the summertime. The approximate 2 1/2" of insulation will add substantial warmth in the wintertime along with stiffness and strength to the roof substrate. Nailers are installed at the perimeter of the roof to accommodate the thickness of the added roof insulation to which a TPO clad-metal drip edge is installed.

Due to the lack of fastener pull-out strength in metal roof panels, the roofing system must be fastened into the purlins that support the metal roof panels to achieve the necessary wind uplift requirements. Special purlin fasteners are used for this purpose.

This 60-mil Mulehide TPO roofing system is of superior strength and durability. As mentioned before, the color of this system will be an important future money saver. Walmart, for example, will use white single-ply roofing systems on all of their stores south of Salt Lake City, UT, whereas their Boise store has a black roofing membrane because they have more heating days than cooling days. Your location will have a great effect on which materials will help your building to be energy efficient.