Learn in detail about TPO roof membranes

Typical rowhome layout

This week we are taking a look at a TPO roof membrane that we recently installed on a Capital Hill rowhome. This particular rowhome is similar to many of the residential buildings across the downtown of Washington DC. Rowhomes like this are built side-by-side with shared demising walls. Generally these houses are long rectangular shapes that run from the front area of the property towards the back. There is also generally a rear ell, a notch or cut-out in the footprint of the building that reduces the width of the rearmost part of the building to allow light and fenestration (sunlight and ventilation) into the rearmost part of the building which is otherwise relatively dark.

The picture below shows the rear portion of the roof, you can see there are two HVAC or air conditioning units on top of the roof.  The parapet wall at the rear outside remains bare and uncovered at this area while work is in progress.   One of the HVAC units (smaller) is an AC condenser and the larger unit is a all-in-one packaged AC unit type unit which provides both heat and air conditioning.  This is similar to a split unit, with a condenser on the outside that runs to create cooling or in the summer work runs in heat pump mode in the Winter, but the all-in-one packaged unit includes both systems and also includes the air handler which generally includes an evaporator to create the cool air during the summer months.

TPO systems are slightly different than the majority of other types of single-ply roof membranes. Single-ply membranes are just one layer of overall membrane material.   Generally, this type of material is a fully adhered system glued directly down to a fastened and plated polyisocyanurate recovery board. Recovery boards are required in most types of applications on existing buildings when a new roof system is installed.

TPO Roofs are high reflectivity with low maintenance requirements

Since this type of system is white in color it extremely high reflectivity. Manufacturers usually claim 97% or higher reflectivity which would mean that it’s almost fully reflecting or shielding the building from the heat and thermal impact of solar exposure.  The empirical claims seem like a bit of a stretch, but it is clear that this option is one of the best available for solar reflectivity and energy savings. 

The next picture below shows the exposed portion of the polyisocyanurate underlayment board. This underlayment board is meant to create a more consistent substrate for adhesion of the TPO membrane. Unlike EPDM membranes, TPO membranes are extremely durable.  TPO does cost more than EPDM but it is not only extremely durable, it also has high reflectivity and unlike modified bitumen membranes, TPO requires only low maintenance for the life of the system. Nonetheless, even though manufacturers claim these systems are maintenance free we still recommend annual or seasonal checkups.

Roof boots and terminations

The next picture shows an example of a commercial vent pipe boot near the rear ell or rear termination of the membrane.   This picture was taken during installation.  At completion of the installation of the system the strap clamp will be trimmed to fit the circumference of the pipe and boot.

Near the same location shown in the picture above, the picture below shows a slightly different angle where the gutter will later be installed. The gutter will tie into a downspout and the TPO covered drip edge will overlay the rear termination feeding directly into the gutter.

Maintainance of Roofing Systems

Smart proactive replacement, construction, upkeep and maintenance of low slope roof systems requires an enthusiastic interest and understanding of waterproofing principles and building science.   Here in Washington DC, historic and modern residential and commercial buildings are extremely expensive and the roof and related systems provide the shield that preserves the building. 

We encourage all of our clients, and all readers of this article and to our blog in general, to prioritize the value of quality construction and building maintenance, and develop a relationship with our company.  You can learn a lot more on our blog.  Feel free to check it out.  If you have questions about the roof and related systems of your building in Washington DC, fill out the webform below and drop us a line.  We will be in touch if we can help.