Many commercial buildings and businesses have flat roofs. A roof of this type is cost-effective and provides significant protection for a long time. A roof membrane’s material can, however, have a significant impact on how long it will last.
You should always ask prospective customers if they are researching other competing products when making a presentation about metal-over-metal retrofit roofs. They usually get pricing based on TPO roofing overlays.
When all other factors are equal, you will lose the price battle, typically by 20% to 25%. Compared to other things, that’s not much, but if your customers believe the products are the same, you are in a tough spot. However, the truth is that the products are absolutely not equal in any way!
TPO Roofing
Thermoplastic polyolefin is probably the most affordable membrane option, and it is a green option, which means it is better for the environment than other options.
TPO roof membranes can last up to 20 years. Generally, this type of roof is applied by adhering or mechanically attaching the materials. You can leave this membrane exposed for its entire life.
These roofing systems are environmentally friendly, as well as resistant to chemical, ultraviolet, and ozone exposure.
A Few very Important Differences
Lifecycle of the product – The Metal Construction Association conducted an independent study. It’s estimated that zinc aluminum-coated standing seam roofs will have a minimum service life of 60 years, while a study on painted PVDF roofs by the National Coil Coaters Association (NCCA) indicates that a PVDF roof will have a minimum service life of 40 years.
Mechanically attached TPO has an expected service life of 18-24 years. You can expect your metal-over-metal roof proposal to last almost three times as long as the nearest competitor for a 20%-25% higher investment.
Amount of wind load – TPO promoters tout their capability to deal with the higher wind loads. Depending on the specific assemblies, yes, the wind uplift requirements of the building code can be met.
Moreover, contractors often design assemblies based on attaching to the existing “roof deck”. Steel roofs do not qualify as decking. Decking consists of heavy-gauge, heavily corrugated, 22 gauge metal panels.
The roof panels of structural metal buildings are typically mildly corrugated, 26 or 24 gauge panels, and have completely different structural properties than structural steel decking.
Loads of snow – It can be tough for TPOs in snowy areas. In new building codes, the minimum ground snow load has been raised and the building must now be checked for “drift loading” or “unbalanced loading” caused by wind piled snow on the roof in an uneven manner.
TPO systems typically include foam insulation and a sheet membrane that is 40-60 mil thick. They rely on the old, often deteriorating metal roof for support, as none of them are structural members.
The roof’s geometry – The metal building design is characterized by one constant. Water cannot remain on a metal roof. There are thin lightweight Zee’s used in metal building purlins, allowing them to deflect more than the typical conventional roof constructed with heavy bar joists and metal decking.
Buildings with metal roof panels can accomplish this because the ribs spaced between 12″ and 24″ direct the water from the ridge to the eaves rapidly and evenly; the water does not sit on the roof.
Contact us today to discuss your roofing project!
