The Importance of a Coating On Some Modified Bitumen Roofs

Why coat modified bitumen roofs?

Today while working on one roof of a row home in Washington DC company took a look at another building between two other roofs that have recently been replaced. The one we’re looking at here is modified bitumen single ply membrane.

What Kind of Coating To Use On Single-Ply Modified Bitumen Membrane

This happens to be a single-ply modified bitumen smooth SBS membrane. This type of membrane is supposed to be coated with an aluminum or high reflectivity paint application after installation. Generally, painting shouldn’t happen at the exact same time as installation because the roof membrane is made from bitumen materials that need to age a bit and then be recleaned paint is applied.

modified bitumen roofs

There are several defects in the original installation, but additionally the coating and ongoing maintenance should have been provided to extend the longevity of this membrane. This type of care and upkeep is actually required by the manufacturer, and for good reason  because when properly cared for, the longevity of a roof membrane of this type is easily doubled.  The length of time a single-ply roof membrane will survive or be usable if it is not cared for can easily be significantly extended through proper care and simple seasonal upkeep.

If you look closely, you can see that there is significant alligatoring, a type of deterioration, at the surface of the single ply modified bitumen roof membrane. The picture below shows an example of an upclose picture with a tape measure extended for reference and scale to understand the size of the cracking shown in the photograph. 

single ply modified bitumen roof

This type of single-ply roof membrane is laid across the roof decking. In this case the roof is laid on top of one or more older layers of roofing. 

Calculating the Quantity of Required Membrane

The Building Code allows for a roof to be overlaid with one additional layer of membrane, but once that original layer is overlaid, it cannot be overlaid again and on any successive re-roofing iterations or new roofs, all substrate layers must be removed down to the substrate wood decking or in commercial applications steel or concrete deck materials.

In a picture below, you can see the roof laps, the overlaid joints of the roll membrane.  Each roll is cut from the manufacturer at roughly 40″, but once laid with a 4″ overlap at the seam, 36″ of the membrane is exposed. This uniform or consistent quantity of shape and size allows for easy and quick calculation of quantity needed per roof for area of roofing.

roof laps

Maintaining A Modern Flat Roof

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, contact us or fill out the webform below and drop us a line.  We will be in touch if we can help.

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