Metal Roof Recoating – Part I

There is tons of information on our website about the building science surrounding and related to roofing, waterproofing and exterior building shell and facade protection, maintenance and upkeep.  We’ve also talked extensively about the damaging effects of ultraviolet rays and how sunlight can damage building materials.

On a microstructural and molecular level, ultraviolet rays, in sunlight, can break down materials by dissociating chemical bonds in the materials.   Some materials such as brick and stone and even types of concrete can be highly resistant to the harmful effects of ultraviolet rays. Single-ply materials on the other hand are generally susceptible to the damaging and harmful effects of these rays found in sunlight, particularly in cases of synthetic or polymer type roll roofing materials. Metal roofing, by comparison though, generally has a very high resistance to withstand and endure the otherwise harmful effects of sunlight. However, in most cases were found in the field as a roofing material, sheet metal is covered with a paint coating, and the paint coating lack an intrinsic resistance to ultraviolet. 

There are several types of sheet metals used for standing seam metal roofs, but often with historic or significantly aged roofing material, we find terne metal roof paint coatings.  Terne metals are generally ferrous metal alloys such as iron or steel, covered with a bonded top layer such as galvalume or zinc galvanization.   Over the last several decades though, these roof systems have needed to be recoated.  Alkyd paints may have been acceptable at some point, but by and large water based paints have replaced the alkyd paints. Alternatives with better performance but significantly higher price points include some types of siliconized, elastomeric, and polyurethane type materials.

The picture below shows an example of a standing seam metal roof where some contractor or homeowner in the past applied an asphaltic type paint. This type of coating is common with modified bitumen roof systems but is not the best option for the standing seam metal roofs.

standing seam metal

We took some quick notes at the initial walk of the property where there were signs of leakage.

signs of leakage metal roof recoating

After transposing those locations to the rooftop, we quickly identified an area of deterioration and even delamination of a previous patch attempt.   In a forthcoming article we will talk about how we identified the location of the leak and identified the deteriorated material and made repairs.

metal roof recoating

Upkeep and maintenance is required every few years because even with historic systems which are designed to last for many decades, the perimeter and termination locations of the roof metal will often need to have a redundant but important layer of elastomeric or similar sealant applied to prevent water entry at the edges of the roof system.

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.

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