Ferrous Metal Rooftop Elements and Upkeep – PART VII

In the past several weeks, on our blog, we have been looking at specific facets of challenges and upkeep requirements of non-roof items on rooftops, in a series on flat roof problems associated with ferrous metal non-roof components.  These are elements that are not actually part of the roof itself. The roof itself will include elements such as the field membrane and the elements of terminations and even elements of flanges or prefabricated rubber type materials to fit around penetrations.  These specific ferrous items are actually different and separate from the roof system itself yet they are installed on top of the rooftop and often have elements of mounting or connection which go through the roof itself. 

Today, we will talk about photovoltaic solar panels and related support  systems, and in the next article we will discuss the implications of ferrous metals and penetrations through roofs for guardrails and fall protection systems on rooftops and some of the potential problems associated with those elements on roofs and methods of preventing leakage and required upkeep.

The outline of this series of articles follows:

    • Common types of non-roof components found or flat roofs
      • Access Systems 
      • Historic Brick chimneys
      • Air Exhaust systems
      • HVAC systems
  • Electrical power distribution
  • Low Volt and communication wiring and satellite / antennas
  • PV Panels and mounting structures
  • Guardrails and fall protection systems
  • Roofing problems caused by oxidation of ferrous metals
    • Delamination 
    • Staining and bondability
    • Structural component failure
    • Leakage through metals
  • Methods of Repair and sustainability 
    • Standard Coatings
    • Substrate preparation
    • Advanced re-coatings
    • Special roofing provisions

In the past we have looked at a few different examples of problems and solutions related to photovoltaic (PV) solar panels, a few of those article links follow:

Today we are looking at the same topic but also talking about the issues associated with ferrous metal and related oxidation.

PV Panels and mounting structures

There are multiple different methods of mounting and installing solar panels, one of the most common ones in DC though is through a purlin type structure frame, which is generally mounted to a parapet of a roof. mounting a system like this directly on top of a parapet is generally problematic because the parapet is a relatively horizontal surface and by drilling holes through a properly installed metal coping, the holes created in the metal coping essentially debilitates the coping’s ability to resist water entry. Solar panel mounting companies will often apply an elastomeric sealant, a type of caulking, to seal around the penetration through the coping but that is generally ineffective over time. Elastomeric materials are considered to be high performance sealants with lots of inherent resistance to the elements, yet they lack an inherent long term resistance to UV rays.  

The picture below shows an example of a rooftop PV system, set on an aluminum purlin framework and where mounted to the aluminum coping at the parapet wall on top of the demising wall between the adjacent row homes.  This type of system is functionally perfect in most ways, but it shouldn’t be mounted on top of and through an aluminum coping without an additional system to seal the mounting brackets.

rooftop pv system

The bolts which secure the system in place and mount through to the masonry wall below are steel bolts, coated in an electro galvanized zinc coating. That electro galvanized coating essentially protects the ferrous metal from oxidation but at the cut ends, the ferrous metal bolts will rust and oxidize as they deteriorate.

However, that’s not the big problem. The big problem is that the bolts secure the panel down and prevent wind uplift but they are installed to the panels through a sandwich of connected materials. Just above the aluminum coping there is a synthetic 1x board cut to shape and drilled with a hole to fit around the bolt itself.

It looks like that small piece of board, at each location of installation, has been set in a liberal bed of elastomeric sealant. Then, above that board there is an aluminum L-bracket with a nut and washer securing the L bracket down to the 1x synthetic board. a liberal application of elastomeric sealant has been applied around where the nut and washer are set on top of the aluminum bracket. However, there is no sealant apparent between the bracket itself and between the top of the nut and the threaded rod. At those locations, between the aluminum bracket and the synthetic board, water can get into the hole bored into the PVC board and from there enter into the area below the coping.

ferrous metal bolts

Another similar installation shows another angle of the problem related to the limited sealing abilities of elastomeric sealants at this type of configuration.  Elastomeric sealants are strong, yet still have limitations.  Here you can see that during the torquing of the nut at this bolt, the sealant was damaged and the PV solar panel installer did not reapply sealant at this location before completing their work and leaving the site.  As well, there has been no sealant applied underneath of the aluminum bracket and no sealant applied at the top of the ferrous metal nut. Both of these locations will allow water to enter into the space between the materials.  With all of these inherent shortcomings, it is obvious why the roof and coping manufacturer’s do not approve of this methodology, and in this case that approval is required for every installation mandated by the building Code.

elastomeric sealants

Smart and proactive replacement, construction, upkeep and maintenance of low slope roof and mansard roof systems requires an enthusiastic interest and understanding of historical methodologies, 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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