In a recent article, back on August 29th, 2023, we wrote an article showing a ferrous metal corrugated roof with significant oxidation and deterioration. Today, we are looking at a different issue, with similar sources of deterioration through oxidation in ferrous metal.
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
Common types of non-roof components found or flat roofs
A flat roof is more than a rubber-like mat on top of a building structure, there are a lot of components in a roof system and there are also many other accessory details on a rooftop. These elements need maintenance and upkeep, especially from corrosion if they are made from ferrous metals. It’s not specifically against building code requirements to use ferrous metals in certain exterior installations. However, if you are going to use ferrous metals, we recommend durable, long-life, high performance coatings, such as hot dipped zinc galvanization, but even zinc coatings can deteriorate on rooftops where exposed to the full brunt of the exterior elements. So, although these non-roof components are clearly not part of the roof themselves, they often are related to serious roof problems. The goal of this article, and our company itself, is to help building stakeholders and stewards to manage their building’s roof proactively to reduce the cost of ownership, use, and repair. Understanding these principles helps in that effort.
The picture below shows a group of rowhomes, you can see the low slope or flat roof systems installed at each of these buildings. In many cases there are chimney’s, exhaust vents, access hatches, and many other elements that are not really part of the roof itself but need to be coordinated and installed within the roof system.
Some of these components on rooftops which are not actually a part of the rooftop, ie: accessory components include the following:
- 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
These systems all have various components, many of which are made from ferrous metals. Ferrous metals are generally iron or steel. Most of these types of ferrous metals will oxidize and rust. In some cases these ferrous metals can be coated to protect them and extend their life cycle by reducing the direct contact with moisture, water and or precipitation.
The picture below shows the old remnants left behind after an iron access stair deteriorated to the point that the rungs of the ladder broke away from the building. These old rusting bars go through the roof membrane and leave a potential source of deterioration and leakage behind.
The problem with oxidation and rust on ferrous metals, when associated with a rooftop system is that where the roof membrane or rooftop elements connect to ferrous metals, particularly when those ferrous metals are parts or components of other roof installed systems, the roof membrane or sealants connecting the main roof membrane to the metal components will separate and delaminate.
Some examples and explanation of the types of different non-roof systems often found on rooftops follow below:
Access Systems
Many roofs do not have built-in or permanently installed access systems to get from the ground, up to the roof. In some cases though where access is required for service to mechanical equipment or where it’s difficult to set up temporary access, sometimes permanent access ladders or stairways are installed to get up to a rooftop. Where these access stairs are mounted in the roof system, special provisions must be installed to allow for continuity despite movement and/or proper flashing, in most cases. These types of elements have a higher degree of movement than the average accessory elements because as people are climbing up and down access letters, for example, there is a lot of structural flex and movement in the shifting weight loads placed on the access stairs or ladders. Also, in general, all building materials expand and contract, to a degree with changes in ambient outdoor temperatures. Metals, in most cases, will move more than some other building materials such as masonry. Roofing membranes and/or elastomeric sealants, in many cases will have a relatively high tolerance for building material movements, because of their inherent material flexibility. In many cases though these materials can still decouple or separate from adjacent materials where they are otherwise bonded or sealed.
The picture below shows a roof access ladder which can allow tradesmen or HVAC service contractors to access a rooftop from a rear deck area of the building.
The next two photos below show this access stair from a different angle. You can see a bigger picture, to understand how the access ladder leads to the roof from the balcony below.
We have categorized these roof accessory items into this set of groupings, starting with access systems, and in addition to permanently mounted ladders, accessories hatched and portals also fall into this category. Access hatches are very common, going back to the original construction of most DC homes. During the manufactured drug wars and crack cocaine epidemics, poverty and associated crime was rampant. The security bar business boomed and access hatches became a weak point in the otherwise secure envelope of a DC rowhome. At that time many people roofed right over their access hatches. So, in some cases access hatches are gone, but the remnants remain below the surface.
The picture below shows the rear of three rowhomes’ high roofs. Each have an access hatch, built into the roof at the time of original construction. However in the case of these three homes, all three access hatches were roofed over. The closest one has a built-up roof, the other two have modified bitumen roofs. These particular rowhomes also have a rear part of the home with an even lower roof at a lower level. These buildings happened to be 3-story above grade row homes but the rear 400 SF of the building footprint only comes up to 2 levels.
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, contact us or fill out the webform below and drop us a line. We will be in touch if we can help.
