Ferrous Metal Rooftop Elements and Upkeep – PART II

In our last article, we talked about roof access systems and how those components, although not part of a roof membrane in themselves, can lead to roof leakage problems.  Today, we continue, in that vein, discussing the topics in the outline below.

The outline of this series of articles follows:

  • Common types of non-roof components found on 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

We continue today by discussing historic brick chimneys, a part of our list of common types of non-roof components found on flat roofs.

Historic Brick chimneys

Historic brick chimneys are prolific. Most rowhomes will have a chimney that goes through a flat roof system. In many cases, some buildings have multiple chimneys which service different fireplaces or other mechanical equipment such as boilers within the home, at the time of original construction.

The picture below shows a typical rooftop chimney in Washington DC. This brick chimney is built with a common brick.  Above the flaunching, a cementitious crown has been built to provide slope or grade out to the edge of the brick above the flaunching. In this case, the terracotta flue cap is missing.  In many cases these chimneys deteriorate from oxidation and/or become loose and blow away in heavy winds.

It is seriously problematic to have an open chimney flue without a cap yet the issue of missing rooftop chimney caps is prolific in Washington, DC.

rooftop chimney

The next picture below shows a closer view of the same chimney top. You can see that portions of the original cementitious crown have deteriorated and eroded away from the chimney to the point that there are significant racks in the remaining cementitious covering. These cracks allow water to enter the interstitial space of the chimney. Water in this area is particularly problematic because it cannot easily dissolve or leave and generally will only dissipate through absorption deep into the masonry chimney on the inside of the building. This type of infiltration leads to accelerated deterioration.   Once a chimney becomes significantly deteriorated on the inside of the house, problems manifest in efflorescence on the surface of the interior parts of the chimney and/or delamination of attached plaster. If the brick is covered in drywall the water entry can lead to even bigger problems associated with mold.

chimney top

tall chimneyThe tall chimney shown in the picture below shows a contrasting example of a historic chimney installed at a detached home.  This particular roof is a shingle roof built or framed in a gable configuration.  This chimney happens to be particularly tall, in comparison to a regular rowhome chimney. In the picture above, even though shown in a top-down view angle, you can see that the rowhome chimneys are often much shorter.  Pitch roof chimneys need to extend above the ridge of the roof making them generally much taller.  For buildings with mostly flat or slightly slanted roofs, the chimney should extend vertically at least 3 feet past the roof surface. In contrast, if a building has a steeply slanted roof, the chimney’s opening should be 2 at least feet higher than the tallest part of the roof, and this rule applies within a 10-foot area around the chimney. These requirements ensure space between the top of the chimney, at the orifice and the adjacent framed building materials.  This helps with fire separation.  The air coming out of the chimney can be extremely hot, and even burning sparks can come out of the chimney at times.  A picture below shows an example of a chimney built extra tall for this specific purpose at a pitched roof.

The next picture below shows a different type of contrasting scenario. This chimney is installed at a flat roof but unlike the photo farther above, of a deteriorated chimney crown and a chimney flu without a cap, this particular chimney, also installed at a low slope or flat roof road home in Washington DC, has already had the crown repaired and a new cap installed.

crown repaired chimney

Next week, we will pick up where we are leaving off today by discussing the next element in our list: Air Exhaust Systems.

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

On Key

Related Posts

what damages metal roof paint

Terne Metal Roof Paint Deterioration

Terne-coated metal roofs are an element of historic architecture, somewhat common in Capitol Hill and other historic neighborhoods of Washington, DC. However, the terne coating