Rooftop Chimney Spark Arrestors PART II

Last week, we took a closer look at roof chimney spark arrestors and examined some of the principles related to the functional purposes and best practices of installation and construction. This week, we take another look at rooftop spark arrestors, looking more closely at the examples and talking about some of those details.

In the picture below you can look further down into the opening of another similar rooftop chimney. You can see that the newer crown, not original to the rooftop chimney, was built and shaped to extend directly from the edge of the opening.


This type of spark arrestor technically might serve two important purposes, but it is not a manufactured product. The two main purposes of this spark arrestor and any spark arrestor for that matter are:

  1. To keep sparks from an organic material fire from floating out of the chimney on to this rooftop and adjacent roofs.
  2. Keep rodents from taking refuge or shelter in the chimney.

In the pictures above and particularly in the picture below you can see that this specific spark arrestor is a field fabricated makeshift type of element. It’s made from hardware fabric, bent in rough form. There is no bottom flange, no cap, and no method of attachment other than the tie wires running over the sides of the crown past the area of flaunching (where flaunching is omitted) and into the sides of the brick where tied around fastener heads.

There’s nothing wrong with field fabricated roofing elements such as: flashings, bent metals, cornice elements, drip edges or other mobile plants or hand-tool produced roofing terminations.  However, this particular makeshift element happens to be sloppily produced for the following reasons:

  1. A rain cap is not an integral part of this installation
  2. A mounting flange is omitted from the base of the spark arrestor
  3. The materials used are ferrous yet unprotected from oxidation.


In the picture below you can see that a common 14 penny nail has been used to secure the wire cables from the spark arrestor to the flaunching area of the chimney. These nails are not rated for exterior use and are just driven into the mortar where at this point they’ve become loose in the masonry assembly.   As a quick side note: nails can be used with masonry, but there are two main types which are both structurally rated for masonry and these nails should be zinc, stainless steel, or similarly coated to protect from oxidation;

  1. Cut nails
  2. Fluted nails


As an alternative to hand driven fasteners such as nails, there are a variety of screw, wedge style, anchor type fasteners which can be used for mounting to masonry construction, in lieu of simple nails.  These types of fasteners are often used in low-slope roofing or flat roof construction.

We recommend that all of our clients in Washington DC who have buildings of value hire professional contractors who are experienced and well versed in both commercial and residential flat roofing systems and historic masonry preservation. Our company, Dupont Roofing, is trained, experienced, and proficient in those areas of roof and masonry construction, building upkeep, and restoration.

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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