Rooftop Chimney Flaunching and Brick and Mortar

This article is inside of a series of articles, but this specific one focuses on rooftop chimney Flaunching and Masonry.

In recent weeks of our blog we have been taking a look at several different components of chimneys because rooftop chimneys are often the source of water leakage into a roof but not actually through the root system itself. Last week we talked about parts of the upper or top of brick chimneys on rooftops, today though we’re going to talk about the chimney brick and mortar and the chimney flaunching. Not all chimneys are built with fllaunching, but in buildings of significant historic architecture and/or value, chimneys were often built with flaunching and a little bit of overall better attention to detail in the brick masonry and the details where the roof terminated to the masonry elements.

  1. Flaunching
  2. Brick and Mortar

Last week, we also took a look at the images or diagrams below. These diagrams show the chimney and even the fireplace layout that would lead from the interior to the exterior of the building.

rooftop chimney flaunching

Rooftop Chimney Flaunching

In reference to the subject and topics of this particular week’s blog and article, in these diagrams you can see the brickwork and flaunching in relation to the remainder of the chimney and in the context of the other parts of the chimney anatomy.  Here where it applies to the area above the rooftop, the brickwork is another one of the areas of susceptibility and at risk of water entry and leakage if not properly maintained. In general, rooftops and roof systems in Washington DC, particularly on historic buildings, require a high degree of upkeep and maintenance.  Repointing and brick tuck pointing often goes a long way.  Repointing once every 30 to 60 years, should be enough. Chimneys have a higher degree of exposure to the elements, more than most other parts of the building. Chimneys are relatively small, compared to building facades, and are generally exposed on all sides by weather conditions such as wind and precipitation. They have a tendency to deteriorate at a higher rate than other areas of the historic facades of a building. Nonetheless though upkeep, maintenance, repointing and tuckpointing should last for decades, even at an old chimney.

The diagram below shows an area of an old chimney in the snow and ice. The icicles are hanging off the edge of the flaunching, and this gives us a somewhat unique chance to get some perspective into how water flows down around a chimney top, from the crown of the chimney, over to the edge of the flaunching.  

mortar to the rooftop chimney flaunching
Not all chimneys are built with flaunching, but here you can see the point of the slightly projecting extension beyond the vertical chimney masonry face, you can see the design working in action to divert a degree of the precipitation and water away from the majority of the base Brick sides of the chimney. As the water runs off the slightly projected historic brickwork at the flaunching, it drips off the edge here, freezing into little icicles a half inch to roughly one inch away from the remainder of the brick chimney’s vertical plane.

Rooftop Chimney Brick and Mortar

Water entering through a brick chimney can be a major culprit in leakage and deterioration from an area that seemingly, ostensibly, appears to be near or in the general area of the roof.  Sometimes it’s complicated, it’s not always easy to distinguish a rooftop leak from a chimney leak. Particularly, when water is leaking through the masonry components of the chimney, this leakage cannot only cause significant damage to the interior of the building, but it can be hard to discern the difference between a chimney leak and a roof leak.

Brick and mortar often deteriorate significantly if not maintained and well preserved. We often find voids that run directly through the mortar joints into the chimney area. In some cases, we can slide a thin object like a roof probe or screwdriver right through without any resistance because the mortar joints will be deteriorated and full of voids that are wide open from the exterior of the chimney to the interior area of the flue.

chimney flaunching on a rooftop

The picture above shows the condition of a chimney that is relatively similar to the average chimney in the historic brick built row home neighborhoods of Washington DC like Capitol hill, Dupont Circle in georgetown. You can see in this photo that there are a few small voids in the brick mortar.  In some cases though the damage will be much worse just below the surface and or in other chimneys where there has been insufficient maintenance or a dearth of  proper attention to repointing and/or tuck pointing. Chimneys with more mortar deterioration will be in desperate need of a rebuild to prevent collapse.

We recommend every building owner in DC who values the longevity of their roof (and their investments) and building use a contractor who values the simple and important principles of proper roof construction like Dupont Roofing DC. Learn more about our company and the proper techniques of working with roofing on historic buildings in Washington DC here on our blog at, and you can call us at (202) 840-8698 and email us at

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