What you need to know about Rooftop chimney crowns – Part I
A few weeks ago we talked about rooftop chimney spark arrestors. The cap to a rooftop chimney and the spark arrest are often integrally combined. However,these components are not alone in the rooftop chimney assembly of building elements. Other elements of design and construction that are part of the overall assembly include the following:
- The chimney flaunching
- The chimney flue
- The chimney crown
- The chimney counter flashing
Although many people might not think of the chimney counter flashing as an important part of the chimney, it is essential. The rooftop itself connects to the chimney at the base and counter flashing assembly, and this detail is extremely important As well. All of these elements are part of the rooftop chimney assembly and work together to keep air flowing in the proper direction and keep water out of the building. As well the spark arrestor helps keep rodents out of the chimney.
The chimney crown, itself, stabilizes the chimney flue and sheds water to the outer edge of the chimney flaunching. Chimney flues can be built with a build-up of mortar, but in large cementitious assemblies without a aggregate, it’s possibly a better practice to include steel reinforcement in the cementitious crown.
Rooftop Chimney With Crown
The following picture shows an example of a rooftop chimney with a Crown between the top of the brick and the terracotta 9″ x 9″ flue.
Rooftop Chimney With Flaws
The picture below shows an example of a rooftop chimney design that almost completely sidesteps the need for a chimney crown. Instead of having an exposed flue, crown, or cap this chimney terminates in a brick archway, similar to a Gothic arch that you might find at a door or window of a Gothic style building. This design has flaws and we are not recommending it, but it’s an interesting historic design.
Rooftop Chimney Without Crown or Cap
The next picture below shows a different chimney without a crown or cap at all. At the top of the chimney as precipitation enters, at each precipitation event, as it is unprotected, the chimney internal masonry and other elements deteriorate. In most cases these historic chimneys were built with a terracotta flue. Two common sizes are 9″ x 9″ or 9″ x 13″. In this case, the flue that was once there has completely deteriorated and fallen into the inner cavity of the chimney.
Roof leaks are generally addressed quickly after they become significantly active. When roof leaks start out slow, people may not notice that water is coming in and deteriorating and causing rot in their ceiling or attic or interstitial building materials. Normally though that leak happens and makes itself evident relatively quickly. In the case of chimney deterioration and the absence of a chimney crown, this damage can be very slow and insidious. As it deteriorates surrounding elements, that deterioration can happen in such a slow way without making itself pronounced and obvious to the occupants on the inside of the building. For this reason, we often find that where there is deterioration at chimneys it’s so extensive that simple upkeep and maintenance type repairs are insufficient and in cases like the picture above, this chimney will need to be almost entirely rebuilt above the roof line.
Rooftop Chimney Maintainance Essentials
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.