Learn about brick copings in this two part series guide
Last week we took a look at a historic brick building built over a 100 years ago with serious damage to the brick wall at the separation between the adjacent building. That brick wall had deteriorated deep into the brick assembly. Historic brick can last for hundreds of years, as apparent from the significant age of the majority of historic brick masonry buildings in Washington DC. We see the historic brick facades, they are visually apparent, but the structure of these buildings is also built with brick beyond the surface. Mostly, common brick was used for the construction of the vast majority of historic buildings in Washington DC.
Why A Roof Coping Is Necessary
A coping at the top of those walls, at the parapet above the roof, is necessary to prevent rainwater and precipitation and weather from entering into the brick assembly. Most of these walls are brick built with a double why the brick assembly.
The picture below shows an example of a historic brick wall with delamination of the existing paint and deterioration of the mortar joints. Where the paint has delaminated you can clearly see that the mortar joint is also recessed and deteriorated from exposure to the elements. Tuckpointing or repointing is needed at this wall. Pointing or repointing or tuck pointing as commonly called, is the process of removing the outermost portion Brick mortar to a depth of 3/4 to 1.25″. After the mortar is removed, a process of cleaning the joint is next, then the remaining mortar in the joint is hydrated to prevent accelerated dry out when the new mortar is applied, through absorption of the remaining mortar. The new mortar is installed in lifts, applied with a tuck point trowel. Finally, the joint is struck with a joiner, a tool which forms, packs, and smooths the mortar to a specific profile.
The picture below shows an angle or portion of the side facade of historic brick building with a ferrous metal coping on top of the parapet wall. In modern construction or renovation, aluminum copings are used, most commonly. Other metals can also be used such as ferrous metal as shown below, but ferrous metal is susceptible to moisture and will oxidized overtime. Many ferrous metals today are covered with a galvanized zinc coating to deter or lessen the extent of oxidation and deterioration.
The roof membrane itself is a modified bitumen membrane and that membrane has been coated with an aluminum or a fiber modified aluminum paint. That coating extends the life of the roof membrane. In this case that coating has also been applied on top of a portion of the exposed ferrous metal coping.
The metal coping is formed or bent with a gravel stop at the outer edge of the parapet wall. The gravel stop, originally named for its use in preventing gravel from spilling over the sides of a roof, in this case is used to direct rainfall or water from running over the edge and instead diverting it back towards the roof membrane.
The picture below shows an example of a historic brick building with a modified bitumen roof membrane. This particular roof membrane happens to be a granulated SBS system. From a distance, the membrane looks OK, this is a relatively simple layout without complications of several penetrations or complicated mechanical equipment on top of the rooftop, but the coping is missing and instead the modified bitumen membrane has been installed overtop of the parapet wall. This type of deviation from the building code requirements is extremely common in Washington DC because there are many different types of roofers and contractors in the area and many do not follow the building code precisely. For good reason, it’s better to install a metal coping at the parapet walls. Coated aluminum copings have better resistance, and superior longevity and when installed properly help to secure the roof membrane in place.
The next picture below shows another set of low slope roof membranes on top of historic brick buildings. At the rear of the building at the left in the picture below, the coping is missing and the CMU or block portion of the rear facade is exposed to the elements.
When you look very closely in the next 2 pictures below, you can see that the modified bitumen roof membrane that was originally installed on top of the rear facade parapet has deteriorated and the cells of the block wall are exposed. Although this wall is built with block and not with brick, the construction is very similar. A 8″ block, for example, is similar in size and dimension to a historic double wythe brick wall.
When you look very closely in the picture below you can see that the modified bitumen has deteriorated over top of the block and the cells are wide open. Any rain that runs or lands directly on top of that section of the wall will then enter into the interstitial space between the block. That water will hydrate that area causing slow deterioration and the water will not escape, except for through slow evaporation and dissipation over time. As the hydration and moisture builds up into the wall, that moisture will cause deterioration and dissolution of the constituent masonry materials. Signs of this type of slow but insidious deterioration can often be seen in the form of efflorescence on the surface of masonry.
Copings, made from impermeable materials will protect this type of masonry building assembly. The next picture below shows an example of a terracotta tile installed on top of a parapet wall as a coping. You could argue that historic masonry is more susceptible to pooling water, but in the case of open block work, the cell and cavity within the brick becomes a place which traps significant buildup of water. Historic lime mortar, by comparison is also susceptible but at least does not have a intentional void or omitted space which can pool and accumulate water.
Terracotta as Roof Coping
Often, when terracotta masonry elements are used as a coping, there are concentric or overlayed portions of the tile, formed at the ends of each masonry coping unit to keep the joints relatively dry, but a continuous metal coping can perform better with much less joints required in the span of each length of fabrication and installation.
Maintaining A Modern Roofing System
To properly maintain, repair, and care for these historic buildings, a knowledge, interest and understanding of historic building principles is required. Here in Washington DC, historic masonry buildings are extremely expensive and the amount of financial loss caused by improper repointing and low quality construction is staggering. However, in addition to the direct financial value of the property, there is also a cultural loss when historic buildings are damaged. By comparison, consider neighboring poor cities, when historic buildings are damaged, it’s not just the loss of value to the property owner, there’s also a loss to all inhabitants and visitors of a city, present and future, who care about architecture, history, and culture.
We encourage all of our clients, and all readers of this article and to our blog in general, to prioritize the historic built environment of Washington DC and neighborhoods such as Capitol Hill, Dupont Circle, and Georgetown and become educated on on the difference between proper historic preservation versus improper work which leads to significant damage to the historic fabric of a building.
From a conservation and preservation perspective, several approaches can be taken to improve conditions related to deteriorated historic brick masonry. Primarily, lime mortar brick joints and low temperature fired soft red clay bricks should be inspected and checked on a routine maintenance schedule, either seasonally or at least annually. If brick masonry is kept in good condition, the life of embedded wood elements can be significantly extended. Hire a professional contractor which specializes, understands and appreciates historic construction elements and buildings.
In this article we talked about the terminology and concepts of historic masonry restoration, follow the links below for more related information from the IDS website:
- Binders in mortars and concrete
- Brick burns
- Butter joint
- Capillary action
- Cantilever
- Cementitious siding
- Cheek wall, masonry — Draft
- Chemical testing
- Code, building — Draft
- Cold joint
- Cold weather masonry work — Draft
- Damp proof course
- Downspout
- Electrical distribution panel — Draft
- Fenestration
- Ferrous metals
- Great Chicago Fire
- Green bricks
- Gutter, roof
- Lime mortar
- Lintel
- Load path
- Oriel window
- Oxidation
- Parapet coping
- Plug, clay
- Pressed bricks
- Raking, of mortar joints
- Raggle, aka reglet
- Rectilinear
- Roman bricks
- Roman arches
- Roof eave
- Roof termination
- Row buildings and row homes
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- Rubbed bricks
- Rubble stone masonry
- Sand, Builder’s
- Sedimentary rock
- Scratch coat
- Sprung arch
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- Squint bricks,
- Strike, or striking of mortar
- Tapestry bricks
- Tooth-in, interlocking masonry connections
- Vitreous
- Water diversion systems
- Zipper-joint
These concepts are part of the fundamentals of historic masonry restoration, tuckpointing, and brick repair.
The links in the list above will take you to other articles with more information on defects, failures, preservation and repair of historic masonry. You can learn a lot more on our blog. Feel free to check it out. If you have questions about the historic masonry 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.