What you should know about how rain affects a brick facade
Last week we took a deeper look into how rain affects a brick facade. This week we’re continuing with that subject to bring you part TWO. This portion of the analysis delves into the details of a brick facade including the components and how several of those components are intended to direct water, in typical rain circumstances, away from the field of the facade. In a typical brick facade, the field area of the brick masonry wall is a continuous uninterrupted area with a continuing bond and pattern of brickwork. That area constitutes the majority of the wall space.
Some of these building elements which are both visually pronounced, as part of the exterior facade, and also part of conveying and directing water away from the horizontal vertical field of brick follow:
- At the base of a wall the plinth is a thickened area where the brunt of splashback can be absorbed, partially protecting the upper areas of the wall by use of a damp proof course lining such as embedded slate above the plinth area.
Projecting arches and headers, eg. Drip lintels and Drip mouldings
- Often in elaborate masonry construction, the stone or brick facade will have projections built around the upper area of window and door opening. This projection will allow water to run and drip away from the facade especially where it would otherwise drip down onto and run downwards along a door window.
- A window sill defines the bottom area of a window opening, but the sill itself is built-in a particular way that allows water to run from the window opening on the external face, away from the external face of the window and convey water away from the building facade. Even though a window sill may only have a depth of a few inches, a slope built into the window sill allows water to run away from the window itself. If water were to instead run towards the window, water would pool at that area and eventually seep into the framed wall cavity, brick, or masonry wall assembly. Water, if allowed to pool and then seep into a building assembly such as this would cause deterioration. Due to the concentrated nature of the water, damage would occur, even in durable materials such as brick and stone masonry which are otherwise somewhat resistant to deterioration from moisture.
The sandstone window sill shown in the pictures below is an example of the intentional slope of a sill, intended to migrate rain water away from the window. The window sill protrudes 2.25″ away from the brick facade above and below. This projection also keeps water from running in concentration down the face of the brick wall.
At an adjacent sill in the same facade, there is a darkened area around the window horns, the sill has also experienced concentrations of moisture, as rain water has been conveyed away from the window. Bioconomization is the growth of plants, algae and similar organisms on masonry and concrete and other building materials, as seen in these examples.
- The image below shows a picture of a sandstone ashlar masonry building facade with a stone enframement built around the window. Above the windows you can see a decorative cornice below a water table.
- Drip edges and flashings are impermeable or low-permeability materials, concentrically built to cover exposed areas susceptible to water entry.
- Cornices can be either made from wood, metal, and even brick itself when corbelled to project in a sequential order. Metal cornices are commonly installed at the front historic building facades in Washington DC. Metal cornices, like aperture headers and sills, ornate doors and casing, and detailed brickwork are part of the architectural accents which make the historic DC neighborhoods unique and classically beautiful. The roof will often extend over a front facade out to and even beyond the wall cornice. Like a pitch roof eave, this projection is very intentional because it allows the majority of the top of the building facade to be undercover which keeps it dry during non-directional rain.
The Image below shows a decorative cornice above a sheet metal formed dentil work and decorative freize.
- Corbels are often decorative supports below superimposed architectural elements and at window and door headers or even at cornices themselves. Corbels and Corbelling sound similar but are actually different. Corbeling is a brickwork that is built in successive projecting courses. In the section above, corbeling is mentioned as a method for creating a brick or stone cornice. Corbeling can also be used as a method to create a flared or widened footing underground at the base of a historic brick or masonry wall.
The image below shows a black decorative corbel, below a water table at the bottom of a slate mansard roof.
- The picture below shows a row of four buildings, with a continuous slate mansard roof. Each of the buildings has a pair of gable dormers. The Gable at each dormer is relatively shallow, but the gable projects beyond the face of the dormer. Below the mansard, a water table conveys water away from the building facade. At each of the individual buildings, the the cornice and slate mansard are at varying stages of deterioration.
- The image below shows a slate turret roof above a brownstone building. The slate shingles terminate at the bottom of the turret at a projecting eave, terminated with a copper metal decorative cornice. The eave projection, in the case of this turret extends approximately 16″ from the face of the brownstone building facade.
All of the elements in the list above are details that are interspersed and laid out among or within the field of an exterior wall. They have different architectural and aesthetic purposes, but they also convey or direct water away from the field area of the building facade. The field of the building facade is the main uninterrupted area of the wall. In building facades, for example, the field is the
part of the wall between windows and generally constitutes the majority of the square footage of the space of the wall. The field of the wall is constructed and intended to be able to handle and survive exposure to rain and moisture and natural elements of weather, but these other elements work together to limit the amount of water washing across the building facade from natural weather occurrences such as non-directional rain.
Rainfall and precipitation takes place in different forms, and those different forms of precipitation have different affects on buildings. For example, in the majority of light rains without heavy wind, many building facades, especially at the field area can actually stay relatively dry. In those types of precipitation, water will drip off of areas like drip edges and eaves of roofs and fall right past the building facade without actually making contact with the building facade.
Often, the base of the wall will be built with a plinth or slight projection where the wall is thicker at the bottom and sticks out away from the field of the facade. Often, the building walls will be built to take splashback into consideration. Splashback is a typical occurrence during rainstorms which accelerates deterioration at the base of a masonry wall. The encyclopedia entry on our company’s website about rising damp talks about the deterioration caused by both splashback and rising damp, at the following link.
The images below show a brick wall, built with a Flemish bond. This wall has a different higher temperature fire brick at the area of the wall at the very bottom and corbeled underneath the adjacent walk area. You can see a dark color covering the bottom 4 to 5 courses of the wall where it is Insistently exposed to splashback
Essentially, splashback is the phenomenon of the base of a wall becoming more wet and hydrated during typical rainstorms than the rest of the building. The base of the wall will often have raindrops or rain water directed from the building details away from the building field of the facade and then directed from there to land on the ground next to the base of the building. Those raindrops or directed channels of water will then splash when they hit the ground and the splash will then bounce and land back onto the base of the building facade. This is the phenomenon known as splash back.
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
- Cementitious siding
- Cheek wall, masonry — Draft
- Chemical testing
- Code, building — Draft
- Cold joint
- Cold weather masonry work — Draft
- Electrical distribution panel — Draft
- Ferrous metals
- Great Chicago Fire
- Green bricks
- Gutter, roof
- Lime mortar
- Parapet coping
- Plug, clay
- Pressed bricks
- Raking, of mortar joints
- Raggle, aka reglet
- Roman bricks
- Roman arches
- Roof eave
- Roof termination
- Row buildings and row homes
- Rubbed bricks
- Rubble stone masonry
- Scratch coat
- Strike, or striking of mortar
- Tapestry bricks
- Tooth-in, interlocking masonry connections
- Water diversion systems
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, fill out the webform below and drop us a line. We will be in touch if we can help.