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Water Conveyance And Facade Leakage

How does water conveyance and facade leakage work?

Masonry facades are built with lots of subtle details which allow for the passive but directed conveyance of water in a controlled manner.  These details are essential to preserve and extend the longevity of historic or contemporary stone and brick masonry facades.  In addition to the important details which carry water from a roof of a historic building away from the building, there are a lot of other important details in the masonry which also direct and control the flow of water.

Elements and Accent Of Historic Brick Facade

The picture below shows an example of a large scale historic masonry building.  Although the building is large, there there is still a variety of interesting details in the masonry which highlight elements and accent of the historic brick facade.   In addition to the cornice at the top of the historic masonry facade, there are three additional bands that run horizontally around the building.   The highest of these bands, the one below the cornice, is a sheet metal water table and not just a architectural accent.   In historic architecture, water tables are very similar to built-in gutters. Built-in gutters, in contrast to modern applied gutters are custom built and fabricated to create a significant projection, like a small roof above the elements of the facade below.

large scale historic masonry building

With architectural assemblies, such as the details of the masonry facade above, these projecting bands and water tables work to shield much of the macery facade from a large portion of typical precipitation.   Weather patterns are somewhat unpredictable, but in most cases the common light rainfall may have very little wind driven rain.   In such a construct, with elements of this design,  intended to create a projection or extension away from the building, much of the typical light rainfall will actually fall outside or beyond the face of the masonry wall, keeping much of the building facade dry.  

Functional Benefit of Projecting Roof Edge

In the next image below, we show an example of a portico roof at a historic row building.  The outer edge of this small roof extends approximately 8″ beyond the entableture or vertical face of the portico below.   The architectural aesthetic of a projecting roof edge is a positive embellishment, but the projecting edge is not intended just for aesthetics, here as well there is an important functional benefit as a part if the building stays untouched by typical light rains.   This is a passive element of design that prolongs and extends the life of a building. Precipitation and rainfall simply accelerate the deterioration of masonry buildings and this simple detail can extend the life of the building in a passive and simple manner, just rooted through the design.

portico roof

Windows sills are built to perform the same function. It’s not a coincidence that window sills happened to be built projected, standing out away from the face of a vertical wall they stand incrementally projected (“proud”), in most cases.   There are other best practices with windows that are important in building a sill properly. The sill should have an angle (referred to as a bevel  or cant in architectural vernacular) to shed water downwards and away from the window.  Window sills often appear to be flat, but they actually must have an intentional angle or slope away from the window.   It’s best practice for a window sill to have a drip edge at the outer most point along the horizontal edge of the bottom of the sill.  In some cases, some sills will have a ¼” kerf intentionally cut on the underside of the projecting portion on the sill.  

Understanding The Effect Of Weather And Precipitation On Buildings

Water has a tendency to bond to itself and to other materials.   Understanding the chemistry helps to understand the effect that weather and precipitation have on a building.  Water is made up of molecules comprising 3 atoms. Those atoms, together, happen to have a light hydrogen or polar bond to most other physical substances.   It would make intuitive sense that a drop of water would fall off a horizontal ledge, but it often doesn’t work that way.  Instead, water will actually run back across the underside of a horizontal ledge of the underside of a window sill and from there the water will run down the face of the wall.

The picture below shows an exact example of this happening at the exterior facade of a historic building in  Washington, DC. When you look closely, you can see that the area directly below the windows sill has a dark, wet area of precipitation or moisture that runs in a stair step type fashion down from the window sill to the brick segmented arch window header below.  

Slowly, every time it rains, even in vertical rainfall with very little wind, rainwater lands on top of the stone window sill and then runs down the vertical face of the stone sill and runs back to the brick wall.  Instead of being shed just an inch away from the face of the wall the water runs back to the surface of the wall, almost as if it were concentrated and then applied directly to an area that happens to be coincident with a stairstep crack. This is causing deterioration and problems for the building because not only does it allow water to enter which can deteriorate organic water sensitive materials, but it also increases the rate of deterioration because as this area becomes the focus of additional excessive hydration, those materials also deteriorate at an accelerated rate.

exterior facade leakage historic building

 A close up view of the window header shows there’s also acute and accelerated deterioration happening at this structural detail.  These historic common bricks are set in a double rowlock course at the window header, but unlike a squint brick header with each brick rubbed and slightly tapered to neatly fit with consistent mortar joints, this type of header cheats by slightly padding each joint to make them thicker at the top.  This methodology avoids the onerous work of shaping each squint brick, but it is less stable over a century of aging and deterioration later as it is exposed to regular weather patterns.

deterioration structural detail

  •  At some locations, it’s not weather causing the deterioration of brick and mortar masonry facades, it’s the human inhabitants and other building systems, such as mechanical condensate from air conditioning units as shown in an example in the photo below.   In this example, as this small electric window air conditioning unit runs throughout the summer months, it’s constantly discharging a stream of condensation.   If manufactured better or in better working condition, the condensate should be collected by a oan and then set to drip through a weep or relief hole farther away from the face of the building. In this case though because it is a historic masonry building, built with a double wythe construction, above grade, the wall happens to be too thick for the bottom of the air conditioning unit to project far enough away from the building . So in this case, the condensation is hitting the window sill and since the window sill, as well, is flush or equal in the vertical plane to the face of the historic brick masonry wall, that condensation runs down the sill and then cascades running all the way down the masonry face of the wall.

water running down brick wall historic building

If you look closely at the brick just below the window, you can see that the mortar joints have significantly accelerated deterioration from constantly being exposed to water running down the wall.   This area clearly needs upkeep and maintenance and now restoration of the brick mortar and repointing or tuck pointing.  However, even after the brick restoration and upkeep process is completed, the root issue of improperly directed water still remains and should be corrected.

water damage mortar joints

Importance Of Cornice On Top Of A Building Facade

Going back to the building in the first image at the top of our discussion, there is a cornice at the top of that building facade. The cornice serves a few functions.  It’s important to understand though that that building was a large commercial building that used a combination of internal roof drains, and scuppers.  The example stands in contrast to the majority of historic buildings in Washington DC.   In comparison, the historic row buildings drain water from the front of the building, flowing downwards with an intentional grade or slope to the rear of the building. At the rear termination or the rearmost part of the roof, there is generally a drip edge which leads into an intentionally sloped gutter.  

Nonetheless, even with all of these provisions intentionally designed and built into the building to  guide and direct the flow of rainwater from the roof and away from the building, there is still consistent incidental rain which hits or lands at the top of the building facade. In the case of the large commercial building shown at the top of the discussion, that water is directed slightly away from the face of the building by the projecting cornice at the top of the masonry wall.  That example stands as a paradigm of good building practice, for design that promotes passive preservation.   The image below shows a contrasting example. This picture shows a rear addition of a Washington DC building. The addition was built without a fascia or cornice at the side of the rear addition. Instead, the modified bitumen membrane was laid directly on top of the brick masonry at the top of that wall, but as the water is not directed away from the building, the rain and precipitation runs directly down the face of the brick and mortar which causes the mortar joints and the brick to deteriorate and fail at an accelerated rate.  The mortar joints are in terrible shape at this location.

water damage brick face

Also come when you look closely you can see that some of the brick has actually spalled.  Spalling  is the phenomenon or tendency to make for masonry to break at a cleavage point near the front face. The front faces of the brick will often fail and shear from the brick itself in a sheet of delamination.   This particular deterioration is a compounding result or effect of both undirected or misdirected rainwater and the lack of maintenance and care for the mortar joints. Often though, we commonly see this type of failure where inappropriate brick mortar is used in the tuck pointing or repointing process.

spalled bricks

How To Maintain, Repair, And Care For Historic Buildings

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
  • Sedimentary rock
  • Scratch coat
  • Sprung arch
    • 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.