Roof water tables – what are they?
Historic building facades will also often use mansard roofs at the top of the front facade. Often these mansards roofs were originally clad in slate and in some cases today those slate roof systems unfortunately been replaced with asphalt shingle roofs, to save money, at a detriment to the historic character of the building.
The picture below shows an example of a historic slate mansard roof at the top of the building facade. Just below the slate there is a water table. In other cases, at typical building assemblies such as this where a roof terminates, there will normally be a gutter to collect and convey water away from the building. Water tables are similar to guttering systems but water tables do not collect and convey that rainwater away; instead they will cascade the water below to the ground, directly from the edge of the water table. Often the water table will end in a or terminate in a drip edge, but in the case of the mansard roof below, this water table terminates without a drip edge.
This water table projects beyond the face of the historic brick facade, and the projection allows for water to run past the face of the building without cascading or running down the face of the brick. Essentially this projection preserves or deters water from the brick which preserves the brick in most weather conditions of precipitation.
In this particular case, a copper counterflashing is installed at the upper edge of the water table which connects the brick facade to the water table in a concentric or overlapped manner. When the copper counterflashing is set into a reglet or raggle, a recess created in the brick mortar joint, the top edge of the roof flashing remains covered and protected from water entry. In modern roof systems, a termination bar, often referred to as a term bar, can also be used as an alternative to recessing the top of the counter flashing into a relglet or raggle.
Maintaining A Modern Roofing System
Upkeep and maintenance is required every few years because even with historic systems which are designed to last for many decades, the perimeter and termination locations of the roof metal will often need to have a redundant but important layer of elastomeric or similar sealant applied to prevent water entry at the edges of the roof system.
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, contact us or fill out the webform below and drop us a line. We will be in touch if we can help.