Tuesday, February 26, 2013


To understand the complete enveloping of a structure, several definitions as well as their relationship to one another must be made clear:

Roofing. That portion of a building that prevents water intrusion (usually from gravitational forces) in horizontal or slightly inclined elevations. Although typically applied to the surface and exposed to the elements, roofing systems also can be internal, or sandwiched, between other building components.
Below-grade waterproofing. Materials that prevent water under hydrostatic pressure from entering into a structure or its components. These systems are not exposed or subjected to weathering such as by ultraviolet rays.
Above-grade waterproofing. A combination of materials or systems that prevents water intrusion into exposed structure elements. These materials can be subject to hydrostatic pressure from wind conditions and are exposed to weathering and pollutant attack.
Dampproofing. Materials resistant to water vapor or minor amounts of moisture that act as backup systems to barrier systems or an integral part of drainage systems.
Flashing. Materials or systems installed to redirect water entering through the building skin back to the exterior. Flashings are installed as integral components of waterproofing, roofing, and dampproofing systems. They also can act as divertor systems.
Diversions. Diversions redirect water being forced against envelope components and divert it elsewhere before it infiltrates or absorbs into the substrate. Examples include flashings, downspouts, sloped concrete decks, and drainage mats.
Building envelope. The combination of roofing, waterproofing, dampproofing, flashing, and divertor systems in combination with all exterior facade elements acting cohesively as a complete barrier to natural forces and elements, particularly water and weather intrusion. These systems envelop a building or structure from top to bottom, from below grade to the roof.

The entire exterior building skin must be enveloped to prevent water infiltration. It is important to recognize that every component used in the envelope or building skin must be waterproof. This would include many features that most people do not recognize as having to be waterproof to maintain the integrity of the envelope, including exterior lighting fixtures, mechanical equipment, signs, and all other types of decorative features.

Each item used or attached to the building envelope should be made waterproof and then appropriately connected to other envelope components to ensure that there are no breaches in the envelope’s integrity. All envelopes contain combinations of several systems, such as the building’s main facade material (e.g., brick), glass curtain walls or punch windows, and decorative features such as concrete eyebrows.

These main facade elements are typically barrier waterproofing systems (e.g., glass is actually a barrier system) or drainage systems, as in the case of brick. Installing divertors where necessary or appropriate for additional protection against water infiltration then completes the envelope.

Each individual system then must act integrally with all others as a total system for complete effectiveness as a weather-tight building envelope. Figure 1.9 illustrates the inter-relationships of the various components of a simplified building envelope.

 typical building envelope.
FIGURE 1.9 A typical building envelope.

In Fig. 1.9, the horizontal roofing membrane terminates in a vertical parapet at the metal counterflashing that also transitions the parapet waterproofing into the membrane roofing. In this specific case, the flashing acts as a transition component between the roofing and parapet materials and ensures the watertightness of the envelope at this transition, enabling these two separate components to act cohesively.

A similar detail occurs at the coping cap. This flashing detail provides transitioning between the brick facade, water repellent on the brick, cavity-wall dampproofing,

wood blocking beneath the coping, and the parapet waterproofing. Note also that sealant in this case was added to protect against any hydrostatic water pressure or wind-driven rain from forcing water up under the flashing. Without this, transitioning and termination detailing the various independent systems involved could not function cohesively to provide building envelope watertightness.

On the vertical facade, vertical and horizontal control joints (not shown) finished with sealant allow for adequate space for the masonry to move during thermal expansion and contraction while maintaining a watertight facade. Note that the brick also has been detailed with through-wall flashing, diverting intruding water vapor and moisture that was collected by the dampproofing back out through the provided weep holes. Additionally, sealant at the window perimeters acts as a transition between brick facade shelf angle and the window frame. The window frame then acts as a watertight transition between the frame and glass, both being waterproof themselves.

To transition between the barrier waterproofing system used below grade to the drainage system (brick facade), a reglet is installed. This reglet provides the detailing nec- essary to transition between the two systems while maintaining the watertight integrity of the envelope. Additionally, sealant is installed in the reglet to allow the systems to move independently at this point but still remain waterproof.

Even the waterstop shown in the concrete foundation provides a very important transitioning and waterproofing detailing that is often overlooked. In this wall section, the waterstop effectively ties together the vertical waterproofing to the horizontal slab waterproofing, providing a watertight seal by prohibiting the lateral movement of water along the concrete wall to foundation joint.

The Fig. 1.9 wall section also details divertor systems by sloping of the adjacent soil or landscaping and installing a French drain system. Each system, while not in itself necessary for the waterproofing of the building envelope, quickly removes water away from the structure, eliminating unnecessary hydrostatic pressure against the foundation walls.

As illustrated in Fig. 1.9, each separate waterproofing material effectively joins together to form a watertight building envelope.

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