Building Envelopes

After our lecture on the building Envelopes, I thought I will look at this topic in more depth, I found this article on a website. I have included the introduction which gives a good summary of what a building envelope is, for the rest of this article follow the link: http://www.wbdg.org/design/env_wall.php

Following the introduction of the article i have chosen a image which illustrates a cavity wall, yet water is shown to penetrate, however, in the second image the cavity wall is seen to be protected by sealant to avoid water penetration.

Introduction
The basic function of the envelope or enclosure of a building or structure is to protect the covered or otherwise conditioned interior spaces from the surrounding environment. This fundamental need for shelter is a concept that is as old as the recorded history of mankind. However, as our needs have evolved and technologies have advanced, the demand placed on designers to both understand, and integrate, a wide range of increasingly complex materials, components, and systems into the building enclosure has grown in equal proportion. This is particularly true when one considers the emerging threat of terrorism and the impact of that threat on the design and construction of the building enclosure. However, despite the recent emphasis on blast-resistant wall systems and hardening of the building enclosure (see the Blast Resistance section for additional information on this topic), uncontrolled rainwater penetration and moisture ingress remain two of the most common threats to the structural integrity and performance of the building enclosure.