{"id":207827,"date":"2024-01-18T10:00:54","date_gmt":"2024-01-18T15:00:54","guid":{"rendered":"https:\/\/www.constructionspecifier.com\/?p=207827"},"modified":"2024-01-12T13:38:32","modified_gmt":"2024-01-12T18:38:32","slug":"rethinking-building-envelopes-for-climate-ready-buildings","status":"publish","type":"post","link":"https:\/\/www.constructionspecifier.com\/rethinking-building-envelopes-for-climate-ready-buildings\/","title":{"rendered":"Rethinking building envelopes for climate-ready buildings"},"content":{"rendered":"

\"\"By Paul Johannesson<\/strong><\/p>\n

As climate change is anticipated, bringing with it an uncertain future, the construction industry needs to seriously consider the preparedness and the proven performance levels of buildings. It also needs to ensure the \u201clarge membrane\u201d that separates the exterior environment from the interior environment, also known as the building envelope, is up to the task.<\/p>\n

The idea of building resilience has become more topical as everyone comes to terms with the fact that changing climate conditions seem inevitable. The Intergovernmental Panel on Climate Change (IPCC) states, \u201cTaken as a whole, the range of published evidence indicates that the net damage costs
\nof climate change are likely to be significant and to increase over time.\u201d1<\/sup><\/p>\n

Will there be an increase in both the frequency and intensification of severe weather events? Will there be a need to resist increased water, wind, and temperature extremes in the exterior environment? Will shifting the focus from the approach prescribed within the current codes and standards to a higher performance-based design and commissioning approach be the answer?<\/p>\n

The building envelope<\/strong><\/p>\n

The building envelope can be imagined as a \u201cthick membrane\u201d that separates the exterior environment from the interior environment on all sides of a building\u2014similar to a balloon. It has been mistakenly conceived as one or two layers of perfectly sealed materials; and there exists a history of building failures to prove it. It is best described as \u201cpart of any building that physically separates
\nthe exterior environment from the interior environment(s) is called the building enclosure or building envelope.\u201d2<\/sup><\/p>\n

It is important to consider this envelope or enclosure is a very complex system of base materials, accessories, pre-manufactured components, riddled with seams and penetrations, and is highly reliant on a systems approach of connecting them to create a weather tight separator of dissimilar environments. These environments are often dissimilar in temperature, relative humidity (RH), wind pressure, and vapor pressure. Each building envelope deals with differences as unique as the climate region or zone it is constructed in. Thankfully, a commonly accepted approach to building envelope and enclosure design has emerged over the years.<\/p>\n

<\/p>\n

\"Figure<\/a>
Figure 1<\/b> An exterior water-resistive layer to resist bulk water, and an interior polyethylene sheet to resist water vapor, or a single layer may be capable of controlling more than one element at a time. <\/span>Illustration credits BuildingScience.com Corporation (BSC). <\/em><\/span><\/figcaption><\/figure>\n

\u00a0Control layers<\/strong><\/p>\n

The control layer systems approach acknowledges there are four primary elements that need to be controlled: bulk water, heat, air, and water vapor; and two secondary elements: UV light and sound. Each element may be controlled by a separate layer within the building envelope. For example, an exterior water-resistive layer to resist bulk water, and an interior polyethylene sheet to resist water vapor, or a single layer may be capable of controlling more than one element at a time (Figure 1). Another example would be a metallic faced membrane serving as a barrier to bulk water, air, water vapor, and UV light (Figure 2).<\/p>\n

Water-resistive air barriers (WRABs)<\/strong><\/p>\n

A critical and often misunderstood component of the building envelope is the WRAB. This component may be capable of performing multiple control functions required by the building envelope.<\/p>\n

WRABs are often constructed using manufactured sheet goods or site-applied liquid membranes, installed to prescribed thicknesses. Each method has its own application advantages and disadvantages, and is often used in combination to leverage these advantages on a project. For instance, a wall assembly may use sheet goods to wrap long straight sections of a window surround, and then apply a liquid to connect more difficult-to-wrap corners or curved sections of the opening (Figure 3).<\/p>\n

\"Figure<\/a>
Figure 2<\/b> A metallic faced membrane serving as a barrier to bulk water, air, water vapor, and UV light. <\/span>Image courtesy Siplast Inc. <\/em><\/span><\/figcaption><\/figure>\n

The role of a WRAB, in order of importance, is as follows:<\/p>\n