Building Envelope for Energy-Efficient Residential Homes, A Case Study for the U.S. Department of Energy Challenge Home Student Design Competition
Creators: name: Tajsic, Milica 
Publisher: name: University of Nevada, Las Vegas
Year: 2014

description: With the continuous rise of population and expansion of urban areas, the need for additional housing and infrastructure is growing rapidly. Building sector is consuming a vast majority of the natural resources to meet the needs of urbanization and is in need of efficient, sustainable solutions that are viable for the customer, the economy and the environment. The building sector is both the problem and the solution to the issues of the carbon footprint of our society (Architecture 2030, 2011). 
The envelope (roofs, walls, and foundations) and windows typically account for 36% of overall energy use, or about 14.3 quads in residential and commercial buildings combined, at an annual cost of $133 Billion. A well designed building envelope can impact 51% of the building energy loads (U. S. Department of Energy National Energy Technology Laboratory, 2009). The purpose of this research is to assess selected types of residential home envelopes and their components. Comparative analysis was used to evaluate the thermal performance and thus the applicability of these components for modern residential buildings, as embodied energy and toxic emissions were also important factors. The research is mainly focused on townhomes as one of the sustainable types of neighborhood development (USGBC, LEED Neighborhood Development program). 
The assumption is that the high performance of the envelope is correlated to the reduction of heating and cooling loads in the interior and consequently, the overall energy and resource consumption of the building through its life-cycle. The derived hypothesis would be that by selecting an appropriate, high-performing building envelope assembly will ameliorate the overall performance of the building, thus lowering its environmental impact in terms of resource depletion and carbon emissions. Further benefits for the users include high levels of thermal comfort, health indoor air, lighting for daily tasks, noise control and an overall reduction in the whole-house energy consumption. This resource management could potentially reflect on the construction budget and later on, the utility costs. 
In order to address the research questions through the most relevant data, a mixed methods approach was selected. Exploratory method, focusing on qualitative research during the first phase was used to examine and document the correlation of different assembly types with their respected components and the thermal performance of the whole envelope. Moreover, quantitative data for the observed characteristic of the assembly components (mostly cavity insulation types) provided numerical values that were compared in order to derive conclusions about different components' lifecycle performance and impact. The quantitative research portion gave firm data necessary for triangulation of the hypothesis and findings gathered in the qualitative, descriptive portion of the research. The research has been informed by examples and case studies elaborated in the literature review. 
The residential attached unit assessed as the case study was designed for the 2014. DOE Challenge Home Student Design Competition. This small footprint, two story townhome unit, was designed to achieve high-performance throughout its lifecycle. Several envelope assemblies were taken in consideration, the decisions being informed by the EEBA (The energy & Environmental building Alliance) and US Department of Energy's Building America Program "Houses That Work" educational training course. The individual assembly parameters were assessed in energy modeling software (REM Rate and HEED) and addressing the issues considering maintenance and durability, as well as construction cost analyses, a specific combination of strategies has been selected. The 1,354 sq.ft residence features SIP and high mass concrete walls, Frost-Protected Shallow Foundations, high performance glazing (U-0.16; SHGC-0.561), a green roof and all ductwork distributed inside the conditioned space. Passive strategies are complemented with efficient active systems including ductless Mini-Split heating and cooling backup units, air circulation through integrated ERV and Radiant Floor Heating. Construction cost strategies included right-sizing and value engineering, elimination of duct systems, elimination of basement, application of prefab or engineered components that lower labor costs and reduce construction waste. 
As a result, this affordable end-unit part of a five-home row housing development for Denver's Sustainability Park was designed to achieve LEED Platinum and Energy Star V3.0 Certification while remaining within financial reach to local families earning Denver's median income. With a Home Energy Rating System (HERS) Index of 7 (100 being the `standard new home'), this all-electric home, is projected to use between 1,157 KWh/year (REM Rate) and 2,263 KWh/year (HEED) and 91% less energy than the LEED Reference Home (Tajsic et al. Aries House. U.S. Department of Energy Home Challenge Student Design Competition. Unpublished) 
High-performing building envelopes designed with sustainable practices in mind have a potential to lower the overall energy consumption of a building throughout its lifecycle and reduce its carbon footprint. Moreover, it's important to select building materials that have the potential to offset the embodied energy of their production through the benefits of their performance within a system. Smart material procurement for wall and ceiling cavity insulation, its proper sizing, installation and maintenance are key for achieving maximum performance of the assembly. Durable, well-sealed sealed envelopes make up for a healthy, long lasting building enclosure that requires the least amount of maintenance or replacement and contribute to the indoor air quality and thermal comfort of the building. 
Topics relating to these issues have a high potential to be evaluated in other research endeavors or tested through different case studies.