Construction Envelope and Architectural Considerations

Various architectural components necessitate careful examination in the formulation of a net-zero energy structure, including considerations for the building's positioning, fenestration, external surface reflectivity, shadowing, and interior finishing.

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Construction Envelope and Architectural Considerations.

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Building Alignment.

Productive daylighting initiates with optimal alignment. Furthermore, the orientation of the building also impacts power generation, solar thermal accumulation, and other factors that influence energy consumption. In environments such as classrooms and most other spaces, the vertical façades which facilitate daylighting should align within a range of 15°, extending to a maximum of 30°, towards either the north or south. Glass installations facing east or west pose challenges due to an increase in solar thermal accumulation, difficulty in providing shade, and a potential for uneven daylight distribution.

The orientation becomes less critical if zenithal lighting is the primary daylighting strategy, given that skylights do not respond to orientation and roof monitors can be manipulated on the roof to achieve a northern or southern alignment. When placing the building on the site, ensure that the daylighting openings are not obstructed by neighboring structures, trees, or elements of the building itself, such as self-shading. Ambient noise levels should also be taken into account when choosing the type of daylighting system.

Fenestration.

The ratio of glazing to wall and floor area impacts daylight harvesting as well as solar thermal gain. The interplay between climate zone, daylighting system, fenestration and ceiling height, shadowing, view necessity, and other design factors contribute to a successful daylighting plan.

Cool Roofs and Outdoor Surface Reflectance.

Exterior surfaces can influence thermal gain and daylighting in a building depending on their material and color. Evaluate the reflective qualities of roof materials, sidewalks, and other surfaces that are nearby or incorporated in the building. Utilizing lighter hues can amplify daylighting intensity and, in certain cases, diminish the glass area required for roof monitors or clerestory windows. However, surface colors and façade design should be critically analyzed, as some configurations may generate undesired reflections and glare.

Shading.

A crucial element of any effectively daylit structure is to restrict direct sunlight penetration. Implement strategies that bounce, redirect, and filter sunlight so that direct radiation does not enter the space for any substantial duration.

Limiting direct solar invasion can be accomplished through proper orientation as well as shading, filtering, baffling, and/or reflecting solar radiation at each daylighting opening.

The successful operation of daylit buildings is also contingent on the occupant's interaction with the daylighting system. This is particularly true for adjustable blinds or shades. Occupants are inclined to close the blinds but less likely to reopen them, tending to set blinds for long-term adjustment. If blinds remain closed, the daylighting potential will not be actualized. Avoid installing shades or blinds on the daylighting glass if temporary darkening of a specific space is not functionally necessary. Superfluous blinds will lead to decreased performance, escalated initial costs, and increased long-term maintenance expenses.

Interior Finishes.

The color selection for the ceiling, walls, floor, and furniture considerably impacts the effectiveness of the daylighting and electric lighting strategy. When considering finishing surfaces, install light colors to ensure that daylight is dispersed throughout the space.

Consider ceiling tiles or surfaces with high reflectivity. Ensure that the reflectance of the ceiling tile light includes the fissures within the acoustical tiles, as these irregularities influence the light absorption level. The color of a tile alone should not be presumed to dictate its reflectance. When choosing a tile, stipulate a minimum reflectivity. Most manufacturers will list reflectance as if it were the paint color reflectance.

Thermal Insulation.

Continuous thermal insulation forms the core of a net-zero energy building’s envelope. Substantial insulation values in the roof, the walls, and below ground level are generally required. This enables the design team to downsize the HVAC system, saving on both initial costs and long-term operating expenses.

Ideal insulation types and values will vary by climate, but continuous exterior insulation is generally recommended to mitigate thermal bridging. For cavity walls, open-cell sprayed polyurethane foam or dense-packed cellulose is additionally recommended. The use of batt insulation in wall cavities is not advised.

Continuous exterior insulation is also desirable for below-grade walls. Rigid extruded polystyrene board is suitable for this application. While interior insulation of below-grade walls has been commonplace in the past, continuous exterior insulation alleviates moisture management issues, simplifies air-barrier and insulation continuity, and facilitates the use of thermal mass for energy efficiency.