Sustainable Building Technical Manual - Etn-presco.net

Decisions about construction details also play a crucial role in design of the buildingenvelope. Building materials conduct heat at different rates. Components of the envelopesuch as foundation walls, sills, studs, joists, and connectors, among others, can createpaths for the transfer of thermal energy, known as thermal bridges, that conduct heatacross the wall assembly. Wise detailing decisions, including choice and placement ofinsulation material, are essential to assure thermal efficiency.. ☛ SUGGESTED PRACTICES AND CHECKLISTIClimate Considerations❑ Assess the local climate (using typical meteorological-year data) to determineappropriate envelope materials and building designs.The following considerations should be taken into account, depending on the climate type.– In hot/dry climates use materials with high thermal mass. Buildings in hot/dry climateswith significant diurnal temperature swings have traditionally employed thickwalls constructed from envelope materials with high mass, such as adobe andmasonry. Openings on the north and west facades are limited, and large southernopenings are detailed to exclude direct sun in the summer and admit it in winter.A building material with high thermal mass and adequate thickness will lessen anddelay the impact of temperature variations from the outside wall on the wall’s interior.The material’s high thermal capacity allows heat to penetrate slowly through thewall or roof. Because the temperature in hot/dry climates tends to fall considerablyafter sunset, the result is a thermal flywheel effect — the building interior is coolerthan the exterior during the day and warmer than the exterior at night.– In hot/moist climates use materials with low thermal capacity. In hot/moist climates,where nighttime temperatures do not drop considerably below daytimehighs, light materials with little thermal capacity are preferred. In some hot/moistclimates, materials such as masonry, which functions as a desiccant, are common.Roofs and walls should be protected by plant materials or overhangs. Large openingsprotected from the summer sun should be located primarily on the north and southsides of the envelope to catch breezes or encourage stack ventilation.– In temperate climates, select materials based on location and the heating/coolingstrategy to be used. Determine the thermal capacity of materials for buildings in temperateclimates based upon the specific locale and the heating/cooling strategyemployed. Walls should be well insulated. Openings in the skin should be shadedduring hot times of the year and unshaded during cool months. This can be accomplishedby roof overhangs sized to respond to solar geometries at the site or by theuse of awnings.– In colder climates design wind-tight and well-insulated building envelopes. The thermalcapacity of materials used in colder climates will depend upon the use of thebuilding and the heating strategy employed. A building that is conventionally heatedand occupied intermittently should not be constructed with high mass materialsbecause they will lengthen the time required to reheat the space to a comfortabletemperature. A solar heating strategy will necessitate the incorporation of massivematerials, if not in the envelope, in other building elements. Where solar gain is notused for heating, the floor plan should be as compact as possible to minimize thearea of building skin.(See also Chapter 11, “Renewable Energy.”)❑ Assess the site’s solar geometry.Solar gain on roofs, walls, and the building interior through window openings can beeither a benefit or a hindrance to heating, cooling, and occupant comfort. A thoroughunderstanding of solar geometry specific to the site is crucial to proper envelope design.(See also Chapter 5, “Sustainable Site Design” for further discussion.)