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Passive design of a home must include an exterior wall system constructed with a superior level of continuous insulation a complete air- and moisture barrier, and a high degree of thermal mass. Continuous insulation keeps heat energy inside a home in the winter and heat energy outside in the summer. The air- and moisture barrier prevents air infiltration through the walls which causes more work for heating and cooling systems and more energy use. Thermal mass walls absorb and delay the impact on interior temperatures of a home caused by changes in external conditions, making occupants more comfortable and further reducing energy use.
The primary goal of passive design is to reduce a home's dependency on mechanical energy. However, passive design must also ensure a healthy indoor environmental quality and provide a high level of comfort to its occupants. Successful passive design of the whole house requires that the wall system and other elements of the building envelope work in combination with the home’s orientation, room and window placement, ventilation, and shading. The best wall construction for a passive design home includes continuous insulation, an air and moisture barrier, and a high thermal mass building system.
Continuous insulation in passive exterior wall design is essential to creating a quality building envelope and energy-efficient home. The ASHRAE Standard 90.1-2013 defines continuous insulation as insulation that is uncompressed and continuous across all structural members without thermal bridges other than fasteners and service openings. Wrapping a building’s envelope, including the exterior walls, with a layer of continuous insulation increases the effective R-value of the home and is a key element of a passive wall design.
A passive wall design must include a weather-resistant barrier to prevent the infiltration of both air and wind-driven rain. The selection of weather barrier on wood-framed homes is especially critical, because the use of continuous insulation can block a wall’s capacity to release moisture from within the wall assembly. High moisture levels within a wall system can cause wood rot (due to fungi) and mold growth, which is unhealthy to the occupants of the house. Therefore, wood-frame passive wall design must include a vapor permeable air and moisture barrier to allow moisture to escape. Mass wall systems are much more resilient than wood, therefore vapor permeability of the air and moisture barrier is not as critical.
A high-quality vapor permeable air and moisture barrier shields the walls of a home from water and air infiltration, along with moisture accumulation within the wall systems. It also contributes toward creating an energy-efficient, healthy and comfortable home. Essential to wood-frame passive wall design is a vapor permeable air and moisture barrier.
An essential component of passive wall design is the use of high thermal mass products. High thermal mass materials stabilize temperature shifts within a home by absorbing and storing heat energy. For example, in a warm climate, concrete walls absorb cool air at night and store it within its mass. During the day, these walls will stay cool longer and so will the interior of the home. Steel and wood have low thermal mass and are not good materials for passive wall design. Concrete, stone, and brick have high thermal mass and are good choices for passive wall design.
The Bautex Block Wall System is a high-thermal mass material that provides continuous insulation and the air- and moisture-resistance required for passive wall design. The Bautex insulated concrete block has an R-14 continuous insulation that stops thermal bridges and exceeds the standards and codes of the ASHRAE 90.1 and 2015 IECC. Also, application of the Bautex AMB 20 air and moisture barrier to the Bautex Block wall creates a moisture resistant and airtight house that is ideal for passive house design.
The best wall construction for a passive design creates a tight building envelope with continuous insulation, a vapor complete air and moisture barrier, and high thermal mass systems. A successful passive design also considers the home’s orientation, room and window placement, ventilation, and shading. Passive design reduces a home's dependency on mechanical energy. Passive design also produces a healthy indoor environmental quality and a high level of comfort to its occupants.