What is The Best Wall Construction for a Passive House?

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 for Passive Wall Design

Con­tin­u­ous insu­la­tion in passive exterior wall design is essential to creating a quality building envelope and energy-efficient home. The ASHRAE Standard 90.12013 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 Vapor Permeable, Weather-Resistant Barrier for 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.

High Thermal Mass Material for Passive Wall Design

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.

Utilize the Bautex Block Wall System for Best Wall Construction for a Passive House

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.