Essential Elements of Passive House Design

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High thermal mass Fox Blocks produce a home with continuous insulation and moisture-resistance, vital factors in passive house design.

Passive house design aims to reduce a home’s depen­den­cy on mechan­i­cal energy while ensuring a healthy indoor envi­ron­men­tal quality (IEQ) and providing a high level of comfort to the family.

A successful passive house design requires that the wall system and other components of the building envelope work together with the home’s ori­en­ta­tion, window and room placement, shading, and ven­ti­la­tion. Ultimately, passive house design strives towards achieving a net-zero energy use home.

The Wall System of Passive House Design

The best wall system for a passive house design includes con­tin­u­ous insu­la­tion (CI), a vapor permeable, weather resistant barrier (WRB), and high thermal mass building products.

CI keeps the heat outside in the summer and inside a house in the winter. The WRB stops air and moisture flow through the walls. Air and moisture flow through the walls puts stress on the heating and cooling systems, and can negatively impact the integrity and indoor environmental quality (IEQ) of a home. It also increases energy use and utility bills.

Thermal mass materials stabilize temperature shifts within a home by slowing the rate of heat transfer, which saves energy and creates a more comfortable space for the occupants of the house.

The Importance of Continuous Insulation for Passive Wall Design

A passive house design that produces a tight building envelope and energy-efficient home, requires CI. The ASHRAE Standard 90.1−2013 defines CI as uncompressed across all struc­tur­al members without thermal bridges except the fasteners and service openings. A critical component of passive wall design involves wrapping a building’s envelope, including the exterior walls, with a layer of CI, which increases the effective R‑value of the home.

Why a Passive Wall Design Needs a Vapor Permeable WRB

Passive house design aims to stop the infil­tra­tion of both air, moisture, and wind-driven rain into the wall system with the use of a vapor-permeable WRB. A vapor permeable WRB also stops water from accumulating within the wall systems.

Wood-framed homes, in particular, require a WRB because CI can block a wood-framed wall from releasing moisture from within the wall system. Moisture within the wall system can lead to mold, which can degrade a home and create health problems for the family. A vapor permeable WRB for wood-frame passive wall design allows moisture in the wall system to escape, protecting both the house and its occupants.

Permeable, mass wall systems, like Fox Blocks, provide more resilience to moisture than wood, which makes the need for vapor per­me­abil­i­ty of the air and moisture barrier not as critical.

How High Thermal Mass Materials Contributes Towards Passive Wall Design

Utilizing high thermal mass materials, like Fox Blocks, in passive wall design contributes significantly to an energy-efficient home. High thermal mass products stabilize tem­per­a­ture shifts within the house by absorbing and storing heat energy. For example, in summer or warm climates, thermal mass walls absorb cold air in the evening and store it within the mass of the wall. During the warmer days, these walls stay cool longer, which keeps the interior of the home cool.

Products like wood and steel contain low thermal mass, so do not contribute towards passive wall design. High thermal mass products, like concrete, stone, and brick will help towards passive wall design.

Home and Window Orientation in Passive Solar Design

Passive solar design works with nature rather than fighting it, which results in reduced energy bills. Specifically, the orientation of a home on its site and window placement maximizes or minimizes solar gains and takes advantage of the sun’s energy.

  • Maximize windows on the south side of a home since it receives sunlight throughout the day. The windows also require overhangs to provide shade in the summer and sun in the winter. These windows also allow natural light to bathe the house throughout the day, which reduces the need for artificial light.
  • Minimize windows on the cold, shaded north side of the house.
  • Limit windows on the west and east side of a home.

Ventilation in Passive House Design

Passive design airtightness can trap pollutants (like radon, formaldehyde, and volatile organic compounds). Therefore, passive house design must include ventilation methods, like an energy recovery ventilation system. An energy recovery ventilation system reduces energy loss by moving energy from conditioned air going out to fresh incoming air. Other useful methods of ventilation for passive house design include spot ventilation, such as exhaust fans, along with natural ventilation.

Fox Blocks - a Superior Wall System for Passive House Design Choose

7 Problems with Wood Frame Construction 3

Fox Blocks insulated concrete forms (ICF) for passive house design, will produce energy-efficient, healthy, and comfortable homes. Fox Blocks provide CI, moisture-resistance, and high thermal mass - all crucial features of passive home design.

  • Fox Blocks provide CI with an R-value of 23, that exceed ASHRAE/ANSI 90.1 energy code requirements. Homes built with ICF need 32 percent less energy to cool and 44 percent less energy to heat than similar wood-framed homes.
  • Utilizing the Fox Blocks Energy Stick insulation insert, the R-Value of the wall assembly may be increased to R34,R42 or R52 for passive design.
  • The high thermal mass of Fox Blocks makes it an excellent wall choice for passive house design.
  • Fox Blocks furnish a solid continuous monolithic concrete wall with a perm rating below 1.0, which controls moisture infiltration and stops the growth of mold, rot, and mildew. Therefore, Fox Blocks, for above grade use, do not require a WRB or a vapor retardant.

The Preserve at Mountain Vista

Greenhill Contracting utilized passive house design to create a net-zero neighborhood in New Paltz, New York. Critical elements towards the performance success of these 2,300 square foot homes included a combination of Fox Blocks ICF and spray foam insulation in the roof and under the slab of the home. Together these components achieve a blower door test result of over two times more than the passive house standard. The sustainable design further protects the homes against tornadoes, hurricanes, or earthquakes.

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Why and How to Achieve Passive Home Design

Passive house design strives to create net-zero energy homes. Achieving net-zero energy use requires that all components of the building envelope work together, along with the home’s orientation and window placement, shading, and ventilation. Fox Blocks ICF provides a superb product towards passive house design.