Passive House

Definition Considerations Cost Appearance How To North American Map

1. What is a ‘Passive House’ building?

A ‘Passive House’ is a building designed and constructed to meet three rigorous building performance benchmarks. The result is a building with very small space conditioning systems, exceptional thermal comfort, exceptional indoor air quality, very durable thermal envelope assemblies and such a low total energy demand that they resiliently coast through potential power disruptions or system malfunctions. Achieving such performance requires passive building envelope strategies that maximize reduction of heating, cooling and dehumidification loads/demand while minimizing potential long term moisture damage  – hence the term ‘Passive’.

A ‘Passive House’ building, simply stated, is one that meets the following 3 pillar benchmark criteria:

  1. Annual space heating/cooling demand  and hourly peak heating/cooling load maximum. For the Central European climate, the values were originally established at </=4.75 kBtu maximum (1.39 kWh) per ft2 per year (15 kWh per m2 per year) [OR peak load heating </=3.17 Btu/h (0.93 W) and cooling </=2.54 Btu/h (0.74 W) per ft2] (10 W heating, 7.96 W cooling/m2). The PHIUS+ 2015 Passive Building Standard – North America adjusts the value to the specific North American climates (annual temperature, humidity and solar radiation). For example, the climate zone in Southern Wisconsin/Northern Illinois, the values are:
    • </=6.3 kBtu (1.85 kW) per ft2 (19.9 kWh per m2) maximum annual heating demand
    • </=3.6 kBtu (1.06 kW) per ft2 (11.4 kWh per m2) maximum annual cooling demand
    • </=7.3 Btu (2.14 W) per ft2 (23 W per m2) maximum hourly heating load, and
    • </=6.3 Btu (1.85 W) per ft2 (19.9 W per m2) maximum hourly cooling load
      • Current U.S. codes do not currently establish a maximum.
      • This benchmark causes a thicker, better insulated, building envelope and strategically located very high performance glazed windows and doors
  2. Building envelope air leakage maximum. </=0.05 cfm/ft2 of exterior surface of total building envelope (including slabs and below grade walls) when tested at 0.2 w.g. (50 Pascals) [1 lb./ft2] pressure differential, OR </= 0.08 cfm/ft2 (0.04 L/s * m2) when tested at 0.3 w.g. (75 Pascals) [1.5 lb./ft2]
    • The definition of an air impermeable material is one that leaks </= 0.04 cfm/ft2 (0.02 L/s m2) of material surface area when tested at 0.3 w.g. (75 Pascals) [1.5 lb/ft2] pressure differential
      • The 2012 and 2015 ICC International Energy Conservation Code (IECC) currently adopted in much of U.S. requires testing only for residential buildings at up to 5.0 interior volume Air Changes per Hour (ACH) at 0.2 w.g (50 Pascals (1 AC/12 minutes). If buildings other than residential chose to test, code allows up to 0.4 cfm/ft2 (2.0 L/s m2) of building surface area when tested at 0.3 w.g. (75 Pascals) [1.5 lb/ft2].
      • This benchmark causes the minimization of air and humidity flowing through the building envelope regardless of the changes in weather. As a result, the risk of vapor laden air moving into the envelope and cooling whereby the vapor condenses into water trapped within the assembly.
  3. Total Source (Primary) energy demand maximum. </= 6200 kWh per person per year for dwelling units (presuming the number of occupants = 2 persons for 1st bedroom plus 1 person for each additional bedroom) and </=38.1 kBtu (11.2 kW) per ft2 per year (120 kWh per m2 per year) for other occupancies/building types. Demand is inclusive of space heating/cooling/dehumidification, domestic (service) hot water production, household (plug load) electricity and auxiliary (equipment/system operation) electricity.
    • Source (Primary) energy, unlike Site (Final) energy includes the amount of energy expended to harvest fuel source, transport it to energy conversion plant (i.e. electrical plant or fuel refinery) and distribute or transmit it to site. Site (Final)) site energy is only that consumed at the project site. In the US, the factors for converting site (final) energy to Source (Primary) are between 2.894 and 4.022 (3.16 average) depending on which of the 4 mixed electric grids the site/building is connected for electricity and 1.1 for all other fuel sources. (Source – US EIA and 2012 ICC IECC)
      • U.S. codes do not currently establish a maximum.
      • This benchmark limits the total CO2e emissions per person or building floor area unit causing the need to maximize efficiency of energy using systems (some of which are already smaller in size due to 1st pillar benchmark above) and conscious efficient use of systems by the building occupants.

Pillar 1 causes need for: Glazed windows and doors of superior air tightness and thermal performance such that interior side maintains a temperature high enough for comfort and condensation prevention and to prevent air and humidity from moving through these ‘weakest links’ in the building envelope.

Strategic design of shading of glazing prevents undesired solar radiation gains in climates or seasons where they could cause overheating of building interior.

Pillar 2 causes need for: Though not required by definition, Passive House recommends maintaining an average intentional ‘balanced’ ventilation rate between 0.3 and 0.4 Air Changes per Hour for air volume within 2.5 m (8.2 ft) of floor in residential dwellings (higher or lower in other building use types based upon occupant load density). ‘Balanced’ ventilation means exhaust rate equals supply rate which helps insure air and humidity leakage through the building envelope is not increased due to pressure differential caused by ‘unbalanced’ ventilation.

Ventilation may be ‘natural’ through open windows and doors when outdoor conditions are pleasant. When ‘natural’ ventilation is not available or adequate, ‘mechanical’ ventilation must be provided to adequately introduce ‘fresh’ outdoor air and exhaust ‘stale’ indoor air for the purposes of human health and comfort.

Passive House does not prevent ventilation rates from being lower during no or low occupant load times and higher rates during times of high occupant load, elevated indoor humidity or elevated indoor odor, so long as the average daily rate is adequate to maintain health and comfort.

Current U.S. codes require a central ventilation system with a rate based upon a formula that considers both floor area and number of occupants. The formula does not give consideration to the number of air changes per hour and does not require the system to be balanced.

Pillar 3 causes the need for: Efficient systems, lighting, appliances and other equipment. This pillar is, in the Passive House way of thinking, to follow meeting the first two pillars. By meeting the first two pillars, the size of systems have been already minimized in size – thus reducing their annual energy demand. Understanding that energy consuming systems are ‘active’ systems requiring maintenance and eventual replacement is why Passive House elects to emphasize passive measures first.

Passive House criteria establish the lowest building energy demand framework in on Earth and results in permanently comfortable, healthy, durable and affordable buildings. The Passive House mantra – First reduce demand so dramatically and permanently that they may maintain comfort with little to no added energy, then, harvest a small amount of energy on site to satisfy the remaining demand for current day conveniences.

passive-house-heating-cooling

2. What does Passive House consider?

Inevitable future costs

  • Routine/recurring maintenance will be reduced
  • Capital replacement for things that wear out will be reduced
  • Energy use will be dramatically reduced (55 to 65% overall, 80 to 90% for space heating/cooling)
  • Reduction in monthly/annual operating costs will be immediate and permanent and will, at least in part, offset initial cost of improved building features. If cost of improved building features are financed monthly or annually, they are offset each month/year by operating cost reduction for term of financing. At end of financing term, operating cost reduction is retained.

Human motivators

  • Long term financial gain (lowest lifetime cost)
  • Recurring expense reduction (lowest operating cost)
  • Improved health (most healthy/clean/hygenic air environment)
  • Increased comfort (most even/consistent temperatures wall to wall, floor to ceiling, adjacent to glazing)
  • Reduced time maintaining own environment (durable materials and compact systems)
  • Increased time for enjoyment (less maintenance, more fun)
  • Feeling positive about reduced impact on environment and others (global conscience)
  • Future energy use reduction retrofit capital costs are virtually eliminated, leap frog to the future
  • Other resource (i.e. water, peoples time, etc.) needs are reduced

Due to very low energy needs

  • Many options for fuel source when fuel need is small to tiny
  • May produce or harvest all energy on site with small systems – therefore the initial and future replacement capital costs are lower and operation and maintenance costs are lower
  • May well be comfortable/usable with no energy input at all, protecting occupants from utility power outages

Lowest Monthly, Annual and Lifetime costs (in lieu of 1st day purchase cost)

  • Revenue producing potential vs. expense limiting need
  • Routine/recurring maintenance and intensity
  • Systems capital replacement frequency
  • Occupancy/use pattern (density, frequency, duration)
  • Free heat gain (internal [occupants, lighting, equipment] and solar radiation) potential
  • Free cooling and heat prevention (strategic shading, natural ventilation [stack, cross, nighttime])
  • Energy loss (transmission and ventilation) reduction
  • Material durability (minimize hygrothermal related moisture accumulation)
  • Existence and/or length of finance/credit maintenance

Technical concern for hygrothermal activity

  • Heat always moves to less heat until balanced
  • Humidity always moves to a drier environment until balanced
  • Humidity that reaches dew point temperature/pressure will condense into water
  • Air and moisture vapor (humidity) will move through the smallest of openings
  • Water will not move through the smallest of openings, therefore may be trapped
  • Elimination of uncontrolled air leakage will dramatically reduce condensation potential
  • Elimination of uncontrolled air leakage will dramatically reduce undesired weather penetration
  • Elimination of uncontrolled air leakage will dramatically reduce undesired and unnecessary space conditioning energy
  • Undesired humidity can be removed by passing air through an environment below dew point (condensing) temperature or above saturation (evaporation) temperature

3. Will a Passive House have a higher cost?

Lifetime cost

  • If all the features, size and accoutrements of a building are the same, its lifetime cost will be lower
  • Fixed monthly/annual cost of borrowed capital for improved building features are typically immediately more than offset by the reduction in monthly/annual operating cost (and this improves as purchased energy operating costs inevitably rise)
  • The availability of easily distributed energy (in any form) is nearly guaranteed to become more difficult and therefore the cost will inevitably rise
  • Replacement and retrofit costs will be reduced by investing a small increment at the initial construction
  • Lifetime of a building is notably longer than other products we use
  • Through a buildings lifetime, it will not likely have comprehensive renovations more frequently than every several decades – if features of the building envelope has leapfrogged to the future, the renovations may be limited to features other than the building envelope

Building type lifetime duration between major renovations

Building Type Lifetime Duration Between Renovations
Wood frame residential 40 to 100 years (30 years)
Mass (concrete/ICF/masonry/log) frame residential 80 to 200 years (30 years)
Retail/commercial 20 to 150 years (10 years)
Industrial 15 to 50 years (25 years)
Public (transportation, government services, schools, museums, etc) 60 to 250 years (30 years)

Operations and recurring cost

  • More airtight, more compact and smaller systems reduce operating and maintenance cost
  • Smaller systems reduce inevitable future capital replacement cost
  • Low energy demand permanently reduces purchased energy cost
  • Low energy demand make size of optional on site energy harvesting systems smaller (and therefore initial, maintenance and future replacement costs lower)
  • Intentional filtered, energy recovering, 100% outdoor, balanced, correct volume ventilation preserve building envelope integrity, reduce occupant health concerns and minimize energy loss due to unintentional/random/varying volume ventilation through a leaky building envelope – better a building breath through its nose than its skin
  • Durable building assemblies reduce maintenance time commitment and cost

First day cost

  • More than 80% of costs associated with a building construction are not affected.  The relative increase in first day costs are primarily for increased insulation, building envelope air tightness measures and high performance (low air leakage, low transmission loss, high or low solar radiation gain glazing) windows and doors. Unlike larger or more complex mechanical systems, these are one-time purchases with virtually no operation, maintenance or replacement cost. High performance windows and doors due to their details of construction are more durable, thus a longer life and therefore can have a lower lifetime cost of ownership.
  • Some insulation, doors and windows, and some level of building envelope air tightness is required regardless. Choose wisely in the beginning and the need for replacement later is reduced.
  • Mechanical systems are both different and smaller – ventilation and heating/cooling are often separated. Space heating load/demand can become so small that the already required and paid for domestic water heating system can easily satisfy the load/demand. If heating load/demand is small enough, space heating/cooling can be provided through the low volume, but constant 100% outdoor air ventilation system. Because of an airtight and very well insulated building envelope, air temperature is near even/constant wall to wall, floor to ceiling – this may allow point source heating/cooling equipment to perform without the need for space using and initial cost or air duct distribution systems and enclosures.
  • Even if an air duct distribution system is provided, it will be smaller and thus will require less space for both equipment and distribution.
  • Because energy demand is low, if on site renewable energy harvesting systems are considered immediately or in the future, they will be significantly smaller and therefore lower in initial, maintenance and inevitable replacement cost

A quote by a now departed colleague
“I am too poor to buy cheap things”

4. Does a ‘Passive House’ building look different than other buildings?

Passive House does not dictate building shape or style. In order to meet the framework pillar criteria there may be some noticeable differences in detail such as:

  • Thicker exterior envelope – foundation, roof and walls (with associated deeper exterior or interior window/door recess)
  • Higher proportion of windows toward desired or away from undesired solar radiation (consideration of orientation based not only on street front, views or aesthetics)
  • Small/compact and more centrally located HVAC and Domestic Hot Water systems
  • Overhead and side/vertical glazing shading devices (roof overhangs, windows recessed, other overhead or side mounted shading devices) to prevent solar radiation gains when they are undesirable
  • Varying glazing types (U value, Solar Heat Gain Coefficient) depending on climate or orientation
  • Vented exterior building cladding to allow moisture within the building wall assemblies to drain and ‘sweat’ to the exterior
  • A high efficiency energy recovery (heat only recovery in climates with stable/comfortable outdoor humidity levels year round) ventilator for continuous, filtered and proper quantity ventilation that recycles/retains desired indoor heat and humidity.
  • May have strategically located operable windows at lower and upper floor levels in climates/seasons where night (cool) time natural ‘stack’ ventilation may be implemented.

passive-house-construction

5. How do I go about creating a Passive House building?

Accomplishing Passive House 3 pillar benchmark criteria requires detailed and diligent energy modeling/calculations during design and quality assurance testing/verifying of building envelope (including doors, windows and penetrations), mechanical/plumbing/electrical systems, and optional energy harvesting systems during construction.

  • Passive House does not mandate or reward for specific strategies or systems to achieve the benchmark criteria, nor is there a single method of meeting the 3 pillar criteria. Approach/strategy is flexible and up to the designers and builders discretion/creativity and cost/availability of materials/components at/near the project site.
  • Prior to construction (new or retrofit) design and modeling/calculations must be prepared to indicate conformance with 3 pillar benchmark criteria. If the building is to be certified, this information must be submitted for review and pre-certification to the Passive House Institute US (PHIUS). Certified Passive House Consultants (CPHC®) have been trained in the skills necessary to prepare or guide the design and calculations.
  • During and at the end of construction inspections and tests must be performed by a qualified independent Rater/Verifier to insure building was constructed to match the design and model/calculations. The most vital tests include:
    • Building envelope air leakage test(s) performed:
      • as soon as building envelope air barrier is in place and not covered/concealed allowing for correction before covering, and
      • when construction complete just prior to occupancy to insure conformance with air leakage framework criteria
    • Balancing/commissioning of mechanical ventilation system to insure total building ventilation rate and individual room exhaust and supply air rates are as designed and energy model calculated
    • Balancing/commissioning of space conditioning systems to insure distribution to each room or space is as design intended and energy model calculated
    • Verifying size, length and insulation on domestic (service) water heating piping to insure they match inputs in energy model calculations
    • Verifying proper operation of equipment, systems and automated controls related to heating, cooling, dehumidification, water heating, pumps, lighting, energy harvesting, etc.
  • If the building is to be certified, inspections and tests must be performed by qualified third party(ies) and documentation submitted to PHIUS for approval.
  • If wish to achieve PHIUS+ certification (which simultaneously obtains the US EPA Energy Star V3 [which uses IECC 2009 as its measure] and US DOE Zero Energy Ready Home [which uses IECC 2009 as its measure]  additional site inspections, and verification checklists must be completed by a PHIUS + certified Rater and other members of the project team. PHIUS+ certification is required for all residential projects certified by PHIUS. Commercial projects are to have all of the same tests and verification required by PHIUS, but need not meet the added requirements of Energy Star V3 or Zero Net Ready Home. Some of these tests and inspections are beyond those listed as required by code.
  • Certified Passive House Consultants CPHC® have been trained in skills in what to look for during inspections and how to direct other third parties for testing building envelope air leakage and mechanical ventilation systems.
  • PHIUS certified Raters have received training from PHIUS that provides them the skills and knowledge specific to Passive House buildings that are beyond those required for HERS ratings, Energy Star or the US DoE Challenge Home. Raters must first be a certified RESNET rater with the skills required to energy model, complete tests, commission ventilation and forced air heating cooling/systems and complete inspection checklists in accordance with RESNET protocols.

6. North American Passive House Map

Passive House is currently the fastest growing energy efficient building techniques in the US. Following the framework pillar criteria results in the lowest energy demand of any building standard and results in very durable and very healthy indoor air quality.  Throughout Europe and Asia, there are 10’s of thousands of Passive House (Passivhaus) Buildings. There are currently many Passive House projects that have been completed, or are currently under construction, all over North America. The map below displays all of the Passive House projects in North America. Simply click the map for an interactive view of Passive House projects. Blue represents certified (designed, energy modeled, constructed and verified). Red represents Pre-certified (designed, energy modeled and under construction – but not yet verified). Green represents registered.
passive house map

Definition | Considerations | Cost | Appearance | How To | North American Map

Passive House