What is a Passive House?

The concept of ‘Passivhaus’ was developed by Dr Wolfgang Feist who wanted to improve the energy efficiency of buildings. In simple terms a Passivhaus, or Passive House, is a super-insulated structure, with minimal thermal bridges, very low air-leakage, has mechanical ventilation and generates power passively through solar gain.
The Passive House standard aims to prevent over and under heating, through the creation of a building envelope which can retain heat and does not require active forms of heating such as radiators and gas fires.
The Passive House standard is neither confined to traditional housing nor to new dwellings. Passive House construction has been implemented on various types of buildings including apartments, office blocks, schools and nurseries. In addition to this it is possible for older dwellings to have a quality-approved energy retrofit with “Passive House Components”.

What is a Passive House Certification?

Although many modern houses employ various methods and systems which benefit from alternative energy, such as air or ground source heat pumps and solar PV systems. Passive House builds must conform to a specific certified building standard issues by the Passivhaus Institut, located in Germany.

To meet these standards a building must meet a long list of requirements relating to air tightness, energy efficiency and construction standards before it can be officially recognised.

What is the Passive House Design Certification criteria?

For a building to meet the standards required of a Passive House, the following criteria must be met:

  • A space heat demand of less than 15 kWh/m ².yr for a new building, and 25 kWh/m ² for a retrofit.
  • An air leak pressure test result of: <0.6 ach @ 50 Pa; or <1 ach @ 50Pa for a retrofit – This measures how much air leaks through the fabric of the building.
  • A primary energy consumption rate of less than 120 kWh/m ².yr – This should account for heating, hot water, lighting, cooking, appliances, and active cooling (air conditioning).
  • A frequency of below 10% for overheating during the summer – This being how many times the internal temperature of a prospective Passive House exceeds 25° C.

How does a Passive House work?

As the Passive House is the world leading standard in energy-efficient construction, with a Passive House requiring as little as 10% of the energy consumed by the standard Central European building, there is great interest shown by those who want to all but eliminate their annual energy costs.

Following the concept created by Dr Wolfgang Feist, these affordable and high-quality buildings utilise the following simple principles:

With the continual improvement of building designs there are fewer joints and cracks which affect the level of airtightness within a building envelope. Due to this the ventilation provided by small openings is not sufficient in allowing air to remain fresh indoors. Potential recommendations such as opening multiple windows will also not be adequate. Fresh air is not merely linked to comfortable living but also to positive health, with high indoor air quality being a basic performance standard for any Passive House. Ventilation systems are a preferred solution to this problem and are vital inclusions in all retrofits and future builds.

Despite good ventilation systems being an additional investment in the short term, they will result in significant savings for monthly and annual energy costs, on the provision that they are highly efficient. Systems which meet the Passive House standard will ensure the operating costs of any build are noticeably lessened.

This principle is a central focus of the Passive House concept, which targets the large volumes of air necessary to be supplied into a building’s interior and utilises it for heating purposes as well. Without demanding any additional air, and not needing any further recirculation the ventilation system pays off twice. Transferring the heat energy from the stale internal air and transferring it to the incoming cooler air.

The notion of ‘supply air heating’ can only be utilised in appropriately insulated buildings. In simplified terms the transmission and infiltration heating loads must be blow 10 W/m² to verify adequate levels of heating can be maintained.

What makes up a Passive House?

Passive House is designed to create a comfortable and stable internal climate without active heating and cooling systems operating. In accordance with this, multiple characteristics must be present to ensure a house could be certified as ‘Passive’:

Airtight Construction: This is required to prevent external moist room air from penetrating into a house’s interior, where it can create mould and adversely affect the conditions of the recycled air present.

Omission of Thermal Bridges: Heated air will commonly follow the easiest and least resilient path to the outside. These pathways are known as ‘thermal bridges.’ Conventional housing builds will have multiple thermal bridges, usually manifested as inefficient windows, openings in doors, and low-level insulation present in walls and roofing. Passive Houses’ remove the presence of these thermal bridges by installing superior insulation throughout a home and setting up sealed windows and doors.

First-Class Insulation: The quality of insulation present within a house is the largest factor in ensuring a home structure reduces the potential for heat transfer between internal and external climates. This insulation will be implemented comprehensively throughout a house’s walls, roofing and even below the build to prevent heat being lost in any direction.

Effective Ventilation Systems: The central ventilation system present must be able to continuously swap out stale and ‘polluted’ internal air, with external fresh air, whilst maintaining a comfortable and consistent temperature with stable humidity levels.

Passive Solar Heating: This, in layman’s terms, is heat provided by the sun which enters the house through highly efficient windows, providing an effective amount of heat energy.

High Spec Windows: As Passive Houses need to effectively allow heat to enter, but prevent escape, it is necessary for triple-paned windows with low e-glazing, argon gas and insulated frames to be utilised.


New House Concept

Does a Passive House need heating or cooling?

Whilst Passive Houses’ have greatly reduced energy and heating demands due to the built-in retention and ventilation recycling system. There may be times where a boiler is needed to speed up a room’s temperature change in extreme conditions. During this time having an efficient heating system, like an air or ground source heat pump in place would resolve these issues. However, due to improved efficiency and heating regulation present within a Passive House, a smaller heat pump system can be installed to meet an owner’s requirements.

How much energy does a Passive House use?

According to Passivhaus Certification Standards a residence must consume less than 15 kWh of electricity per square meter annually for heat regulation. With conventional total energy usage not exceeding 120 kWh/(m²a). Additional renewable sources such as solar panels the energy supply may come under 60 kWh/(m²a).

Passive Houses’ must also be airtight with air change rates being limited to n50 = 0.6/h. As such during the warmer seasons of the year, excessive temperatures may not occur no more than 10% of the time.

How thick are a Passive Houses’ walls?

Passivehaus Standards do not demand any particular method of construction, allowing for solid, wood or composition construction to take place depending on an owner, or architects, preferences. The Exterior Insulation and Finish System (EIFS) state insulation thickness should range between 150 and 300mm within a Passive House.  This level of thickness can also be bonded up to 400mm depending on house specifications.

Having a thicker wall will result in a greater U value, translating to more energy being retained within a property; with this improved retention comes lowered heating demands.

What is Passive Heating and Cooling?

Passive heating and cooling can be differentiated from one another by the manner in which they employ energy.

Passive heating uses available energy sources such as heat created as a by-product of an appliance, solar energy and body heat to increase the temperature of a house; with the various components of a build such as the walls, windows and floors being designed to retain and recycle this heat where suitable.

Passive cooling is a design which aims to control heat conditions and thermal dissipation in order to improve the indoor thermal comfort of a residence. This process will use little to no energy. The process of passive cooling works by preventing heat from entering the interior (heat gain prevention) or by removing unnecessary heat during hot conditions (natural cooling).

Natural cooling employs energy in close proximity to a premises, such as the natural environment and the building envelope to dissipate heat without the use of electrical or mechanical devices.

Passive House builds allow for heating and cooling related energy savings of up to 90% when compared to standard buildings, and still over 75% when equated against average new builds.

What is a Passive Heating System?

Passive heating systems can also be known as passive solar designs, which sees a building design take advantage of a building’s site, climate and materials present to minimise energy usage. A comprehensive passive solar home will first reduce the heating and cooling loads through energy-efficient strategies and then compensates for any supplementary loads with solar energy.

Passive heating systems will often take advantage of window positioning and orientation to increase window glass exposure to the daily sunlight. General guidelines recommend windows and other devices facing within 30 degrees of true south and should avoid obstacles which can block out this solar exposure during the heating seasons during peak hours.

From this concept stems a ‘Direct Gain’ system design which sees sunlight enter the house through south-facing windows and striking masonry floors and/or walls, which will absorb the solar heat. During the night-time, when temperatures have cooled, the thermal mass material will release the heat back into the house.

Thermal Mass is also a major consideration for any passive heating system as different materials such as concrete, brick and tile ought to absorb heat from the Sun during heating seasons and absorb heat from the warm interior during the cooling season.

Is a Passive House worth it?

One of the main questions asked when regarding Passive Houses’ is the perceived expense which comes alongside a new build. Whilst the initial costs may be higher than those of a standard building, it is important to recognise a Passive build as being a long-term investment which will greatly reduce energy costs on a daily basis.

Whilst the costs of construction for items such as high-performance triple glazed windows and thickly insulated walls can be higher than their standard counterparts, these expenses will be recouped over the years due to lower running costs.

As Passive Houses’ make efficient use of the energy in their surroundings there is little need for significant temperature corrections made by devices such as powerful air-conditioning units. Passive House builds do not necessarily have to be overly complex requiring high building costs but can instead be comparable to standard builds so long as passive build guidelines are followed. As such a smaller, more financially lenient option can be taken.

In addition to this as the heating requirements for these houses are so low, homeowners are presented the possibility of not needing to install gas lines. Instead of using gas lines to power fires and oven hobs, an electrical hob/fire supplied by a solitary electric cable can be used as an alternative. This would cut another noteworthy build cost. With heat loads reduced by up to 90% electricity becomes a viable alternative for powering heat pumps in the event they are needed. Zero Net Energy buildings can actually cost less with a passive design due to the buildings reduced energy footprint.

A final point to consider it that due to Passive House’ being so efficient, everyday expenses will be substantially lower than average houses, with monthly outgoings being reduced noticeably. Some banks may recognise the savings made from this and offer cheaper mortgages due to the energy efficiency. These points combined make a compelling argument for why a Passive House can be just as price competitive as standard houses.