Townscape Architects have experience with new build PassivHaus and refurbishment Enerphit projects, and can offer guidance from concept design, assessment, contractors and completion certification. Whether it is a new eco home or retrofitting and old one, Townscape Architects can assist you throughout the project. Please contact our team for further advice.

Passiv Haus Standards Introduction

The term ‘PassivHaus’ refers to a low energy construction standard developed by Dr Wolfgang Feist of the PassivHaus Institute in Germany. It is now the fastest growing energy performance standard in the world.

The core focus of the PassivHaus Standard is to dramatically reduce the requirement for space heating and cooling, whilst also creating excellent indoor comfort levels. This is primarily achieved by adopting an envelope first approach to the design, by specifying high levels of insulation to the thermal envelope with exceptional levels of airtightness and the use of whole house mechanical ventilation.

The PassivHaus – definition       “A PassivHaus is a building, for which thermal comfort can be achieved solely by post-heating or post-cooling of fresh air mass, which is required to achieve sufficient indoor air quality conditions – without the need for additional recirculation of air.”

PassivHaus do not conform to any one design style; therefore a PassivHaus can either be of traditional, or a more contemporary design.

 

Basic principles

As Passivhaus is a performance based ‘energy’ assessment the following targets define the standard and need be met in order for certification to be achieved.

Specific Heating Demand

(or) Specific Heating Load

 

≤15kWh/m2.yr

≤10W/m2

 

Specific Cooling Demand

 

≤15kWh/m2.yr

 

Specific Primary Energy Demand

 

≤120kWh/m2.yr

 

Airtightness ≤0.6ach @50pascals(n50)

 

 

Thermal comfort is also a very important issue within Passivhaus. A certified Passivhaus should not fall below 16°C, even without heating during the coldest winter months; this is due to the excellent thermal performance and low air infiltration rates.

Guideline Targets

Achieving a space heating requirement of 15kWh/m2/yr or less means that the following guideline targets need to be achieved as a minimum:

  • A recommended opaque fabric U-values of ≤0.15W/m2.
  • U-values for windows and doors (for both the frame and glazing) need to be ≤0.8W/m2K (0.85W/m2.K installed).
  • Thermal bridging ideally needs to be eliminated or minimised, a psi value of <0.01W/m2K is considered thermal bridge free.
  • An air pressure test must result in an n50 airtightness level of 0.6ach, averaged over pressurisation and depressurisation.
  • Whole house mechanical ventilation with heat recovery (MVHR) that is 75% efficient or better, with a low specific fan power.

 

EnerPHit Standard

Whilst it is possible to achieve the new build Passivhaus Standard in the refurbishment of an existing building and be fully certified as a “Quality-Approved Passivhaus”, it is often difficult to achieve without undertaking major works which involve greater costs.

The EnerPHit Standard has been developed as a good practice refurbishment guide for Passivhaus renovations and, provided the verification criteria are met, certification to the EnerPHit Standard can be achieved by achieving slightly more generous standards compared to Passivhaus.

The EnerPHit specific energy demand criteria, compared to Passivhaus, are as follows:

Criteria Passivhaus EnerPHit

 

Specific Heat Demand ≤15 kWh/ m².yr

 

≤25 kWh/ m².yr

 

Primary Energy Demand

 

≤120 kWh/ m².yr

 

≤120 kWh/ m².yr

 

Airtightness n50 ≤0.6 n50 ≤1.0

 

 

PHPP Passivhaus Planning Package (PHPP)

The Passive House Planning Package (PHPP) is a Excel based energy calculation tool. It is based around the same core energy calculation methods used throughout Europe.

It is produced by the Passivhaus Institut as a design tool to model the performance of a proposed Passivhaus building. The PHPP is intended for use by anyone involved in the design of a Passivhaus, and a Passivhaus must be modelled by using the PHPP to verify that the Passivhaus criteria have been met.

Within PHPP there are a series of tools designed for:

  • calculating energy balances
  • calculating U-values
  • designing comfortable ventilation
  • calculating the heating and cooling load
  • summer comfort calculations
  • localised climate data
  • many other aspects of Passivhaus dwellings.

 

Certification

Passivhaus certification is a quality control process that ensures your building will perform as designed.

The following targets define the standard and need be met in order for certification to be achieved.

Specific Heating Demand

(or) Specific Heating Load

 

≤15kWh/m2.yr

≤10W/m2

 

Specific Primary Energy Demand

 

≤120kWh/m2.yr

 

Airtightness ≤0.6ach @50pascals(n50)

 

 

 

Certifying Passivhaus units

A single Passivhaus unit can be a detached house or multiple dwellings, meaning a row of terraced houses, a multi-storey apartment block or a single story bungalow can all be certified as one Passivhaus unit. The reason is that Passivhaus certification always assesses the thermal envelope of the entire block.

To calculate the treated floor areas it is important that all areas outside the thermal envelope but are still within the construction of the development are excluded ie, integrated garages, entrance lobbies, unheated loft space (cold roof), unheated basements and stairwells in multi-residential buildings that are not heated are to be excluded from the floor areas. These areas may introduce some sheltering effect and require a temperature reduction factor calculation; hence, details of their thermal properties (if any) may be required.

Detached dwelling

A detached dwelling is considered to be one Passivhaus unit.

 

Semi detached dwellings

A semi detached dwelling is considered to be one Passivhaus unit even though there are two dwellings, as these dwellings would normally form part of the same thermal envelope, they therefore should be certified as one Passivhaus unit. [Note it is possible to certify each dwelling separately provided they are thermally separated and the party walls have a known thermal resistance].

 

Terraced dwellings

Terraced dwellings are considered to be one Passivhaus unit even though there are multiple dwellings, as these dwellings would normally form part of the same thermal envelope, they

therefore should be certified as one Passivhaus unit. [Note it is possible to certify each dwelling separately provided they are thermally separated and the party walls have a known thermal resistance].

Multi storey apartment block

Multi Storey apartment blocks whether they are single story, double or triple storey should be certified as one Passivhaus unit, provided the dwellings form part of the same thermal envelope. If there is an unheated space or stairwell separating the habitable areas then this requires further assessment.

Multi storey apartment block with non-domestic unit

Multi storey apartment blocks with non domestic units can be assessed separately provided they are sufficiently thermally separated between the building structures of both units, or if there is an unheated space or stairwell separating the habitable areas from the commercial unit. If the dwellings and non-domestic unit are not thermal separated then they should form part of the same certification.

Non domestic units

Non-domestic Passivhaus units are treated in the same way as domestic Passivhaus units and the thermal envelope should always form the boundary of the certified Passivhaus.