The Low-Carbon House:
Performance Energy Standards:
CSH Level 6 / Carbon Lite 'Gold'

• The following standards correspond to:
  - Code for Sustainable Homes Level 6
  - AECB Carbon Lite Programme 'Gold'

• Excellent levels of insulation.
• Minimal thermal bridges.
• Advanced windows.
• Excellent levels of airtightness.
• Effective orientation for winter solar gains and summer cooling.
• Mechanical ventilation with heat recovery and very efficient in its use of electricity.
• Space and water heating normally from a large solar heating system supplemented by a lowpowered gas, oil or LPG fired condensing boiler.
• Lighting by high-efficiency fluorescent lamps.
• Electrical appliances normally A+ rated or better.
• Sufficient on-site electricity generation from renewables to offset the electricity used for lighting, appliances and ventilation.
• A guidebook to explain to users how/why the building differs from normal.

This page sets out the details of the performance version of the energy standard for CSH Level 6 / Carbon Lite 'Gold'. It explains the underlying objectives of the standards - specified as savings of 85% in energy and 95% of CO₂ relative to the existing building stock (Based on an 80 m² semi-detached house) - but it does not state in detail what one must do to meet these objectives.

Performance standards appeal mainly to building designers who want greater freedom than the prescriptive version of a standard allows. They allow designers who cannot meet one or more elements of the prescriptive version of the standards; e.g., a maximum ratio of glazing to wall area, or a principal facade orientated within 30° of due south, or windows with a low frame fraction, to trade off these parameters against others to a limited extent.

The performance version of the standards still sets upper limits to some parameters which cannot easily be upgraded later, such as floor, wall, roof and window U-values and air permeability. This is to ensure that the building's CO₂ emissions are minimised without reliance on extra highperformance heating and ventilation systems, or solar panels on the roof; i.e., equipment which could later be removed or whose performance could later degrade. These minimum levels help to ensure that CO₂ emissions are more reliably reduced in the long term.

• Basic passive solar design, subject to site limitations.
• Design the building so that daylighting can displace substantial amounts of electric light.
• Set aside an area of wall or roof to retrofit solar thermal or photovoltaic panels if ever
needed.
• Provide space to retrofit solar tank if applicable

• Calculations using the performance version of the standards must normally be performed using PHPP. This is available directly from the Passivhaus Institut or from AECB. PHPP-2007 covers most small to medium domestic and non-domestic buildings fairly thoroughly. More sophisticated simulation tools may be used for larger and/or more complex domestic and non-domestic buildings. Use Manchester weather data, which is close to the UK average, for complying with overall energy targets.
If, using PHPP or a more advanced tool, the predicted primary energy use and CO₂ emissions are both ≥15% below the limit for that building type and size, designers may describe the project as follows: “Exceeds the minimum requirements of the CSH Levels 4,5 and 6”.

• Calculations using the performance version of the standards must normally be performed using PHPP. This is available directly from the Passivhaus Institut. PHPP- 2007 fully covers domestic and non-domestic buildings of various types.

3 For further details of U-values, please see the footnotes to the prescriptive standards. The procedures for calculations of space heating energy consumption are set out in CLP VOLUME TWO: PRINCIPLES AND METHODOLOGIES - Calculating and minimising CO₂ emissions and heat loss from buildings.

The first group of U-values is based on the UK convention of measuring elemental areas internally and expressing the additional impact of the non-repeating thermal bridges as a y-value. The second group of U-values presupposes the use of "thermal bridge-free" construction and the practice of measuring elemental areas externally, as in PHPP.

4The uninstalled and installed U-values for external doors and windows are weighted averages for the whole building. The weighted average can be calculated using PHPP for the proposed window sizes and styles.

Because the glazing edge and frame U-values exceed the centre-of-glass U-value, buildings with many small windows, or windows with many divided lights, have a higher window U-value than buildings with larger single-light windows from the same manufacturer, even though all these windows have exactly the same frame and glazing type. Fenestration made from certified Passivhaus windows but containing large numbers of transoms and mullions can have U-values of >>0.90 W/m²K.

5 The acceptability or otherwise of a design can be assessed with PHPP. Use 25°C as the maximum comfort temperature. Use the geographically closest weather station for overheating calculations; see notes to the prescriptive standard.

To meet the limit, buildings with a high surface-to-volume ratio; e.g., small detached and semidetached houses, need U-values below the maximum.

All individual dwelling units in a group of attached dwellings must meet this limit to useful space heating energy. So under Steps 2 or 3, the average dwelling in a row of houses, or in a block of flats or maisonettes, will normally use less than 15 kWh/m²yr, but the most exposed dwellings in the block will use very close to 15 kWh/m²yr. The weighted average for the block of flats or the row of houses, if the block or the row is viewed as one building, will be less than 15 kWh/m²yr.