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 Alf Calculation

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Results graph - Energy Gains and Losses (kWh/year)

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ALF Calculation Report

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Project Description

Current Design:

Designed by:

  • Address:
  • Owner Name:
  • Street:
  • City:
  • Phone No.:
  • Lot No.:
  • DP No.:

ALF Results Energy

The results in this section are calculated from the designer inputs including occupancy, and heating temperatures and schedules.

Energy Heat Flows

The information in the table gives you an overview of all the heat flows in and out of the designed building, based on the heating temperatures, climate and schedule the designer has selected. It allows you to evaluate the importance of the thermal performance of individual building components - for example, of particular windows.

  Net Area Loss Gain Useful Gain
  m2 kWh/year % kWh/year % kWh/year
  • Suspended Floor Loss:     kWh/year
  • Slab Floor Loss:     kWh/year
  • Wall Loss:     kWh/year
  • Window Loss:     kWh/year
  • Roof Loss:     kWh/year
  • Skylight Loss:     kWh/year
  • Air Leakage:     kWh/year
  • Warm-up:     kWh/year
  • Total Load:     kWh/year
  • Solar Gain:     kWh/year
  • Internal Gain:     kWh/year ( occupants)
  • Total Gain:     kWh/year
  • Gain Load Ratio:    %
  • Effective Thermal Mass Density (per m2 total floor area):     W/m2 °C
  • Specific Heat Loss Density (per m2 total floor area):     W/m2 °C
  • Usefulness of Gains:    %
  • Useful Gains:     kWh/year
  • Required Heating Energy:     kWh/year

NZ Building Code Compliance

In order to comply with the Energy Efficiency Clause H1 of the New Zealand Building Code a building has to have a BPI of less than 1.55 kWh/(m² . °C . month) in any location throughout New Zealand.

The current design's BPI is:       

The acceptable solution of Clause E3 of the NZBC requires that R-values for walls, roofs and ceilings shall be no less than:

  • For light timber frame wall or other framed wall constructions with cavities, 1.5.
  • For single skin normal weight masonry based wall construction without a cavity, 0.6.
  • For solid timber wall systems no less than 60 mm thick, 0.6.
  • For roof and ceilings of any construction, 1.5.

Modelling Assumptions

This section lists the modelling assumptions concerning the building design, climate and heating. It defaults to the Building Performance Index assumptions & requirements as set out in H1.

Building Design


  • Total Floor Area:     m2
  • Number of Occupants:     (BPI calculation formula adjusted)

Suspended floor:

  • Floor area:     m2
  • Perimeter Length:     m
  • Perimeter Height:     m
  • Floordeck R-value:     m2°C/W
  • Subfloor R-value:     m2°C/W
  • Bulk Insulation R-value:     m2°C/W
  • Floor Covering R-value:     m2°C/W
  • Total Suspended Floor R-value:     m2°C/W

Slab Floor:

  • Floor Area:     m2
  • Perimeter Length:    m
  • External Wall Thickness:    m
  • Soil Conductivity:    W/m°C
  • Under Floor R-value:    m2°C/W
  • Slab and Ground R-value:    m2°C/W
  • Floor Covering R-value:    m2°C/W
  • Total Slab Floor R-value:    m2°C/W

Air Leakage:

  • Basic Airtightness:   
  • Chimneys for open fires:   
  • No. of flued heaters:   
  • Window Passive Vents:   
  • Retrofit airtightening:   
  • Kitchen vents over hob:   
  • The location-independent Air Leakage Rate is
  • Site Exposure:   
  • Wind Zone Factor:   
  • Local Air Leakage Rate:   
  • House Volume:    m3

Thermal Mass:

Floor type Area Thermal Mass Density
  • Total Floor Area (used for Furniture and Ceiling):    m2
  • Total Thermal Mass:    kWh/°C
  • Effective Thermal Mass:    W/°C


  • Location:    in the
  • Annual Loss Factor:   
  • Annual Gain Factors:
  • Internal Gain Multiplier:   
  • Wind Zone Factor:   
  • NZS 4218:1996 Climate Zone:   


As set by BPI requirements:

  • Heating Schedule:   
  • Heating Level:   
  • Calculation Date:   

This copy of ALF 3.2 is registered to .

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Base design.
  • Load: kWh
  • Gain: kWh
  • Useful Gain: kWh
  • BPI:
  • Heating: kWh
Current design.
  • Load: kWh
  • Gain: kWh
  • Useful Gain: kWh
  • BPI:
  • Heating: kWh

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Moisture results

Room Mould likelihood Time walls >80% Relative Humidity (hrs)
Time for wall to dry (hrs)

Current Project:

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Results Summary

BPI target:

Specific losses

Susp. floor: W/°C
Slab floor: W/°C
Walls: W/°C
Windows: W/°C
Roof: W/°C
Air leak: W/°C
Warm-up W/°C


Loss: KWh
Warm-up load: KWh
Window gain: KWh
Internal gain: KWh
Heating: KWh

 Create an ALF account

Register now to create your free ALF account.

Every user needs to create an ALF account. Creating an ALF account will ensure:

  • Confidentiality for your project.
  • Allow BRANZ to record usage of the ALF tool – BRANZ cannot access any individual projects. Your privacy is assured.