G7/VM1
The guidance herein summarises G7 Natural Light Verification Method G7/VM1 Natural Light for all buildings, including those with borrowed daylight, and should be read in conjunction with that below. Speckel provides a unique approach to automate the specific requirements of G7, as per Appendix C. Computer modelling of natural light.
What is G7/ VM1 Natural Light?
Verification Method G7/VM1 applies to all housing, old people’s homes (which includes aged care facilities, rest homes, and retirement complexes), and early childhood centres. It covers buildings with habitable spaces with complex room shapes, borrowed daylight, multiple windows, and other scenarios not included in G7/AS1 and G7/AS2.
The aim of provision G7 is to protect individuals from potential illness or a reduction in comfort resulting from a lack of exposure to natural light and the external environment. Per functional requirement G7.2, habitable spaces must have sufficient openings to allow for natural light and to maintain visual contact with the outside surroundings, ensuring a healthy and connected living environment.
G7/ VM1 Compliance Pathways
Verification Method G7/VM1 provides a solution for complying with the performance criteria in Building Code clauses G7.3.1 and G7.3.2.
G7.3.1 Natural light shall provide an illuminance of no less than 30 lux at floor level for 75% of the standard year.
G7.3.2 Openings to give awareness of the outside shall be transparent and provided in suitable locations.
The Compliance Pathway also includes Table 1.1.3.2, which provides options for demonstrating compliance with G7 Natural Light through Acceptable Solutions and Verification Methods.
For the performance clauses G7.3.1 and G7.3.2, the following solutions and methods are relevant:
Simple buildings up to 3 storeys in low-density developments without borrowed light can demonstrate compliance through G7/AS1.
Simple buildings in low, medium, and high-density developments (including higher-rise buildings and apartments) without borrowed light can demonstrate compliance through G7/AS2.
All buildings, including complex higher-rise buildings, apartments, and those with borrowed light, can demonstrate compliance through G7/VM1.
Determining the Habitable Space
To comply with Building Code clause G7 Natural Light, a habitable space is used for activities normally associated with domestic living. However, it excludes spaces such as bathrooms, laundries, water closets, pantries, walk-in wardrobes, corridors, hallways, lobbies, clothes-drying rooms, or other spaces of a specialised nature that are not occupied frequently or for extended periods. The aim is to ensure that occupants within buildings have access to adequate natural light and are aware of the outside environment to maintain their health and well-being.
Demonstrating G7/ VM1 Compliance
Natural light should illuminate at least 30 lux at floor level for 75% of the standard year for habitable housing spaces and is verified by computer-based daylight modelling and the modelling method chosen.
The minimum daylight factor requirements are deemed to meet the illuminance of no less than 30 lux at floor level for 75% of the standard year.
Modelling Method for Verification of the Design
The design is verified by demonstrating that natural light provides the required illuminance. This can be done using Climate-Based Daylight Modelling (CBDM) or Daylight Factor (DF) modelling. CBDM provides outputs as absolute quantities expressed in lux (illuminance).
When DF modelling is used, outputs are expressed in terms of the percentage of outside available daylight. The calculated daylight factor (DF) should be equal to or more than the values of Table 2.1.2.3 (below) for minimum daylight factor (DF) values for different climate regions (e.g., Auckland, Wellington, Christchurch, Invercargill). Use the daylight factor value for the closest location for locations not listed.
Auckland
0.26
Wellington
0.32
Christchurch
0.27
Invercargill
0.34
Requirements for the Computer Model
Speckel meets all the modelling requirements of G7 - Appendix C. Computer modelling of natural light, using Radiance as the calculation engine (validated per CIE 171) using the Perez All-Weather Sky Model. National Institute for Water and Atmospheric Research (NIWA) weather data for the closest weather is automated, or an alternative climate file can be selected. Illuminance values are calculated for each hour between 8 a.m. and 5 p.m. for the 21st day of each month of the standard year. Illuminance calculation grid placements are defaulted per AS/NZS 1680.1 Appendix B2 “Calculation Grids”.
The computer model should simulate the ingress of daylight into habitable spaces of the building and should accurately represent the geometry, reflectance, and visible light transmittance (VLT) properties of the building and spaces.
The orientation, location (including latitude, longitude, and altitude), and any change of plane (such as a step change in alignment) exceeding 100 mm should be accurately represented in the simulation. This includes architectural features like coves and dropped ceilings, steps in floors, steps/alcoves in walls, etc.
Appendix C Checklist
The following checklist enables a review of the technical requirements of Appendix C. Computer modelling of natural light.
C.2.1 Walls
Are offsets larger than 100 mm in any dimensions included in the simulation? Are curved surfaces simulated as smooth, with the option to facet with a maximum facet dimension of 100 mm?
C.2.2 Internal Details
Are all internal partitions, fixed furniture, and joinery elements that are permanent within the internal area included in the simulation? Is loose furniture excluded from the simulation?
C.2.3 External Details
Are all fixed overhangs, louvres, balconies, and fins that are a permanent part of the building and restrict natural light entry included in the simulation?
Are structures or natural land features restricting natural light entering the building included in the simulation?
If trees are known or anticipated to be present, are mature trees' general form and size represented as solid objects in the simulation? For simplicity, is this suggested to be done?
C.2.4 Windows, Skylights and Openings
Are the dimensions of windows and daylight openings simulated to the nearest 10 mm? Are window opening details (wall thickness, sills, projections, frames, mullions) simulated to the nearest 10 mm?
Is glazing simulated with a visible light transmittance (VLT) based on manufacturer’s data?
C.2.5 Reflectance Factors
Are reflectance factors used in the simulation based on the manufacturer’s product reflectance data and consistent for the final finishes of the building? If the manufacturer’s data is unavailable, are values from Table C.2.5.1A (for interior surface finishes) and Table C.2.5.1B (for other typical New Zealand building finishes) used?
Is the minimum surface reflectance for ceilings, walls, and floors meeting the required medium and high reflectance levels specified in Table C.2.5.1A?
Are the approximate reflectance values for typical New Zealand building finishes as listed in Table C.2.5.1B used when the manufacturer's data is not available?
C.3 Climate Based Daylight Modelling
Is the computer modelling software used for climate-based daylight modelling validated per CIE 171?
Does the computer modelling software use sky luminance based on the CIE 110 Overcast Sky or the Perez All-Weather Sky Model, with input IWEC data from the closest weather station?
Is the weather data derived from a weather station that best represents the building's location and represents an average year for the site over at least a 10-year period?
Is the weather data available online in digital form from the National Institute for Water and Atmospheric Research (NIWA)?
Are illuminance values calculated for each hour between 8 am and 5 pm and for the 21st day of each month of the standard year?
Is the illuminance calculation grid placement applied per AS/NZS 1680.1 Appendix B2 Calculation Grids?
If an interior habitable space is less than 2000 mm in width, is a single line of calculation points placed centrally in the area to be calculated?
AS/NZS 1680.1 Appendix B2 Calculation Grids
The following text is a verbatim replication from AS/NZS 1680.1 Appendix B2 “Calculation Grids”.
When performing lighting calculations using computer programs, if the grid spacing is too large, there will be unacceptable variation in the average illuminance and uniformity with variations in the location of the grid relative to the luminaires. Reducing the grid size will reduce the errors in uniformity and average illuminance. Still, if a small grid is applied over a whole room, the effects of the walls produce unduly pessimistic predictions of these parameters.
Reducing the grid spacing will also increase the calculation time.
When calculating horizontal illuminance in a room using a program that calculates at each of a grid of points the following minimum criteria should be applied:
(a) The maximum spacing of the points should be 200 mm (In very large areas or areas with high ceilings the spacing may be extended to 500 mm).
(b) No calculation point should be closer than 1000 to a wall, partition or vertical obstruction that is included in the calculation.
(c) Uniformity calculations should only be applied to areas of less than 50m². Larger spaces can be subdivided for the purpose of calculation of uniformity.
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