External Shading Devices - how to calculate and meet compliance

Created by Vicki Marshall, Modified on Fri, 20 Dec, 2024 at 11:08 AM by Vicki Marshall

State: All

Assessor Question:

How are external shading devices calculated and how is compliance met?

In my example, Could the 80% shade reduction, or 20% direct sun be calculated 20% of daylight hours?

Summer solstice in Victoria is about 15 hours. 20% is about 3 hours, so will compliance be demonstrated if direct sunlight only reaches the glazing system for three hours or less during summer solstice?

I'm interested in the solar angle calculations, I've searched online for information on this. Does DMN have resources or links to calculation methods?

TechLink response:

Shade cloth and shade sail fabrics, and awning blind material alls come with shade % specifications.
Any cloth with 80% or higher values would satisfy the requirement.
Opaque slats and lattice panels would need to have 80% of the surface area occupied by the solid material.
Angled louvre blades that are angled to admit winter sun, but shade summer sun would need to have some solar angle calculations carried out to confirm that 80% of summer sun was excluded.
Any adjustable blind/screen would need to have summer performance confirmed.
The explanatory information panel provided with 13.3.4(b) assists with understanding the intention of shading devises

Explanatory Information

Shading devices can include fixed louvres, shading screens and other types of perforated or fixed angle slatted
shades.
However, such devices need to be designed for the climate and latitude to ensure that summer sun penetration is restricted, while winter sun access is achieved. Winter access refers to the availability of winter solar gains to offset conducted heat losses.
The impact of shading is assessed with respect to the solar heat gain of the glazing.

The requirements of 13.3.2 and 13.3.3 consider solar heat gain to be either beneficial or detrimental to the energy efficiency of a building based on seasonal variation (winter/summer), climate zone, orientation and P/H. Higher P/H values are more beneficial in minimising summer solar heat gain where as lower P/H values are more beneficial in allowing winter access.
Gutters can only be considered as providing shading if attached to a shading projection such as a verandah, fixed

The definition of the shading effect as envisaged by 13.3.4(b) hinges around the word 'Device' and is explained in the extract here.

be provided by an external shading device, such as a shutter, blind, vertical or horizontal building screen with
(b)blades, battens or slats, which;
(i)is capable of restricting at least 80% of the summer solar radiation; and
(ii)if adjustable, is readily operated either manually, mechanically or electronically by the building occupants.

Eaves are building elements not a device and are covered in 13.3.4(a)

Wing walls and neighboring obstructions are not included within the Elemental DtS provisions for impact on shading.

The use of NatHERS assessments are more flexible and nuanced than Elemental DtS provisions and accordingly have the ability to deliver more cost- effective specification results in most situations.

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