Satisfying NCC Performance Requirements with Skylights

Authored by Damon Stewart, Building Solutions Engineer at DDEG

The use of natural light in buildings is not a modern idea. One of the most effective methods of incorporating natural light into a building is via skylights, the first examples of which can be found back in Ancient Rome, which were open to the outside as the technology to implement glazing within buildings had not yet been developed. While the technology of glass has progressed significantly since then, the powerful statement that natural light can make within a building remains constant. Skylights are a popular method to harness the power of natural light within buildings.

In addition to providing buildings with natural light, skylights also provide a range of benefits to buildings, and the occupants within them. These include a variety of health benefits to occupants, reduced energy costs, increased spaciousness, enhanced aesthetics and increased property value. These are some of the many reasons as to why skylights remain a popular feature within both domestic and commercial buildings to this day.

The Building Code of Australia (BCA) recognises that skylights/roof lights are an effective method of providing natural light to buildings. Deemed-to-Satisfy (DTS) Provision F4.2 from the BCA Volume 1 and Acceptable Construction Provision 3.8.4.2 from the BCA Volume 2 stipulate that required natural light can be provided by windows that have an aggregate light transmitting area of not less than 10% of the floor area of the room, or via roof lights that have an aggregate light transmitting area of not less than 3% of the floor area of the room. A proportional combination of windows and roof lights can also be used when necessary.

As per the Guide to the BCA Volume 1, a roof light generally receives greater exposure to sunlight than a window because of its orientation to the sky and consequently, the size of a rooflight as a percentage of the floor area served is permitted to be smaller than for a window serving the same floor area, hence the 3% of the floor area of the room for skylights compared to 10% for windows. While the BCA recognises that skylights are an effective tool to provide buildings with natural light, skylights are not a Deemed-to-Satisfy type of roof cladding under both Volume 1 and Volume 2 of the BCA.

The inclusion of skylights as a roof covering is contrary to the approved materials detailed under BCA Volume 1 DTS Clause F1.5. BCA Volume 1 DTS Clause B1.4 states that for Performance Requirements BP1.1 to BP1.4 to be satisfied, glazed assemblies such as skylights must be designed and constructed in accordance with AS 1288. Although the BCA Volume 1 DTS Provisions do not list skylights as an acceptable roof covering, skylights that satisfy Performance Requirement FP1.4 will be deemed as acceptable roof coverings.

Under Part 3.5 of the BCA Volume 2 for Roof and Wall Cladding, the inclusion of skylights as a roof covering is contrary to the approved materials detailed in this section. Part 3.5.1 and 3.5.2 from the BCA 2019 Volume 2 stipulate that where an alternative roof cladding is proposed as a Performance Solution, that proposal must comply with Performance Requirements P2.1.1 for Structural Stability and Resistance and P2.2.2 for Weatherproofing in order to be considered as acceptable roof coverings. Acceptable Construction Provision 3.6.0(b)(iv) stipulates that Performance Requirement P2.1.1 is satisfied for glazing if skylights are designed and constructed in accordance with AS 1288. The Acceptable Construction Provisions found in the BCA Volume 2 do not provide any guidance on satisfying Performance Requirement P2.2.2.

As such, skylights need to be covered by a site specific Performance Solution to evaluate the proposed skylight design against the relevant Performance Requirements outlined in the BCA, in order to be considered as an acceptable roof covering.

On July 1st, 2021, the formal Performance Solution process came into effect under A2.2(4) of the BCA. A2.2(4) states that where a Performance Requirement is proposed to be satisfied by a Performance Solution, the following steps must be undertaken:

(a) Prepare a performance-based design brief in consultation with relevant stakeholders.

(b) Carry out analysis, using one or more of the Assessment Methods listed in (2), as proposed by the performance-based design brief.

(c) Evaluate results from (b) against the acceptance criteria in the performance-based design brief.

(d) Prepare a final report that includes—

?????????????????(i) all Performance Requirements and/or Deemed-to-Satisfy Provisions identified through A2.2(3) or A2.4(3) as applicable; and

???????????????(ii) identification of all Assessment Methods used; and

??????????????(iii) details of steps (a) to (c); and

??????????????(iv) confirmation that the Performance Requirement has been met; and

????????????????(v) details of conditions or limitations, if any exist, regarding the Performance Solution.

The Performance Solutions that DDEG provides follow the process of A2.2(4). DDEG can provide Performance Solutions for skylights that meet relevant Performance Requirements of the BCA and have done so for a wide range of buildings under both Volume 1 and Volume 2 of the BCA. Furthermore, these Performance Solutions have covered a variety of skylight manufacturers and designs including Velux, Atlite, Belle, Solatube, and many different custom skylight designs.

Ultimately, the need for a Performance Solution for skylights is at the discretion of the Relevant Building Surveyor. However, as skylights are not a Deemed-to-Satisfy type of roof cladding, a Performance Solution can be provided such that skylights can be considered to achieve the required performance outlined in the BCA.?

References

ABCB. (2019).?Guide to NCC Volume 1 - Building Code of Australia 2019.?Canberra: Australian Building Codes Board.

ABCB. (2020).?National Construction Code Series Volume 1 Amendment 1 - Building Code of Australia 2019.?Canberra: Australian Building Codes Board.

ABCB. (2020).?National Construction Code Series Volume 2 Amendment 1 - Building Code of Australia 2019.?Canberra: Australian Building Codes Board.

Crystal Structures. (2016, August 12).?The History of Skylights - How the Idea of Daylighting Began. Retrieved from Crystal Structures: https://crystalstructuresco.com/skylights-history-daylighting

Inspired Spaces. (n.d.).?The Benefits Of Having A Skylight. Retrieved from Inspired Spaces: https://www.inspiredspaces.com.au/the-benefits-of-having-a-skylight/

Sorenson, J. (n.d.).?15 Reasons You Need As Much Natural Lighting In Your Home As Possible. Retrieved from Elemental Green: https://elemental.green/15-reasons-you-need-as-much-natural-lighting-in-your-home-as-possible/