Roof Light Common Practice Solution

Why Develop A Common Practice Solution?

Local common practice is to use “dome skylights” to provide natural light to internal spaces. This Common Practice Solution has been developed to allow industry to take advantage of skylight natural lighting performance that three times that of vertical glazing, and to provide the generic thermal performance data that verifies energy efficiency compliance.

Where, When, and Who Can Use This Common Practice Solution?

This Common Practice Solution is recognised by Building Industry Development (BID).

It can only be used in Western Australia, only applies for the Building Code of Australia Volume 2 for Class 1 and 10 Buildings (BCA), and must be declared to the approving Local Authority prior to the issue of a Building Licence.

How Is DTS Equivalence Achieved?

BCA Part 3.8.4.2 Natural lighting describes construction that is Deemed-to-Satisfy (DTS) Performance Requirement P2.4.4 Lighting (natural light at a level of illuminance appropriate to function or use).

3.8.4.2 Natural lighting – sub-clause (a) (i) requires natural light to be provided to a habitable room by a window. In Part 1.1.1 Definitions, a window includes a roof light or other device (skylight) which transmits natural light directly from outside a building to the room concerned.

An area of vertical glazing that is 10% of the floor area of a habitable room is deemed to satisfy the level of natural light illuminance required. Expert evidence is provided to verify that a skylight (0 to 35 degrees above the horizontal plane) is (at least) three times as efficient as a source of natural light illuminance sourced from a vertical window. Therefore a roof light that is 3% of the floor area provides an equivalent level of illuminance to vertical window that is 10% of the floor area.

BCA Part 3.12.1.3 Roof lights describes DTS construction that meets Performance Requirement P2.6.1 Building (level of thermal performance to facilitate the efficient use of energy).

3.12.1.3 Roof lights – sub-clause (a) (i) requires roof light (skylight) performance to be as per Table 3.12.1.2 for nominated ranges of shaft index and roof opening area (as a percentage of floor area).

A typical “dome skylight” is defined as having a 3mm thick acrylic roof dome (clear or opaque), an enclosed roof-to-ceiling shaft, and an imperforate (sealed) ceiling diffuser.

Expert evidence is provided to verify that the Total U-value and SHGC performance data for the roof light configurations nominated, when translated from calculated NFRC values to accepted ANAC equivalence, comply with Table 3.12.1.2.

What Evidence Is Provided To Verify DTS Equivalence?

Click the link below to read the full text version which includes construction sketch and expert verification.

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