What’s the difference between Class 1 and 2 Dwellings? Here are the basics.

Class 1a Dwelling Units
Class 1a Dwelling units have a separating wall between each dwelling unit that extends continuously from the ground to the underside of the roof of the units.

Class 1 buildings cannot be built on top of each other, and each is totally independent of the adjoining class 1a except they share a separating wall.

Please note I did not use the term fire wall. Separating walls function as fire separation, however, they are not fire walls as defined in the BCA Volume 1.

Class 2 Dwelling Units
Class 2 dwelling units are not independent of each other like Class 1a buildings. They can share entries, hallways and roof space, or be built on top of each other.

In a Class 2 Dwelling, the space contained within the floor, walls and ceiling of the dwelling unit, is separated from the other common parts of the building or other Class 2 Dwellings. The separation is achieved by constructing the bounding floor, walls, and ceilings of the dwelling to comply with the required fire, sound, impact and insulation ratings.

Please note I did not use the term fire walls or separating walls. Class 2 buildings do not use fire walls or separating walls to separate dwelling units.

You can read the technical definitions of these classifications here.

Documentation of Decisions

Documentation of Decisions

Decisions made under the BCA should be fully documented and copies of all relevant documentation should be retained.

Examples of the kind of documentation which should be prepared and retained include:

(a) Details of the Building Solution including all relevant plans and other supporting documentation.
(b) In cases where an Alternative Solution has been proposed:

(i) details of the relevant Performance Requirements; and
(ii) the Assessment Method or methods used to establish compliance with the relevant Performance Requirements; and
(iii) details of any Expert Judgement relied upon including the extent to which the judgement was relied upon and the qualifications and experience of the expert; and
(iv) details of any tests or calculations used to determine compliance with the relevant Performance Requirements; and
(v) details of any Standards or other information which were relied upon.

*Extract from the Building Code of Australia (BCA) – Introduction


BCA (Volume 1) A0.9 Assessment Methods and
BCA (Volume 2) 1.0.9 Assessment Methods are similar as below*


The following Assessment Methods, or any combination of them, can be used to determine that a Building Solution complies with the Performance Requirements:

(a) Evidence to support that the use of a material, form of construction or design meets a Performance Requirement or a Deemed-to-Satisfy Provision as described in A2.2 of Volume 1 or 1.2.2 of Volume 2.

(b) Verification Methods such as:

(i) the Verification Methods in the BCA; or
(ii) such other Verification Methods as the appropriate authority accepts for determining compliance with the Performance Requirements.

(c) Comparison with the Deemed-to-Satisfy Provisions.

(d) Expert Judgement.


*Extract from the Building Code of Australia (BCA)


BCA (Volume 1) A0.5 Meeting the Performance Requirements and BCA (Volume 2) 1.0.5 Meeting the Performance Requirements read exactly the same as below *


Compliance with the Performance Requirements can only be achieved by:

(a) complying with the Deemed-to-Satisfy Provisions; or

(b) formulating an Alternative Solution which,

(i) complies with the Performance Requirements; or

(ii) is shown to be at least equivalent to the Deemed-to-Satisfy Provisions; or

(c) a combination of (a) and (b).


*Extract from the Building Code of Australia (BCA)


BCA (Volume 1) A0.10 Relevant Performance Requirements and
BCA (Volume 2) 1.0.10 Relevant Performance Requirements are similar as below *


The following method must be used to determine the Performance Requirement or Performance Requirements relevant to the Alternative Solution:

(a) Identify the relevant Deemed-to-Satisfy Provision of each Section or Part that is to be the subject of the Alternative Solution.

(b) Identify the Performance Requirements from the same Sections or Parts that are relevant to the identified Deemed-to-Satisfy Provisions.

(c) Identify Performance Requirements from other Sections and Parts that are relevant to any aspects of the Alternative Solution proposed, or that are affected by the application of the Deemed-to-Satisfy Provisions, that are the subject of the Alternative Solution.


*Extract from the Building Code of Australia (BCA)

Building Class

Building Classifications and Classes

When you talk to professionals in the industry, they will refer to your building by its classification or class. A classification groups together buildings of a similar use so that the rules that apply to a class, apply to all the buildings in that class. So, it really pays to know the category your proposed building will be under. We have put together a quick list that will help you to easily identify your building project.