{Originally wrote as technical note around 2005}


The following technical note indicates some of the constraints on design that need to be considered when modifying an existing dwelling, by increasing internal floor area by enclosing a roofed area with glazing. (eg. A verandah or porch).

Such extensions are generally not intended to increase habitable floor area, and are unique in that the existing external wall will retain its external characteristics: weather-proof wall, windows and external door. The major risk posed by such an extension is its impact on access and egress to the main dwelling and the building in total. With respect to energy efficiency the enclosure is more of a weather-lock that should be considered to improve the energy efficiency of the existing dwelling. However, an enclosed space needs a building classification, and once classified it then needs to comply with Building Code of Australia (BCA) or SA Housing Code requirements for that class of building. If the space is classified as habitable then the new room and the rest of the house are subject to the most stringent of requirements.

What follows is therefore an attempt to more clearly define and otherwise specify the new space and evaluate the most appropriate methods for assessing its compliance with the BCA. The starting point therefore needs to be with Planning SA, the SA Housing Code and the BCA.

Planning SA, Advisory Notice Building 28/02 (November 2002) states:

“The Building Code of Australia (BCA) provisions for energy efficiency in housing will be adopted for implementation from 1 January 2003.”

 And then goes on to further indicate:

“The SA Housing Code will incorporate BCA provisions for energy efficiency, as they apply in South Australia, in Amendment 9, also to be adopted from 1 January 2002. The Housing Code includes further useful information on insulation values for various forms of construction to assist designers and builders to meet the requirements of the BCA.” [take 1 January 2002 to mean 2003]

 It indicates that there are several options available for assessing compliance with the energy efficiency requirements:


These methods of assessment are principally concerned with assessing the energy efficiency of the building fabric, and exclude assessment of building services, such as the hot water supply.

Planning SA, Advisory Notice Building 29/02 (November 2002) states:

Where it is reasonable to increase the energy efficiency of the house, then the deemed-to-satisfy provisions should be applied to both the alterations and the existing house.

 For example: – Alterations to roof cladding or ceilings are an opportunity to introduce the required roof insulation.

Additions of one or more new habitable rooms must comply with the deemed-to-satisfy provisions (walls, floors, roofs and windows).

Although non-habitable rooms do not need to comply, consideration should be given to maintaining continuity of the insulating barriers to habitable rooms (walls, floors,roofs).

Where a habitable room is increased in size the extended portion must comply with the deemed-to- satisfy provisions (walls, floors, roofs and windows) and it is reasonable to expect that the roof insulation will be carried back into the house at least sufficient to completely cover the room being extended.

The energy efficiency of the roof/ceiling, walls, floor and glazing of the alteration or addition should be not less than the energy efficiency of the building before the alteration or addition.”

What is actually required and acceptable is dependent upon the meaning of the term : “TO THE DEGREE NECESSARY”. A table is attached to the advisory note indicating priority areas for compliance. In general this table indicates that only the new work needs to be assessed against the energy efficiency requirements, but in some instances the existing building also needs to comply but typically only to the extent of roof/ceiling insulation.



Porches tend to be small spaces, whilst verandahs tend to be large spaces, either case people typically spend a significant amount of time occupying such space especially during summer. The reason for enclosing such space is to extend its usefulness throughout the other seasons. The reason for choosing glazing for the enclosure is to retain the views available from the space, and also from the windows of the main dwelling. The human comfort levels expected from the space are no different than those expected from a verandah, a lobby, conservatory or garage. Such comfort levels being either hot or cold, damp and draughty. Activities carried out in such a space being compatible with such an environment.

Unfortunately Building Surveyors and other Building Controllers assess spaces on their future potential rather than their actual usage. The future potential of such spaces is as family rooms, lounges, studies and even bedrooms. However, it does need to be pointed out that such potential is relative to the acceptance of the existing comfort levels for such purpose. Some cultures spend their entire lives outdoors or living in tents, caravans or make shift dwellings. Hence comfort levels are subjective and not absolute.

It should also be noted that there is also a trend towards adopting some of the more traditional tropical architecture for summer conditions. This architecture brings the outside into the house, and brings the inside out into the garden. In consequence there is a region that is neither garden nor dwelling, but an interface between the two, an exterior-room, if wanting for a simple name. If the weather conditions at any time prove uncomfortable within the exterior-room, then intelligent occupants would retreat to the security and comfort of the dwelling-proper.

The question therefore is when is a room with external walls to be classed as an exterior-room and thus assessed by differing criteria than the BCA would otherwise require, and what is this criteria?


  1. All enclosures, glazed or otherwise attached to the exterior wall of a house/dwelling are best described as “exterior-rooms” or “indoor/outdoor” living areas. Whilst they may well become the most used rooms within a dwelling, there is no justification for them to be fully compliant with the Building Code of Australia requirements for a habitable room.
  2. The exterior wall to the existing or main dwelling shall retain the functionality and characteristics of an exterior wall though now interior to the extended dwelling. That is both windows, and external doors are retained, along with the external finish of the wall.
  3. Features that characterise its exterior nature are to be retained. All modifications that detract from or otherwise mask its exterior character are unacceptable.
  4. Performance characteristics that are considered suitable for exclusion from full compliance are weather proofing and energy efficiency.
  5. The integrity of the main dwellings exterior with respect to compliance with the BCA is to be retained at the interface with the exterior-room. (eg. The weather-seal is to be re-instated at structural connections.)
  6. The building fabric is not required to be fully weatherproof. (eg. Heavy rainfall can leak into the room, but no construction detail shall permit transport of such moisture to the main dwelling.)
  7. Internal Linings to walls and ceilings to be wet-area quality.
  8. Floor to meet the wet-area set-down requirements or equivalent.
  9. Only floors and floor coverings suitable for exteriors and/or wet-areas are acceptable. (eg. Brick paving is acceptable, and actually most preferable). A concrete floor slab shall be clearly jointed so as to visibly permit moisture penetration, otherwise it shall be fully compliant with BCA weatherproofing requirements for habitable areas.
  10. Electrical Lighting to the room is to use exterior quality light-fittings.
  11. Electrical Power points to the room are to be external quality weatherproof fittings.
  12. An exterior-room is only partially weather-proof, but being an enclosed space is subject to the access and egress requirements necessary to ensure security from hazards.
  13. Being a structure the exterior-room is subject to all the requirements of structural adequacy. Adequacy however is defined at a lower level of serviceability. (eg. Higher deflections are permitted as is compatible with a lack of weather-proofing).
  14. Heating, cooling and ventilation of the space is purely a consequence of the enclosures fabric and human activity. The main dwelling is considered to loose heat to, and gain heat from the exterior-room. The exterior-room is a weather-lock or trap, between the internal and external environments.
  15. An exterior-room is expected to be cooler and/or warmer than other rooms in the main dwelling. It is also expected to be “damp” by comparison with other interior rooms.
  16. The room would generally be used for activities that could and would otherwise be conducted outdoors, if factors other than but also including the weather are considered. Such other factors include, but are not restricted to : privacy, noise.
  17. The use of the room would generally include activities that generate significant heat loading from human action itself: physical exercise for the sake of exercise, playing games, gardening etc.
  18. Typical description would include but not limited to: conservatory, sunroom, sun-porch, work-room, lobby, weather-lock, vestibule, patio, anteroom, outhouse, exterior-room. But with such description subject to the above conditions.
  19. Such room is explicitly excluded from conversion to any of the following or similar: bedroom, lounge, dining room, family room, study.
  20. All modifications to rooms with external walls require building approval. (this includes internal-walls with the characteristics of an external-wall)
  21. A register of properties with rooms given building approval for exterior-rooms will be maintained, and such properties will be subject to random checks. And they shall be checked for compliance prior to sale of said property.
  22. If desired the building owners can be required to sign a statement of acceptance of the above criteria.

A room that does not comply with all of the above points is not an exterior-room and shall be fully compliant with existing BCA classification requirements.

Building owners are thus provided with two cost options comply with:

  • Exterior-room specification OR
  • Habitable room requirements


Failing to get acceptance of the above concept of an exterior-room, and failure to obtain classification as a non-habitable area within the current context of the BCA, will require the enclosure to comply with all the rigours of the BCA, including weather-proofing and energy efficiency requirements. Here we are only concerned with the energy efficiency requirements, and that poses a compliance problem, hence the reason for attempting to define the space in such a manner that it is excluded from compliance.


The problem largely concerns glazing. Whilst the building addition/extension itself only generates a requirement for itself to comply with the BCA, with the existing dwelling being exempt, the addition/extension in general cannot comply with the SA Housing code prescriptive requirements. Whilst it is easy enough to provide prescribed levels of insulation for the walls and roof of the addition/extension, prescriptive limitations to the glazing are likely to result in the building modification not being wanted.

Inclusion of the entire house into the energy efficiency assessment using prescriptive measures will typically require increasing the insulation levels of the entire building. This would tend to put a low cost renovation into the too expensive basket. Forcing improvements to energy efficiency prior to improvements to space arrangements.

Another unfortunate situation is that many households have taken measures to improve the energy efficiency of their houses, but the level of insulation added to the dwelling is not compliant with the now regulated levels of insulation required. Any additional insulation added to comply with the energy efficiency requirements, will most likely result in exceeding such requirements. Whilst this maybe considered good, it does not necessarily result in any additional benefit to the building occupants. Lifestyle is the greater determinant of fuel consumption and the installed heating/cooling appliances.

Given that the capacity of typical heating/cooling appliances is around 1.8 kW to 2.4kW, it is the efficient use of such appliances that is the primary determinant of over all energy efficiency. A 2.4kW portable fan heater for example is not very effective at warming anything other than a small room. In a large room it can provide personal warmth to anyone close by and who does not move. The typical household does not employ heating/cooling and ventilation systems that have been engineered to maintain the entire air-mass of the building or a given room at comfortable conditions. For the most part heat is lost to the internal airspace long before it reaches the building fabric and is lost to the external environment. That is a significant temperature differential exists within the building spaces itself. Thus proper conditioning of household airspaces is likely to result in increased energy demands.