Add an Exterior-Room for Improved Energy Efficiency

An exterior-room is a term I adopted a while back to describe a room which does not meet the building code of Australia habitable space requirements, but which is better than an open verandah, but otherwise does not match the function of a sunroom or conservatory.

When new regulations were introduced requiring estate agents to check building approvals, it became apparent that lots of people had enclosed verandahs and converted them into extra bedrooms without building approval. The owners of these houses were issued council notices requiring they apply for development approval or remove the structure. The current owners of the buildings were not necessarily the people who had enclosed the verandah. We were generally involved inspecting the structures and issuing certificates of structural adequacy. Whilst such certification removed the need to demolish the structures, the rooms were not permitted to be described as extra bedrooms or any other form of habitable space. The reason is that verandahs do not have suitable floor slabs, there is no moisture vapour barrier (MVB) below the slab, the other reason is that roof cladding for verandahs have extended spans because such roofs do not need to be as weather proof as the roof over an habitable space.

The reason a verandah roof does not need to be weather proof is because the wind and rain can blow underneath an open verandah. So roof cladding for verandahs does not have to fully comply with AS1562.1 “Design and Installation of sheet roofs – Metal”. Therefore when testing the cladding it only needs to be strong enough to stay anchored in place, and do not have to be concerned too much about how much it deflects under wind load. The main deflection concern is point load test, and the de-indexing of sheets, that is the separation of the sheets where they over lap. If the sheets separate when a person stands on the sheeting their foot may get trapped under and between the cladding sheets. The result is that steel roof cladding profiles are permitted to span further when used on a verandah roof than when used on a habitable building.

So from the experience of testing roof cladding for use on verandahs, and otherwise certifying structural adequacy of enclosed verandahs, it became apparent that the councils did keep some form of register of non-habitable spaces in approved dwellings: so as to prevent a house from being sold as having 4 bedrooms when it only has 3 such habitable bedrooms.

The next problem encountered, which gave rise to the exterior-room concept, was aluminium window suppliers having a side line enclosing verandahs, and being required to meet the energy efficiency requirements of the BCA. Whilst only the renovated space needs comply with the current version of the BCA, the amount of glass used for such enclosure means that the space has too great a solar gain in summer and too great a heat loss in winter. The only way to counter such requirement is either use less glass for the enclosure, or consider the energy efficiency of the whole house. A renovation which started has low cost starts to escalate into something expensive. The purpose of the exterior-room was to bypass BCA performance requirements, by defining a space which requires different performance criteria.

Since that time other issues have arisen. For example people have gone with the traditional style Australian house providing verandahs all round, and when assessed against the BCA energy efficiency requirements have been found to be inefficient due to heat loss. Crazy! This is Australia our houses get too hot, not cold. in such situation it was also discovered that not allowed to use curtains or similar removable devices to reduce heat loss or heat gain. Something is wrong with the energy efficiency assessments. Using more materials in the construction of our houses is not energy efficient.

People have attempted to set up businesses using Structurally insulated panels (SIP’s) using polystyrene insulation, with limited success. Others have tested extruded plaster panels, but it is clear that the BCA has few if any actual criteria for the performance of building fabric and materials, the BCA is mostly about spaces not building enclosures. The situation also isn’t helped by building surveyors who themselves no longer have architectural or engineering qualifications and as a consequence have limited to no understanding of the fundamentals of design and the required performance characteristics of buildings. Modern building surveyors for the most part just know the regulations, and has I say the BCA has very little to do with buildings and even less to do with construction (NCC).

Similarly there are insulated concrete forms (ICF), and light weight polystyrene external panels. Personally I don’t like any of this use of polymers in buildings. Mostly because I did flame tests at university.

Flame tests on polymers: I cannot remember the details of the tests, they were mostly investigative awareness rather than formal. For example our test specimens were the same as those used for tensile tests, rather than the preferred shape for the flame tests. The tests were carried out in a fume cabinet, unfortunately the fan kept blowing the flames out and so we couldn’t conduct the test. The tutor indicated none of the polymers produced that much smoke, and to turn the fan off. We did so, and carried out the tests, for most of the polymers the flames fizzled out. But one of the polymers created a black viscous, oily smoke, which escaped the fume cabinet, filled the lab and escaped into the corridor filling the top floor of the mechanical engineering laboratory before the extraction fan was switched on {there was some debate about getting it switched on}. This is a test specimen which would be less than 3mm thick and no more than about 150mm long, and only a few millimetres were consumed. Since the tutor was wrong about the smoke, we doubly checked he was right about none of them being toxic. The point is a few millimetres filled the room, so all the wall and ceiling panels in a room setting on fire: that doesn’t strike me as a survivable event. What the polymer was I cannot remember for certain: but it was something like polystyrene or polyethylene.

I don’t care if the polymers can be treated with fire retardants. Most additives added to polymers are volatiles and are released with age, so that at some point in the future the material is no longer protected. As a consumer how do we know the material is properly protected and in the future how do we know it is still protected? Such is not quality robust. To be quality robust the product needs to have and maintain an acceptable level of performance with variations in the production environment and variations in its in use environment.

Consequently I do not like the idea of wrapping an existing house in polystyrene panels to improve its insulation, even less so after the report of the Grenfell Tower Fire in the UK, and the earlier Lacrosse building in Melbourne Australia. Not just because of the materials used but because of the effect of the cavity between the cladding and the existing building fabric. There are detailing issues to consider, and covering a house in external insulation panels, will result in detailing issues at windows and doors, and there is potential for a lot more hassle and hazard than benefit.

It seems to me the best way to improve the house is to go with the passive solar renovations of the 1970’s and earlier. I have another issue, and that is with solar panels (photovoltaic kind PV’s): the extra wind load added to the roof and the needed maintenance of the roof cladding below. If roof cladding needs replacing before the PV’s then it is a large expense getting the panels removed and reinstalled: and that means no power whilst the roof is replaced. {Installing PV’s to sell power to the power companies, isn’t overly sensible and the whole connect to the grid thing is highly questionable. We seem to be living in a world of virtual reality tied up in all kinds of crazy financial wranglings, and losing sight of what takes place in the real world.}

Another issue I have with PV’s, is that the main energy usage in a house is indicated has being for heating/cooling, refer the the your home web site. It is relatively inefficient to convert chemical energy into, thermal energy, into mechanical energy, then into electrical energy and then transport to local houses. If need thermal energy then a district heating scheme is better use of the available energy sources. Not needing the heating at all is even better. Also PV’s are not exactly created from common garden variety materials: thus the more energy you need the more PV’s required and thus the more of these less than common and expensive to produce materials. Thus before considering installing PV’s should first consider the energy efficiency of the house, and energy use requirements.

So energy requirements for heating and cooling the house can be reduced by appropriate design of the house, and such does not require increased use of insulation. Heating of hot water can be done without electricity, and Australia already has experience with the use of solar hot water systems. No sun then no hot water. But then again compare electric storage heater against inline gas heating: with the electric system if the storage tank isn’t large enough, which it often isn’t then no hot water. So if have storage system then use solar heating with larger storage tanks, if use gas or electricity then have inline heating system. That just leaves cooking, large household appliances (freezer, refrigerator, washing machine, dryer, dishwasher, vacuum cleaner), lighting and electronic gadgets. Alternatives to electricity for cooking and refrigeration are natural gas supplied by mains, or there is bottled gas. Though bottled gas may pose a scheduling problem, or be considered an onsite hazard. Anycase for most of the things our ancestors seemed to get by without, or using alternatives which did not require electricity. It should therefore be possible to significantly reduce our power demands such that PV’s and local battery storage meet our needs. But the first big change is to cut the heating and cooling load, and not for new houses but for the existing housing stock: further more the change needs to show immediate benefit.

Insulating a house doesn’t show immediate benefits. The house owner has to incur the expense of the insulation and then wait for their next power bill to see if there is an improvement: chances are there isn’t. The home owner has to do more than simply have insulation installed they need to also change their behaviour: they need to switch their air conditioners and heaters off, and to do that they need a reason. If the devices are thermostatically controlled then the devices may turn themselves off and stay off for longer. But chances are the owners will switch the devices back on and adjust the settings. One important aspect of comfort is airflow, not just the temperature. Since the primary issue in Australia has traditionally been cooling most houses have installed air conditioners, but otherwise use portable fan heaters. So whilst the air conditioner may turn off because the temperature has dropped, the occupants may still need the fan on to keep cool air circulating.

Ceiling fans are better for circulation than the fan on the cooler, but few houses have ceilings high enough for such fans to be safe. The 95th percentile reach is 2264 mm, therefore assuming a ceiling fan space of 300 mm, a minimum ceiling height of 2600 mm would be required. Taking an extra 200 mm rise for walking, then a ceiling of 2800 mm would be better. Such increased height however increases building volume and the required energy to heat and cool. Then again increased volume means it takes longer for the sun to heat the building up, and therefore lower required cooling load.

Portal fan heaters typically only provide local personal warmth, and a lot of heat is lost to the greater space of the room. So whilst added insulation to the house reduces heat loss from the building, it does little with respect to the space immediately surrounding a person. Which is the big problem with the energy efficiency requirements of the BCA because they assume that the internal space of a building is fully conditioned, when it is not. Energy loss is from immediate personal space to the greater volume of the room and then from the room to the building. This is important because our houses have lost the traditional weather-lock porches and mud run/room.

In the past our houses had porches where we could remove our muddy shoes, leave umbrella’s to dry and hang up wet coats. These gave way to open plan housing, such that go for outdoors directly into the house: the wind and rain having direct access to the house. A porch on the other hand acted as a weather-lock between the outdoors and the interior. The door of the porch, typically at right angles to the entry to the house, the outer door closed before the inner door opened. Not only does such arrangement keep the weather out, it also prevents unwanted visitors from viewing the interior of the house. Have two doors to get in and out off the house. Though often only the main front entrance had the porch with rear entrance not having such. In such cases the rear entrance becomes the main entrance for furniture and large appliances. However given that gardens are typically at the rear, it is preferable that the rear entrance is also protected by a weather-lock: where muddy garden shoes can be changed.

The addition of verandahs seems to be big business. Verandahs are seen as a low cost renovation which adds value to a house, which doesn’t have the inconvenience of a house extension. In reality however adding verandah attached to the house structure is a problem. The industry and TV DIY series tend to push the notion of lightweight structure which doesn’t pose a structural problem to the house. This is not so. Attaching a verandah increases the wind load on the house framing, and the bottom plate tie-down connections are not accessible. Therefore the extra wind load added to the house structure cannot exceed the reserve capacity of the bottom plate tie-down connections. For wind class N1, it is highly likely that the timber framing code AS1684, has already permitted these connections to be 10% over stressed, hence there is no reserve capacity. Therefore the house rafters to which the verandah is typically attached need to be connected directly to the house footings. This requires either attempting to place a structural element down the wall cavity and attach either to footing or brick veneer, or alternatively taking the structural element down the outer face of the house wall. In either case it’s a potential waste of material brought about by inadequate connections in the first place: the wall studs have tie-down adequate capacity but the connections do not. As far as owners are concerned the strengthening of the house does not add any immediate value, and merely adds to the cost of the renovation without desired value. The desired value is increased living space, and increased price to the sale of their house.

So increased value is immediately seen  when it comes to increasing space under roof. Not from PV’s and not from insulation. The increased space is usable for storage and living. But the verandah needs to be installed without need to strengthen the house.

The traditional Australian house had verandahs around the entire house, not just to back or front. Such verandahs I believe were around 1200 mm wide. Whilst an eaves overhang of around 600 mm is typically adequate to keep out summer sun and allow winter sun in through windows. Thus the 6m to 12m verandahs currently being installed are beyond the requirements to improve energy efficiency of the housing. More to the point likely to decrease energy efficiency as they block solar gain in winter: and so heat loss through conduction through the windows is not balanced by heat gain. Further inefficiencies result from the increasing use of outdoor heaters and coolers in these outdoor living areas. Once again this is an inappropriate response to airflow rather than temperature differences. Airflow can be blocked by walls. Which leads to the enclosure of verandahs. Whilst enclosure of a verandah leads to increased lateral wind load (horizontal), it can lead to reduced uplift on the verandah. Wind uplift on an enclosed building structure is typically less than uplift on an open roof.

The requirement therefore is to create a room that can sometimes be open and otherwise be closed: designed structurally for both the loading of an enclosed building and an open roof. These outdoor/indoor living spaces, outdoor rooms, or exterior rooms do not just add extra storage and living space, they also have potential to increase the energy efficiency of the buildings to which they are attached. However, it is important to separate the interior habitable space from the exterior rooms. Heat loss or gain from the exterior room should not be an issue, it is the heat loss from the interior habitable space  that is the issue.

Now adding rooms for energy efficiency is not a good idea when do not have the land, and modern Australian houses lack land, and certainly lack the space for surrounding verandahs. However the issue considered here is existing housing stock on large blocks of land. It should be noted that our modern building codes originated with problems due to lack of circulation: two notable examples being the great plague of London and the great fire of London. Building houses from property boundary to property boundary is a really bad idea, it should be possible to fully walk around a house in open space. The South Australian development regulations have a requirement that a building is either on the boundary or 600 mm away from the boundary. This is a health and amenity requirement of the BCA, it is required so that pest exterminators have access. It is also beneficial to have access to gutters and the house in general for general maintenance and repair. The 95th percentile shoulder width is 504 mm so the requirement doesn’t provide much clearance. Any case newer houses are tending towards side walls being minimum distance from boundaries with roof gutters up against the boundary and only accessible from the roof or the neighbours property. With still other houses built boundary to boundary: very poor design. The newer houses become existing, and whilst these may comply with the BCA, the energy efficiency achieved is still not high enough to really provide benefit to the occupants.

Airspace is a reasonable insulator, and airflow is a major problem for heat loss/gain. As air flows along a wall or over a roof, it either takes heat away or leaves heat behind. So to reduce the loss of heat, need to reduce airflow against the surface of the building. To cool the building down in summer need to improve the flow of air against the surface of the building.

To improve airflow around the building, need to ensure adequate open space around the whole building, therefore no boundary to boundary construction. To reduce airflow to the surfaces of the habitable space, need to enclose the surfaces. The way to enclose the surfaces is to provide exterior rooms, or indoor/outdoor rooms. That is enclosed verandahs, not verandahs using sheet metal roofs, but using materials which produce the greenhouse effect: such as glass, polycarbonate, polythene. In summer the doors/walls can be opened to improve circulation, in winter the doors/walls can be closed to provide solar gain. The solar gain to the indoor/outdoor space reduces the temperature difference between the interior habitable space and the exterior space. It is important however to differentiate between the interior and exterior rooms when getting a energy efficiency rating. The exterior room slows the rate of heat loss from the interior and heat gain to the interior. The interior is considered to have adequate ceiling insulation, but inadequate wall insulation. Wall insulation is difficult to retrofit, and is a potential hazard with respect to internal wiring hidden in the walls. The forms of insulation which can be installed in wall cavities also lose their insulation value with the passage of time, as do all insulation materials. So passive solar design, not reliant on insulation is preferable.

The important point is that the exterior room is not part of the dwelling proper, it is an intermediate space between the outside and the interior. Heat loss/gain to the interior is to based on the temperature difference between the exterior room and the interior, not between the interior and the outside environment. The exterior room has a temperature intermediate between the interior and the outside environment. It can be considered a conditioning chamber, where the body adjusts to the difference between the interior temperature and the external environment. The exterior room permits a temperature gradient between the interior and the exterior, rather than the unrealistic expectation that the whole building is conditioned to one temperature. For example whilst the interior may be expected to be maintained at say 20 degrees celsius, the exterior room is maintained at say 10 degrees in winter or not maintained at all, whilst the outside temperature is 5 degrees. Few people have household heating/cooling systems which attempt to maintain a uniform temperature throughout the whole building: it therefore unacceptable not to permit a temperature gradient through the building. It is neither green nor energy efficient to use more materials in the construction of a given enclosed space, and the BCA imposes such demand.

Another problem with energy efficiency rating schemes in Australia is that it is based on software, and the software is licensed only for certification and rating of buildings: the simulation model provided is not available as a design level model. Clearly we need to be able to design buildings and become familiar with what works, not specify something then send it off for rating and hope it meets the performance requirements. Where software is simply operated by persons who have little more training than the use of the software: they are not designers: not architects, not building services engineers, and not HVAC engineers. So its not surprising that actual buildings do not meet their ratings.

So when designing a veranda and/or exterior room it is important to be able to check the energy efficiency that it may contribute to the dwelling, and the appropriate comfort level zoning of such space. That is rather than seek a business which can supply  a energy rating certificate need to find a business which can provide energy efficient design.

Adding a verandah and/or exterior room has both structural and energy efficiency implications for the house, it is not just the provision of extra living space: though the extra living space is the value sought.


  1. [01/09/2017] : Original