Green Oversite



Common Errors in New Housing

Design and Construction

By Bruce Barbour - May 2020

As I live in a new housing estate on the outskirts of Melbourne Australia I get to see some of the errors that are quite common in new housing design and construction as I walk around the estate.

Use of Natural Gas - A large percentage of new housing is still being connected to reticulated natural gas. In Victoria there is even a rule that if you don't have natural gas connected, where available, you have to have a minimum 2 kL rain water tank. While having a water tank has benefits (though not financial!) it is problematic if there is insufficient space to install a tank - and anyway it is a nonsensical requirement - the use of gas and having a water tank are completely unrelated. The only reason for the rule is to blatantly prop up the reticulated gas industry. For this purpose it seems to have worked  - the rule may account for my observation at the start of this paragraph about the prevalence of the installation of gas on new housing. Having to spend a lot of money on a rainwater tank and the associated pumps and pipework impacts badly on the economics of not installing gas for new housing.

There are a number of issues with the use of natural gas:
  • Natural gas is predominantly methane, one of the most dangerous greenhouse gases, having many time the warming effect of carbon dioxide. A percentage of the natural gas escapes into the atmosphere unburnt. And when natural gas is burnt it releases carbon dioxide, the main anthropogenic green house gas.
  • Natural gas is no longer the cheapest means of both space heating and water heating in a house. The use of electrical powered heat pumps does the job cheaper. Also the price of natural gas is going to increase over the coming years as Australia's natural gas supplies run down.
  • In terms of green house gases in Victoria / Melbourne, where electricity is largely generated from the use of brown coal, there is not much difference in the green house gases produced. However as the electricity grid converts to renewable over the coming years, as it must, this will improve. As you should hope to get at least 20 years life out of new household heating equipment heat pumps are the way to go.
The use of ducted evaporative cooling systems. It seems that this type of cooling system is installed on over 50% of new housing in the Melbourne estates I have seen. While in terms of running cost they are not too bad however there are a couple of issues with them:
  • The use of ducting means that the ceiling vents punch holes through the ceiling insulation so lessening the the thermal performance of the house all year round, both summer and winter.
  • The evaporative units on the roof are often poorly placed on the northern facing section of the roof. There are two issues with this:
    1. it takes away prime roof area that could be used for photovoltaic panels; and
    2. the unit can shade the panels that are installed, decreasing their generating capacity (though provided the panels have by pass diodes this may not be as significant as it might otherwise be).
    If an evaporative unit is installed it should be on the south facing roof, or if it can't be placed there, on the east or west roof face, as far south as possible. (It is possible this may not apply if you are building a single storey house to the south of an existing double storey house which would block all northern sun to your roof. Hopefully this is a rare exception.) Evaporative unit placement is a no cost change so there should be no barrier to it being done.

    This also applies to the placement of other roof penetrations such as Whirlybirds (see below), chimneys and flues and other venting pipes, and television antennas - even a thin line of shading risks adversely affecting photovoltaic panel performance. Even if you don't intend to install photovoltaic panels straight away (or even at all) taking into account these points leaves open the possibility, preserving the largest possible north facing roof space for panels.
  • Evaporative units are not that effective on either very hot days or very humid days.
  • They consume quite a bit of water - one reference from simple Google search suggested that a whole of house ducted unit may use up to 25 litres per hour - but this depends on the size of the unit and the weather conditions - one website even said it was much higher than this. The level of water consumption may be important in years of drought and more so these days when in many places water supplies are supplemented by energy consuming desalination plants.
If the house is well designed and has reverse cycle heat pump air conditioning it may be better to just use this - and ceiling and other fans - for all cooling requirements. This is especially beneficial if the house has a photovoltaic system which may be sufficient to run the air conditioning during the daytime. Last summer (2019/20) I used my air-conditioning for about 2 hours for the whole summer period. This was probably not a typical summer (the longest "heat wave" was 2 days), my house is rated 7.2 stars (above the mandatory 6 stars), I am careful in the operation of the house on hot summer days and I was prepared to live with inside temperatures of 27/28 degrees on a couple of occasions. It still seems to be a complete waste of money to install a whole new cooling system for such a small use, at least in Melbourne. (It may be more effective in warmer climes where cooling requirements predominate.)

The use of "Whirlybird" roof space ventilators. These ventilators do not extract enough hot air to have a significant impact on the heat in a roof space. It is amazing that they are still so popular. Is it because people are demanding them or because builders are just installing them because they have done it in the past? The other issue I have with them are that they operate all year round so even in the middle of winter when some heat in the roof space might be beneficial they are still allowing that heat to escape. I understand that there are hoods that can be put on them for winter - I have yet to see one. If you decide you require some roof space ventilation (which is still not necessary) it would be better to use a solar powered ventilator - one that has their own dedicated PV panel. They exact many times the volume of air compared to an unpowered Whirlybird and some models can often be switched off so they don't operate over winter. If they are to be used, as per the previous section, try to ensure that they don't disrupt the future placement of PV panels on the north facing roof. Probably the west face would be the best location as it would allow operations later into the afternoon on hot days. (I also think they should have a duct so that the air removed is from the top of the ceiling insulation batts rather than the top of the roof space where the temperature doesn't matter - but I have no data to back up the comparative effectiveness of this arrangement - nor even read of anyone else recommending this arrangement!) But all in all I think it is better to save your money - it would be better to buy an extra PV panel or install thicker ceiling insulation with the savings.

The use of ducted heating and cooling. As stated in the evaporative heating system section above ducting punches holes though the ceiling insulation. They can also leak their heated air and lose their cool air into the roof space where it is wasted. Instead of ducted heating / cooling systems new housing should be using split reverse cycle air conditioning systems. These systems usually have a unit mounted on the wall inside and an external unit. While the inside unit is usually wall mounted you can get floor mounted and ceiling mounted units - though these are usually more expensive. You can also have one external unit connected to multiple internal units. This is called a multi-head split air-conditioning unit and it limits the number of external units is neater than having multiple single units.

Poor placement of Photo-voltaic system inverters. I sometimes see the inverters placed on the northern wall of the house. The issue with this is that the inverter may well be subject to the full force of the sun on the very days that they are working at their hardest, e.g. sunny forty degree plus days. I have read that this is potentially very bad for the inverter - with overheating shortening their life. I have not experienced this myself - I have only ever had on PV system and that has micro inverters - one per panel on the roof. Overheating may be more of a problem for some brands of inverters than others. As a general rule inverters should be placed out of the sun preferable on the south side of the house or if not possible/practical on the east side or else with some kind of very well ventilated shading so it is not subject to direct sunlight.

Lack of summer shading on northern, western and eastern windows. This can lead to a large heat load on the house from sun ingress during summer. This heat often has to be removed by the use of the air-conditioning system leading to higher energy use. Look at passive house design information for methods of eliminating / controlling this. Most housing designs seem to pay scant regard to solar passive design methods.

Size. Large houses are still the rule rather than the exception. A large house will require increased energy use for heating and cooling compared to a smaller house, all other things being equal.

Other Errors or Easy Improvements for Housing Design and Construction

These are not errors that can be seen from the outside of the house but stuff that I know is common place in new housing that could be improved.

Zoning. The lack of internal zoning in a house means that often the whole house has to be heated or cooled even when large sections of the house are not being used. A particular problem is open stair wells which acts as a chimney to draw heat from main downstairs living rooms.

The use of "Tastic" bathroom light, infrared lamp and exhaust fan. These (and similar brands) seem quite ubiquitous - I have them installed in my house! These units require a large hole to be left around the unit in the ceiling insulation. I also find that the heating lamps are not that effective at keeping the person warm. I think it would be better to have these functions split into individual units - lighting from a batten fix LED globe, exhaust fan as a separate fan unit and heating from a wall mounted radiant bar heater or panel. It will cost more but I consider worth it.

Widespread use of down lights. Even though these are LED these days (rather than the power guzzling halogen variety) they still require holes in the insulation. While these holes are usually improved by having down light covers it is still better to not use down lights at all (or just use sparingly). I just use the old fashioned batten fix fixture with an LED globe and a nice looking batten fix lampshade.

Poor Window Coverings. Windows are the thermal weak point in the housing envelop. Good quality window coverings at least partially address this. Good quality covering are heavy drapes with pelmets and also concertina blinds (also called honeycomb or cellular blinds). "Verticals" and Venetian blinds are poor insulators.

Non installation of ceiling fans in living areas. Ceiling fans - and other portable fans - are a low cost way of cooling a person. They will usually allow a person to feel comfortable at a higher temperature and to therefore put off turning on the higher energy using air conditioning. A couple of issues though - the ceiling height needs to be at least 2550mm. While I have them installed in my bedroom my issue is that if I use them overnight I will often wake in the morning quite cold. For bedrooms the ceiling fan needs to have a timer on it but the installation electrician did not know of an appropriate timer and I have not been able to source one since.

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