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:
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:
- 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.
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 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:
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.
- it takes away prime roof area that could be used
for photovoltaic panels; and
- 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).
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.
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
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
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
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
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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