The Overton House - Nathers Climate Zone 24 -
Sub-alpine, dry
Orientation: Very Good – Careful attention
to positioning of the building in relation to its
boundaries and the site levels has produced a house with
uninterrupted Sun access for the
full day after 8.30 AM, even in mid-winter.
Insulation: Maximum in ceiling, walls and around
edge of slab – There are two forms of
insulation – convective (fibreglass batts and polystyrene
foam) and radiant
insulation (reflective foil sarking built into the walls
and roof).
Thermal Storage: High – A passive solar house
such as this can be simply defined as a structure
which “has characteristics enabling it to collect,
store and regenerate energy from the sun.”
Thermal storage material such as heavy concrete floors
or brick walls will have the physical
characteristics of high mass and high specific heat value
– they will perform the energy
storage and regeneration tasks. If a building has a high
thermal mass (or thermal inertia) it
has the capacity to passively heat itself, even at night
after the sun has long gone over
the horizon, or, for a time, in cold, cloudy weather.
The block walls in this house, along with
the tiled concrete floors (carpet actually prevents floors
acting as efficient thermal stores
by breaking the surface connection with the air) serve
as the heat storage elements.
Natural Ventilation Paths: During the summer months,
the interior comfort of the house is most
directly influenced by the level of ventilation, especially
at night. This house uses two main methods
to manage passive cooling – a ventilation path running
east-west through the long axis of the house
and at the eastern end, high level windows and roof windows
to allow hot air to be exhausted
to the outside, thus creating an artificial draft which
can drag cooler air from lower levels
(close to surrounding vegetation) through the whole house.
When the windows are
closed during the day the structure remains significantly
cooler than outside.
External walls: Reversed Brick-Veneer – The
brick veneer walls are turned back-to-front in order to
gain the most thermal benefit from the structure. Clad
with rendered fibre-cement sheets, behind
which is a thick glass-wool insulation layer and a radiant
heat barrier. The heavy blockwork walls lie
behind this insulation layer and face into the living
spaces. By configuring the wall in this way, a high
convective and radiant insulation level can be attained,
with the added benefit that the solar energy
stored in the concrete blocks can be regenerated into
the living spaces at night, rather than
being lost to the outside air.
Floor: Slab-on-ground – The floor insulation
around the edge of the concrete floor is visible in places.
Extruded styrene is placed around the perimeter of the
slab floor to retard heat loss to the cold air and
ground surface outside the wall.
Roof: Insulated Colourbond corrugated steel –
Metal roofs like this offer advantages in summer over
the more common tile variety. The thin, highly conductive
metal will dissipate heat to the outside air
very quickly once the sun goes down, thereby reducing
heat-load in the ceiling space. Heavier tiles
store heat for longer, and will keep your roof space (and
house underneath) hotter for longer.
The reverse, however, will not occur in winter.
Zoning: Living areas to the north – The northern
zone is inherently warmer in winter than the southern,
and the east and west extremities will be more prone to
high heat loads from low level summer sun.
This house locates its most often-used spaces along the
northern zone where the winter sun has
most penetration into the interior.
Glazing/windows: Double Glazing – The house
has efficient types of insulating window. The windows
have double skin, insulating glass built into timber frames.
Frames made of timber limit conductive heat
loss. Each opening casement is also fitted with foam rubber
weather seals to minimize air leakage. It
is important to realize that even a very effective window
will only achieve an R-rating of around R0.5,
or R1.0 in the case of very expensive units while an insulated
wall achieves a rating of around R2.0 and
an insulated roof will be rated around R4.0
Appliances & equipment: Gas appliances are
used throughout the house for all main energy intensive
uses – cooking, water heating and back-up space heating
and highly efficient electrical appliances are
used everywhere else.
Special features: Trombe Wall – In order
to maximize the northern heat collection glazing, a small
trombe wall has been constructed behind the kitchen joinery.
A full-length window sits in front of a
1200mm high block wall running past the back of the kitchen
cupboards on the north wall. The trombe
wall is painted black on the outside to maximize absorption
and emission and vents are provided
under to cupboards to allow air supply to the base of
the wall. During winter, the wall behind the
glass quickly heats up and acts as a passive radiator
throughout the day and night.
Energy Consumption: While the original house
was not given a star rating as such, it achieves a target
yearly heating energy use of around 2 Gigajoules. To get
things in perspective, many equivalent sized
houses in the region use between 10 and 15 Gj per annum
for heating purposes.
Other: Weather seals, finishes, colours –
All external doors and windows are well sealed to prevent
air leakage and all internal doors to wet areas (any room
with an exhaust fan) are sealed off from the
rest of the living spaces to prevent heat loss through
the exhaust fans to the outside. Walls are
mainly painted concrete block, while floors are either
tiled or painted concrete slab-on-ground, except
in bedrooms where carpet is used. Tiles, (if laid on plain
cement adhesive, not rubberized adhesive) are
very conductive and maintain the thermal connection between
the concrete and the air volume within
the house. Similarly, the painted block walls also allow
a high level of heat exchange to occur. While
dark colours increase heat absorption and emission, reflectivity
is reduced. Mainly light wall colours
are used here, with darker mid-toned floor colours.
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