The McCook House -
Located on the north side of a ridge, for shelter from
southerly
winds and maximum solar exposure, the house uses a very
interesting slab
on ground construction with perimeter polystyrene insulation
surrounding the
footings. The internal walls are 130mm thick solid reinforced
concrete slabs,
which were poured on site in horizontal formwork and then
lifted by
crane and bolted together in position.
Although this "tilt-slab" construction was
not chosen over solid brick for thermal
reasons, the concrete will perform slightly better than
bricks, because it has a
higher conductivity and thermal capacitance, so it can
absorb heat more rapidly
AND store a greater amount of heat. 50mm thick high-density
polystyrene
insulation was incorporated into the external wall cavities,
resulting
in a total wall R-value of approximately 2.
Pale metal roof sheeting was chosen to reflect summer
heat and the house has
timber-framed double glazing to all windows other than
the entry air-lock and
the garage with double weather seals and cam action latches
to ensure they seal tight.
The clerestory windows along the middle of the house allow
natural warmth and
daylight deep into the building and stub trombe walls
inside all northern windows act
as storage panel radiators and allow furniture to be placed
close to the windows
without losing solar heat gain to the floor slab.
The entry air-lock is kept closed off from the house
during hot or cold weather and
the west facing windows are shaded by the pergola and
fernery. During 2002,
the house has required NO HEATING AT ALL throughout winter
whilst remaining
comfortably warm at all times of day and night. The designer
and original occupant
says "the three basic concepts most important
in any passive building design
are radiant comfort, thermal mass and controlled solar
radiation."
Whilst insulation is not strictly a passive building
measure, as it is equally important
in any type of building, it is critical to the performance
of a passive building. Good
insulation is important for any building. In a passive
building, it is required to ensure
the internal mass holds its temperature. In an air conditioned
building it will not only
save energy but also improve the comfort for the occupants
by preventing
uncomfortable radiation from hot or cold surfaces.
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