Civil Engineering Reference
In-Depth Information
product at a very low cost. However, the potential infestation of moths, mice and other
little furry fellows is significant. I remember the disgust and disappointment on Jan's face
the day she opened a plastic bag of wool that she had kept for spinning, only to see a mass
of moths fly from the bag. One can only imagine how comfortable and inviting clean
wool would be for mice. Treated against vermin, wool insulation is a great product, but
without treatment I dare not contemplate it. When applying for a building permit you
have to meet insulation requirements as specified by the building code. It would be
unwise to make the assumption that the building inspector would accept your form of
insulation if the R rating were unsubstantiated.
Wood shavings for insulation
I have boyhood memories of the demolition of an old cool room in my home town of
Numurkah in Victoria. It was an old building with planks of timber nailed to each side of
the timber framed wall. I remember asking my father where all the saw dust came from,
as it was heaped up among the rubble. He explained to me that the saw dust was good to
stop the heat from outside getting into the cool room where the butter was kept, and that
the cavity of the timber framed wall had been filled with saw dust and wood shavings for
this very purpose. This form of insulation was evidently quite common at the time of
building the cool room. I imagine that this form of insulation would also provide
significant acoustic benefits.
Roof insulation
In this section I will be speaking specifically about the insulation that is fixed above the
rafters as opposed to insulation that is fitted between or below the rafters.
There are three reasons for the application of roof insulation: heat control, noise
control and the control of condensation. Heat is transferred by conduction and radiation.
The bulk insulation, such as fibreglass insulation, is specifically targeted at the heat
transferred by conduction, as the small pockets of air trapped within the insulation
reduces the free flow of heat from one area to the next. The radiant heat is reduced by the
installation of reflective barriers such as sizalation; a foil product supplied in rolls
approximately 1.35 metres wide and of varying lengths. When a roof is to be clad with
roof tiles or shingles the sizalation is fitted directly to the top of the rafters below the
roof battens. When roofing iron is used, the sizalation can be fitted either above or below
the iron.
Air-Cell building insulation
One of my owner-builders introduced me to a product called Air-Cell, which combines
both bulk and reflective barriers. Air-Cell is made up of what looks like a sheet of heavy
bubble wrap sandwiched between two layers of sizalation. The sizalation provides the
reflective barrier while the enclosed air pockets of the centre layer provide resistance to
conductive heat transfer. I have found this product not only beneficial from an insulation
perspective, but also because of the ease of installation. The R rating of Air-Cell varies
with different installation methods. When fitted on top of the roof battens Air-Cell is
rated at R2.5, whereas when installed on top of ceiling joists it is R3.0. I am told that it is
