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Building thermal envelope is a very important concept that provides thermal (heat and coolth) security to the external perimeter of your home.

It is another one of the critical interrelated disciplines that combine to form passive solar design. The greater the thermal integrity of your building the greater the ability your building has to remain cool in summer and warm in winter.

Even if the building is poorly designed form a solar perspective and has no micro climate design advantages you can still achieve major gains in comfort and reduced running costs by ensuring your building perimeter is thermally intact. A thermally secure building thermal envelope will physically reject the burning sun and freezing winds without causing a major impact to the internal living comfort of your home.



Insulation is a major step towards energy efficiency in a new house and, considering the cost of the new home today, it is relatively inexpensive.

The external components of your building; your floor, roof and walls as well as your windows and doors, are the only barrier you have to the weather that permanently surrounds your home


It stands to reason that the greater the ability to keep that hot or cold weather outside where it belongs, (unless you are using it to your advantage by manipulating it for heating or cooling), the more comfortable your home will be.

The thermal envelope of your home is an inexpensive area of building design and construction that has been overlooked in Australia.

It is vitally important to insulate your walls and roof and floor, (in most cases) from the outside weather conditions and it is not difficult to do. The correct insulation or building material (or both) installed in the most appropriate location within your walls and roof will provide amazing measurable benefits to your home.



You can judge the value of the insulation properties of your home by the R value or U values of a wall or roof or floor. R values define the resistance to heat flow of individual items. The higher the R value the greater the resistance to temperature. A material with a an R value of 4 has much better resistance to heat and cold transfer than a material with an R value of 1.' values define the heat resistance of a combined number of components .The lower the U value the better the ability to resist temperature transfers.

In Australia an R value of 5 is considered very high. In Europe and America an R value of 30 is common.



That high R value (or low U system value) is like putting an impenetrable barrier against temperature transfers. Temperature levels will be much more controllable .Keep those freezing or boiling conditions outside, where they belong.



Another vitally important component of building thermal envelope integrity is your windows.

Standard windows in Australia provide almost no restriction to temperature transfer .Over 80% of all temperature loss or gain from your home is through your windows. They must be thermally double glazed to provide the barrier to temperature flow so important for improving comfort levels. If you have a thermally secure building envelope yet don't do any thing to your windows then you have reduced the effectiveness of that insulation by at least 60%!


Most Australian homes are thermally poor yet use artificial heating or cooling to make their homes more comfortable.

Most of that heating or cooling is going out through the poorly insulated walls, roof and windows. In effect you are paying to heat or cool the outside air! If you have a thermally secure building and used artificial heating or cooling, the size of the equipment could be a lot smaller and the running costs would be significantly reduced.

A thermally secure building is crucial to reducing running costs and green house emissions while adding significant benefit to comfortability. It will improve efficiencies and provides an important backbone to sustainable house design.


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