Home insulation advice

Press, 16 July 1986, Page 30

Home insulation advice

In new houses insulation can be added very simply during construction. For existing houses, however, the celling and floor can still be Insulated, but there is no simple way to insulate existing walls. A typical house loses heat in all directions and due to heat’s natural tendency to rise, more is lost through the ceiling and roof, than through the floor.

Bigger glass areas dictated by modem architecture are not necessarily a disadvantage. Glass is a poor thermal insulator and double glazing, to improve thermal resistance, is expensive. A simpler and more economic means of cutting heat loss through windows is by drawing thermal drapes at night. Since the greatest heating requirements occur in the evening, when drapes are drawn, this reduction is Important. Windows, however, are very effective at admitting radiant heat from the sun into a home, while allowing only a small part of this heat to escape. During winter, when the sun is at a lower altitude, the amount of heat admitted is the greatest. In this way, provided well-fitting heavy drapes are kept closed in the early evening and at night, windows can be an advantage. Insulating materials fall into two broad categories:

® Fill, blanket or batt (air entrapped within the material provides the insulation. • Foil insulation: foil must always be used facing an enclosed airspace of not less than 2cm in width. To achieve an enclosed air space, the foil insulation, if used as a separate membrane, must be without large tears and should be sealed or lapped sufficiently at joints.. Most foil material is in the form of an aluminium layer bonded to plaster-board or to a paper sheet. If paper bonded foil is used it should be double sided, as it is more durable than single sided foil. It will also save time as the foil will always face an enclosed air space and lengthy discussions on site about which way it should face are eliminated. Aluminium foils do not allow the passage of water vapour and incorrect Installation may result in condensation problems. All foils must be installed on the inside of domestic wall framing. The increasing cost of heating makes floor insulation a viable proposition also.

The performance of perforated foil insulation below a suspended timber ground floor is comparable with the performance of 6cm thick glass fibre. Insulating concrete floors is somewhat easier. Insulation is only required when the floor is heated,

when the width of the floor is less than 3m, and if the groundwater table is high. Insulation is only needed at the floor perimeter if the ground is dry.

Existing wallscan only be insulated at considerable expense by strapping over the interior linings and installing new internal linings with foil-back-ing or with fill insulation between the strapping.

This is also a disadvantage because is reduces room size and leaves a further need for redecoratlon. Spraying or gluing expanded plastics direct to the walls is not recommended as this can result in an increase of fire hazard. New wallsare easier to insulate. Foil or blanket or batt insulation can be used. It is usually unnecessary to insulate internal partitions. Blanket or batt insulationmust fit snugly at all edges, otherwise the heat escapes through gaps and may give rise to pattern staining on the interior surface. Foil insulationshould always be placed on the interior side of wall framing. Plaster-board with factory-applied foil insulation is available and this automatically places the Insulation in the correct position, saving installation time.

(All information obtained from the Building Research Association of New Zealand.)