Home & Garden
Close the doors, stop up the draughts, pull the thick curtains, eliminate leaks - and then splash out on insulation.
"To make a home drier and more comfortable you can't just look at insulation alone. You have to close the envelope," says Christian Hoerning, technical adviser on home insulation for the Energy Efficiency and Conservation Authority.
"The four things you have to tackle are insulation, heating, ventilation and dampness. If one is missing, the outcome from insulation might not be what was hoped for. Insulation slows down the loss of heat but you need to heat the house to enable insulation to work. There is no silver bullet. We need to look at the home as a system in which insulation is one of the basic things."
Insulation, with the fillip of the Government's subsidy scheme, has become the modern must-have home addition.
"In other parts of the world where it's colder, insulation became important many decades ago. People needed to be warmer or die. Here you can get through winter without insulation and without dying but with cold, coughs and flu."
New Zealand, he says, introduced its first guidelines in 1978 in alignment with other parts of the world reacting to the oil crisis of the 1970s.
Three decades later and three years after its introduction, the Government scheme, for which the authority is the linchpin, has been tapped by almost 200,000 homeowners.
Hoerning says most pre- 1978 houses were not insulated, or poorly insulated and even houses built later are not necessarily well insulated.
"Ceiling and underfloor insulation can be retrofitted very easily if there is accessible roof or crawl space. It can halve heat loss and typically costs $3000." Insulation in walls is more difficult and expensive to retrofit and requires building change and possibly building consent so is normally left for when building work is being done.
He recommends people retrofitting ceilings and under- floors should seriously consider a trained installer.
"There's not a great deal of difference in the cost of getting a professional or getting the material from the hardware shop." Anyone can set up an installation business but the authority, after finding quality "issues", has helped set up a manufacturers and installers association which trains to a standard.
There are, Hoerning says, a multitude of insulation products in rolls or pieces and also loose fill which can be blown into ceilings.
Loose-fill density and performance is variable and there needs to be a gap above older recessed downlights or metal flues. New downlights must be able to be abutted to insulation. In a ceiling with 20 or 30 old downlights, a 100-millimetre gap for each can reduce the insulation's effectiveness. Insulation can't touch the roof underlay or it could cause moisture problems. Extractor fans also need safety clearance to prevent trapped material causing the motor to overheat, possibly causing a fire.
The authority's recommendation is bulk insulating products pre-cut to fit between ceiling joists, or blanket-like rolls installed across the ceiling, including joists. They could be fibreglass, polyester or wool. The ceiling needs to be dry and rodent- free.
The authority does not recommend foil insulation although it's still used and available.
Foil, says Hoerning, can rip and is hard to install so that it performs well. "Leave it only if it is in perfect condition."
And, he says, foil is metal so it conducts electricity and could be electrified, "and there is always a risk you might staple into an electric wire. Foil is never recommended. Its only advantage is it's very cheap."
There are newer, better bulk-insulation products made of polyester, wool and polystyrene, and a new type of semi-rigid polyester that is stiff enough to stay in place without the need for glue or stapling.
Cavities need to be dry, and building paper, which many old houses do not have, needs to be in excellent condition. Electric wiring needs checking. Insulation needs to be optimum thickness. "The quality of installation is critical."
Hoerning says there is promising new, inexpensive insulation for retrofitting walls in the form of polystyrene beans which can be blown in without having to remove the wall lining.
Scientist Ian Cox-Smith, of building research organisation Branz, confirms this. The only current retrofitting method, which is fraught with potential problems, has been pumping air foam into walls.
"The primary one is drilling large holes through the cladding and more importantly the building paper." This can interfere with weather- tightness.
Air foam, he says, is about marketing and lack of choice. In a typical home, 200 litres is used and the material contains formaldehyde, a potent irritant. There is shrinkage, "and people can end up paying $50 a square metre and getting half of what they pay for".
The sales argument, he says, "is something is better than nothing".
If weather-tightness issues do follow, Cox-Smith believes people might be loath to own up to them.
Wait, is his advice. There will be a much better, much cheaper choice within a year: the beans. "We're testing at the moment." From a scientific point of view, beans are fixed in volume. "You don't have to take their word for it."
Wellington architect Rob Vorstermans, with a philosophy of sustainability, says Pink Batts give the best amount of insulation for the lowest price.
- © Fairfax NZ News