Wall and floor insulation
in Greener Homes on 16 May 2010
Insulation works all around the house.
CEILING insulation is taking a lot of political heat this year. But while the federal government admits its rebate scheme was flawed, the insulation itself shouldn’t be left in the cold.
Caitlin McGee, from the Institute for Sustainable Futures at the University of Technology, Sydney, says good insulation is always a crucial part of construction. “It has many benefits: greenhouse gas reduction, better comfort and lower energy bills.”
And the ceiling isn’t the only spot for it. “The roof cavity is the most important place, but if you want to insulate well, you need to think about the walls and floors, and the building shell as a whole,” she says.
If you’re building your house, get the wall insulation right first time – it can be difficult and expensive to add later. According to Ms McGee, in existing homes, the best opportunity to retrofit is “when you’re renovating or pulling apart your walls for some other reason.” In all cases, it’s wise to consult a building sustainability assessor for detailed advice.
Because heat transfers in different ways, a combination of both reflective (foil) and bulk insulation (such as batts) works best. When you’re choosing a product, consider its green credentials, such as recycled content, as well as its performance, measured by the R-value.
In Melbourne, the building code requires that walls rate a minimum of R2.2. “Generally, the more extreme the climate, the more insulation you should have,” Ms McGee says. But she warns DIYers not to buy overly fat batts that must be squashed to fit. Bulk insulation works by trapping air; it’s less effective when compressed.
Another retrofitting alternative is to add the insulation outside. On her home, Ms McGee affixed polystyrene and cement panels to the external walls. “The material I used as my cladding is also part of my insulation strategy,” she says. “It’s worthwhile thinking about less conventional materials that have good insulating properties.”
Underfloor insulation is more straightforward, so long as there’s enough access space. Maurice Beinat, from home retrofitting business ecoMaster, says you need about 400 millimetres to work in.
Although floors cause less heat loss than ceilings and walls, insulating them can make a big difference to winter comfort. “The special thing about floors, particularly polished timber, is the contact your feet make with them,” he says. “Floors don’t need to be very cold to make you uncomfortable.”
He suggests that well-insulated floors should reach R2.5. (Uninsulated timber floors rate R0.7, and with good-quality carpet and underlay, they rate R1.)
Mr Beinat says there are two requirements for floor insulation: that it doesn’t hold moisture and won’t become a rat nest. For those reasons, he recommends polyester insulation (manufactured in a roll, rather than a batt, for convenience). Before stapling it in place, seal any gaps in the flooring.
In homes that have a lot of underfloor airflow, such as weatherboards, ecoMaster also fastens a layer of reflective insulation to the joists, making the sub-floor nearly air tight. They charge between $28 and $35 per metre, installed.
Mr Beinat says it’s a job well suited to DIYers, but with one serious warning: “The main danger is electrocution by stapling through wires. People do die underfloor.” He advises purchasing a double-insulated, electric stapler, rather than cheaper handheld models that won’t protect against electrocution.