Eco-thrifty renovation: Cut draughts and plug heating costs

Passive House is a worldwide organisation promoting sustainable energy-efficient buildings.

The secret to Passive House's success is that "the houses are airtight". Passive homes have an air-to-air heat exchanger which controls the ventilation and "recovers" warmth from the exhausted stale air.

It is all rather cool, and requires good design, good engineering, and great attention to detail in the building process. Think about all of the possible leaks in a home, and then think about sealing every one of them.

For a builder, it requires a great understanding of how homes work, and the patience to ensure that all the detail work is properly done.

A whole bunch of little things can add up to something big. That's exactly what I have been saying during the first 50 free home energy audits I've carried out over the past two months. It's also how we were able to convert a draughty, cold villa into a warm, cosy home.

The biggest difference between our home and most of the homes I've audited and a Passive House is the level of thoughtfulness of design, and the level of attention to detail in the construction.

This is why, according to a University of Otago study, 75 per cent of New Zealand homes fail to meet new energy standards, and unhealthy homes contribute to 1600 deaths each year and cost millions in lost productivity.

Many of the same principles that go into a Passive House went into renovating our villa.

In its most basic form, the secret to comfortable, energy efficient homes comes down to this: good insulation and great draught-proofing. But, as with things from vege gardens to wastewater treatment plants, it's easier to do things properly in the first place than to go back and correct mistakes later.

Dollar-for-dollar, draught-proofing is one of the cheapest and most effective ways to slow the loss of heat from a home.

A good way to find draughts in a home is to perform a blower door test. I made a blower door out of two fans, some coated fabric, and a bit of timber. I fitted this unit into our front door and turned both fans on high, pushing air outside.

This created low pressure within the structure and "pulled" air in through every little gap. Identifying the gaps can be done with a burning candle or incense. Plugging the gaps can be done with a variety of products. Until the day we all live in Passive Houses, this is about the best we can do.