By Philip O’Sullivan

Improving insulation in older homes has been a Government priority for some time and more recently a poorly insulated home has been associated with a death of a child.

There are always demands for immediate answers in such situations and top of this list is insulation; as though this alone creates a healthy home.

Recent moves by Government help reinforce this belief: “Housing Minister Nick Smith has announced plans to strengthen residential tenancy laws, including requirements for landlords to provide smoke alarms and insulation, and to declare the standard of insulation on tenancy agreements”.

Warm and dry

Frequently with insulation we hear the term “warm and dry”. Obviously insulation helps to maintain warmth, but does not necessarily mean a dry home.

My parents were both raised in large families in uninsulated houses of the time – one a bungalow and the other a villa. Today we would class these overcrowded and unhealthy homes, but they managed to thrive despite the state of the housing and being raised during the depression.

So what’s changed? During some of our building surveys utilising internal air testing, we notice an abundance of airborne skin flakes, which generally correlates with poor ventilation. 

We know that modern houses are much more airtight than the draughty old villas and bungalows in which my parents were raised. We also notice in houses and schools a reluctance to open windows, especially during the colder months.


This is not surprising given buildings are now better insulated and heated.

As internal temperatures increase, occupants become reluctant to open windows, letting cold air in and all that lovely warm air out.

There are also security concerns and different social patterns meaning many homes are left locked and unoccupied during the day, while others are occupied for extended periods.

When temperature rises, relative humidity drops, which is desirable, but then more moisture is able to be absorbed into the air from cooking, showering and drying clothes.

So, without ventilation, when temperatures drop, more severe condensation occurs.

In certain circumstances this can be extreme. An owner of a two storey home in a shady location experienced this. At around 3am she would awake to find her bedding coated in condensation.

The house was well insulated and had an efficient wood-fire. She dried her clothing on a rack in the lounge in the evening. Bedrooms were upstairs and were lovely and warm, but as the house cooled down, around 3am the dew point was reached and all surfaces were suddenly coated with water. The simple cure was to install a trickle vent to let the worst of the warm humid air escape before she went to bed.

We are achieving better ventilation with range hoods, clothes-dryers and extract vents, if they vent to the outside. However, in older villas and bungalows, garden beds are raised and timber decks often are added. These can block subfloor ventilation and feed damp sub-deck air into subfloors.

A damp subfloor means a damp house. Increasing heating, because the house feels cold, can exacerbate the situation as explained above.

Opening windows?

As our mothers knew, windows were made to be opened! The best time during colder months is the middle of the day, when internal and external temperatures can be at their closest.

I suspect windows are now mainly opened during the summer for cooling and kept firmly shut during winter. So our requirements for opening windows in housing may well belong to a bygone era, but still suit many.

Mechanical ventilation

Mechanical ventilation may well be the answer, but not all mechanical systems are equal.  The best systems include heat exchanges, so extracted warm air warms incoming cooler air, air filtration and positive pressure to minimise infiltration of unfiltered air.

So if this is your preference, look for websites that explain rather than sell, and provide useful information rather, than endless testimonials.

Philip O’Sullivan is the director of Prendos New Zealand Limited and a past-president of NZIBS. Article provided courtesy of Frank Wiemann, member of the executive, New Zealand Institute of Building Surveyors. For more information visit: www.buildingsurveyors.co.nz  or call 0800 11 34 00.

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