This section is particularly relevant to anyone who is considering investing in a ventilation system which uses the roofspace as its source of ventilation air.

Rodents urinate and defecate in roofspaces.

In fact, mice urinate almost constantly (they do this to lay trails which they can follow later).  A recent episode of the NZ Channel 3 consumer affairs programme “Target” was dedcated to the subject of pest control.  During the programme the presenter held aloft a beer glass filled with an amber liquid, this was not beer however, it represented the amount of urine deposited in a kitchen by a pair of average mice in a year.

Your kitchen is constantly being cleaned and any evidence of infestation would quickly result in a call to the exterminators, but how often is your roofspace cleaned?  How long would it be before any mice were discovered up there?  Corpses of rodents, mites, moths, flies, etc, their droppings and urine dry out and disintegrate, then become airborne in the roofspace air.

When rodent urine dries out, it turns to dust, the size of a single particle of rodent urine dust is smaller than the finest talcum (approx 0.03 microns). Most roofspace ventilators are fitted with a pollen air filter (EU4).   These filters have difficulty “holding” particles that are 2 microns in diameter, so will be no defence against particles nearly 100 times smaller.

Airborne dried rodent urine can transmit a host of potentially fatal diseases:


Rats blamed for first leptospirosis death

AUCKLAND — Helensville fisherman Ken Scott was a fit 48-year-old whose only health worry was recurring back pain from a teenage injury.

When he stated aching again just before Christmas, he thought the old problem had flared up.

But on January 1, after developing a high fever, he was urgently admitted to the renal unit at Auckland Hospital.

Blood tests showed only a general infection but his condition deteriorated. By the time Mr Scott was moved to intensive care, he was yellow with jaundice and bleeding from the gums.

On January 3, he cheerfully told his wife, Lorene, that doctors had pinpointed the problem. It was leptospirosis — formerly known as ‘dairy farm fever’ — and could be treated with antibiotics and a few weeks in hospital.

The news gave him a huge boost, Mrs Scott said “They think it’s lepto, and they’re going to kill it,” he told her.

Instead, leptospirosis killed him. Mr Scott’s death is believed to be the first in New Zealand from the disease. Rats at the HeIensville wharf could be the source of the infection.

New Zealand has a relatively high rate of leptospiroels infection, with at least 100 cases each year, yet some victims do not know they have had it at all.
Thirty years ago, leptospirosis was well known in rural areas. More than 800 cases were recorded in the worst year.

A vaccine and other control measures have reduced the over-all incidence of the disease.

Anyone who comes in contact with animal urine, or water contaminated with animal urine can catch leptospirosis.

The leptospire bacteria thrive in water – rivers effluent ponds, and on damp soil and pasture. The main source of infection was traditionally cattle, sheep, deer, and pigs. But figures now show that 20 per cent of infection are from another strain carried by rats, mice and hedgehogs. —NZPA

Note the last paragraph — which confirms that Leptospirosis in NZ is carried by, and can be transferred to humans from rodents.

Unless you can guarantee that there will never be any rodent urine in your roofspace, make sure that you never breathe any air from a ventilation system that takes air from your roofspace and forces it into the living space of your home. You may not live to tell the tale!!!.

Another airborne disease is tuberculosis

This again on the rise in developed countries after being practically eliminated in the twentieth century. A question raised in the ‘Ask A Scientist’ column of ‘The Christchurch Press’ October 30, 2000, shows that we should be concerned about transmission of this disease from birds or animals that live and die in our roofspaces:

Path of tuberculosis

Victor Perry, of Ngahere School, asks: How long does it take for Tb to develop, and do birds have a different disease to mammals?

Sandy Smith, a microbiologist at Otago University’s School of Medical Sciences, responds:

Tuberculosis in humans is usually caused by the germ (bacterium) Mycobacterium tuberculosis, though the closely related Mycobacterium bovis and Mycobacterium avium may occasionally be responsible. These latter two germs have respectively other mammals (for example cattle, possums) and birds as their normal hosts.

Tuberculosis, or Tb, can thus be an important zoonosis, a disease usually found in lower animals but transmissible to humans following contact with a diseased animal.

This is one of the main reasons why we now pasteurise milk from cows, and why all cattle and deer in New Zealand killed for human consumption must be certified free of tuberculosis.

Tuberculosis usually involves the lungs (a respiratory disease) and is acquired by inhalation of

M. tuberculosis germs that have been coughed or sneezed into the air by a person with active lung disease.

Following this exposure, a few people progress to active (overt) disease with lung lesions. This may happen rapidly (in a few weeks) or take many years (eg, 70) to develop.

What happens to the inhaled germs and how fast disease develops depends on the ability of the patient to fight the bacterium. Poor housing conditions and malnutrition favour the development of active lung disease. When patients have serious underlying associated disease, such as AIDS, Tb may spread rapidly from the lungs to involve other body organs. Treatment of active Tb is not easy and requires a combination of three or four drugs for at least six months.


Legionnaires disease is commonly associated with air conditioners, but also occurs in compost.  Composting of spider, fly, rodent or bird droppings takes place constantly in your roofspace.

THE CHRISTCHURCH PRESS (7th November 2000)

“A Christchurch man has died and another is seriously ill, after contracting legionnaires disease….

…. Legionellosis is a bacteria that can be found in garden soils, compost, potting mix, hot-water systems, and some air conditioning units, especially if they are poorly maintained.

Infection occurs by breathing in air which contains the bacteria and often affects the elderly or those with an impaired immune system.

[Canterbury medical officer of health] Dr Breisman said the Canterbury district usually had between eight and 10 cases notified each year.”

In September 2000 a major outbreak of salmonella was reported to be killing sparrows by the thousands throughout NZ. Newspaper, TV & Radio news warned restaurants to keep sparrows away from food. If one of these sparrows died in your roofspace and your home is ventilated by a roofspace fan, what better way to introduce the Salmonella bacteria into you home, than as airborne particulate, forced under pressure, into your living space by the Roofspace Fan?

Salmonella bacterium measures less than .03 microns, and cannot be stopped by an EU4 (Pollen Grade) Air Filter.

SALMONELLA is one of a host of dangerous bacteria that may often be present in your roofspace.

If salmonella is present in water, the advice is to boil it, but it is not practical to “boil ventilation air” from a roofspace.


0800 DRY AIR  (0800 379 247) 


Products are New Zealand made by Avon Electric Ltd.


Avon Electric Ltd
25 Taurus Place, Bromley
P.O Box 19748, Christchurch 8030 
Ph: 03 381-5595  - Fax: 03 381-5596