Auckland Allergy & Eczema Clinic

Designing an Allergy-Friendly Home in New Zealand

Designing an Allergy-Friendly Home in New Zealand

New Zealand is known throughout the world as being very ‘green’ and eco-friendly. It seems like a ‘double-edged sword’ that New Zealand also has one of the highest prevalence of Allergies in the world.

Unfortunately, for about 30% of the population there is a ‘down-side’ to living in a ‘green country’, like New Zealand, i.e. Regardless of where you live in the country, you won't be out of reach from pollens (especially grass and weeds), as pollens are known to travel for hundreds of miles under the right conditions.

Patients will often ask, "Is there any place in New Zealand that is better for allergy sufferers". My standard answer would be: "It is not where you live in New Zealand that matters to the allergy sufferer, but how well designed your home is, and how you prepare yourself against your enemies".

Highly allergic patients who move to New Zealand are usually already sensitized to house dust mites, and they usually become sensitized to the local allergens (pollens etc.) within two to four years. This is the same for highly allergic individuals who move to other Western countries, like Australia.

There are studies that show improvement in allergy symptoms when patients are moved to the low allergen (house dust mites) environment of the high altitude of alpine sanitoria in Switzerland (Davos) and Italy (Misurina). Davos, Switzerland is situated at an altitude of 1556m, is well known as the highest town in Europe. Mount Cook, at 3764m is the highest mountain in New Zealand. If the allergy sufferer were prepared to live even halfway up Mt Cook, they would be expected to have similar improvements in allergy symptoms as living in Davos.

Other reasons for New Zealand having such a big "allergy problem" include:

  • Some of the highest levels of house dust mites are found in the homes in New Zealand. This fact is related to the climate being very humid and the design of the old homes with poor ventilation, poor energy efficiency, and carpets creates a haven for house dust mites and moulds. Well-controlled epidemiological studies in the US, Europe and Australia have established that sensitization to house dust mite allergens is one of the strongest risk factors for asthma.
  • New Zealanders, like the British, Canadians & the Americans are pet lovers, and the Western culture dictates that pets should live indoors. In Brazil and SE Asian countries where pets live outdoors, the prevalence of pet allergy and allergy on the whole is much less than in New Zealand.
  • New Zealanders love their gardens. It is the dream of most New Zealanders to own their own home, with a garden. Unfortunately, it is also very fashionable to plant exotic trees, like birch and more recently, olive in these gardens. This has caused an increase in sensitivity and allergy to these pollens. In my practice birch is the commonest tree pollen causing allergies, and of recent I am seeing several patients with very significant sensitization and symptoms related to olive trees planted in their garden.
  • Several studies have examined the relationship between indoor fungal spore counts, fungal allergen levels, and allergic symptoms. Studies conducted in Ontario, Canada showed that allergic symptoms were higher in patients living in a damp residence. In Dutch children with known allergies, 63% lived in homes that had increased indoor fungal levels. 

Recent publicity of the "leaky building crisis" in New Zealand serves to emphasise the point that proper design of the home, and ensuring building practices and materials were of a proper standard is very important for reduction of allergy symptoms. A building construction rule change in New Zealand in 1996 allowed widespread use of untreated timber in houses and this has led to 'an epidemic of wood rot in leaky homes'. To put a stop to this leaky home crisis a new bill was recently introduced, which will make it compulsory to use chemically treated timber throughout all new houses, for protection against rot in leaking homes.

Scientists have confirmed the mould stachybotrys, growing in several water-damaged homes around New Zealand, but until now researchers had not proven this fungus found in New Zealand homes was toxic to humans. The presence of this mould does however confirm the level of indoor dampness, linked to increased allergies.

Since indoor allergen exposure is an important factor in allergic diseases, and environmental allergen reduction has been demonstrated to improve asthma symptoms, medication use and lung function, indoor environmental control should be the first line approach to allergic diseases.

The commonest allergens in New Zealand and most western societies is the house dust mite. Therefore an allergy-friendly home is one that makes it difficult for the house dust mite to survive (ideally humidity less than 50% and temperature < 70°F (21°C). The other important indoor allergens include pets (cat & dogs) and mould. Mould thrive in similar environments to dust mites, ie high humidity (dampness).

In designing an Allergy-friendly home in New Zealand, the important issues to consider are:

1. Site / Location

  • Choose the right neighbourhood away from factories, which pollute the atmosphere.
  • Avoid dampness, therefore you should build or find one in an elevated area. This is better than being close to streams or rivers because there is higher moisture content of the air in those areas. The higher the humidity in your home the more likely it is you will encourage mould and dust mite growth. 
  • Build a house with a full basement. Every living area of the home needs to have part of the basement underneath it. Avoid basement bedrooms. The basement should be a storage area only.
  • Avoid laying carpet directly on cement slab. This is the perfect environment for dustmites, due to the higher humidity, that is possible v carpets on breathable wooden floors.

2. Building Materials

  • Every new home will create some outgassing because of the preservatives used in woods, the preservatives and glues used in particleboard and the materials used in constructing our homes today. The air indoors can be further contaminated by synthetic Volatile Organic Compounds (VOCs) in many manufactured products you use around the home including glues and solvents, new carpets, aerosol products, dry-cleaned garments, etc. 
  • After living in the house a while and opening the windows the amount of gas decreases. The amount of outgassing becomes less and less and the problem eventually is no longer an issue.
  • Use chemically treated timber throughout all new houses, for protection against rot and mould growth.

3. Bedrooms and Bedding

  • All mattresses harbour dust mites. Studies show that even new mattresses brought from the showroom will have significant dust mites when vacuumed and measured.
  • The most effective solution is to fully encase all bedding with anti-allergen barriers
  • Keep pets out of bedroom.

4. Flooring

  • The best way to reduce allergen-levels in the home is to minimise fabric surfaces, such as carpets and rugs. Carpets act as a continuous reservoir for house dust mites.
  • Hard-surface flooring is ultimately the preferred choice of flooring in creating a low-allergen home. But avoid grooved wood surfaces that become dust traps.
  • Ceramic tiles are particularly suitable for 'wet' rooms such as the bathroom and kitchen. Porous, unsealed tiles may harbour bacteria and other micro-organisms. To ease cleaning, porous tiles should be sealed.

5. Wall Covering

  • Paint is the first choice, recommended over wallpaper. However, solvents used in certain brands can cause more irritation over others. As a general rule, the higher a product's VOC content, the stronger the odour. Water-based paint has fewer odours than oil-based types, due to reduced solvent content.

6. Window Dressing

  • Wipeable vertical blinds or shades collect less dust and are easy to clean.

7. Furniture and Fixtures

  • Minimise soft furnishings. Leather and vinyl are best for covering soft furnishings, as they are not good dust collectors.
  • Avoid Gas Stoves – excess moisture, high in carbon release and reduced oxygen.
  • Built in, externally vented Vacuum Systems: All microscopic debris that normal vacuum filters re-release are dumped outside during every vacuuming. 

8. Ventilation or Humidity Control

  • New or recently built homes will or should (by law) have proper insulation.
  • Conditions for optimal house dust mite growth is relative humidity >55% and temperature of 65°F (19°C) – 75°F (23°C).
  • Many allergens, including animal dander and mould spores are found in the air, while others, such as mite droppings and cockroach droppings, are in carpets and bedding but become air-borne when disturbed. 
  • Improving ventilation is the key to minimising air pollutants indoor
  • Keeping windows and doors open for part of the day is useful in improving indoor ventilation naturally, but remember that pollens and moulds will get indoors this way.
  • Dehumidifiers are not considered useful in reducing dust mite levels in New Zealand. However, they are good to reduce excess humidity (for mould etc). High humidity and low temperatures of typical homes where winter can drop the unheated house temp to +5 overnight, are ideal breeding grounds for mould.

9. Heating (and cooling) and Air filtration of the house

Unique to NZ is the use of portable gas heaters, outlawed in many countries.

Recommendation: Don’t use – High moisture content and high carbon content, as well as reduced oxygen levels.

  • The ideal heating system is radiant.
    Heat pumps are recommended – High efficiency, and can have electrostatic filters built in or plenum mounted. Can easily hold a home at the preferred 70°F (21°C). With the filter it can reduce airborne contamination on an ongoing basis where radiant does not.
  • Avoid gas fires as they increase indoor humidity in winter. Wooden fireplaces are atmospheric, but are sources of indoor pollution, which can aggravate asthma.
  • Air-conditioning system is good at keeping the humidity normal, which will have a significant impact on dust mite allergen concentrations. An electrostatic air filter must be installed, and cleaned monthly.
  • Air conditioning systems fitted with filters will also reduce the ingress of pollen and moulds into the house.
  • Air filtration may be more useful for allergens associated with small particles that remain airborne longer (ie. cat) rather than for allergens associated with large (ie. mite faecal) particles, which settle out quickly and arise from local sources.
  • If the house is vacuumed regularly then a ceiling fan is acceptable.

10. Landscaping

  • Avoid canopy of trees above and also bushes right up against the house, as this will create dampness and encourage the growth of moulds.
  • Keep bushes trimmed back at least 2 feet from the house.
  • Avoid planting highly allergenic trees live birch and olive.
  • Pine and privet are common irritants for many allergic patients and should also be avoided.
  • Cutting the lawn at frequent intervals will help to prevent it from flowering.