Passive Design

Common pollutants include airborne formaldehyde, polyaromatic hydrocarbons, inorganic compounds, volatile organic compounds, particulates, and bio-contaminants such as mould and fungi which release spores into the air.

Inorganic compounds

Inorganic compounds are airborne chemical molecules sized less than 0.001 micrometers. Common ones include:

• nitrogen dioxide – from geothermal activity, vehicle emissions migrating into the house from garages or outside, emissions from kerosene heaters, unvented gas stoves and heaters, and tobacco smoke – which can cause irritation of the nervous system and irregularities in the circulatory system
• sulphur dioxide – from geothermal activity, coal combustion and vehicle exhausts – which can cause asthma attacks, eye irritation, coughing and chest pain
• carbon monoxide – from geothermal activity, unvented gas stoves and heaters, breathing, vehicle emissions migrating into the house from a garage or from the outside, kerosene heaters and tobacco smoke – which takes the place of oxygen in the blood, causing sleepiness, headaches, sickness and pulmonary oedema, and is potentially fatal
• carbon dioxide – from breathing and carbon fuel combustion – which can cause nausea, migraines, breathlessness and a feeling of heavy-headedness.

In general, inorganic compounds can be dealt with by providing sufficient ventilation and not specifying unflued gas appliances (see passive ventilation and active ventilation). For buildings close to a major road, fresh air supply should not be sourced from that face of the building.

Volatile organic compounds

Volatile organic compounds (VOCs) are hydro-carbon chemicals that have become airborne as a gas. They often react together and produce other compounds. Over 900 types have been identified in indoor air in buildings, with more notable compounds including toluene, xylene, styrene, acetaldehyde, paradichlorobenzene, ethylbenzene, chloropyrifos, tetradecane, di-n-butyl phthalate and diazinon. Their effects vary, but can typically include:

• irritations – for example to the eyes and mouth
• respiratory problems
• neurological disorders.

Some VOCs are toxic in large enough concentrations. Some cause allergies, though not in everyone.

VOCs are generally released from domestic building products, such as:

• paint, polyurethane and varnish – those manufactured with formaldehyde, mercury, arsenic, selenium, lead or cadmium
• adhesives and resins
• solvents
• wallpaper, vinyl sheet and tiles, carpets and carpet backings
• furnishings (fabric or foam)
• LOSP timber treatments
• particleboard, medium density fibreboard and pressed wood products such as plywood.

In general, VOCs can be dealt with by:

• providing adequate ventilation – particularly during construction and during the first 4 - 6 weeks of occupation (see passive ventilation and active ventilation)
• specifying building materials/products that contain few or no VOCs
• specifying sealing where practicable to retain the compounds within the material by using ‘safe’ polyurethanes, alkyd or acrylic paints.

Formaldehyde

Formaldehyde (sometimes categorised as a VOC) is an irritating gas with a pungent odour that can off-gas at room temperatures. It is commonly used in the production of resins and glues (often with nitrogen) which are incorporated into many building materials. Therefore it is generally associated with pressed wood products. It is also emitted by cigarettes and gas stoves. Formaldehyde is considered to have an impact on health and performance with levels above about 0.1 ppm. Materials containing formaldehyde may be able to be sealed or left (together with good ventilation) for the gases to dissipate.

Providing adequate ventilation – particularly during construction and during the first 4 - 6 weeks of occupation, will reduce the risk of problems from formaldehyde.

Particulates

• Particulates are airborne particles, typically sized between 0.01 and 100 micrometers. They include:
• smoke – for example, from cigarettes, oil and gas combustion, open fires
• fumes – for example, from chemical processes, cleaner agents like ammonium chloride
• ash – for example, from burning solid material, cigarettes
• dust – for example, from coal, insecticides.

They can all cause respiratory problems. In general, particulates can be dealt with by providing ventilation that extracts contaminated air and discharges it outside, and filters any incoming fresh air supply. See active ventilation for more.

Bio-contaminants

Bio-contaminants are sometimes also referred to as microbial contaminants or micro-organisms. They include mould, fungi, bacteria, viruses, protozoa, pollens, legionella, and dust mites. In general, they are associated with moist environments and can cause problems with the respiratory system. Mould and fungi can cause swelling of building materials and can be released as spores into the air. Dust mites thrive in temperatures between 18ºC and 22ºC with relative humidity above 70%.

Many moulds are harmless to occupants. One, stachybotrys, can be toxic to a significant number of people when airborne spores are inhaled. To grow, stachybotrys needs moisture and cellulose. Building materials that contain cellulose include:

• wood
• paper (the facing paper to plasterboard)
• fibre-cement (cellulose fibre reinforcing)
• wallpaper (and wallpaper paste)
• particleboard and medium density fibreboard
• paper-based insulation materials
• hardboard.

Bio-contaminant risk can be minimised by specifying:

• adequate fresh air ventilation to reduce relative humidity and remove airborne bio-contaminants (see passive ventilation and active ventilation)
• exhaust ventilation directly from appliances and rooms where a lot of water vapour is produced (for example, kitchens and bathrooms)
• levels of insulation and/or heating systems (see passive heating and active heating) that keep spaces warm (see controlling temperature)
• surface finishes that are easy to wipe down or clean
• surfaces and finishes that are not conducive to mould growth or which harbour micro organisms – such as polished wood, concrete or cork.
• ensuring that the design allows floor areas that have a carpeted finish to be exposed to sunlight regularly.

For designers involved in building repair or renovation work, work must cease on the discovery of any mould growths with the mouldy area being sealed off with plastic taped over the area. The mould must be identified to determine the specific to determine the nature of the mould present. To obtain a sample of mould for testing take a 50 mm long piece of self adhesive packing tape, place it carefully over some mould, lift it carefully off (so as not to disturb the spores) and immediately place it in a sealed plastic bag (wear disposable gloves and a dust mask when doing so). Send the sample to a testing laboratory. Where a toxic mould such as stachybotrys is identified, it must be removed under specifically controlled conditions.

Polyaromatic hydrocarbons

Polyaromatic hydrocarbons are combustible compounds carried in the air. They typically result from a combustion process. In houses, they are associated with heating supply (e.g. for air, water, oven) by combustion of gas or oil. Polyaromatic hydrocarbons can be dealt with by providing ventilation directly from where the combustion products are created. See active ventilation for details.

For your clients

To help your clients understand moisture and air quality issues, refer them to www.smarterhomes.org.nz/design/moisture and www.smarterhomes.org.nz/design/unhealthy-air.