Passive Design

Designing the building and the spaces within it to benefit from natural light, ventilation and even temperatures.

Controlling airborne contaminants

Airborne contaminants such as formaldehyde and combustion products can harm building occupants' health.

On this page:

  • Combustion products
  • Volatile organic compounds (VOCs)
  • Biocontaminants
  • Air purifiers.

There are a number of common indoor air pollutants that are of concern. They can be classified as combustion products, VOCs (volatile organic compounds), formaldehyde, fibres and biocontaminants.

Wherever possible, contaminants should be eliminated or removed at source - for example by specifying low-VOC paints and finishing materials, or by venting gas heaters outside. Risks from some contaminants can be dealt with through adequate ventilation - either passive or active.

Combustion products

Cigarette smoke contaminants

A wide range of toxic and carcinogenic products are produced by smoking, many of which are adsorbed onto surfaces in the room from where they revolatilise into the room even without a smoker present.

Inorganic oxides

Carbon monoxide (CO), carbon dioxide (CO2) and nitrogen dioxide(NO2) are combustion products from the burning of fuels, both fossil and biofuel (such as wood). Humans and animals also emit CO2 as a metabolism waste product.

Relatively high levels of CO2 makes a space seem stuffy, and very high levels cause drowsiness, headaches and dizziness. CO is far more hazardous, as it is taken up in blood in preference to oxygen, which can lead to death when exposure is high enough. CO is produced by poorly maintained gas appliances, including unflued portable gas heaters. It also occurs when appliances are being run in very airtight spaces, where oxygen depletion leads to incomplete combustion and the formation of CO as a result.

NO2 is produced by devices such as unflued portable gas heaters and aggravates asthma. At high levels, it can lead to respiratory distress.

Polyaromatic hydrocarbons

An emission from combustion, polyaromatic hydrocarbons are particularly from burning coal and wood. Some of these compounds are carcinogenic.


Particulates are tiny particles suspended in the air as a result of combustion, such as fires, gas appliances and smoking cigarettes. The smallest of these particles can lodge deep within the lung and cause respiratory issues.

Dealing with combustion products

To minimise harmful effects from combustion products:

  • specify efficient appliances - ones with low emissions of harmful poducts ((for example, ultra-low emission burners in preference to regular woodburners)
  • vent harmful combustion products outside - for example, using range hoods over gas burners and using only flued gas heaters.

Volatile organic compounds (VOCs)

Volatile organic compounds (VOCs) include a wide range of hydrocarbon compounds that are emitted as gases from different materials. Many building materials that are used and produced in the manufacture of paints, resins, adhesives, polyurethanes, epoxies, solvents, sealants and some cleaning products contain VOCs. The term ‘organic’ indicates that the compounds contain carbon.

They can have a range of effects on occupants including headaches, dizziness and respiratory irritation. Long-term exposure at high levels, which is more common at the workplace than at home, can cause kidney and liver effects, cancer and chromosomal damage.

VOCs can be controlled by careful choice of products and by ventilating the house well. It is important to know that VOC levels are quite high when a house is just built while materials off-gas their most freely evaporated volatiles but VOC levels then fall as time goes by.

Building products that release VOCs include:

  • paints, polyurethanes and varnishes that are manufactured from formaldehyde, mercury, arsenic, selenium, lead or cadmium
  • adhesives and resins
  • solvents
  • wallpaper, vinyl and carpet
  • furnishing foams and fabrics
  • LOSP-treated timber
  • manufactured wood products such as some particleboards, medium density fibreboard (MDF) and plywood.

Cleaning products and chemical processes

VOCs may react together and produce other compounds. Over 900 compounds have been identified in buildings including toluene, xylene, styrene, acetaldehyde, paradichlorobenzene, ethylbenzene, chloropyrifos, tetradecane, di-n-butyl phthalate and diazinon.

Formaldehyde and urea-formaldehyde

Formaldehyde is a chemical used extensively in the manufacture of building materials and household products. It is also a byproduct of combustion from unvented, fuel-burning appliances, such as gas stoves, unflued gas and kerosene heaters and from cigarettes.

It is commonly used in the production of resins and glues (urea-formaldehyde products), which are incorporated into many building materials, particularly manufactured wood products such as some particleboards, plywood and medium density fibreboard (MDF).

Formaldehyde and urea-formaldehyde gases have an irritating, pungent odour and are considered to have an adverse effect on health and performance when levels are above about 0.1 parts per million (ppm).

They will off-gas at room temperature particularly when the building products are new, so new buildings should be well ventilated, particularly during construction and for the first 4–6 weeks of occupation, to allow new building products to off-gas most of their formaldehyde and thus reduce the risk of formaldehyde gas irritation.

Controlling VOCs

VOCs are primarily released when materials or products/pplied. Over time, the level of emissions will reduce.

VOC emissions can be controlled by:

  • providing adequate ventilation, particularly during construction and the first 4–6 weeks of occupation
  • using low-VOC or VOC-free building materials/products
  • sealing materials, where practicable, to contain the VOCs by using low-VOC or VOC-free polyurethane, or alkyd or acrylic paints.


Biocontaminants include mould, fungi, bacteria (including legionella), viruses, protozoa, pollens and dust mites. They are sometimes also referred to as microbial contaminants or micro-organisms.

They are generally associated with moist environments and can cause respiratory problems.

Biocontaminant risk should be minimised by:

  • providing ventilation to reduce relative humidity and remove airborne biocontaminants
  • removing moisture and pollutants at source by installing automated extract ventilation systems in spaces such as bathrooms and kitchens
  • installing insulation and/or heating systems to help maintain warm interior spaces
  • having clean surface finishes that are easy to wipe down
  • having surfaces and finishes that are not conducive to mould growth or do not harbour micro-organisms
  • designing so that floors with carpet finish have regular exposure to sunlight.

Experts think that viruses such as the flu (influenza) or COVID-19 are mainly spread when infected people cough, sneeze or talk and droplets in the air land on people nearby. It is also possible, however, that a person might become infected when they touch a surface that the droplets have landed on, and then touch their face.

Household devices that can be operated hands-free therefore have potential health benefits. Pedal-operated rubbish bins are the most obvious example, but there are other fixtures and appliances that could also be considered.

Air purifiers

Air purifiers cannot be used to meet Building Code requirements but can still be useful for people susceptible to health problems where there is an excess of pollutants in the air. The HEPA filters in many purifiers can take out particles as small as 0.3 microns (less than one-hundredth the thickness of a human hair). This means they will trap dust, pollen, pet hair and dander.


Updated: 26 January 2021