We want to use plywood in the internal lining of our tiny house because its easy to work with, strong, made in NZ, takes well to different finishes and is relativity inexpensive. So it seems to tick all the boxes until you find out it off gasses formaldehyde which is linked to all sorts of health concerns including cancer. Various products produce formaldehyde, but the main focus throughout this post is plywood.

What is Plywood

Plywood is made by gluing together multiple thin sheets of wood, with grains at right angles to the previous layer. This gives it strength and warp-resistance. The outside layers can be finished to different grades depending on application.

What is Formaldehyde?

Formaldehyde is a colourless, flammable, strong-smelling chemical that is used in building materials and to produce many household products. It is produced in small amounts by most living organisms (eg. trees) as part of normal metabolic process.

What are its effects?

When formaldehyde is present in the air, some individuals may experience adverse effects such as watery eyes; burning sensations in the eyes, nose, and throat; coughing; wheezing; nausea; and skin irritation. Some people are very sensitive to formaldehyde, whereas others have no reaction to the same level of exposure. Formaldehyde has been classified as a known human carcinogen (cancer-causing substance) by the International Agency for Research on Cancer and as a probable human carcinogen by the U.S. Environmental Protection Agency. Research studies of workers exposed to formaldehyde have suggested an association between formaldehyde exposure and several cancers, including nasopharyngeal cancer and leukemia. source

However it must be stressed that the cancer causing properties of formaldehyde are only evident at very high concentrations, hundreds of times greater than levels emitted from plywood and laminated veneer lumber products. source

Where else can Formaldehyde be found?

• Cosmetics and toiletries - fingernail polishers and hardeners, antiperspirants, makeup, bubble bath, bath oils, shampoos, creams, mouthwashes and deodorants. 

• Household cleansers - disinfectants and polishes

• Paper products - formaldehyde is used to improve the water resistance, grease resistance, shrink resistance and other characteristics of paper

• Building materials - particle board, plywood, MDF, Vinyl flooring, Plastic wallpapers, Carpets

• Medications - wart remedies, medicated creams, orthopaedic casts and root canal preparation disinfectant

• Paints - polyurethane, primers and paint-stripping agents

• Smoke - burning wood, coal, charcoal, cigarettes, natural gas and kerosene

What levels are acceptable?

According to a 1997 report by the U.S. Consumer Product Safety Commission, formaldehyde is normally present in both indoor and outdoor air at low levels, usually less than 0.03 parts of formaldehyde per million parts of air (ppm). With increasing concern and consumer interest in eco-friendly products, the industry is becoming stricter on regulations. Below shows formaldehyde levels in parts per million (ppm) and the associated formaldehyde emission standard used to rate plywood in NZ and other parts of the world.

What can be done to reduce formaldehyde levels?

It is recommended to use exterior grade plywood to limit formaldehyde exposure in the home. These products emit less formaldehyde because they contain phenol resins, not urea resins.

Formaldehyde levels in homes can also be reduced by ensuring adequate ventilation, moderate temperatures, and reduced humidity levels through the use of air conditioners and dehumidifiers.

The best way to reduce formaldehyde is to buy a product without it.

Columbia Forest Products in the US do just that. They have developed and sell plywood sheet bonded using a natural soy based glue. In the US this product is approx 25% more expensive than standard ply. This product is available in NZ at Plymasters . Another approach is to enclose external surfaces with laminate or water based sealant. But of course these products too can give off formaldehyde. Safecoat another US company produces paints and sealer's that are non toxic that give off low or no formaldehyde.

Let new materials time to off gas for a month or two before living with them.

The final approach is to use a alternate product like metal or timber for example.

Conclusion

We have concluded using plywood in your house seems to be safe if you observe the following.

• Use no or low formaldehyde plywood.

• Or use E1 or better still E0 rated plywood.

• Ventilate and control temperature and humility.

• Seal plywood.

• Limit its use if possible.