What Gives Wood it’s Odor?
The majority of the identified odorants in wood from one study were 1) fatty acid degradation products 2) terpenoic substances and 3) odorous substances resulting from the degradation of lignin. (Source)
1. Fatty acid degradation products (69% of the odor of wood)
These include alkenals, ketones, alkylic acids and intramolecular esters.
Examples include pentanal, hexanal (grassy odors), octanal, nonanal, linalool (citrus-like odors), (E)-non-2-enal, (E,E)-nona-2,4-dienal (fatty odors), butanoic acid (cheese-like odors) and γ-octalactone, γ-nonalactone (coconut-like peach odors).
2. Terpenes (13% of the odor of wood)
Terpenes are unsaturated hydrocarbons that are produced predominantly by plants.
Terpenes (and terpenoids) are the main constituents of the essential oils from plants – but the two are not interchangeable terms.
Examples of terpenes in wood include α-pinene, β-pinene, limonene, Δ3-carene, and camphene.
3. Phenyl compounds from lignin degradation (13% of the odor of wood)
Odor-active phenyl derivatives include vanillin, 3-phenylpropanoic acid, phenylacetic acid, p-cresol, and thymoquinone.
The products from the breakdown of lignin and cellulose produce formaldehyde as a secondary compound. Source
Naturally Occurring Formaldehyde Levels in Wood
The natural formaldehyde content in wood is not the main factor that makes a wood species higher in odor.
One study found that the softwoods they examined had higher formaldehyde contents than the hardwoods.
There was also a difference between juvenile and mature wood.
The average formaldehyde values were:
- Pine at 0.54 mg/100 g
- Spruce at 0.47 mg/100 g
- Oak at 0.36 mg/100 g
- Beech at 0.27 mg/100 g
- Poplar at 0.29 mg/100 g
(As a reference point, E1 allows formaldehyde at at least 20x this with contents up to 8 mg/100 g or 0.1 ppm released. CARB II allows half that amount, so 10x more than pine’s natural contents.)
Pine is known as a higher odor wood in general, with formaldehyde being just one volatile compound that the wood gives off.
Though the formaldehyde levels in oak are on the lower level, oak is still a relatively fragrant wood.
Examples of Odorants Found In Trees/Wood
One study looked closely at pine. They found that in pine, the odorants (which include terpenes) are:
- phenylacetic acid
- 3-phenylpropanoic acid
In fir wood the following terpenes have been identified:
Woods That are Low Odor
Lowest Odor Woods
Maple and poplar are low odor woods that the chemical sensitive usually do the best with.
Aspen is a type of poplar (usually Populus tremuloides in North America) and so is also likely to be tolerable for many people.
Many find hickory to be low odor as well.
Birch works well for many chemically sensitive people too.
Medium Level Odor Woods
Oak is a fairly fragrant wood (though not as much as cedar and pine). Those sensitive to wood odor vary in their ability to tolerate oak. In a poll it ranked quite high on tolerability though it’s higher in odor than most people think.
Walnut and cherry are also mildly aromatic. Because we are all so different there are some people who do better with walnut or cherry over the lower odor woods.
Woods That are High in Odor
Most Fragrant Woods
Among commonly used woods used in buildings in North America, cedar is the higest odor.
The most fragrant woods include cedar (varies species), Brazillian Rosewood, and Sandlewood. But you won’t find much Rosewood and Sandlewood in homes.
Next up as the most fragrant are pine, fir, and spruce. Pine, fir and spruce are commonly used as the woods in framing a home and in structural plywoods.
The Best Wood Species for Those with Chemical Sensitivities
Those with sensitivities to the natural odors and VOCs in wood vary greatly in which species we do well with.
Make sure to get samples of the woods so you can check them out for yourself.
Make sure the wood samples are relatively fresh. You will notice a big difference between wood that is more recently felled and cut and older wood.
I have received wood flooring samples that were old enough to have essentially lost their odor.
I have also received samples of solid wood flooring that had noticeably picked up odors from the hardware store, such as glues and other chemicals. Be sure to ask that the samples are coming from the same source as the final flooring.
Corinne Segura is a Building Biologist Practitioner with 6 years of experience helping others create healthy homes.
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https://www.wood-database.com/wood-articles/wood-odor/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6268138 https://www.nature.com/articles/s41598-018-26626-8 https://www.researchgate.net/publication/235664413_Wood-borne_formaldehyde_varying_with_species_wood_grade_and_cambial_age