Wooden House and Human Health by Shuichi KAWAI


Air quality affects on human health. Brain requires fresh air. We inhale the fresh air around 20kg/day which occupies 90% of total in-taken substance. As 90% of time is spent in the house, the indoor air quality is very important for human health.


EPA’s report (2008) shows that Indoor Air Quality (IAQ) affects the ability of concentration, calculation and memory of school children. IAQ is affected by temperature, humidity, air pollutants, micro-organisms, and so on. And wooden house is good at humidity control and anti- air pollutants and micro-organisms.


Optimum Humidity Range for Human Comfort and Health

This figure shows the comfort zone of micro-organisms such as BACTRERIA, VIRUSES, FUNGI, MITES, and RESPIRATROY INFECTIONS, ALLERGIC RHINITIS AND ASTHMA, and OZONE PRODUCTION on the relative humidity conditions. The decrease in orange bars indicates decrease in their effects. Therefore, optimum humidity range for human health and comfort is around 40-60%. ASHRAE Report in 1985 shows this range of 30-60% in US due to rather dry area. And Japan takes this range of 40-70% in R.H. being located rather moist monsoon area. 

Japanese cedar (Cryptomeria japonica) is a Japanese inherent species. It is a typical interior material due to straight grain, light weight, easy for processing, superior thermal and humidity control, and air-purification ability. 


Japanese cedar removes air pollutants. Relative research indicates that ozone was removed around 75%, nitrogen dioxide around 50%, and formaldehyde around 20%. Through research, it was found that NO2 was related to the tissue structure. Cross section was much effective, and heartwood was more effective than sapwood.More detailed info please check the video link: https://youtu.be/MNPgWCYfyMo

As to commercial application, a simple machining process of “Slit” on the Japanese cedar was developed in order to expose the cross-section in both sides of grooves. This processing is very simple but effective. 


Wooden house with "Slit” cedar timber is good at humidity control and human health for both mind and body.

we evaluated the air quality of cedar flat sawn timber grooved across the grain, being set in a full scale store room of a ware house. The "Slit” cedar timber were applied to the wall, ceiling, or both the wall and ceiling. 


Temperature change decreased with the increasing the area of the wooden material in the room. Humidity change was mitigated in the similar manner to that of temperature, as well. The daily R.H. changed less with the increase of "Slit" cedar timber in the store room. And R.H. in the storeroom with cedar timber in both ceiling and wall varied basically in the optimum range of human health through the year.


Psycho-physiological experiment in the room with Japanese cedar timber were also measured. The VOCs in the room with “Slit” cedar timber were identified as sesqui-terpenes, such as δ-cadinene, α-muurolene, and β-caryophyllene. These chemical compounds were typical extractives of Japanese cedar.


Significant difference was found on the item of good or bad smell in the room with/without cedar timber. This suggests that the test subjects felt the good smell in cedar VOCs. As to other items, for examples, the room with cedar timber tended to be assessed as more natural, coziness and calm than the control room. VOCs affect the autonomic nervous system and induce physiological relaxation. 

Being the superior air-purification performance of Japanese cedar, “Slit” cedar timber 

is now widely applied as an interior material to the many areas, such as wall, ceiling, fittings, and even furniture. Wooden house of Japanese cedar timber improves the indoor air quality and contributes to the human health.


Other Related Links:

Using Japanese SUGI as Exterior Timber (https://youtu.be/Y66RNcsxMGo)

The Tategu and decorations with Japanese woods and Kumiko-Zaiku