According to a study completed in late 2021, wooden school buildings provide students with an excellent learning environment. This study on the health effects of wood construction compared the Tuupala wood school in Kuhmo with a control group of schools. The results show that the wooden school has a low noise level, less fluctuation in humidity than in the control group, and reduced stress among the students. The stress level differences were sometimes statistically significant.

Text: Pekka Kilpeläinen and Veijo Sutinen
Read the article in Finnish: Tutkimus Tuupalan puukoulusta: Melua on vähän ja oppilaiden stressitasot ovat alhaiset

Artikkeli jatkuu mainoksen jälkeen

The Tuupala wood school in Kuhmo is the first school built from solid wood CLT elements. Nearly 1,700 visitors already came to see the school during the construction phase, and more than 1,500 people had time to visit the completed school in the two years before the pandemic broke out. In 2018, the school received the national wood construction award as the Wooden Building of the Year.

The pioneering nature of the building, the abundance of wood surfaces and the limited nature of the surface treatments – the interior walls only have a wax coating and the exterior surfaces are treated with a colorless preservative – also make it an excellent research site to investigate the effects of wood on interior environments. Our study sought to thoroughly examine the physical, microbiological, and chemical properties of the school, as well as how stressed the students were.

For the control group, our study selected two schools: the Tuupala stone school, which is next to the wooden school and was built in the 1950s, and the Vaala integrated school, which was completed in 2012 and was designed by the same architects (Antti Karsikas, Karsikas Oy, and alt Arkkitehdit Oy) as the Tuupala wooden school. The integrated school is also located in an environment similar to the Tuupala wooden school, namely a rural town in the middle of a relatively forested area with no industry nearby.

Less humidity fluctuation and lower noise levels in wooden schools

We used continuous sensor monitoring to compare the physical conditions of the schools from February 2020 to November of the same year. Four rooms were monitored in all three schools. The clearest difference between the schools was in how much the indoor humidity fluctuated. The study compared the neighbouring Tuupala wooden and stone schools to ensure the outdoor humidity was the same for both. Measurements were taken during the weekends when no one was in the buildings to affect the humidity. The ventilation was already set to matching levels in both buildings, which was also apparent in the similar rates of carbon dioxide cleared during breaks.

The monitoring period included a total of 41 weekends. The difference between the highest and lowest humidity was smaller in the wooden school than in the stone school on 39 of those weekends (Figure 1). On average, the difference was 0.24 g/m³. The ventilation systems use different heat recovery mechanisms. The wooden school uses rotating cells, and the lower secondary school has liquid circulation (glycol circulates between the cells in separate inlet and outlet channels). Moisture can condense on the surface of rotating cells under certain conditions, and a small portion of the outgoing air returns as the cell rotates, which may slightly even out fluctuations in humidity.

Sensor monitoring was scaled up in October. In practice, this meant that additional sensors were placed in one classroom in both the wooden school and the Vaala control school. A total of four sensor packs were used in each classroom, with the three new ones also capable of measuring noise levels. This study found the average noise level during an entire month of school days was 5.0 decibels lower in Kuhmo than in Vaala (values of 47.9 and 52.9 dB respectively). If we look at average (effective average) sound levels, which emphasises higher noise levels, the difference is only 1.0 dB. This means that background noise is lower in Tuupala, but there was also a difference in the “ambient noise” in the class.

Decibels are a logarithmic measure, so a difference of 5 decibels is actually considerable. The Tuupala school carpet and the good acoustics of the wooden surfaces can partly explain the difference in noise levels. Wall thickness does not explain explain the difference, quite the contrary. When corridor noise occurs, it clearly carries into the classrooms in Tuupala. In Vaala, the ventilation system’s sound level is slightly louder, as can be seen in the overnight results. Finally, it is worth reiterating that noise was only monitored in one class in each school.

Cortisol levels and smart ring measurements used to study stress

The stress experienced by students was monitored using two different methods. Saliva cortisol testing was conducted on large groups of students. This specific stress marker indicates a response mediated by stress hormones released by the hypothalamus, pituitary gland, and adrenal cortex. Moodmetric smart rings were used with smaller groups to monitor electrodermal activity (≈ the electrical conductivity) of the skin. These readings indicate the activity of the sympathetic nervous system and the stress response mediated through it. This is the same response pathway that causes adrenaline to be secreted in “fight or flight” situations. Stressful situations and days can induce large increases in cortisol levels. When people feel exceptionally stressed, their cortisol levels may remain elevated for the next 1-2 days. However, “stress peaks” usually flatten out by the next day after a good night’s sleep.

Since the cortisol measurements were taken from saliva, the samples were easy to take independently in classrooms with a little training and guidance from the researchers. The study included students from four classes in Kuhmo (fourth graders at the beginning of the study) and three classes in Vaala (grades 3–5). A total of 52 students from Kuhmo and 37 from Vaala participated. Saliva samples were collected for a week in February and again for a week before and after the autumn holiday in October. Samples were taken once per school day, always at the same time. If the participant was in school on all days of the study, they provided a total of 15 samples. About 1,300 saliva samples were collected all in all.

There was a statistically significant difference between the cortisol levels of the students in the Tuupala wood school and those of the Vaala integrated school during the week before the autumn holidays (p <0.05, Figure 2). The statistically significant difference may stem from the timing: the extreme stress spikes that might cause abnormal results were at a minimum. In other words, the conditions more closely reflected an ordinary school day and its environment. It is worth noting that a similar difference was detected more or less across the entire monitoring period, although it was not statistically significant.

Surprisingly, there was also a statistically significant difference in cortisol levels between the week before and the week after the autumn holiday in both schools. It’s hard to know with certainty what the reason is. Either the children were active after the autumn holiday and were enthusiastically doing all sorts of things until they were slightly exhausted or their circadian rhythm had switched over to sleeping late during the autumn holiday. Going back to an early morning rhythm is known to be stressful. In addition, the switch to Daylight Savings Time took place between the measurement weeks: at the beginning of the autumn holiday in Vaala and at its end in Kuhmo. This meant waking up even earlier in the morning.

The smart ring monitoring involved smaller groups, 9 pupils from Kuhmo and 12 from Vaala. Although the group observed was small, the smart ring monitoring showed a statistically indicative difference (p <0.1) in excitement (~stress) in the week before autumn holiday. Again, the Kuhmo students were measured as being less stressed than their counterparts. When the averages of the smart ring monitoring and cortisol measurements were compared for daily changes, the changes were surprisingly similar. This supports their significance. This is a very interesting finding because these two factors show the activity of two separate stress response pathways.

Conclusions

It is impossible to say with certainty why the students in Kuhmo were less stressed than their counterparts in Vaala in the week preceding the autumn holiday. The monitoring was done in three classes, which means the result cannot be due to a different class schedule or an individual event stressing individual classes. A potential explanation for the consistent difference between the two schools in this very quiet rural setting is that there is some difference in their everyday school environment or its routines.

The Tuupala school is made of wood and may also be remarkably quiet compared to Vaala school. The actual school building is an important part of a school day environment. Studies conducted on groups of people in uncontrolled daily life often find it difficult to identify the underlying causes of observed effects. More of this kind of monitoring will undoubtedly be conducted in Finland and abroad in the near future. If these studies, or at least most of them, show similar effects, the significance of our results will be confirmed in time.

Why have several studies found that a short-term stay in a wooden room results in lower blood pressure or a lower heart rate and an increase in heart rate variability? Several explanations have been offered, with the same explanations applying to regular stays in these rooms. Individuals may find environments more pleasant when there is less fluctuation in humidity and temperature, volatile compounds from wood may have positive effects, wood surfaces have good acoustics, and they reduce the growth of bacteria and mold at least when fresh. Wood feels pleasantly warm to the touch, and its colour is also perceived to be pleasant and warm. Wood’s inviting and natural appearance is increasingly part of the debate. Such a pleasant environment in all respects would, after all, make a building feel comfortable and calming.

Our study opens an interesting portal to show that stress can be monitored daily in schools, even in primary school children. Much remains to be studied. How do wood surface treatments and the aging of the surface affect wood’s properties? How can the best aspects of wood to be brought out in different environments? We will continue our work with our European network in a project funded by the ERA-Net ForestValue program.

CREDITS

This study was funded by the Finnish Forest Foundation and the Mainland Finland Rural Fund through the Kainuu ELY Centre. The study was carried out by the Measurement Technology Research Unit at the Kajaani University Consortium of the University of Oulu. This is where the authors of the article, Pekka Kilpeläinen Ph.D. and Veijo Sutinen Lic.Sc. work – Kilpeläinen as a research manager and Sutinen as a laboratory engineer. The study is the first in Finland to monitor the effects on individuals of a longer stay in a wooden building.