Paper topics: 1 - inive

RENOVATION OF JAPANESE TRADITIONAL HOMES
AND
IMPROVEMENT OF INDOOR CLIMATE
Kanako Sasaki 1† , and Taeko Yasui 2
1 Himawari Kenchiku Kobo, Sendai, Japan
2 Yasui Sekkei Kobo, Sendai, Japan
ABSTRACT
The traditional house of Japan, Kominka, is constructed of wooden pillars and beams, and clay walls.
The indoor space in the Kominka remains cool in summer because overhanging eaves block solar
radiation and the open frame airs out. Technology to make small cracks airtight is undeveloped.
Consequently, drafts enter the indoor space and chill occupants during winter. Improvements of indoor
climate have not been realized. This report describes "Yuki’s house," which is a Kominka built in the
latter 1700s, defined as a residence of the privileged class. Large-scale renovation of the home was
done through high insulation and airtightness reainforcement in 2006. The temperature and humidity in
winter in Yuki’s house and in "T’s house," an unrenovated Kominka built in 1897, were measured, and a
comparison was done for verification. In Yuki’s house, the overall heat transmission was decreased by
progress of capability for insulation and airtightness. Thereby stable and comfortable indoor
environment was provided. A clay wall contributes as thermal storage and a cooling influence in
summer. This paper clarifies the renovation techniques used for Yuki’s house and the effects for indoor
environment improvement. Renovation of Kominka to achieve high comfort is reported herein.
KEYWORDS
Traditional house, Renovation, Comfort, Insulation, Airtightness
INTRODUCTION
Japan was revolutionized from a feudal society to a democracy by its defeat in 1945. Subsequent
changes were drastic and ongoing in its culture, food, clothing, housing, family systems, etc. There is a
traditional style of building before the Building Standard Law was enacted in 1950. I call them Kominka.
The enactment of this law provided minimum standards. From that time, construction using traditional
industrial methods became difficult. An important difference in post-war Japan was dismantlement of
the privileged class, which affected Kominka. Many families that had lost farmland, which was their
economic foundation, were not able to maintain vast homes; they were demolished one after another
and quickly became rare. However, the Japanese Government did not seize forests. This is one reason
Yuki’s house stands to this day. However, in addition to the reason described above, the main cause of
Kominka scarcity is that measures against the cold are few. The clay walls control humidity and are well
ventilated. The thatched roof, with large, deep eaves, blocks solar radiation in summer. These
traditional merits of Kominka have become the faults that let heat slip away in winter (Figure1, 2).
Renovations of Kominka typically divide the grand space into smaller rooms, which decreases the
room’s heated area. Kominka can become long-lived homes that endure for hundreds of years if
measures for leaks in the roof are done. Removing the fault of cold through increased insulation and
airtightness reinforcement of Kominka produces a comfortable indoor environment. Moreover, a facet
of traditional culture is thereby defended. Yuki’s house, which was built in the latter 1700s, has
remained intact for more than 200 years with its original construction. For this study, one of the authors,
† Corresponding Author: Tel, Fax: + 81 22 247 9601
E-mail address: k-sasaki@coffee.ocn.ne.jp

Ms. Yasui, an architect, developed methods of renovation for Yuki’s house. The author, Sasaki
managed its reconstruction and verified its indoor environment after it had been renovated. This paper
clarifies the method of renovation in Yuki’s house, and examines its comfort based on measured
temperature and humidity data.
METHODS
We describe the renovation method used in Yuki’s house. The main technology elements are three:
insulation and airtightness reinforcement; heating devices and ventilators; and seismic reinforcement.
Insulation and airtightness reinforcement
Yuki’s house renovation was based on exterior insulation methods to acquire the house performance
model recognition (by Asahikasei Co.). Filling the thermal resistance value necessary in each part
according to the region fulfilled “Next generation Energy saving Standards” in Japan. Efficient phenol
foam heat insulation board t=30 mm (thermal conductivity lambda=0.020 W/(m·K)) was used for the
wall and the roof. The regulation thickness of the heat insulation of the roof is 50 mm. The building was
built to face the east. Trees taller than 30 m stand west and south of the home. The influence of solar
radiation is sight because of such conditions of location on summer days. Therefore, the thickness was
decreased to 30 mm. It was laid outside and underground with 450mm width extrusion polystyrene
foam board (thermal conductivity lambda=0.028 W/(m·K)) t=50 mm. This is a principle of the “Skirt
insulation method.” At the perimeter, extruded polystyrene foam board, t=30 mm, was laid into the
ground within 900mm width. The regulation thickness of the underground heat insulator was decreased
in expectation of using geothermal energy. As a vapor barrier and airtight barrier, 0.2 mm of Linear Low
density Polyethylene Film (LLDPE) was laid. A sash made of aluminum with high insulation efficiency
(coefficient of heat transmission 3.49 W/(m2·K) or less) with double glass of 12 mm in the air layer was
used for the opening. Gas urethane foam was filled into the part where the space of insulation was
available. The parts where the heat insulator was not consecutive easily were continued using wood,
which was considered to be a heat insulator. Concrete was placed in the ground to 100 mm as a
thermal storage body in summer. Moreover, the existing clay wall was left as a thermal storage body to
the greatest extent possible, plastered, and reinforced. For other walls, plasterboard was put on the
ground of the bearing wall, and was plastered for finish.
Heating device and Ventilator
A forced-draft balanced flue stove (3.01–2.58 kW×1; heating output 6.15–2.49 kW×2) that used
kerosene fuel was installed as a heating device. The air supply is carried in from five ducts of 150Φ set
up in the attic at a flow velocity 0.62 m/s. The exhaust gas is carried out from five ventilating fans (total
200 m3/h) set on the wall. For smoking, exhaust fans in limited areas were set up in five places (total
1,260 m3/h). The ventilation fan for air supply and exhaust gases (530 m3/h) and differential pressure
unit are set up for cooking; it is concluded at a short cycle. The ventilation fan (80 m3/h) was set up as a
circulator below the floor level without a heat source. (Figure5, 6)
Seismic reinforcement
Pillars stand independently on cornerstones. The column bases were fixed with connections at the
bottoms of two or more pillars using wood (150 mm × 120 mm). The newly established wall, which was
assumed to meet specifications of a bearing wall, was based on bulletin No. 1100 in the Building
Standard Law in Japan. It was reinforced to a rigid structure by these two points. The thatched roof was
regrettably reroofed with Galvalume steel plates. For the roof shape, the past shape was followed.
Maintenance of the thatched roof had become difficult because the number of capable artisans had
decreased. Furthermore, it is advantageous to decrease an upper load as an earthquake
countermeasure. For those reasons, the roof material was changed.
Indoor environmental measurement
The temperature and humidity were measured in the room and outdoors using a temperature and

humidity data logger (Ondotori TR-72U; T&D Co.). Five measurement positions were used at Yuki’s
house: the air outside, below floor level (FL-200), the lower side of the Doma (FL+200), the upper side
of the Doma (FL+6,000), and the Dei (FL+3,000) (Figure 4, 5). In the non-renovated Kominka "T’s
house," built in 1897, similar measurements were done for comparison. The measurement positions of
T’s house were four: the air outside, lower side of the Chanoma (FL+200), upper side of the Chanoma
(FL+2,400), and the Toori (FL+2,400)). Judgment standards by owners about the rational energy use in
houses (Next-generation Energy-saving Standard) were revised and annotated in 1999. Yuki’s house is
located in Region 3 according to the region that this standard sets; T’s house is located in Region 2. In
the geographic region to which both belong, the maximum snowfall depth is 60 cm or less, and the
heating degree-days are 3,000–3,500°C day. Indoor environments are inferred to be comparable
before and after renovation because the outside environment is similar. Measurements were done
during the month of 11 January – 10 February. The recording interval was 30 min. Data of ten days
were extracted and used for verification.
RESULTS
Temperature
Various conditions of Yuki’s house and T’s house, and comparisons of temperatures in each house are
shown (Table 1,2 and Figure 7). The forced-flue type kerosene stove runs continuously in Yuki's house.
In the Doma (Ave. CH=6m), the temperature of the upper part of the room was 17.4°C–20°C and that of
the lower part was 15.6°C–18°C. The heater adjusts the preset temperature at 17°C. The heating
volume is large in the Doma. For that reason, the heater ran continuously. The difference of
temperature between upper and lower levels was within 4.4°C or less. In the Dei (CH=3.2m), the
temperature was 17.3°C–20.8°C. The preset temperature of the heater was 17°C. The heater stopped
running when the room temperature became 20°C. It began running when the room temperature
dropped below 18°C; it stopped when the temperature reached 20°C. The run stopping time was about
2–3 h daily. The value was always indicated as higher than that of the air when the clay wall surface
temperature was measured using the radiometer. Below the floor level, they showed a steady value of
15–15.8°C. On the other hand, at T’s house, the kerosene of the room’s open stove was used
intermittently. The upper part of the room was 5.8°C–27.1°C; the lower area was 4.5–14.5°C. After
heating had stopped, it decreased rapidly to about 6°C in 30 min. The upper and lower temperature
difference became 22.6°C maximum.
Humidity
A comparison of the humidity in each house is shown (Table 3 and Figure7). The change was steady at
Yuki’s house. The change was large in T’s house according to running of the heater.
Heating and cooling load
Yuki’s house was heated continuously for six months, from the end of October to the end of April. No
cooling load is applicable because air-conditioning was not installed. The amount of kerosene use
during year was about 4,750 l. That amount of kerosene can be readily converted into the amount of
heat. The caloric value of kerosene is 36.84 MJ/ l; therefore, 4,750 l/year×36.84 MJ/ l = 174,990
MJ/year.
Effect of thermal storage
The clay wall of about 100 m2 was retained as a thermal storage body in the entire building in Yuki’s
house. The clay wall thickness was 70 mm on average; its capacity became 100 m2×0.07 m=7 m3.
The volume specific heat of the clay wall was specific heat 0.88 kJ/kg·K × specific gravity 1,300 kg/m3
= 1,144 kJ/m3·K. The thermal capacity of the entire clay wall was volume specific heat of 1,144
kJ/m3·K × volume 7 m3 = 8,008 kJ/K. The volume of concrete placed in the ground was 280 m2 ×
thickness 0.1 m = 28 m3. Thermal capacity is specific heat 0.88 kJ/kg·K × specific gravity 2,200 kg/m3
× volume 28 m3 = 54,208 kJ/K.

DISCUSSION
First, the temperature and humidity data of Yuki’s house shall be addressed. The heater radiates air of
70–80°C. The heater’s temperature sensor detects the change of air temperature by 2–3°C, and
adjusts its running program. Engawa and the garret space are adjacent to the Dei, and neither the wall
nor the ceiling is bound directly to air. The heating capacity of the heater on the Dei is less than that of
the Doma. The heater stop time is used for the heater that is set up on the Dei, but that set up in the
Doma is always running. This practice might differ depending on conditions. Next, the adaptability to
the Next-generation Energy-saving Standard, which provides for a high level in the present, is
evaluated. A Next-generation Energy-saving Standard is needed whether to suit the "Judgment
standard by the owner (performance regulations)" or "Indicator of the design and construction (detailed
regulations)." Detailed regulations are assumed to be met by the measures described in the Methods
section. Adaptability with the performance regulations is verified here. In Region 3, where Yuki’s house
is located, the Demand Standard of heating and cooling loads has been provided as below 460
MJ/m2·year. The amount of the energy use was 174,990 MJ/year. An area of 310 m2 exists. The
running efficiency of the heater is 86% (Depending on manufacturer specifications). Consequently, the
heating and cooling load becomes 174,990 MJ/year/310 m2×0.86=485 MJ/m2·year. The Demand
Standard assumes a room of about 2.5 m height between heat insulators. Therefore, the load amount
will be assumed as 310 m2×2.5 m=775 m3. The heating area of Yuki’s house is about 1,744 m3, it is
said to have about 2.25 times greater capacity than assumed. Considering this element, It can be said
that the heating and cooling load is 485 MJ/m2·year divided by 2.25=215 MJ/m2·year, which reaches
necessary performance regulations. It has been converted from an open system building (before
renovation) to a closed system building (after renovation) by maintaining insulation and airtightness
performance. The amount of overall heat transmission was decreased, and control of the thermal
environment was achieved. The clay wall and concrete demonstrate sufficient effects for thermal
storage and cool storage. Therefore, the indoor temperature and humidity are stabilized by the reduced
influence of air. Because insulation and airtightness performance are low, and because air exerts a
strong influence, the effect of thermal storage cannot be demonstrated in T’s house, although it also
retains the traditional clay wall. The rapid temperature decrease after heating cessation occurs for this
reason.
CONCLUSIONS
This study compared and verified the thermal environment in an unrenovated Kominka residence to
those in one that was renovated with insulation and airtightness reinforcement. A steady thermal
environment, which was not influenced easily by external air, was obtained through renovation of Yuki’s
house. Additionally, two values obtainable only in the Kominka became apparent. The clay wall with
large thermal capacity contributed by insulation and airtightness reinforcement demonstrates the effect
of thermal storage. The clay wall retains residual heat from heating; its surface temperature thereby
becomes higher than that of air. The clay wall radiates that heat; consequently, the temperature
decrease in the indoor air is mitigated in winter, thereby providing a comfortable environment with little
airflow. The thermal storage clay wall with convection heating demonstrates an effect that resembles
that of a radiant type heating panel, and can be designated as a "clay wall type radiant heating panel."
In summer, opening the skylight at nighttime, thereby cooling the clay wall, can cool the room.
Moreover, cooling is provided by concrete from the low temperature of the ground. It is possible to live
without an air conditioner using this radiant cooling. Recently, clay walls have not been adopted for
reasons such as determining the term of works, worker shortages, and high prices. Merits such as the
high thermal inertia and the ability to adjust moisture appear to have been overlooked. About 60% of
the clay walls were retained in Yuki’s house; their merits were exploited. A second valuable aspect of
Kominka is rediscovery of traditional homes. The owner is proud of the residence, and looks forward to
the succession of culture to the next generation by the existence of Kominka. The indoor comfort is not

only an element shown by the energy efficiency figures of the equipment, heat performance, etc. And it
also is achieved by the humanities, the dignity based on history, the security that the traditional homes
bring, and so on. The latter wants to be taken as a comfortable element, and to be evaluated although it
is not clearly shown in figures. It is difficult to show effects for the second element clearly in a figure.
Nevertheless, such an index would evaluate the comfort highly. Future studies will explore
improvements in the energy used for manufacturing and processing, improving cost performance, and
reproducing materials using easy construct techniques. As a contribution to the accumulation of
technology that achieves a comfortable indoor environment, this paper reviews the value of renovation
of a traditional house.
ACKNOWLEDGEMENTS
We would like to express my gratitude to Professor Motoya Hayashi at Miyagi Gakuin Women’s
University. We borrowed measuring instruments from him, and received guidance. We wish to express
my gratitude to Professor Yasuo Utsumi, Miyagi National College of Technology, and Mr. Kenju
Ninomiya, Maeda Construction Co., Ltd. Valuable guidance and teaching were given. We wish to
express my gratitude to Mr. Jun Yuki, owners of Yuki’s house, and everybody of T’s house. Their
cooperation in measurement is greatly appreciated.
REFERENCES
1. Architectural design material collection (Environment 1) 1979, 2007, Architectural Institute of Japan
Corporation.
2. Cyclopedia of architecture unit, 1992, Shokokusha.
3. Quick guide of Next-generation Energy-saving Standard, 1999, Japan Construction Material
Industries Federation Corp.
4. Investigation concerning suitable house for Tohoku, 1998, Residence and environment – Tohoku
forum.
Table1 Outline of Yuki’s house and T’s house
Outline
Yuki's house
T's house
Location
Lat.38゚N
Lat.39゚N
Built year latter 1700s 1897
Region
Region Ⅲ
Region Ⅱ
Maximum snowfall depth
60cm or less
Heating degree days
Heating method
3,000-3,500℃day
forced-draft balanced forced-flue type
flue stove kerosene sotove
Figure 3 the ducts of air supply
and insulator
Figure 1 The Doma in Yuki’s house
(Before renovation)
Figure 2 The appearance of Yuki’s house
(Before renovation)

A
Figure 4 Section A-A’ (Measurement positions)
Dei
FL+3,000
FL+6,000
FL+200
Doma
Figure 5 Positions of Ondotori and Heating
3.01~2.58KW
N
bedroom
bedroom
Dei
6.16~2.49KW
Figure 6 Flow of ventilation
Engawa
exhaust f ans[m3/h]
40
( :for
smoking) 80
40 20
air supply
0.62[m/s]
Doma
530
FL-200
6.16~2.49KW
A'
Table 2 Comparison of temperature[℃]
Yuki's house
T's house
Outdoor Min -2.2 Outdoor Min -3.3
Max +8.6 Max +9.6
Below floor Min +15.0 Toori(upper) Min -0.7
FL-200 Max +15.8 FL+2400 Max +6.2
Doma(lower) Min +15.6 Chanoma(lower) Min +4.5
FL+200 Max +18.0 FL+200 Max +14.5
Doma(upper) Min +17.4 Chanoma(upper) Min +5.8
FL+6000 Max +20.0 FL+2400 Max +27.1
Difference at Doma
(upper-lower) 4.4
Difference at Chanoma
(upper-lower) 22.6
Dei(upper) Min +17.3
FL+3000 Max +20.8
Table 3 Comparison of absolute humidity
[g/kg・DA]
Yuki's house
T's house
Outdoor Min 2 Outdoor Min 2.1
Max 4.6 Max 4.7
Below floor Min 4.9 Toori(upper) Min 2.4
FL-200 Max 5.5 FL+2400 Max 4.5
Doma(lower) Min 3.5 Chanoma(lower) Min 2.7
FL+200 Max 4.5 FL+200 Max 6
Doma(upper) Min 3.9 Chanoma(upper) Min 2.6
FL+6000 Max 5 FL+2400 Max 8.2
Difference at Doma
(upper-lower) 1.5
Difference at Chanoma
(upper-lower) 5.5
Dei(upper) Min 3.8
FL+3000 Max 4.9
bedroom
Doma
200
20
bedroom
Dei
300
300
300 160
Figure 7 Graph of measurement results
The variation of temperature of Yuki's house 2007/02/01-02/10
The variation of temperature of T's house 2007/02/01-02/10
Temperature [℃] [
30
25
20
15
10
5
0
-5
-10
2/1 2 3 4 5 6 7 8 9 10 day
outdoor
below floor(FL-200)
Doma(FL+200)
Doma(FL+6000)
Dei (FL+3000)
The variation of absolute humidity of Yuki's house 2007/02/01-02/10 The variation of absolute humidity of Yuki's house 2007/02/01-02/10
Absolute humidity [ g/kg DA ]
9
8
7
6
5
4
3
2
1
2/1 2 3 4 5 6 7 8 9 10 day
outdoor
FL-200
Doma+200
Doma+6000
Dei +3000
Temperature [℃] [
Absolute humidity [ g/kg DA ]
30
25
20
15
10
5
0
-5
-10
2/1 2 3 4 5 6 7 8 9 10 day
outdoor
Toori(FL+2400)
Chanoma(FL+200)
Chanoma(FL+2400)
9
8
7
6
5
4
3
2
1
2/1 2 3 4 5 6 7 8 9 10 day
outdoor
Toori(FL+2400)
Chanoma(FL+200) Chanoma(FL+2400)