D E S I G N R E V I EW

Folded roof house: Design solution to optimize theenvironmental condition with generic equipment andtechniques

Kaoru Suehiro1,2 | Noriko Suehiro1 | Yoko Masuda3 | Kazuko Ito4 | Kazuhide Ito5

1NKS Architects, Fukuoka, Japan

2Faculty of Human-Environment Studies,

Kyushu University, Fukuoka, Japan

3TOURI-SHA Structural Design Office,

Osaka, Japan

4WEST Japan Engineering Consultants, Inc.,

Fukuoka, Japan

5Faculty of Engineering Sciences, Kyushu

University, Fukuoka, Japan

Correspondence

Kaoru Suehiro, Faculty of Human-

Environment Studies, Kyushu University,

Fukuoka, Japan.

Email: kaoru@nksarc.com

Kazuhide Ito, Faculty of Engineering

Sciences, Kyushu University, Fukuoka, Japan.

Email: ito@kyudai.jp

Abstract

We covered a rectangular site in a residential area oriented at a 45° angle to the

north, and rotated the roof of the second floor on top of the rectangular first floor

and created a large window on the side at the south corner. To realize an open

interior with a limited footprint, we created a single-volume space connecting the

first floor to the second floor with stairs. The timber frame of the second floor sits

on the concrete box of the first floor. The stiff timber box consists of a folded roof

and exterior walls to realize a large pillar-free space. We set the main windows

higher to maximize the effect of natural light, placed eaves in front of the large win-

dow to block direct sunlight, and used slit windows between the first and second

floors to promote natural lighting and ventilation.

K E YWORD S

environmental optimization, environmental simulation, passive design, small residential house,

sustainable design, timber construction

F IGURE 1 Overall interior view of folded roof house in Kasuga

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any

medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

© 2017 The Authors. Japan Architectural Review published by John Wiley & Sons Australia, Ltd on behalf of Architectural Institute of Japan

DOI: 10.1002/jar3.3

Jpn Archit Rev. 2017;1–6. wileyonlinelibrary.com/journal/jar3 | 1

1 | INTRODUCTION

We present a small house for a family of four, specializing in architec-

tural environmental engineering. The primary design objective for this

house was to optimize the indoor environmental quality within a lim-

ited site space and budget. Along with the social trend of sustainable

and energy efficient private houses in Japan, relatively high percent-

age of new houses has been equipped with sophisticated new tech-

nologies and energy creation systems. However, these systems are

generally costly and the design of houses is not harmonized with

these technologies. We believe that the “folded roof house” is a

design solution that optimizes the pleasantness, comfort, environ-

mental conditions while using generic equipment and techniques, and

achieved an architectural expression together with technologies.1–5

Figure 1 shows overall interior view of folded roof house in Kasuga.

2 | ARCHITECTURAL CONCEPT

2.1 | Site planning

The single-family house is located in a suburban residential area,

where many private houses are situated side by side on similar hous-

ing lots (Figure 2). The rectangular lot with 176.7 m2 size is oriented

approximately 45° to the north. Because the carport with about

5.7 m depth needs to be along the street, the house has to be situ-

ated very close to the southern boundary, just a step behind the

neighboring houses. We considered the solution of rotating the sec-

ond floor by 45° on top of the first floor to open a large window at

a higher level facing south (Figures 3 and 4).

2.2 | Floor planning

We produced a single continuous interior volume to create an open

indoor environment in the limited footprint of 79.2 m2 and accom-

modate different places for the family’s daily life. The floor of the

main living space was raised approximately 800 mm from the

entrance and the ground floor level, on which a bathroom, a toilet

and a kitchen are located. A large and symbolic dining table as the

meeting place of the family is located next to the kitchen and its

height is just 300 mm above the kitchen counter top (Figure 1). The

main living space is connected to the second floor with large steps

as benches or shelves. The second floor is divided by furniture into

two spaces for bedrooms. These different levels help maintain a dis-

tance between various places in the volume (Figures 5–7).

2.3 | Structure system and roof construction

The foundation and the exterior walls of the first floor are made of

250 mm thick concrete, while the structure of the second floor and

other components are all made of small-size timber materials with

120 mm dimension prevalent in the market. We also used the con-

ventional technique and the generic steel joints for the timber con-

struction, which local carpenter can afford. The stiff timber box

F IGURE 2 Overall view from the street

F IGURE 3 Site plan

F IGURE 4 Roof study model

2 | SUEHIRO ET AL.

structure consists of the folded roof panels and the exterior wall pan-

els realize a pillar-free space of 7.7 m 9 10.2 m. While we set the

section of the folded roof with right angle to make the construction

easier, the whole roof slants about 10° for drainage and scale adjust-

ment of interior space. There were some joints with unusual angles at

the meeting points of folded roof and walls, and we made 3D models

and drawings to explain them for carpenters (Figures 8 and 9).

2.4 | Natural lighting and ventilation

We designed the house to have sufficient natural daylight and venti-

lation, meanwhile the area of the window surface was minimized to

reduce thermal loss. We set four main windows at higher level to

maximize the natural lighting effect, from which the light comes in

along the pitched ridges of the folded roof. The large window has

eaves to block direct sunlight during summer season, two ventilation

windows lit from the both side of the central ridge, and the small tri-

angular skylight facing north is at the peak of the roof (Figures 10

and 11). The second-floor timber box was set on arms popping out

from the first-floor concrete box. We used the slit between the two

boxes as horizontal windows. Ventilation windows perforated the

house in many directions and at different levels; this was effective

at not only exploiting various wind directions but also realizing venti-

lation caused by temperature difference (Figure 12).

2.5 | Insulation and air conditioning

We set the insulation specifications to optimize the thermal perfor-

mance. The first-floor concrete was covered with insulation and

worked as heat storage to stabilize the interior thermal conditions.

The second-floor timber panels were filled with onsite forming insu-

lation to prevent heat bridges and condensation. It is generally diffi-

cult to realize an effective heating system for the winter for an

interior volume with a high ceiling. The underfloor heating system

consists of an energy-efficient air conditioning unit, and a circulation

fan keeps the first floor warm. The air flow along the folded roof

created by the circulator fan minimizes the non-uniformity of air

temperature in the space. Because of the exterior heat insulated

concrete wall with large heat capacity and under floor air condition-

ing system, it is possible to maintain comfortable indoor thermal

conditions all year round (Figure 13).

2.6 | Conditions of sustainability

Owing to these environmental design solutions, the observed data

showed mostly expected results with regard to energy consumption.

If solar cell panels are introduced on the roof in the future, the

house will be a zero-energy building. The introduced generic tech-

nologies and construction systems were quite effective to keep the

building cost reasonable. However, sustainable building issues are

not dependent only on technologies. Although the house looks quite

closed from the street, the inhabitants can see the sky and truly

experience the outside environment. The distinctive folded roof,

F IGURE 6 1F corridor view

F IGURE 7 2F bedroom view

F IGURE 5 1F and 2F plan

SUEHIRO ET AL. | 3

altered light conditions, and stepped floor levels differentiate the

character of each place in the continuous interior space. These

places can be used flexibly according to future changes in the fam-

ily’s lifestyle. It is crucially important for a house being sustainable to

keep having affection from residents. We expect the house to keep

accommodate their happy and comfortable life for longer period.

3 | ENGINEERING CONCEPT

The design of a personal residential house from an engineering point

of view seems to be very similar to school education. The success or

failure of education becomes apparent by degrees obtained over a

long period of time and has a dominant influence on life. Individual

abilities and demands are diverse, but there is also an averaged-com-

mon basis to adapt to society and culture. In this regard, failure is

not permitted in school education. It becomes difficult to challenge

existing experiences and standardized theories. The design of a per-

sonal residential house, especially environmental design, may be the

same.

A house, along with the family living there, exists on the same

time scale as life. Introducing state-of-the-art environmental control

systems and equipment can improve the initial environmental perfor-

mance, but these technologies may become obsolete within a few

years and may need to be replaced with new state-of-the-art tech-

nology. The basic strategy of a small residential house design may

be to adopt a reasonable structure on firm ground, reduce the exter-

nal heat load by improving the thermal insulation and airtightness,

and utilize sunlight, outdoor air, and groundwater as necessary. In

subsequent phases, we should consider introducing reasonably and

efficient active-type environmental facilities from a comprehensive

viewpoint.

Based on this engineering design concept, we introduced the fol-

lowing environmental control devices/methods.

(i) Utilization of well water;

(ii) Introduction of horizontal slit-type windows for natural ventila-

tion and ambient daylight;

(iii) Materials-integrated photocatalytic oxidation reaction activated

under visible light6–9;

(iv) Floor heating system with an underfloor chamber using a heat

pump-type air conditioner;

(v) Air circulator fan on the ceiling to manage heterogeneous air

and temperature distributions;

(vi) Exterior heat insulation finish.

The following performances were analyzed by using environmen-

tal simulation techniques:

(i) Optimization of the window opening position by solar radiation

and indoor light environment analysis;

(ii) Natural/cross-ventilation design supported by computational

fluid dynamics (CFD) simulation10–12;

F IGURE 8 Structure concept diagram

F IGURE 9 Timber frame construction

4 | SUEHIRO ET AL.

(iii) Optimization of opening position of horizontal slit-type win-

dows by using wind pressure coefficient analysis with CFD;

(iv) Annual heat load calculations to optimize the thermal insulation

and natural/mechanical ventilation.

As the numerical simulation/analysis tools provide deterministic

information for environmental conditions, the flexibility of design

might decrease greatly when aiming at environmental optimization.

Against this trade-off problem, collaboration between architect, envi-

ronmental engineer, and resident, from the design stage until the

completion, enables harmonization of architectural design and envi-

ronment.

4 | CONCLUSION

For this residential house, the indoor air/thermal environment and

utility demands (eg, electricity and tap water usage) have been con-

tinuously measured immediately after the families moved in. The

owner, an expert on environmental engineering, has been investigat-

ing ways of environmentally optimizing the family’s lifestyle. Contin-

uous efforts to optimize the indoor environmental quality

immediately after the completion of construction lead to the pleas-

antness of this residential house.

5 | PROJECT DATA

Main structure: Reinforced concrete (RC) structure + Wooden (in

part)

Site area: 176.76 m2

Building area: 79.20 m2

Gross floor area: 102.49 m2

Completion: August 2015

Location: Kasuga-shi, Fukuoka

Construction company: Kawakita Construction, Co. Ltd.

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F IGURE 11 Triangular skylight

F IGURE 12 Horizontal slit-type windows for natural ventilationand ambient daylight

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How to cite this article: Suehiro K, Suehiro N, Masuda Y,

Ito K, Ito K. Folded roof house: Design solution to optimize

the environmental condition with generic equipment

and techniques. Jpn Archit Rev. 2017;00:1–6.

https://doi.org/10.1002/jar3.3

F IGURE 13 Section/environmental design concept

6 | SUEHIRO ET AL.