Miura Residence - A Study in Sustainable Design
Location: Miura Peninsula, Japan
Function: Single Family Residence
Construction: Guesthouse Inc.
This project is a single-family house located on the Miura Peninsula in Japan, situated very close to the ocean. In collaboration with the client and a consultant specializing in Passivhaus, the design and material specifications have been made with a passive house goal in mind. While the house has not been formally registered as a passive house in an official rating system, it meets and surpasses many of the criteria of equivalent rating systems.
Below are five points of the project that contribute it its high sustainability performance.
- Sustainability Point 1: Orientation and Sun Protection
- Sustainability Point 2: Foundation as Thermal Mass
- Sustainability Point 3: Insulation and Airtightness
- Sustainability Point 4: Materials
- Sustainability Point 5: Equipment Efficiency
View of Kitchen
View of Kitchen and Hall
Section through Living/Dining Room
Section through hall
Sustainability Point 1: Orientation and Sun Protection
An important standard in Passivhaus performance is mitigating heating or cooling load to concentrate on simple conditioning the incoming supply air, and utilizing windows to let in valuable sunlight during the winter yet providing proper shade during the summer is important. For this reason, the wall to glass ratio balance was considered, and both thermal and shadow studies were conducted to determine the best orientation. Deep overhead eaves and a pergola structure helped in shading the windows from excess heat gain during the summer.
Radiant Heat Study
Sustainability Point 2: Foundation as Thermal Mass
Rather than creating a crawlspace under the first floor, which is the de facto foundation configuration in Japan, this house utilizes the concrete floor as thermal mass set directly onto the earth. The concrete foundation wall is insulated from the outside, and furthermore the concrete floor itself is separated by a 100mm insulated gap to eliminate a thermal bridge. The insulation under the concrete slab helps it to retain heat during the winter, but the amount of insulation is regulated to also allow the thermal mass of the earth to absorb heat in the summer. The isolated thermal mass floor also functions to regulate the overall temperature of the interior from room to room and from day to night.
Sustainability Point 3: Insulation and Airtightness
Insulation and airtightness are critical factors for the Passivhaus standard. The roof utilizes 384mm of blown-in insulation and an interior plastic vapor barrier to achieve an R value of 14.59m2(K/W). The walls utilize the same blown-in insulation system with an extra layer of exterior rigid insulation to achieve an R value of 8.36m2(K/W). The plastic vapor barrier is taped and sealed at all window and outlet locations, achieving a very high rating of 0.47 ACH (Air changes per hour) at a pressure of 50 Pascals. The windows are triple pane glass imported from Finland with a glass U value of 0.59 W/m2K and a calculated frame U value of 1.22 W/m2K.
Sustainability Point 4: Materials
Materials for this house have been chosen with longevity and sustainability as a priority. The interior finishes of the house are of wood paneling or tile, and materials such as formaldehyde emitting wallboard were not used. The wooden structure system is of glue-lam eco-friendly composite system, with column dimensions of 120mm allowing for greater insulation depth. The polished concrete with glass accents provides a beautiful yet economic and durable floor surface.
Sustainability Point 5: Equipment Efficiency
Considering the high airtightness performance of this house, ventilation is via a mechanical heat exchange system that minimizes energy loss when taking in fresh air. Due to the high insulation performance of the house, heating and cooling is achieved by one central unit with duct connections to each room. Hot water is supplied by an “eco-cute” unit that extracts heat from the outside air via a heat pump system.