April 25, 2002

"Sky Oasis" Rooftop Greenery Completed on Roof of
Head Office Building (Mido Building)
Effectiveness of Three Types of Gardens Verified

Takenaka Corporation

Recently, at Takenaka Corporation (Head Office: Osaka; President: Toichi Takenaka; Capital: 50 billion yen) the rooftop greenery on the roof of the Head Office Building (Mido Building) has been completed, and the new "Sky Oasis" will be opened to the public from April 26.
This building was completed in 1965, and greenery has been completed on 320 square meters, or about 20 percent of the total rooftop area of 1,600 square meters (including 130 square meters of lawn and wood deck furniture area), with about 3,000 plants of 120 varieties of olives, Quercus myrsinaefolia and other trees and flowering grasses.
Recently, rooftop greenery has been attracting attention as an effective way to improve the environment, by alleviating the heat island phenomenon in large cities. While some government departments are now requiring rooftop greenery, there has been an increase in public support through such measures as tax relief, financial assistance, low interest loans and the relaxation of building floor area ratios. An increase in rooftop greenery is expected in the future.
The greenery of the existing building rooftop was carried out as a model project, both to verify the effectiveness of greenery, and positively promote future system and technological development.


Features of the greenery structure

With this greenery, the following three "friendly" themes were identified, and three different types of gardens were built: 1. friendly to people; 2. friendly to the environment; and 3. friendly to the building management.

1. The "Fragrance Garden," friendly to people (area: about 53 square meters)

This garden has the physiological and psychological effects making it possible to relax and console people's minds.
The garden consists of an area with low and medium height conifer trees that have a feeling of volume, and a herb garden with lavenders, geraniums and other fragrant plants.

2. The "Natural Garden," friendly to the environment (area: about 80 square meters)

This garden was learned about from the close-to-home natural thickets.
By contributing to the recycling-oriented society with temporary rainwater storage and by using products recycled from construction waste materials, this garden aims at creating a landscape, city amenities and biological network. Pampas grass, pasturage, Quercus serata and other plants found close to home have been planted here, small ponds and a babbling stream have been built, creating a biotope garden where wild creatures can live.

3. The "Dry Garden," friendly to the building management (area: about 57 square meters)

This is a garden which does not require any sort of maintenance.
It uses a low-maintenance type thin-layer rooftop greening system (sedum carpet), with sedum varieties that can grow in harsh environments (such as Mexican sedum lineare).
This system, which was developed last year by Takenaka, has the following features:

(1)
The load of 40 kilograms per square meter is light, so it can be used without having to be concerned about load limitations.
(2) There is no need for sprinkling or fertilizing, greatly reducing maintenance costs.
(3) The planting mat is held down using a fastening system that enables it to be easily removed and put back in place, making it easy to take off and inspect.
(4) Taking into consideration the climatic conditions of Japan, soil is selected that can maintain adequate dryness and oligotrophic conditions, and with the special cross-section structure, while the growth of weeds is controlled there is a suitable environment for the sedum varieties to grow.
(5) Installation is completed by simply laying down the planting mats that are preplanted.


 Features with the construction

When it comes to the rooftop greenery of existing buildings, reduction in load, measures to cope with winds, waterproofing and workability are important issues.

1. Load reduction

The permissible live load of each building is different, but some measures have to be taken to reduce the load. In this case, measures were taken with the plant selection, by using sedum varieties, as well as by using artificial soil and planters. The soil has a perlite base (made into a foam by heating), and with a unique Takenaka blend of various soil improvement materials is about one-third the weight of ordinary soil.
The planters use mesh metal planter boxes, unwoven to allow for breathability and water permeability.

2. Wind measures

As per the Building Standards Act values, the garden can withstand winds of up to 34 meters per second (equivalent to maximum velocity of up to 70 meters per second). Thyme, sedum and other ground cover plants are used to control any scattering, the trees are firmly fixed inside the planter boxes, wind prevention nets are attached to the fences around the greenery area, and the thin-layer greening system uses bolts to firmly hold the planting mats and the waterproofing and root prevention sheets together.

3. Waterproofing measures

If planting is done directly on the rooftop, there is a possibility that the waterproofing layer could be damaged, so a two-millimeter-thick waterproofing and root prevention PVC sheet that can easily be laid out is used. For the 320-square-meter greenery area, about 400 square meters of waterproofing was necessary.

4.
Workability

All the materials for the greenery work have to be taken up in an elevator, so they have to be made lightweight and compact. All the parts are processed at plants, brought in as units, allowing the on-site work to be simple assembly, creating little waste, and enabling good workability.


Features with the maintenance
1. Watering

The thin-layer greening system does not require any sprinkling, but for systems that do require watering, two methods are used. One method involves laying a drip hose over the top of the soil for automatic watering. The watering is controlled by a timer, and it uses a sensor to stop watering after measuring a certain amount of rainwater when it rains. The other method involves efficiently supplying water to the plant roots, and uses a water supply tank at the bottom of the plants and trees. Water is added about once a month.

2. Pond water cleaned using wind power generators and solar batteries

There is a small pond in the "Natural Garden" that is friendly to the environment, and to clean the water in this pond, electric power from wind power generators and solar batteries is used to run a recirculation filtering system. One 400-watt output rated wind power generator is installed, and with an average annual wind speed of two meters around the Mido Building, it is estimated that 66 kilowatt-hours of electricity can be generated per year. The solar battery has a solar panel measuring 94 by 107 centimeters, and has a maximum output of 128 watts, able to provide 147 kilowatt-hours of electric power per year. The total electric power supply is therefore 213 kilowatt-hours per year.

3. Heat environment effectiveness measurement

To measure the effectiveness of the greenery, temperature sensors were installed at four locations: a nongreenery location, under the greening system (the sedum carpet), under a tree planter and under the lawn. This allowed real time measurement and analysis of temperature movements, by using a PC.

The rooftop greenery project for this building received assistance from the Osaka Prefectural Government, and will be open to the public from April 26.

Details of the opening to the public are as follows:
.
Day
:
Friday every week
(except public holidays, the holiday period between December 29 and January 3, and the summer holiday period around August 15)
.
Time
:
12 to 1 pm (open when it is raining but closed when there are strong winds)
.
Place
:
1-13, 4-chome, Honmachi, Chuo-ku, Osaka (the northwestern corner of the Midosuji and Honmachi-dori intersection)
(exit 5, stairway C of "Honmachi Station" on the Midosuji subway line)


 Outline of the "Mido Building"

Location
1-13, 4-chome, Honmachi, Chuo-ku, Osaka
Design and Construction
Takenaka Corporation
Date of completion
March 1965
Site area
3,705.7 m²
Total floor area
44,592.6 m²
Structure
SRC
Number of floors
4 Fl. below and 9 Fl. above ground, and 4 penthouse floors

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Copyright 2002, Takenaka Corporation