Lecture for Tele-Conference Discussion on “Asian Architecture and Environment 2009” How to keep buildings dry from rainwater 2009.7.3 by Hirozo Ishikawa Professor Emeritus, Tokai University The most common building defects in newly built buildings in Japan Rain penetration
Lecture for Tele-Conference Discussion on “Asian Architecture and Environment 2009”
How to keep buildings dry from rainwater
by Hirozo Ishikawa
Professor Emeritus, Tokai University
Number of consultation received from house owners by building failure types
Rain penetration in roofs
Number of payment
Sum of Money
Rain penetration in external walls
Proportion of insurance payments by building failure types
1.Waterproofing sidingsHow to prevent rain penetration
History of using waterproofing materials in buildings
Roof membrane : 150 years
Joint sealants : 60 years
2. Rain excluding design of building shapes and details
example：Waterproofing roof membranes, Sealant filled joints.
“Forming continuous impervious skin over building envelopes utilizing waterproofing materials. “
example：Large eaves overhangs.
example：Adequate slope and enough lap length for roofing tiles.
Rain excluding design and details
“Choosingbuilding shapes and combination and layout of building components so as to be effective to prevent adverse movement of rainwater on and into the building fabric.”
“Rain excluding design and details”
Ama - Jimai
Putting in order
Designing building shapes and the details to control the behavior of rainwater in order to avoid inconvenience.
Typical Ama-jimai design sidings
Rainwater is smoothly shed away from the structures below.
Traditional timber framed gate building
Board overlapping keeps run-off rainwater out.
Suiten-gu Temple Gate, formerly built in Nihonbashi, Tokyo, now in Shonan Campus of Tokai University
Moisture-vulnerable materials are protected from wetting.
Ama-Jimai from wetting.
Advantages and disadvantages from wetting.
Rain freely fall and run over the wall
Materials are fully exposed to rainwater
Walt Disney concert hall, Los Angels (2004) Architect: Frank Gehry
Source:World Weather Information Service ( Ama-JimaiWMO-sponsored web site) http://www.worldweather.org/pilot.htm
Facts behind the hall design
Rainy days once a week at max. in L. A.
L. A. rainfall only one-fifth of Tokyo.
Little possibility of snowfall in L. A..
The roof and the external wall are now under urgent remedial works due to severe rain penetration spending six years and sum of 1 billion Yen.
We should be aware of the maintenance costs after the completion.
The Tokyo metropolitan government office, Tokyo (1991)
Architect: Kenzo Tange
What is the essence of Ama-Jimai Yen(rain excluding design and details)?
Three conditions needed for occurrence of rain penetration
Method for preventing rain penetration
1. Blocking holes
2. Prevent wetting
3. Control the forces
Prevention of penetration can be achieved by eliminating any of the three conditions.
Ama-Jimai(rain excluding design and details)
The second principle of Ama-Jimai splashes on the ground/roofs that reach the foot of walls.
Surface adhering force
Forces causing movement of rainwater on and through the building skin.
2. Controlling the movement of rainwater both over the building surfaces and within the building envelopes.