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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

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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



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Annual report of Japan Advisory Center for Maintenance and Dispute Settlement for Housing (2008)

Rain penetration

Number of consultation received from house owners by building failure types


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Annual report of Japan Organization for Housing Warranty (2007)

Rain penetration in roofs

Number of payment

Sum of Money

Rain penetration in external walls

Proportion of insurance payments by building failure types





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1.Waterproofing sidings

How to prevent rain penetration

History of using waterproofing materials in buildings

Roof membrane : 150 years

Joint sealants : 60 years

Before then?

2. Rain excluding design of building shapes and details


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Definition sidings

example:Waterproofing roof membranes, Sealant filled joints.

Waterproofing

“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.”


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Traditional Japanese technical term for sidings

“Rain excluding design and details”

Ama - Jimai

Putting in order

Rain

+

Designing building shapes and the details to control the behavior of rainwater in order to avoid inconvenience.


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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


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Upper part of walls or openings sheltered by eaves or hoods from wetting.

Moisture-vulnerable materials are protected from wetting.


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Ama-Jimai from wetting.

  • Used to be the only technique for craftsmen to keep buildings dry from rainwater before the introduction of modern waterproofing materials.

  • Successfully protected buildings from rain for thousands of years.

  • Principles still useful.

  • Insufficient scientific explanation bars its effective application in modern building design.


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Advantages and disadvantages from wetting.

  • Waterproofing

    • Can work against any rainstorm condition unless being damaged.

    • Liberates architectural design from gravity.

    • Finishing materials must be water-resistant.

    • Performance very much depends on craftsmanship.

    • Relatively short service life. Needs for frequent maintenances.

    • Blocks moisture permeation.

  • Ama-Jimai (Rain excluding design and details)

    • Performance depends on severity of rain and wind condition.

    • Results in rather traditional architectural design.

    • Finishing materials need not to be water-resistant.

    • Performance less depends on craftsmanship.

    • Maintenances can be minimized by using durable materials.

    • Allows free moisture permeation.


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An example of architecture with design concept opposite to Ama-Jimai

Rain freely fall and run over the wall

Materials are fully exposed to rainwater

Walt Disney concert hall, Los Angels (2004) Architect: Frank Gehry


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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..


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Built 17 years ago. Total cost for completion:160 billion Yen

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


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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

  • Presence of holes (or gaps) through which rainwater can enter.

  • 2. Presence of rainwater over the holes.

  • 3. Action of forces that make rainwater pass through the holes.

1. Blocking holes

Waterproofing

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)


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The first principle of Ama-Jimai Yen

Wetness of building façade is caused by;

  • Direct hit of wind driven rain.

  • Splashes of rainwater fallen on the ground/roofs.

  • Run-off rainwater from above.

  • Wrongly designed /broken gutters.


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Studies needed for preventing/reducing wetness of building façade include;

  • Knowing the behavior of wind driven raindrops around buildings.

  • Estimating amount of rainfall on external walls.

  • Evaluating the extent of shelter provided by projections over the wall against wind driven rain.


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  • Knowing the distance, height and amount of rainwater splashes on the ground/roofs that reach the foot of walls.

  • Knowing run-off rainwater shedding performance of drips over the walls.

  • Developing a method for evaluating overall severity of exposure of external walls against rainfall.


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The second principle of Ama-Jimai splashes on the ground/roofs that reach the foot of walls.

Forces causing movement of rainwater on and through the building skin.

Kinetic energy

Gravity

Surface adhering force

Capillary suction

Pressure difference


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Forces causing movement of rainwater on and through the building skin.

Capillary suction

Kinetic energy

Pressure difference

(gap filled)

Gravity

Pressure difference

(gap unfilled)

Surface adhering

force


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Considerations for designing building details against adverse movements of rainwater include ;

  • Guiding rainwater to harmless directions.

  • Weakening the forces that cause the movement of rainwater.

  • Limiting the extent of penetration to a tolerable level.


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Some design vocabularies for rainwater movement controlling details

Labyrinth joints

Sloping

Drips

Capillary break

Overlapping

Pressure equalizing


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Design vocabularies for rainwater movement controlling details

Capillary break

Labyrinth joints

(capillary action)

(kinetic energy)

Overlapping

Sloping

(pressure difference,

gap filled)

(gravity)

Pressure equalizing

Drips

(surface adhering

force)

(pressure difference,

gap unfilled)


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Conclusions details

  • Preventing rain penetration is the most essential function of buildings, but many buildings still fail to fulfill it.

  • The traditional rain excluding design concept of Ama-Jimai is still an important tool to keep buildings dry from rainwater in spite of development and wide availability of modern waterproofing materials.


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Conclusions details

  • The essence of Ama-Jimai is;

    • Sheltering building façade from the effects of rain and wind.

      2. Controlling the movement of rainwater both over the building surfaces and within the building envelopes.


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Conclusions details

  • Scientific approach based on meteorology and hydraulics /fluid mechanics is necessary for the effective application of Ama-Jimai design concept to modern architectural design.

Thank you for your attention!

Any question is welcome.

Write to: [email protected]


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