●Research Trends and Results

Experimental research on rain infiltration of woodenhousing
MUKAI Akiyoshi, Research Coordinator for Advanced Building Technology
Building Department
MIYAMURA Masashi, Senior Researcher
Building Department, Structural Standards Division(Key words) Wooden housing, rain infiltration, spraying test
1. Background to the research
Along with studies of the prevention of rainfall
infiltration in order to contribute to the smooth
enforcement of the Law for the Execution of Warranty
Against Housing Defects enacted in October 2009,
measures to prevent infiltration of rain must be studied
in order to establish future technological standards.
Cases where rain infiltrates from exterior finishingmaterial to conspicuously deteriorate body materialand connecting material have also been reported, andthe external finishing material’s bonding force
declines so that when an earthquake strikes, peelingoff the external finishing material, fire prevention
performance and seismic resistance are impacted.
Consequently, the NILIM has carried out a variety offact-finding surveys of design and execution, surveysof rainfall infiltration, outdoor exposure experiments,
and accelerated deterioration tests in order to ensure
the safety and assets of inhabitants, and this is a reportof some strong wind and rain tests.
2. Outline of the tests
2.1 Specimen
The specimen consisted of a structural body madeby the conventional frame construction method andexterior finishing made by the ventilation construction
method executed using ceramic siding. The major
object members were a roof without under-eave
ceiling, external wall tie-ins, and balconies, which arelocations where rain often infiltrates.
2.2 Testing method
The testing was done by, hypothesizing that themembers of the wood house to be tested would be
subjected to a typhoon or other strong wind and rain,
applying wind and rain at wind speeds at intervals of
5m/s from 5m/s to 20m/s for 15 minutes at each speed
accompanied by a water spray of 32 liters per minute.
The directions of the spray on the roof and exteriorwall tie-ins were one direction each to the eave sides
and to the verge (right angles to the eaves), and for thebalconies, from the sides of the outside surfaces.

Verge

Specimen

Test
apparatus

Photo 1. State of Specimens and Testing ofStrong Rainfall Testing
3. Major test results
Even when rain infiltrates inside the ventilation
layer, because there is usually a permeable waterproof
sheet, the rain does not easily infiltrate inside the wallbut, because the permeable sheet used for the test
easily curled up vertically when it was laterallyapplied as an effect of the layer configuration etc., orbecause there was no tape between it and thefoundation drain, at a wind speed of 5m/s, rain wasobserved infiltrating into the room between thepermeable waterproof sheet and the foundation drain(see Fig. 1).
Permeable

Moisture-proof
防湿気密シート
airtight sheet

透湿防水シート
waterproof sheet
Column柱Interior

Ventilation

Exterior

通気層layer

Exterior finishingmaterial
外装材

No waterprooftape

防水テープなし

Sheetscurled up
シートの捲れWind
風雨and水切りrain
Drain
Foundation

Strong windand rain

基礎

Ventilation Furring

Sheets curled up

Exterior finishingmaterial

Foundation drains

Figure 1. Rain Infiltration Through Curled
up Permeable Waterproof Sheets
Recently, as a result of setback line limits anddesign trends, many roofs have short extended eaves
and extended verges, so at the same time as a lot ofrain strikes exterior wall surfaces, it is difficult towaterproof the area around the eaves, so rain often
infiltrates. The test caused rain to infiltrate at a wind

●Research Trends and Results
speed of 5m/s, confirming that it is necessary to fully
ensure extended eaves and extended verges. And at
the tie-in of exterior walls and roofs, to ensure
long-term waterproofing performance, it is important
to not only perform sealing, but to appropriately apply
metal plates. It is important to prevent deterioration ofbody material by applying waterproof tape between
the permeable waterproof sheets and the foundation
drains. During the balcony test, rain did not infiltrate
between the FRP and sashes, but it is necessary toseparately study long-term impacts, because ofvibrations caused by the opening and closing of sashes
and by earthquakes, and continuous minute tremors.