# Inside the World's Wettest Building ![[images/Inside-the-Worlds-Wettest-Building.webp]] **Creator:** The B1M · **Published:** 2026-03-02 · **Length:** 12:37 · [Watch on YouTube](https://www.youtube.com/watch?v=INt4sBK8WPU) > Caption source: YouTube **manual English (UK)** captions (`en-GB`, json3) downloaded with **yt-dlp** on the first attempt — TubeAlfred was not needed (0 credits used). The manual track covers Fred's narration and pieces to camera but skips the interview with Dr Sakai and the news clips, so the YouTube auto-generated English track was used only to fill in what those parts say (marked as interview/clips below; the interview is in accented English and the auto-captions are rough, so only clear points are reported). Names, spellings and figures were cross-checked with The B1M's companion article, [Why Japan Built a Storm Simulator](https://www.theb1m.com/video/why-japan-built-a-storm-simulator) (headline on page: "Inside Japan's Largescale Rainfall Simulator"; byline **Ian Parkin**, 1 March 2026, "Video narrated and hosted by Fred Mills."). The video description identifies the interviewee as **Naoki Sakai**, Associate Director, Research Division for Storm, Flood and Landslide Disasters, **NIED** — which the description expands as the National Research Institute for Earth Science and Disaster **Resilience** (its current English name), while the narration and companion use "Disaster **Prevention**". Figures that match the companion: Tsukuba **75 km** north-east of Tokyo; hangar about **75 × 15 m**; nozzles **16 m** above the ground (terminal velocity); up to **300 mm/hour**; very heavy rain **8–10 mm/hour** (companion: the upper limit is "nearly 40 times greater"); established in **1974** after destructive typhoons; more than **80%** of Japan mountainous; houses replaced after around **30 years**; droplets **0.1–8 mm**; the building moves on rails; flood-proof house with car-door-style gaskets, float valves and backflow prevention. The narration's **2,176** nozzles of **four** types appear in the companion as "2,000-plus"; the **1 m per minute** speed, the **1947** rainfall record, **Hurricane Ida**'s **200 mm** in one day (2021), the "half of fatalities and missing people" landslide share and the **Ichijo Komuten** credit for the flood-proof house are from the narration only (the companion credits additional footage to **NIED** and **Daiwa House**). YouTube chapters used for section headings; they line up with the captions. Screenshots from the 720p stream (format 136). Host **Fred Mills**. No paid sponsor segment in this video; the description promotes Fred's book ***Mega Builds*** (pre-order), The B1M's **Get Construction Talking** mental-health initiative and *The World's Best Construction Podcast*. Additional footage and images (companion): **NIED**, **Daiwa House**. ## Outline ### 0:00 Storms - **0:00** Cold open: imagine a storm so powerful it can wash away roads, destroy an entire neighbourhood or even collapse a mountain. - **0:16** Now imagine taking that terrifying power of nature and being able to control it with the push of a button — that's what happens in this building in Japan. - **0:32** So what is it, how was it built — and how was Fred talked into going for a walk in "the rainiest place on earth"? ![[images/Inside-the-Worlds-Wettest-Building-t0008.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0013.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0020.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0030.webp]] ### 0:45 Lucky Fred - **0:45** Fred at the **Large-Scale Rainfall Simulator** just outside Tokyo: large scale because it's absolutely enormous, "like an aircraft hanger," much bigger than he expected — and he's been dreading the day. - **1:02** The production team tell him the **US Geological Survey** classifies **8 mm** of rainfall an hour as heavy rain, and the machine behind him can go up to **300 mm an hour** — "it's not natural… but for your viewing pleasure, we're doing it." - **1:24** He's brought one of those lovely **clear Japanese umbrellas** — "not sure it's going to be enough." But before the "ritual humiliation," some work. ![[images/Inside-the-Worlds-Wettest-Building-t0050.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0068.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0085.webp]] ### 1:37 Japanese Houses - **1:36** Before how it was built and why it's necessary: a strange quirk of **Japanese housing**. Major cities are dominated by mid- and high-rise apartment blocks, but towns, villages and suburbs are full of typical detached houses. - **1:56** Looking for a bargain in Japan? Buy an old one — unlike basically every other country, **housing in Japan loses value over time**; after about **thirty years** houses are knocked down and replaced with a newer model. - **2:17** The countryside's lush mountains, hot springs and ancient temples reflect a deep connection with nature — but that connection isn't always peaceful. - **2:34** Japan was forged by **tectonic forces** that pushed it out of the sea millions of years ago, making it the **most earthquake-prone country on the planet**. - **2:49** It also faces some of the most violent storms on Earth: **typhoons** bring torrential rain, floods and roof-tearing winds — and with over **80%** of Japan covered in mountains, **landslides** too. Even a house that survives an earthquake could be swept away in a river of mud and rock. - **3:15** Largely because of this, **impermanence** — that nothing lasts forever — is ingrained in Japanese culture; many homes use **semi-permanent, prefabricated** designs as a pragmatic response to an unpredictable landscape. - **3:35** The other half of the response: world-leading research into **flood-proof urban planning** and **landslide prediction** technology. ![[images/Inside-the-Worlds-Wettest-Building-t0105.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0125.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0146.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0175.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0200.webp]] ### 3:37 Science in Tsukuba - **3:44** **Tsukuba**, **75 km** north-east of Tokyo, has a good claim to be Japan's scientific centre: home to the **Japanese space agency** and the headquarters of the "snappily named" **National Research Institute for Earth Science and Disaster Prevention (NIED)**. - **4:04** The B1M came while making its "epic documentary" about Tokyo's disaster-resilience infrastructure and couldn't leave without seeing inside this building. - **4:12** Interview (Dr **Naoki Sakai**, NIED): the building was **established in 1974** after big typhoons caused much damage in Japan; researchers now use it to study the mechanisms of **flooding and landslides**. - **4:30** Other simulators exist around the world, but none match the size or sheer power of this one. - **4:37** The USGS classifies very heavy rain as **8–10 mm per hour**; here that's not even the first rung — Sakai: the system ranges from **50 mm** to **300 mm per hour**, a very wide range. - **4:52** **300 mm per hour** is just shy of the strongest rainfall ever recorded, in **1947**. - **5:08** For context (news clip: a "category 4 hurricane slamming into the US"): when **Hurricane Ida** hit the US in **2021**, the maximum rainfall recorded in one day was just **200 mm**. ![[images/Inside-the-Worlds-Wettest-Building-t0225.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0245.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0262.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0285.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0310.webp]] ### 5:26 How it Works - **5:26** The simulator is a huge **75 × 15 m hangar** suspending a latticework of thousands of **pipes and nozzles 16 m above ground** — high enough for droplets to reach **terminal velocity**. - **5:39** They're fed by a pipe on the outside of the building from an **underground reservoir**; a series of **drains** around the test area collects the water and stops flooding. - **5:50** The test space is used to trial everything from **homes** to **self-driving cars**; soil-erosion and landslide tests use **permanent facilities** elsewhere on the site. - **6:03** How do you test in different areas? **The building moves** — Sakai (interview): it runs on long rails on either side, driven by an **electric motor on each wheel**. - **6:27** In effect a **self-powered railway carriage**, moving at **one metre per minute**. ![[images/Inside-the-Worlds-Wettest-Building-t0330.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0345.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0375.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0395.webp]] ### 6:47 Groundbreaking Research - **6:39** But how does this relate to housing? **Landslides** are common and deadly in Japan — responsible for **half the fatalities and missing people** in natural disasters. - **6:54** **Japan's met office** issues warnings so people can evacuate homes and workplaces, but landslides happen so quickly it's a constant challenge to warn people in time. - **7:05** Enter Dr **Sakai** (interview): the research aim is resilience for people — developing **sensors** for slope conditions whose data show whether a slope is safe or not. - **7:23** What makes the research unique is the **scale** of the experiments, giving far more reliable insights than smaller-scale projects. - **7:33** Reproducing different rain conditions is more than cranking up the power — Sakai: it mimics natural rainfall in **drop size**, **speed** and **intensity**. - **7:59** Controlling those is what makes the simulator unique: water sprays from **2,176 nozzles** of **four types**, producing raindrops from **0.1 to 8 mm**; bigger drops fall faster, and the nozzle height helps spread the rain evenly. - **8:22** Landslide science is only part of the work: an experiment by **Ichijo Komuten** and NIED developed the **world's first flood-proof house**. - **8:36** Flooding is usually impossible to stop because a house has so many entry points, but this one had countermeasures: windows sealed with a **hollow gasket** like those on car doors; air vents fitted with a **float valve**; and utility pipes protected by a **backflow prevention valve** that lets rainwater out but not in. - **9:01** An incredible development that wouldn't have been possible without this facility. ![[images/Inside-the-Worlds-Wettest-Building-t0415.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0430.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0485.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0505.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0530.webp]] ### 9:16 Fred Gets Wet - **9:05** Fred starts to sign off — "ah ok ok, I can't sign off yet, they want to put this bit in": a couple of minutes of him getting wet. - **9:14** Unsure of the dress code for a large-scale rain simulator, he's worn stuff that can get wet, plus borrowed **wellies** that make him look like he's walked out of the **Village People** ("I hate you so much right now"). - **9:52** "This is unreal!" — he's told this is only **light rain**, which blows his mind; it's about to get heavier. "It's a good ad for the **$2 umbrella**." - **11:43** "I have never seen rain like it… completely unnecessary, completely unnatural" — soaked to the bone; subscribe outro for "the channel that puts me in some of the wettest places imaginable while you sit in the dry." - **12:12** Post-credits reflections: like a monsoon — you couldn't see out of the door; surprisingly warm and refreshing on a hot day in Japan; the drops were so big they hurt, "like a mixture of hail and just being hit with three showers at once." ![[images/Inside-the-Worlds-Wettest-Building-t0575.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0620.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0690.webp]] ![[images/Inside-the-Worlds-Wettest-Building-t0716.webp]] ## Things mentioned ### Facilities and research - **Large-Scale Rainfall Simulator**, NIED, Tsukuba — established 1974; ~75 × 15 m hangar; pipes/nozzles 16 m up; 2,176 nozzles of four types (companion: "2,000-plus"); droplets 0.1–8 mm; 50–300 mm/hour; underground reservoir feed and perimeter drains; mounted on rails, moves at 1 m/min with an electric motor on each wheel - Permanent soil-erosion and landslide test facilities on the site; full-scale landslide experiments and **slope sensors** for early warnings - **World's first flood-proof house** (Ichijo Komuten and NIED): hollow car-door-style window gaskets, float-valve air vents, backflow prevention valves on utility pipes - Test subjects: homes, **self-driving cars** ### Organisations - **NIED** — National Research Institute for Earth Science and Disaster Prevention (narration/companion) / Disaster Resilience (video description) - **Japanese space agency** (Tsukuba is "home to" it, per narration) - **US Geological Survey (USGS)** — heavy rain 8 mm/hour; very heavy 8–10 mm/hour - **Japan's met office** (landslide/evacuation warnings) - **Ichijo Komuten** (flood-proof house experiment); **Daiwa House** (footage credit in companion) - On-screen news logos in clips include **ABC** and **VOA** ### Hazards and concepts - Earthquakes (Japan the most earthquake-prone country), **typhoons**, torrential rain, flooding, **landslides**; **terminal velocity**; rainfall intensity, droplet size and speed - **Impermanence** in Japanese culture; houses that lose value and are rebuilt after ~30 years; **semi-permanent, prefabricated** homes; flood-proof urban planning; landslide prediction ### Places - **Japan**; **Tokyo**; **Tsukuba** (75 km north-east of Tokyo); Japanese countryside — mountains, valleys, hot springs, ancient temples; the **US** ### Events - Strongest rainfall ever recorded (**1947**, per narration); **Hurricane Ida** (US, 2021; max 200 mm in one day) ### Culture and props - Clear Japanese umbrella ("the $2 umbrella" / "two quid umbrella"); wellies and the **Village People** ### The B1M and promotions - **Fred Mills** (host); **Ian Parkin** (companion byline); The B1M's documentary on Tokyo's disaster-resilience infrastructure (referenced) - ***Mega Builds*** by Fred Mills (pre-order); **Get Construction Talking**; *The World's Best Construction Podcast* ### Figures and facts - Heavy rain 8 mm/h; very heavy 8–10 mm/h; simulator up to 300 mm/h (Sakai: 50–300 mm/h); Ida 200 mm in a day (2021) - >80% of Japan mountainous; houses replaced after ~30 years; landslides = half of disaster fatalities and missing people - Tsukuba 75 km NE of Tokyo; established 1974; hangar 75 × 15 m; nozzles 16 m up; 2,176 nozzles, 4 types; drops 0.1–8 mm; moves 1 m/min ## Biographies ### Fred Mills Co-founder and on-camera host of **The B1M**. He presents from inside the NIED hangar, admits he's been dreading the day, explains why Japanese houses lose value, and ends the video in a clear umbrella and borrowed wellies being drenched by "light rain" and then far heavier downpours — "I have never seen rain like it." ### Naoki Sakai Associate Director of the Research Division for Storm, Flood and Landslide Disasters at **NIED** (as identified in the video description). Interviewed in a hard hat inside the simulator, he explains that the facility was established in 1974 after damaging typhoons, that it can produce rainfall from 50 to 300 mm an hour with natural drop sizes, speeds and intensities, that the building moves on rails, and that his team is developing slope sensors to give earlier landslide warnings. ### Ian Parkin (The B1M) Byline on The B1M companion article *[Why Japan Built a Storm Simulator](https://www.theb1m.com/video/why-japan-built-a-storm-simulator)* (1 March 2026, "Video narrated and hosted by Fred Mills"), which expands on the facility's 1974 origins, full-scale model slopes and flood-resistant housing tests, and credits additional footage to NIED and Daiwa House.