Japanese Foundation Rules: Depth, Concrete & Rebar Cover

Japan's strip-footing dimensions — embedment ≥240 mm, base slab ≥150 mm thick, stem ≥300 mm high and ≥120 mm thick — from MLIT Notification No. 1347/2000, plus concrete strength (≥12 N/mm²) and rebar cover (20–60 mm) from the Enforcement Order.

Building Standard Law Enforcement Order (施行令), Art. 38, 74, 79; MLIT Notification No. 1347/2000 (平成12年建設省告示第1347号) Clause JP BSL Order

The requirement

In Japan, a strip footing (布基礎) must go at least 240 mm into the ground. The base slab must be at least 150 mm thick. The stem must stand at least 300 mm above ground and be at least 120 mm thick. Those figures come from MLIT Notification No. 1347/2000, §一・4, not from the Law itself.

Here is the rule chain. The Building Standard Law and its Enforcement Order cover foundations in Article 38. Art. 38 §1 only sets a duty. A foundation must pass the building’s loads and forces safely into the ground. It must also stay safe against settlement or deformation of the ground. §3 then hands the structural method, and the actual numbers, to an MLIT Notification (告示). Which one applies depends on the building and the ground. For an ordinary strip footing, that is Notification No. 1347/2000 (平成12年建設省告示第1347号), §一・4. It fixes these minimums:

Dimension	Minimum	Clause
Embedment depth (根入れの深さ)	≥ 240 mm	§一・4・一
Base-slab thickness (底盤の厚さ)	≥ 150 mm	§一・4・一
Stem/upstand height above ground (立上り部分の高さ)	≥ 300 mm	§一・3・三 (carried into §4)
Stem/upstand thickness (立上り部分の厚さ)	≥ 120 mm	§一・3・三 (carried into §4)
Base-slab width (底盤の幅)	table-driven, roughly 180–600 mm by ground bearing capacity, building weight class and storey count	§一・4・二

Four of those rows are flat minimums. Base slab width is the odd one out. No single figure sets it. You read it off a table in the Notification. The table keys off your ground’s bearing capacity, the building’s weight class, and the storey count.

MLIT Notification No. 1347/2000, §一・4

1 footing
2 ground

Frost depth is a local rule, not a national one. In cold regions such as Hokkaidō or Tōhoku, a footing must sit below the frost line. That depth comes from a prefectural or municipal ordinance. It sits outside the national Building Standard Law and Enforcement Order. Check your local government’s rules for the figure.

The concrete. Reinforced concrete needs a 4-week compressive strength of at least 12 N/mm² (12 MPa) with normal aggregate. With lightweight aggregate the floor is at least 9 N/mm². That is Enforcement Order Art. 74 §1, items 1–2. It covers RC footings, even under a timber house. It is only the legal floor. Your engineer sets the real design strength for the job, above that floor.

Rebar cover is tiered by member, not one number. Art. 79 §1 sets:

Member	Min. cover
Non-bearing wall or floor	20 mm
Bearing wall, column or beam	30 mm
In direct soil contact, incl. a strip footing’s upstand/stem	40 mm
Footing base itself (excl. upstand & blinding layer)	60 mm

Work it out on site

The 240 mm embedment is a legal floor, not a target. Your real depth still answers to the ground, its bearing capacity, and any local frost rule. The width comes off the Notification’s table. Once your engineer or building official confirms both, the concrete volume is simple maths. It feeds straight into the calculator. Say you have a strip footing to pour. These are example numbers, not the code minimums:

Total length of trench: 30 m
Footing width: 0.45 m. Example only. Yours comes off the Notification’s width table for your ground.
Footing depth: 0.5 m. Example only. Never less than the 240 mm floor. In practice your ground, its bearing capacity, and any frost rule set it.

Volume is length times width times depth:

30 × 0.45 × 0.5 = 6.75 m³

So you would order about 6.75 cubic metres. Then add a bit for spillage and an uneven trench. Most builders tack on 5 to 10 per cent. Swap in your own numbers and the calculator does the sum.

Do it in 5 seconds

Part of the Japanese building-rules hub. One national Law, its Enforcement Order, and the calculators that solve it.
Setting out the stairs on the same build? See Japanese stair rules.

Sources

Building Standard Law Enforcement Order (建築基準法施行令), Art. 38 (foundation general duty and delegation to MLIT Notification), Art. 74 §1 (concrete strength), Art. 79 §1 (rebar cover, tiered by member). Read the current consolidated text at laws.e-gov.go.jp.
MLIT Notification No. 1347/2000 (建設省告示第千三百四十七号, 平成12年5月23日; 建築物の基礎の構造方法及び構造計算の基準を定める件), §一・3–4 — strip-footing embedment, base-slab thickness, stem height and thickness, and the base-slab-width table, issued under Enforcement Order Art. 38 §3. Read MLIT’s own hosted copy at mlit.go.jp.

Read this first. Japan’s Building Standard Law and Enforcement Order are a single, continuously-amended text, checked here as of 29 July 2026 at the official e-Gov law database. Foundation depth, stem height/thickness and base-slab thickness are fixed not by the Law or Order themselves, but by the MLIT Notification they delegate to — MLIT Notification No. 1347/2000, read directly against its own primary text for this page. Base-slab width stays genuinely table-driven, not a single mm figure. Frost depth is set locally by prefectural or municipal ordinance, not nationally. Always confirm the current text at laws.e-gov.go.jp or mlit.go.jp, and get your ground properly assessed by a structural engineer, before you dig.

Frequently asked questions

Is there a minimum foundation depth set in Japan's Building Standard Law?

Not in the Enforcement Order itself. Art. 38 §1 just says a foundation must carry loads safely to the ground and resist settlement or deformation. §3 hands the numbers to an MLIT Notification. That Notification, No. 1347/2000, does fix one: a strip footing needs at least 240 mm of embedment (§一・4・一).

What about frost depth?

Frost depth is set locally, not by the national code. In cold regions such as Hokkaidō or Tōhoku, it comes from a prefectural or municipal ordinance. That sits outside the national Building Standard Law and its Enforcement Order.

What concrete strength is required?

The floor is a 4-week compressive strength of at least 12 N/mm² with normal aggregate, or at least 9 N/mm² with lightweight aggregate (Enforcement Order Art. 74 §1, items 1–2). It covers reinforced concrete, so RC footings too. That is the legal floor. Design strength for a real footing is normally set higher.

What rebar cover is required on a footing?

It is tiered by member under Art. 79 §1. A non-bearing wall or floor needs at least 20 mm. A bearing wall, column or beam needs at least 30 mm. A member touching soil, like a strip footing's stem, needs at least 40 mm. The footing base needs at least 60 mm, excluding the stem and blinding layer.

Where do the specific mm figures for depth and thickness that I've seen online come from?

MLIT Notification No. 1347/2000 (平成12年建設省告示第1347号), issued under Enforcement Order Art. 38 §3. For a strip footing (布基礎), §一・4 fixes: embedment at least 240 mm, base slab at least 150 mm thick, stem at least 300 mm high above ground and at least 120 mm thick. We read the Notification's own text, so these are confirmed.

How wide does the base slab need to be?

No single number sets it. §一・4・二 uses a table instead. It keys off your ground's long-term bearing capacity (three tiers: 30–50 / 50–70 / ≥70 kN/m²), the building's weight class (timber or light steel versus heavier), and the storey count (1 or 2). Widths run roughly 180–600 mm. Read the table for your own ground and building.