Structure: the timber frame of a 木造 house, check by check

The Structure menu holds every frame tool: posts, bracing walls, beams, corner braces, foundations, the checks and the clash check. Bracing & structure checks… (or Ctrl+B, or the Structure chip in the status bar) opens the panel beside the Navigator.

The checks follow the wall-quantity route for small timber houses (the 4号 / 新2号 route of 令46条): no structural calculation is needed, but every number must be right — and this house has real NG items to fix.

The panel checks in the background, so you can keep drawing; the status bar keeps the count (Structure: 16 NG). On this house wall quantity is OK on both floors and both directions — and Balance, Post size, Beams and Floor stiffness have NG items. The chapters below fix them one by one, easy to hard.

The open step here is Wall quantity 壁量: per story and direction, the bracing length needed for earthquake and wind against the length you have (Need cm / Have cm / Ratio).

Why these numbers? opens the inputs and formulas behind the table: the floor areas the law counts, the need per m² from the 2025 table for this roof weight and snow area, the wind need from the elevation areas, and each bracing wall with its length and multiplier (倍率). Compare it line by line with a permit spreadsheet; if a number looks wrong, the line that made it is here.

The region, loads and snow depth come from Setup (the first row): they are read from Permit data and the address.

Bracing is set per bay (post to post) on the walls you already drew — not as a separate element. In this view the braces show as crosses, the panels as hatching, and the number by each bay is its multiplier: 筋かい 45×90 single = 2.0, cross = 4.0, structural plywood 9 mm = 2.5 (2025 values), combined up to the legal cap.

Shift+click adds or removes bays, so one change can set several walls at once; the line under the buttons says what the bays get. Check runs the structure check at once and the Wall quantity row updates. It is an ordinary edit: Ctrl+Z takes it back.

A bay narrower than the minimum set in Setup, or a bay with a window, does not count: the wall-quantity table lists it with 0 cm and the reason.

Wall quantity can be OK for the whole floor and still be badly spread: all the bracing on one side lets the house twist in an earthquake. The quarter method (4分割法) checks each end quarter of the plan on its own.

The NG card names the story, the direction and the quarter, gives both ratios and the missing length — and the other route the law allows: keep the plan and show an eccentricity ratio (偏心率) of 0.3 or less (告示1100), a separate calculation.

Under it: one-click fixes (structural plywood or cross braces on the walls of that quarter) and Edit bays… to choose the bays yourself. The table below lists every quarter: low side, high side and the wall ratio (OK from 0.5, or when both sides are fully braced).

The two bays already carry OSB 9 on one face; a 45×90 brace on top raises their multiplier, and the west quarter gets the length it lacked. Check re-runs the checks: the Balance row turns green and the NG count drops.

The one-click buttons do the same on every free bay of the quarter. On this house the west quarter is mostly windows, so choosing the bays by hand is the clean way.

The N値 method (平12建告1460号) gives each post top and foot a value from the multipliers of the walls on both sides and where the post stands (corner, outer wall, 2F over 1F). The value picks the joint class (い, ろ, は … ぬ) and its tensile strength in kN. Change a bracing wall and the N-values follow; the Hardware panel (next) lists every post end with its value and product.

In this step: Corner posts of two storeys are through posts — 通し柱 at the corners (令43条5項), for the whole house or corner by corner.

Each row is one post end with its N-value and the product that covers it. Maker switches from generic names to a maker's catalogue; the chips filter by kind and by story. Clicking a row shows the post in the plan.

The same view is in the Navigator under each story (Views › 1F › Hardware), next to Hardware · foundation for the anchor bolts. Add structural sheets to layouts in the structure panel puts the N値 table and these plans into the layout book.

Every corner of a floor frame (床組) and a roof beam frame (小屋梁組) needs a corner brace — unless structural plywood nailed on that frame does the job (令46条3項, 告示691). The floors of this house are fine; the open corners are on the 2F roof frame: the plates (桁) and roof beams on top of the 2F walls.

Two fixes: Auto-place corner braces (火打ち), or declare a plywood roof deck — the next step shows where.

The table counts, per level, the corners that need a brace, the braces placed and the open ones: 1F floor on the sill, 2F floor frame, 1F roof frame (the lower roof) and the 2F roof frame.

Under Rigid floor / roof deck declarations each level says how it is stiffened: Rigid floor 24 mm ply, nailed all round (3.0), nailed on the joists (1.2), 12 mm ply on joists 根太, nailed (1.0) for a floor on joists, or No (corner braces). A roof frame can declare a plywood roof deck (Notice 691 item 3) or the roof sheathing (item 1). New projects start with 24 mm plywood floors; a concrete 土間 needs no corner braces at all.

The 2F roof frame now has a 火打ち in every corner of its plates and beams, and the open count goes to 0. Where a plate slopes, a flat timber brace cannot sit: the check then asks for a steel corner brace (火打金物) or the plywood roof deck instead. The braces show in the roof framing plan, the 3D Structure view and the hardware list.

令43条 sets the smallest post size as a fraction of the free length between the beams (l / 25 … l / 33 by roof weight and floor). A tall 1F of 3 m with a heavy snow roof is past what a 105 post covers by the table — the other route is each post with its own load (告示1349), which the card gives: the load, the buckling ratio and the stress ratio.

The fixes are listed from best to last: a post or beam beside it that shares the load, a shorter free length (a belt beam), a stronger wood — and bigger posts only as the last resort. Agree the route with the examining body (審査機関).

Each NG card names the member (its code on the framing plan), the story, its section and wood, and what fails — bending, shear or deflection — with the numbers. The fix offers the advised section that passes, checked on a copy of the house first so nothing else fails.

The plates (桁) on top of the walls and the 2F floor beams are in the same list; a red member on the framing plan is an NG here.

The other beam NGs work the same way. Fix everything that can be fixed at the top runs all the fixes at once (bracing, belt beams, corner braces, bigger beams, footings) as one undo step — handy, but fixing row by row shows you what changes.

The anchors are placed automatically and move with the walls and posts; Anchor bolts by hand adds or moves one (Shift: a hold-down anchor), Reset anchors to automatic puts the layout back.

The foundation itself — stems, slab, profiles, passages and 土間 — has its own tutorial: Foundations.

Floor framing shows the beams, joists and posts of the story with their member codes and the bracing walls; Roof framing the plates, roof beams, purlins, ridge, struts and rafters above it. Each plan carries its member list (部材リスト: code, section, wood, length, count) — the list you check the precut factory's drawings against. Beam sizes are the ones the beam check uses.

SumiCAD does not write a precut CAD file: the member list and the framing plans are what goes to the factory.

The members are built from the model and meet cleanly at the joints: posts stop under the beams, braces run post to post, rafters sit on the plates. No post below 下に柱なし marks posts that stand on nothing — worth a look before the precut order. Hardware, Ply and Foundation turn their layers on and off, Rafters hides the roof members, Cutaway opens a section box.

Structure › Clash check… looks for members, pipes, ducts, foundations, openings, stairs, walls and objects that run into each other.

The clash check runs on demand (Recheck), not on every edit. Results are sorted Hard (must fix), Soft and Advice; each line names both elements, the amount and a fix (raise or move the member, enlarge the stair opening, move the object). Clicking a line shows the place in the plan and the 3D view. What to check chooses the pairs; Copy report copies the list for the team.

The headroom value is the conservative reading — the Building Standard Law has no explicit stair headroom for houses — so the line says so.