Foundations: from the automatic layout to the estimate

The foundation plan (基礎伏図) is a view of the lowest story seen through its own layer combination: the walls turn grey and the foundation layer comes forward. It exists only under the lowest story.

For this tutorial the house's foundations were taken out of a copy, so you see them being made from nothing.

The Structure menu holds the foundation commands: Foundation (the tool), Passage 人通口, Foundations under walls and Foundation under selected walls (any floor) for a footing under walls of an upper floor (a step-down, a garage wall).

A profile (断面形状) is the cross-section every stem of that type shares: stem width, top above GL, footing width and thickness, bottom below GL, slab, lean concrete and crushed stone. The house brings three: FD-01 mat foundation, FD-02 strip footing 布基礎, FD-03 high strip footing +1000 for deep snow.

The tool can also draw by hand: Footing along a line (click start and end, like the Wall tool) or Mat slab (polygon).

The command reads the walls that carry load and the posts that need support, runs a stem along each, joins them at the corners and closes the slab inside the outer ring. Walls that already have a footing are skipped, so it is safe to run again after you add walls.

The status bar says what was made (FD-01 … footings + 1 mat slab added on 1F).

Everything on this plan is live: anchor bolts ● and hold-down anchors (M16 HD-B15 …) come from the posts and the N値 of the frame above, and move when a wall or post moves. The dashed outline is the footing, the hatched band the stem.

A footing is picked on its outline (the dashed footing edge), so a click inside the slab does not grab it. Shift+click adds more stretches; then one change applies to all of them.

This is the house as drawn (with its real FD-02 strip stems under the slab).

This is the way to correct the foundation in one place: give that stretch another profile. Typical uses: a higher stem where snow piles up, a wider footing under a heavy point load, a stem without insulation.

The tag on the plan changes, and the sections, 3D and quantities follow at once.

One chip per profile. The fields are the whole cross-section: Stem width 立上り幅, Top GL+ 天端, Footing width ベース幅, Footing thickness ベース厚, Bottom GL− 底, Slab thickness 土間厚, Lean concrete 捨てコン, Gravel 砕石. The sketch on the right redraws with every change.

The buttons on top: Foundations under walls, Generate from this profile, Steps (step the footings where the ground or the floor changes), Vents, Follow the terrain, Foundation plan.

Changing the profile changes every stem of that type — the opposite of the last step. Use it for the decisions that hold for the whole house: the footing width the soil needs (告示1347 table), the stem width, the lean concrete.

The plan redraws the dashed footing edges wider everywhere FD-02 is used; the FD-03 stretch is untouched.

Heights in SumiCAD are measured from the design GL (設計GL, set in the Site panel). With Levels follow the frame on, the 1F floor level is built up from the frame: stem top + sill packing + 土台 + floor. Here the stem top is GL+600 (FD-01 / FD-02, Top GL+ 600), so the stem stands 600 mm above the ground.

Raise the 1F floor to 855 and the stems that follow the frame come up with it (stem top GL+750); the upper floor moves too.

Notice 1347 (告示1347) asks for a stem at least 300 mm above the ground; the app also gives a hint under 400 mm (common practice for snow and splash) and checks each footing against the real terrain when there is one. The check lists every profile in use with its errors and hints: base width for the soil, the soil bearing estimate, under-floor ventilation, the 床下 access.

Note the Info Box: the profile keeps its total stem height, so the bottom went down with the top (GL+250 · GL−1,350). Ctrl+Z puts it back.

In Hokkaido and other cold regions the footing bottom must go below the frost line (凍結深度), set by each municipality's rules. SumiCAD knows the value for the address and uses the deepest value where a town has sub-areas until you pick yours (the structure panel asks for it). A number typed here overrides it.

The footing bottom (底 GL−) is the embedment 根入れ the law also checks: at least 240 mm for a strip footing and 120 mm for a mat (告示1347), and below the frost depth. A footing less than 100 mm under the frost line gets a hint. Inside stems of an insulated foundation are not held to the frost depth.

The Foundation row of Bracing & structure checks (Ctrl+B) shows the same errors with the rest of the structure.

The slab thickness (土間厚 · mm, 150 here) and the gravel and lean concrete under it are in the FD-01 profile; the plan writes ベタ基礎 t=150 · slab top GL+300. Notice 1347 asks for at least 120 mm and D10 bars at 300 mm or less both ways; the profile's bars feed the rebar take-off.

Drag the slab's corner grips to change its outline, or redraw it with Mat slab (polygon).

Every under-floor compartment must be reachable from a floor hatch 床下点検口 for inspection and plumbing work — through passages in the inner stems. The check counts the compartments and tells you which ones cannot be reached.

Under More: the opening reinforcement 開口補強 from the profile's bars (top and bottom 1-D13, diagonal D13 per corner), and the warnings — here a post stands over the opening with no stem under it, and the 床下 access is not complete (no floor hatch yet: 7 compartments cannot be inspected).

Use switches between a passage and Lowered stem 玄関・階段 (a stem lowered under an entrance or stair, also on the outer ring).

The position is the centre of the opening from the start of the footing (the total length is shown: / 3,185). A passage needs a clear span between posts; when no position works, move the post or give the stretch a stronger beam over the opening.

Place a floor hatch (Design › Floor hatch 床下点検口) and the access line turns green when every compartment is linked.

Under-floor ventilation (床下換気, 令22条) asks for 300 cm² of vent every 5 m of outer stem. The house uses ventilated sill packing t21 all round (100 cm²/m — the check confirms it is enough); the plan labels it along the outer stems. The choice applies to the profile in view, or to every profile in use.

土間 is a property of the room, not a separate slab. An entrance, a garage, a 土間リビング: the floor framing stops over it, and the foundation slab, sections, 3D and concrete quantities follow. Here the large living room becomes a 土間 — every edit in this tutorial is undone with Ctrl+Z.

Doma top starts on the stem top (FL−105, linked to stem top): the 土間 then follows the frame.

Typing a level unlinks the 土間 from the stem top (↺ stem top links it again). A slope names the high side and the rise: the concrete top is the Doma top at the low side and rises by the given height — a garage slab rising from the shutter to the back, an entrance draining to the door. Plan, sections, 3D and the concrete take-off follow.

A door at 土間 level puts its sill on the 土間 finish, cuts the 土台 and lowers the stem under the opening — a lowered stem element linked to the door: it moves, resizes and disappears with it. On the foundation plan the lowered part shows as a gap in the stem line at the door.

The same Passage element, Use = Lowered stem, lowers a stem by hand (under a stair, a garage shutter); over 2,000 wide the app asks for the bars of that shallow beam to be checked.

Foundation insulation 基礎断熱 belongs to the profile: side (inside / outside), thickness, material and depth — FD-02 here has 50 mm XPS on the inside down to 850 mm. Per stretch you can only switch it off, for example on an inner stem between two heated rooms. The insulation is drawn in the sections and 3D and counted in the quantities (Foundation insulation — XPS board).

Foundation turns the foundation on and off, Cutaway opens a section box to look at a stem, its footing and the slab. The legend counts every kind; the foundation sits exactly under the 土台 at the stem top of its profile.

Anchor bolts are placed automatically along every sill: within 200 mm of post ends and sill joints and at most 2.7 m apart; a hold-down anchor goes under every post whose N値 needs one (HD-B10 … HD-B25). The check also tests the bolt length: at least 250 mm in the concrete under the 土台 and the sill packing.

It is a view of the lowest story (Navigator › Views › 1F › Hardware · foundation), ready for the sheets; the permit set has it as P.28 アンカーボルト配置図・金物集計表.

The automatic layout stays the main way; bolts placed by hand sit on top of it and are kept when the walls change. Reset anchors to automatic in the Hardware panel removes them all.

The sheet shows the plan you edited, not a copy: change a profile and the sheet follows. The permit set has its own P.12 基礎伏図. Publish (発行…) writes the PDF.

Each section is drawn from its profile: 1FL, the stem top, slab top and design GL, the 土台 and sill packing, the bars (main bars, verticals @250, footing bars), the XPS, lean concrete and crushed stone. Under it: embedment GL−800 · frost depth 600 → OK. Change a profile and its section is redrawn.

On this house: concrete for the stems 13.35 m³, the footings 4.59 m³ and the slab 9.30 m³ (net of the stems), lean concrete 4.63 m³, crushed stone 13.89 m³, formwork 191.49 m² (stem faces, footing and slab edges), and the rebar in metres and tonnes per diameter (D10, D13, with laps). Excavation includes 300 mm working space; the backfill and surplus soil follow.

CSV export… hands the list to a spreadsheet.

Type a unit price in the row, or fill the price list (価格表…) once for the firm and every project uses it. The estimate keeps the same quantities as the Quantities tab (with the loss rate), so a change to the foundation changes the estimate.