Slabs
A slab is a horizontal plate defined by an outline, a thickness and which face sits on the level you gave it.
Three ways to draw one
Section titled “Three ways to draw one”| Slab on the toolbar | rectangle, two clicks, or type width;depth |
| Polygon — ← / → in the Slab tool | click the corners, double-click to finish |
| Slab from Walls — select walls, right-click | pick walls that enclose a space and let the outline follow them |
Rectangle and polygon are two modes of one tool. ← / → switches between them before the first click, and the toolbar button starts whichever you used last.
From Walls is the one you will use most. Click walls to add them, press Enter, and the outline follows their outer faces. It does not need a perfectly closed loop — the corners are worked out from the faces.
Which face sits on the level
Section titled “Which face sits on the level”| Top | the level is the top of the slab — a floor you walk on |
| Bottom | the level is the underside — a ceiling below |
| Center | the level runs through the middle |
Most of the time you want Top for a floor: the storey elevation is the finished floor, and the slab hangs below it.
For a slab built From Walls there is a second switch — whether the outline sits at the base of the walls or at their top. Base for the floor of that storey, top for its ceiling.
Openings
Section titled “Openings”Right-click the slab → Archeform → Slab Tools:
| Opening | draw a shape on the slab face and cut it |
| Del Open | click inside an opening to remove it |
| Move Open / Copy Open | slide or duplicate one |
| Off Open | resize an opening, or inset it from the slab outline |
Openings are stored on the slab in the same way openings are stored on a wall — as parameters, not as holes cut into geometry. Move the slab and they go with it; change its thickness and they are re-cut.
Off Open does two different things depending on what you point at: inside an opening it resizes that opening, on the slab outline it makes a new opening inset from the edge — a light well or a frame around the perimeter.
Openings for stairs
Section titled “Openings for stairs”Do not draw these by hand. Select the stair or ramp, right-click, Archeform → Cut Slab Opening Above. Archeform finds the slab above the top landing and cuts an opening matching the footprint.
It is a one-off action — the opening is then an ordinary slab opening you can move and resize. Changing the stair later does not update it, so re-cut if the stair moves substantially.
Reshaping
Section titled “Reshaping”Offset moves the whole outline in or out by a distance you type or drag. Use it to take a slab from the outer face of the walls to the inner face, or to add an overhang.
Parameters
Section titled “Parameters”| Field | Default | What it does |
|---|---|---|
| Thickness | 250 mm | measured perpendicular |
| Justify | Top | which face sits on the level |
| Composition | none | layered build-up, drawn in sections |
| Section fill | concrete | hatch used where the slab is cut |
In IFC and in drawings
Section titled “In IFC and in drawings”Exports as IfcSlab with PredefinedType BASESLAB, plus
Qto_SlabBaseQuantities and Pset_SlabCommon. Openings are deducted from the
net quantities, so the area and volume you get are the ones you would bill.
In plan the slab is cut by the storey’s cut plane and hatched. In sections it is hatched by material, layer by layer if it carries a composition.