Free Structural Grid Generator

The bay size is the fundamental decision and it is driven by span. A structural member's depth grows roughly with the square of its span, so doubling a bay from 6 to 12 metres does not double the beam depth — it roughly quadruples the bending moment, and the section required grows accordingly.

That relationship is why bay sizes cluster. In-situ concrete office construction settled on something around 7.5 to 9 metres because that is where the slab depth stays reasonable. Steel frames can go further. Timber, until recently, much less.

Car parks are the clearest case of a grid driven entirely by one dimension. A parking bay is about 2.4 metres wide, so a structural bay has to be a whole number of them plus tolerance — which is why car park grids cluster around 7.2 to 7.8 metres, three parking spaces wide, and why a car park designed on any other grid wastes spaces on every floor.

Offices have a similar constraint at a different scale. The planning module for an office is typically 1.5 metres, driven by the width of a partitioned cellular office and the ceiling and lighting layouts that follow from it. A structural bay of 7.5 metres is five modules; 9 metres is six.

The grid reference system — letters across, numbers down — exists for a coordination reason rather than a design one. A building generates dozens of drawings from different disciplines, and they have to agree about where things are. Saying "the column at C4" is unambiguous across every drawing, every schedule and every conversation on site.

Regularity in a structural grid buys more than it does in a layout grid. Identical bays mean identical beams, identical connections, identical formwork, and repetition is the largest single driver of construction cost after materials. A building with twelve different beam sizes costs materially more than the same building with three.

That is why an irregular structural grid needs justifying in a way that an irregular layout grid does not. It is often the right answer — a difficult site, an existing building, a programme that genuinely varies — but it is a decision with a price attached.

The historical arc runs through the material. Masonry construction has no grid in this sense: walls carry load continuously and openings are subtractions from them. The grid arrives with the frame, when load concentrates into points and the points have to be located.

The structural grid overlay page follows that history, beside the rest of the architecture grid overlays. Cast iron frames in nineteenth-century mills are the first clear examples. Steel and reinforced concrete generalised it, and by the 1920s the free plan — Le Corbusier's Maison Dom-Ino diagram of 1914 is the canonical statement — had made the separation of structure from enclosure the defining idea of modern architecture.

That separation is what a structural grid represents. Once the columns carry the load, walls can go anywhere or nowhere, and the plan is free in a way it had never been. Everything that follows in twentieth-century planning depends on it.

The most useful thing you can do with an overlay like this is check the relationship between a plan and its structure. Lay the grid over a floor plan and see whether the cores, the walls and the circulation relate to the columns, or whether the structure has been fitted around a plan drawn without thinking about it.

The second is testing bay counts by comparison. Set the grid to 5 × 4 and look at the plan, then 7 × 5, then 6 × 5. The right answer is usually obvious side by side and hard to reason about from a span table alone, because the question is as much about how the plan divides as about what the beams can do.

A caution about using it over a photograph: a floor plan works, an aerial view of a site works, and a perspective photograph of a building does not. The grid is a plan construction, and applying it to a perspective view will give you a relationship that is not there.

Where the grid is genuinely useful over a photograph is a plan drawing you have received as an image — a scan, a PDF page, a screenshot from a planning portal. Laying the grid over that and adjusting until it fits recovers the setting-out, which is often not stated anywhere on the drawing.

The node markers can be turned off, and should be for a drawing where the lines alone are the information. They are there for the moment when you are deciding the bay count and want the column quantity in front of you rather than in your head.

The labels can be turned off too, and for an export that will sit under a design they usually should. They are construction-drawing furniture: essential while setting out, clutter once the drawing has moved on.

For interiors and fit-out work, the structural grid is a given rather than a decision, and the overlay's job changes accordingly. Lay it over the base build and the question becomes which partitions can land on lines and which have to span between them.

The grid draws over your own image rather than exporting a fixed template because a structural grid is only meaningful against a specific plan. The bay count on its own is a number; the bay count over a floor plan is a design decision.

The export sizes itself from the paper format and the DPI you choose rather than from your screen. SVG keeps every line editable, which is what you want when the setting-out becomes a construction layer in a CAD drawing.

Everything runs in your browser. Images you load are never uploaded, because there is no server for them to reach. The drawing, the transform and the export all happen on your own machine.