# How to calculate tributary area for a wall

> A wall collects a tributary strip, not an area like a column. Here is how to find its tributary width, turn it into a line load, and where the strip method applies.

**Category:** Fundamentals  
**Author:** Sam Rivera (Structural engineer · Educator)  
**Published:** 2026-05-20

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A wall is a line support, so it gathers floor as a strip and carries it per metre, not per point. To find a [load-bearing wall](https://en.wikipedia.org/wiki/Load-bearing_wall)'s tributary, take its tributary width, the half spacing to the parallel support on each side, and multiply by the floor pressure for a line load in kN per metre. StructLoads models walls as line supports collecting this strip, and the method below mirrors the column case with one key difference.

## A wall collects a strip, not an area

A column draws a two-dimensional tributary area and carries a point load. A wall, being a line, draws a tributary width: the strip of floor nearest to it, bounded by the lines halfway to the parallel supports on each side. It is the same nearest-support idea, a clipped [Voronoi diagram](https://en.wikipedia.org/wiki/Voronoi_diagram), but for a line the result is a strip rather than a polygon around a point. The strip width is what converts the floor pressure into a line load.

## Wall versus column tributary

The two differ in shape, units and what they feed.

| Property | Column | Wall |
| --- | --- | --- |
| Tributary | Area (region) | Width (strip) |
| Load form | Point load, kN | Line load, kN/m |
| Goes to | Pad footing | Strip footing or beam |
| From | Half-bay on four sides | Half spacing on two sides |

So a wall's tributary is conceptually a width times its length, but in practice you work with the width and the resulting line load, the form a wall and its strip footing are designed for. Real design guides work in exactly this per-unit-length form: the worked example in [CMHA's TEK 14-05A on loadbearing masonry wall design](https://www.cmha.org/resource/tek-14-05a/) designs its wall for an axial dead load of 520 pounds per foot and live load of 250 pounds per foot, the line-load numbers a tributary width produces.

## The calculation

Take the half spacing to the parallel support on each side and add them for the tributary width, then multiply by the floor pressure. A wall midway between supports at 5 metre spacing takes 2.5 plus 2.5, which is 5 metres of width. At a 5 kN per square metre floor [load](https://en.wikipedia.org/wiki/Structural_load), that is 5 times 5, which is 25 kN per metre of wall. Add the wall self weight per metre on top. This is the same width logic as [tributary width for a beam](/blogs/tributary-width-for-a-beam).

## From strip to line load to footing

The line load runs along the wall and is delivered to a strip footing beneath it, or to a beam if the wall is supported on one. You size the strip footing by dividing the service line load by the allowable soil bearing pressure, and the full wall takedown, including self weight and load from above, is in [bearing wall load takedown](/blogs/bearing-wall-load-takedown). Keep dead and live separate within the line load so the factors apply correctly.

## When the simple strip does not apply

The uniform strip is exact for a one-way floor spanning onto the wall. It does not apply when the wall supports a two-way slab, which delivers a triangular or trapezoidal load, when the framing is irregular, or when concentrated loads land on the wall. There you set out the real load shape. The strip method is the right tool for the common one-way case, the same boundary as for columns in [how to calculate tributary area for a column](/blogs/how-to-calculate-tributary-area-for-a-column).

## Key takeaways: wall tributary area

A wall collects a tributary strip: its tributary width, the half spacing to the parallel support on each side, times the floor pressure, gives a line load in kN per metre. Unlike a column's point load, this runs along the wall to a strip footing. The strip method is exact for one-way floors. StructLoads carries the wall line load as a preliminary figure a qualified engineer confirms.

## Quick answers

### How do you calculate the tributary area for a wall?
Find the wall's tributary width, the half spacing to the parallel support on each side, then multiply by the floor pressure to get a line load in kN per metre. A wall between supports at 5 metre spacing takes 2.5 plus 2.5, which is 5 metres of width; at 5 kN per square metre that is 25 kN per metre. The wall carries this line load along its length.

### What is the difference between a wall and a column tributary?
A column draws a tributary area, a two-dimensional region, and carries a point load in kN. A wall draws a tributary width, a strip whose width is measured across the wall, and carries a line load in kN per metre along its length. The wall is a line support, so its tributary is a strip and its load is distributed.

### How do you turn a wall tributary into a load?
Multiply the tributary width by the floor pressure to get the floor line load on the wall in kN per metre, then add the wall's own self weight per metre. The result is a uniform line load that the wall carries to a strip footing or a supporting beam below. Keep dead and live separate so they can be factored.

### When does a wall not take a simple tributary strip?
A wall does not take a simple uniform strip when it supports a two-way slab, which delivers a triangular or trapezoidal load, when the floor framing is irregular, or when concentrated loads land on the wall. There you set out the real load shape rather than a uniform strip. The strip method is exact for one-way floors spanning onto the wall.