Quick answer: A strip footing is a continuous strip of reinforced concrete that runs under a load-bearing wall, or under a row of closely spaced columns, and spreads their load onto the soil. It is a shallow foundation used for low to medium-rise buildings on stable ground. Where the soil is weaker, the strip is made wider.
Every building needs a foundation that spreads its weight evenly onto the ground. Foundations are grouped into two kinds, shallow and deep. A strip footing is a shallow foundation and one of the most common types of footings used for houses and small commercial buildings.
What is a strip footing?
A strip footing, also called a strip foundation or wall footing, is a single continuous strip of concrete that runs along the line of a wall or a row of columns. It is reinforced with steel bars. The strip is wider than the wall it carries, so the load reaches the soil over a larger area and the pressure on the ground stays within what the soil can bear.
The width and thickness of the strip are not fixed. They are chosen for the load coming down and for the bearing capacity of the soil on that plot, which is why the same building can need a different footing on a different site.
When is a strip footing used?
Strip footings are used mainly in these situations:
- Load-bearing walls: the wall carries the floors and roof, and the strip supports the wall along its whole length.
- Closely spaced columns: where columns stand in a row and their separate footings would nearly touch, one continuous strip is more economical and more compact than individual footings.
- Good ground: soil with a high bearing capacity close to the surface.
- Low to medium-rise buildings: houses, small commercial buildings and compound walls.
On soil with a lower bearing capacity, a wider or more heavily reinforced strip may be required. A structural engineer should assess the soil and design the footing.
Types of strip footing
- Deep strip footing: the trench is taken down to a firm, stable layer and the reinforced concrete strip is cast there, to the minimum depth and width the design calls for.
- Wide strip footing: used on soil with a lower bearing capacity. The broader base spreads the load over more ground, and the strip is reinforced across its width.
How is a strip footing built?
- Soil check: the bearing capacity is established first. It decides the width and depth of the footing.
- Setting out: the centre lines of the walls are marked on the ground from the drawing.
- Excavation: trenches are dug to the design depth, down to firm natural soil. The trench bottom is levelled and compacted.
- Levelling course: a thin bed of plain concrete is laid on the trench bottom to give a clean, level base.
- Reinforcement: the steel is placed on cover blocks as per the structural drawing, with starter bars for columns where needed.
- Concreting: the strip is cast in one continuous operation as far as possible and compacted well.
- Curing: the concrete is kept wet until it gains strength.
- Masonry and backfilling: the foundation wall or plinth beam is built on the strip, and the trench is refilled in layers and compacted.
Strip footing vs isolated footing
| Point | Strip footing | Isolated footing |
|---|---|---|
| Shape | Continuous strip | Separate pad under each column |
| Supports | A wall or a row of close columns | A single column |
| Typical building | Load-bearing wall construction | RCC framed construction |
| Excavation | Continuous trench | Individual pits |
| Later changes | Difficult, because walls carry the load | Easier, because walls between columns are not structural |
What makes a strip footing suitable?
- Load distribution: it suits walls or columns that need even support along a line.
- Continuous support: supporting a load-bearing wall along its full length reduces the risk of uneven settlement.
- Adaptability to soil: the engineer can adjust the width, depth and steel to the soil on the plot.
- Space efficiency: one strip takes less room than a line of overlapping individual footings.
Advantages of strip footing
- Even load distribution: spreads the weight and limits settlement.
- Cost: more economical than individual footings for closely spaced columns.
- Versatility: can be designed for different soils and loads.
- Simplicity: straightforward to set out and build, which saves time.
- Stability: gives dependable support to load-bearing walls.
- Design options: deep or wide strips to suit the site.
Disadvantages of strip footing
- Load limits: not suited to large structures with heavy loads.
- Hard to modify: altering a building that stands on strip footings is complex.
- Height limits: not effective for high-rise buildings.
- Site constraints: where the soil is weak or changes across the plot, a strip footing may not be workable and another foundation type is needed.
What to check on site
- The trench has reached firm, undisturbed soil, not filled-up earth.
- The trench bottom is level, dry and free of loose soil before any concrete is placed.
- Width and depth match the drawing along the full length, including at corners and junctions.
- Steel sits on cover blocks and is not lying on the ground.
- Bars are lapped and continued properly around corners and at wall junctions.
- The strip is cured before the wall is loaded onto it.
Common mistakes
- Skipping the soil test: the footing size is then a guess.
- Founding on fill: stopping the trench in loose filled soil leads to settlement cracks in the walls.
- Water in the trench: concreting into standing water weakens the footing. Pump it out first.
- Uneven depth: a strip that steps up and down without design causes uneven settlement.
- Adding floors later: a strip designed for one or two storeys cannot simply take more. Have the foundation checked before any vertical extension.
Strip footings are a sound choice for low to medium-rise buildings on good ground, provided the soil and the loads are properly assessed first.
Related guides
For buildings on columns, compare the isolated footing and the combined footing. Where the ground is too weak for any shallow footing, see pile foundations and their types. The footing size starts with the soil report, explained in soil testing before construction, and the next element above the footing is the plinth beam. Foundations are part of the structural work in our house construction service.
Frequently asked questions
What is a strip footing?
A strip footing, also called a strip foundation or wall footing, is a shallow foundation in which one continuous strip of concrete runs along the length of a wall or a row of columns. It contains steel reinforcement and spreads the load evenly onto the soil.
Where is strip footing used?
It is used mainly under load-bearing walls and under rows of closely spaced columns, on ground with good bearing capacity. Typical cases are houses, small commercial buildings and boundary walls of low to medium height.
What are the types of strip footing?
There are two main types. A deep strip footing is taken down to a firm, stable layer of soil. A wide strip footing has a broader base and is used where the soil has a lower bearing capacity, so the load is spread over more area.
What is the difference between strip footing and isolated footing?
A strip footing is continuous and supports a wall or a line of columns. An isolated footing is a separate pad under a single column. Strip footings suit load-bearing wall construction; isolated footings suit framed buildings with well-spaced columns.
What are the disadvantages of strip footing?
It is not suited to large structures with heavy loads or to high-rise buildings, it makes later structural changes difficult, and it depends on site conditions: where the soil is weak or varies across the plot, another foundation type may be needed.
