Question 1

What is a strip foundation?

Accepted Answer

A strip foundation (also called continuous footing) is a type of shallow foundation that runs continuously along the perimeter of a building or under load-bearing walls. It distributes the building load over a wider area of soil. Strip foundations are commonly used for residential and small commercial buildings. They are more economical than slab foundations for smaller structures and provide good load distribution.

Question 2

Do I include internal walls?

Accepted Answer

Include internal walls only if they are load-bearing walls that require strip foundations. Non-load-bearing partition walls typically don't need foundations. To determine if a wall is load-bearing, check your structural drawings or consult with a structural engineer. If you have internal load-bearing walls, measure their total length and add it to the perimeter calculation using the 'Include Internal Walls' option.

Question 3

How to measure strip height?

Accepted Answer

Strip height (depth) is measured from the bottom of the foundation to the top of the footing. It depends on several factors: frost line depth (foundation should extend below frost line), soil bearing capacity (deeper for weaker soils), and building load (deeper for heavier loads). Typical depths: 30-60 cm (12-24 inches) for light structures, 60-100 cm (24-40 inches) for heavier structures. Always check local building codes and consult with a structural engineer for specific requirements.

Question 4

How much extra concrete to order?

Accepted Answer

It's recommended to add 5-10% extra concrete (waste margin) to account for formwork variations, spillage, and to ensure you have enough material. For complex foundations or when using site mixing, consider adding 10-15% extra. It's better to have a small amount left over than to run short during pouring, which can cause delays and may result in inconsistent concrete batches or cold joints.

Question 5

Strip vs slab foundation?

Accepted Answer

Strip foundations are continuous footings that run along the perimeter and load-bearing walls. Slab foundations are large flat concrete slabs that support the entire building. Strip foundations are more economical for smaller structures and provide good load distribution. Slab foundations are better for larger buildings, provide a finished floor, and distribute loads over a larger area. The choice depends on building size, soil conditions, and budget. Consult with a structural engineer for the appropriate foundation type.

Question 6

How do I measure building dimensions?

Accepted Answer

Measure the outer dimensions of the building footprint (length and width). This is the distance from the outside edge of one wall to the outside edge of the opposite wall. For rectangular buildings, measure the longest side (length) and the perpendicular side (width). For irregular shapes, break them into rectangles, calculate each separately, and add the perimeters together.

Question 7

What strip width should I use?

Accepted Answer

Strip width depends on building load and soil bearing capacity: Light structures (residential): typically 30-50 cm (12-20 inches). Medium structures: 50-60 cm (20-24 inches). Heavy structures: 60-100 cm (24-40 inches). Wider strips distribute load over more area, reducing soil pressure. Always check your structural drawings or consult with a structural engineer for the specific strip width required for your project.

Question 8

Can I use this for irregular building shapes?

Accepted Answer

This calculator works best for rectangular or square buildings. For irregular shapes (L-shaped, U-shaped, etc.), break the building into rectangular sections, calculate the perimeter of each section separately, and add them together. Alternatively, measure the total perimeter manually and use that as the 'building length' with width = 0, then manually enter the total perimeter length.

Question 9

What about stepped foundations?

Accepted Answer

Stepped foundations change depth or width at different sections. This calculator assumes uniform strip dimensions. For stepped foundations, calculate each section separately based on its dimensions, then add the volumes together. Measure the length, width, and height for each step, calculate volume for each, and sum them.

Question 10

How accurate is this calculator?

Accepted Answer

The calculator provides accurate volume estimates based on geometric formulas. Accuracy depends on precise measurement of building dimensions and strip dimensions. The formulas are mathematically correct, but actual concrete needs may vary slightly due to formwork, surface irregularities, and compaction. Always add a waste margin (5-10%) for real-world projects to account for these variations.

Question 11

What about reinforcement (rebar)?

Accepted Answer

Reinforcement (rebar) is calculated separately and doesn't affect the concrete volume calculation. Rebar displaces a small amount of concrete (typically less than 1-2%), which is usually covered by the waste margin. This calculator focuses on concrete volume only. Rebar quantities are calculated based on structural design requirements, spacing specifications, and local building codes.

Question 12

Ready-mix vs site mix for strip foundations?

Accepted Answer

Ready-mix concrete is delivered pre-mixed from a plant, while site mix is mixed on-site. For strip foundations, ready-mix is often preferred because: it ensures consistent quality, saves time, and is suitable for continuous pouring. Site mixing may be more economical for small projects but requires proper mixing equipment and expertise. This calculator helps you estimate volume for either option.

Question 13

How do I convert between units?

Accepted Answer

The calculator automatically handles unit conversion: 1 m = 3.28084 ft, or 1 ft = 0.3048 m. For volume: 1 m³ = 35.3147 ft³, or 1 ft³ = 0.0283168 m³. For cubic yards: 1 yd³ = 27 ft³ = 0.7646 m³. Simply select your preferred unit system (meters or feet) and enter dimensions in that unit. The calculator will provide results in both the selected unit and cubic meters (for consistency), plus cubic yards if using imperial units.

Question 14

What about foundation excavation?

Accepted Answer

Foundation excavation volume is separate from concrete volume. Excavation removes soil to create space for the foundation, while concrete fills that space. Excavation volume is typically larger than concrete volume due to formwork space and over-excavation. This calculator focuses on concrete volume only. Calculate excavation separately if needed, accounting for formwork and working space around the foundation.

Question 15

Do I need to account for formwork?

Accepted Answer

Formwork (the molds that hold concrete) doesn't directly affect the concrete volume calculation, but it can cause slight variations in the actual concrete needed. Formwork may not be perfectly square, and concrete can settle or spread slightly. This is why adding a waste margin (5-10%) is recommended. The waste margin accounts for formwork variations, spillage, and ensures you have enough material.

Strip Foundation Calculator – Concrete Volume for Continuous Footings

Calculator

How to Calculate

Examples

Simple Perimeter Only

With Internal Load-Bearing Walls

Larger House Footprint

With Waste Margin

Imperial Units Example

Frequently Asked Questions