Estimation & Costing for Building Foundation Works: Footings to Grade Beams

**Why foundation estimation matters**

Foundations are literally the base of every building. Underestimating the volume of concrete, steel and excavation leads to significant cost overruns and delays. Accurate estimation and costing ensure footings, columns and grade beams are sized correctly and that you procure the right quantities of materials.

**Who this helps**

This guide is for quantity surveyors, estimators and civil engineers responsible for preparing BOQs and cost plans for building foundations. It also benefits site engineers and students who want to learn how to measure and cost foundation works for both shallow and deep footings.

## Foundations: types and components

Building foundations transfer loads to the ground through footings and beams. Common types include isolated footings, combined footings, strap footings, raft foundations and pile foundations. Key components are:

- **Excavation**: removal of soil to design depth, including dewatering and shoring if necessary.

- **Blinding concrete**: lean concrete layer at the bottom of excavation to provide a clean surface.

- **Footings**: reinforced concrete pads under columns or walls.

- **Grade beams**: reinforced concrete beams connecting footings to distribute loads.

- **Reinforcement steel**: main and distribution bars for footings and beams, plus hooks and dowels.

- **Backfilling**: compacted soil around foundations after construction.

## Step-by-step quantity take-off

1. **Review structural drawings**: identify footing sizes, depths, grades of concrete and reinforcement details.

2. **Measure excavation volume**: calculate length × width × depth for each footing and trench. Include extra width for formwork and working space.

3. **Blinding concrete**: measure the plan area of each footing or base and multiply by thickness.

4. **Footing concrete**: calculate volume for each isolated footing (plan area × depth). For combined or raft foundations, use slab area × thickness.

5. **Reinforcement for footings**: measure the number and length of main bars and distribution bars, apply bar bending schedule (BBS) and multiply by unit weight.

6. **Grade beams**: determine beam lengths between columns, cross-sectional dimensions and reinforcement. Compute concrete volume = length × width × depth.

7. **Formwork**: measure the surface area of formwork (sides of footings and beams). Some contracts include it as part of concrete item.

8. **Backfilling and compaction**: compute volume of backfill = excavation volume – concrete volume.

9. **Miscellaneous items**: anti-termite treatment, waterproofing membranes, anchor bolts and dowels.

### Example BOQ lines

| Item | Unit | Qty | Rate (INR) | Amount (INR) |

| --- | --- | --- | --- | --- |

| Earth excavation for foundations up to 2 m depth | m³ | 250 | 500 | 125,000 |

| Plain cement concrete 1:4:8 blinding 75 mm thick | m² | 120 | 600 | 72,000 |

| Reinforced concrete (M25) in isolated footings | m³ | 100 | 7,200 | 720,000 |

| Reinforcement steel in footings (Fe500) | kg | 8,000 | 75 | 600,000 |

| Reinforced concrete (M25) in grade beams | m³ | 40 | 7,200 | 288,000 |

## Key formulas

- **Excavation volume** = length × width × depth.

- **Concrete volume** = footing area × depth or beam length × cross‑section.

- **Reinforcement weight** = number of bars × bar length × unit weight.

- **Formwork area** = perimeter of footing × depth × number of faces.

- **Backfill volume** = excavation volume – concrete volume – blinding.

## India vs GCC differences

In India, isolated and combined footings with M25 concrete and Fe500 steel are common. Excavation is often manual in tight sites, with reinforcements bent on site. In GCC countries, raft foundations or piles with higher concrete grades (M30–M40) are prevalent due to poor soil and heavier loads. Ready-mix concrete is mandatory, and reinforcement is often prefabricated off site. Heat of hydration is a concern in hot climates, so water curing and admixtures are specified.

## Mistakes and fixes

- **Wrong excavation depth**: misinterpreting datum levels leads to over‑ or under‑excavation. Always check reduced levels against site benchmarks.

- **Ignoring overlap and hooks in reinforcement**: BBS must include lapping lengths, anchorage and bends. Use standard codes (IS 456 or ACI) to compute lengths.

- **Overlooking formwork costs**: although sometimes included in concrete item, formwork materials and labour can be significant. Provide a separate item if required.

- **Incorrect unit conversion**: mixing up m² and m³ can inflate or deflate quantities. Double‑check units for each item.

- **No allowance for wastage**: include reasonable wastage factors for concrete (2–3%) and steel (5%) to account for spillage and offcuts.

## QC & QA checklist

- Inspect excavation size and depth before placing blinding concrete.

- Ensure blinding surface is level and cured before setting reinforcement.

- Verify reinforcement size, spacing and cover blocks as per drawings.

- Check formwork alignment, bracing and release agents.

- Confirm concrete grade through batch tickets and slump tests.

- Supervise concrete pouring and compaction using vibrators.

- Monitor curing methods (water curing, curing compounds).

- Inspect removal of formwork and finish of concrete surfaces.

- Verify anchor bolts and dowels are positioned correctly.

- Record cube test results and maintain a site quality log.

## Frequently asked questions

**How do you determine footing size for estimation?**

Use structural drawings which specify footing plan dimensions and thickness. Do not scale from architectural drawings.

**What is the difference between isolated and combined footings?**

Isolated footings support single columns; combined footings support two or more columns when loads are close. Combined footings require larger plan areas and continuous reinforcement.

**Should formwork be measured separately?**

It depends on contract documents. Some BOQs include formwork with concrete; others list formwork surface area separately. Read the specifications carefully.

**What is the standard wastage factor for steel?**

A 5% allowance is common for cutting and bending waste. For high-rise or complex shapes, allowances may be higher.

**How do you cost grade beams crossing under walls?**

Grade beams are measured by volume; include excavation, concrete, reinforcement and formwork. Provide separate items for beam reinforcement if required.

## Level up your skills

To deepen your understanding of foundation estimation, check out **BHADANIS – Quantity Surveying & Estimation Level  1**. Complement your knowledge with **Construction Project Planning & Management Level  5** and **Tendering & Construction Contracts Management Level  3 & 4** to learn planning and contract strategies.