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Allowable Wastage of Construction Materials on Site
Wastage is a menace to every construction project that can never be eliminated completed but rather can be reduced and managed to acceptable percentage. As an Engineer with extensive site experience in Kenya, I often get asked by contractors, project managers, and site supervisors about the acceptable levels of wastage for construction materials and how this impacts costs and sustainability. Understanding these standard allowable wastage percentages is not just a budgeting exercise, it’s a crucial aspect of project quality, compliance, and environmental responsibility.
What is Allowable Wastage in Construction?
Allowable wastage is the maximum percentage of material that can be lost during normal site operations, due to handling, storage, cutting, transport, spillage, and even human error, without breaching contract or code requirements. These values are used for estimating, procurement, and billing, and can sometimes be specified in local or international standards, project contracts, or best-practice guidelines.
For example, Indian Standard IS 1200 and IS 456 provide clear baselines for allowable wastage of key materials
Why Does Wastage Matter?
Allowable wastage directly impacts:
Project cost estimation and control
Sustainable resource usage
Project scheduling
Legal and contract compliance
Environmental impact
I’ve seen firsthand how failing to account for these margins can cause huge cost overruns or, on the other hand, how proactive waste management yields big savings.
Standard Allowable Wastage Percentages in Construction
Based on industry standards and practical site experience, the following table summarizes typical allowable waste rates for major construction materials in Kenya and East Africa. These align with global norms, but consult your project specs for contract-specific allowances.
| Material | Allowable Wastage % | Typical Causes |
|---|---|---|
| Cement | 2–3.5% | Spillage, air loss, packaging residue |
| Concrete | 2–5% | Pouring/placing losses, over-order |
| Sand | 8–12% | Sieving, transport drop, weather |
| Aggregate | 5–8% | Dropping, breakage, over-delivery |
| Reinforcement Steel | 3.5–5% | Cutting, bending, offcuts |
| Structural Steel | 10–15% | Fabrication, offcuts, rust, miscuts |
| Bricks | 2–3% | Breakage, cutting for fit, transport |
| Tiles | 4–10% | Cutting for corners, breakage |
These figures may differ based on your site's location, complexity, logistics, and workforce skills.
Allowable Wastage Table by Source
| Source/Site | Cement | Concrete | Sand | Aggregate |
|---|---|---|---|---|
|
Kenya Site Average (Practical) |
2-3.5% |
2-5% |
8-12% |
5-8% |
|
IS 1200/456 (India) |
2% |
2-3% |
7-10% |
3-5% |
|
UK Practice (Ready Mix,block) |
N/A |
1-2% |
N/A |
N/A |
|
Sir Lanka Study (Typical Observed) |
14% |
N/A |
25% |
NA |
| Source/Site | Rebar | Struc. Steel | Bricks | Tiles |
|---|---|---|---|---|
|
Kenya Site Average (Practical) |
3.5-5% |
10-15% |
2-3% |
4-10% |
|
IS 1200/456 (India) |
3-5% |
10-15% |
5% |
10% |
|
UK Practice (Ready Mix,block) |
N/A |
N/A |
3-5% |
N/A |
|
Sir Lanka Study (Typical Observed) |
7% |
N/A |
14% |
10% |
Entities Impacted Most by Allowable Wastage
Persons:
Project Managers
Quantity Surveyors
Site Engineers
Storekeepers
Organizations:
Contractors/Builders
Material Suppliers
Regulatory Bodies (NCA, KEBS in Kenya)
Products:
Ready-mix concrete
Pre-cut steel
Modular bricks/blocks
Places:
Urban construction sites (Nairobi, Mombasa)
Rural and peri-urban sites (with higher logistical risk)
Understanding and Reducing Material Wastage: Practical Insights
In my experience on sites across Nairobi and Kisumu, controlling wastage starts from procurement and ends with after-action reviews. Here’s what works:
Key Practical Steps to Minimize Wastage
Material scheduling: Avoid premature deliveries.
Proper storage: Protect from rain, theft, contamination.
Training labor: Especially on cutting and mixing.
Efficient site logistics: Reduce on-site travel distance.
Adopting precast/precut elements: Reduces offcuts.
Regular waste audits and tracking: Monthly log reviews.
Clear labeling and quantification: Prevents double handling and misplacement.
Related Questions
Q: How does allowable wastage affect project cost?
A: Even a 1% material overrun can cause big cumulative budget overruns on large projects. For example, 5% wastage in rebar on a 10-ton order is 500kg extra steel—often overlooked in budgets.
Q: Are there standards for allowable wastage globally?
A: Yes, but they vary. Indian Standards (IS codes), British Standards, and local regulations (e.g., NCA guidelines in Kenya) provide starting points, but always check your contract.
Q: Can I claim extra payment for wastage above the allowable?
A: Only if additional wastage results from client-requested changes or exceptional circumstances; otherwise, the contractor absorbs the cost.
Formula for Calculating Wastage
Here’s the commonly used formula for percentage wastage:
Track actual site figures using monthly site returns or inventory logs.
Major Factors Influencing Wastage on Kenyan Sites
Inadequate supervision
Poor weather (rainy season damages)
Substandard storage facilities
Untrained labor force
Unexpected project design changes
Example: Wastage Management on a Kenyan High-rise Project
On a recent multi-storey office project in Nairobi, we reduced tile wastage from 10% to under 5% by:
Ordering a mix of modular sizes to minimize cuts
Allocating a “wastage bin” onsite for reusable offcuts
Appointing a tile “champion” among the fixers, responsible for optimizing use
Impact of Wastage on Cost Overruns
| Material | Average Unit Price (KES) | 5% Wastage Cost per Ton |
|---|---|---|
| Cement | 9,500 | 475 |
| Steel | 100,000 | 5,000 |
| Sand | 2,500 | 125 |
| Bricks | 10 | 0.5 |
Data based on current Nairobi market averages. Even small percentages add up exponentially on large orders.
Related Questions Included in Each Section:
What are allowable wastage percentages by material?
How do you measure wastage on site?
How do these values affect project cost and supply chain integrity?
What entities are most involved in material wastage management?
How can site teams proactively reduce wastage within allowable limits?
How can you practically reduce wastage on site?
Train your workforce on precise cutting, mixing, and stock management.
Store materials properly—in sheds, raised pallets, or covered yards.
Schedule “just-in-time” delivery for sensitive materials like cement and reinforcement steel.
Use modular products to reduce cut-offs, especially tiles and bricks.
Regularly audit material usage against project targets.
Who is responsible for controlling wastage on a construction site?
Site Engineer: Daily monitoring, immediate action on bad practices.
Quantity Surveyor: Monthly reporting, loss investigation.
Project Manager: Policy, staff training, and major procurement decisions.
Contractors and Subcontractors: Implementation and accountability.
Troubleshooting and Solution Guide
| Problem | Possible Cause | Solution |
|---|---|---|
| Excess cement wastage | Poor storage/rain | Use watertight sheds, maintain FIFO inventory |
| High sand/aggregate loss | Windblown/ground spill | Stack on raised beds, cover, reduce handling transfers |
| Rebar wastage >5% | Cutting errors | Pre-plan cutting lengths, train steel fixers, use offcut mapping |
| Tile breakage >10% | Bad handling/cutting | Deliver pallets close to workface, use tile saws, mix sizes |
| Over-ordering concrete | Poor estimation | Use digital quantity surveying, batch in small loads |
Frequently Asked Questions
What is considered “wastage” in different materials, and why does it differ?
Wastage varies because each construction material faces unique site conditions and handling practices. Cement can spill or get wet. Concrete often sticks to mixers or forms. Sand and aggregates are prone to losses from wind, improper storage, or over-handling. Steel and tiles mostly waste through cutting and breakage. The acceptable percentage depends on local standards, practical experience, and project specifications.
Are there international or Kenyan standards governing material wastage?
Absolutely. While Kenyan contractors often refer to guidelines from entities like NCA (National Construction Authority) or standards such as KEBS (Kenya Bureau of Standards), many projects also use Indian Standards (IS 1200 for measurement, IS 456 for concrete), and sometimes British Standards, depending on the project owner or consultant's requirements. Always confirm with your contract documents and project specs for precise figures.
Is there a digital tool/technology for monitoring wastage?
Yes! Modern sites use inventory and site management software to track deliveries and consumption—giving alerts for abnormal wastage rates and helping automate documentation for audits or claims. Kenyan firms are increasingly adopting these solutions, some with mobile apps for on-the-go recording.
Does allowable wastage change for prefab or modular construction?
Absolutely. Prefabricated approaches tend to have much lower wastage—sometimes under 1%—due to factory-controlled processes and just-in-time delivery.
Can cost savings from reducing wastage be quantified easily?
Yes. As shown in the previous cost impact tables, reducing even 2–3% wastage on high-volume, costly materials like steel or cement can mean hundreds of thousands of shillings on larger Kenyan commercial projects alone.
