Hidden CO₂ traps on the construction site

Most people are familiar with A4 transport emissions. Fewer have an overview of what actually drives the A5 budget. Looking at a typical distribution of total A4+A5 consumption, the picture is surprising:

Item	Typical share	kg CO₂e/m²/year
Construction waste	~38%	0.536
Fuel (machinery)	~11%	0.157
Electricity	~10%	0.143
Heating (drying, site huts)	~6%	0.081
Waste hauling	~4%	0.06
Soil hauling	~4%	0.06

Waste and energy together account for approximately 65% of the total budget. This is where the real savings lie — and where most surprises occur. See our complete BR18 A4-A5 guide for the full overview.

BR18 Annex 2, Table 11 defines emission factors for 15 waste fractions. The difference between the mildest and harshest factor is enormous — a factor of 74:

Fraction	kg CO₂e/kg
Plastic	5.17
PVC	4.95
Glass	2.02
Iron/metal	1.97
Stone wool	0.69
Glass wool	0.69
Cardboard packaging	0.44
Unglazed brick	0.36
Sanitary/tiles	0.36
Fibre cement board	0.33
Gypsum	0.33
Natural stone	0.29
Concrete	0.17
Wood	0.14
Asphalt	0.07

Plastic has a factor of 5.17 kg CO₂e/kg. Asphalt sits at 0.07. That difference is crucial to understand, because it is directly linked to the most common mistake in waste management.

BR18 has one non-negotiable rule for unsorted waste: if you mix fractions in one container, the entire container's weight must be calculated using the highest emission factor among the mixed materials.

In practice: If there is a single piece of plastic film in a container of concrete and wood, the entire container — all weight — must be calculated using the plastic factor of 5.17 kg CO₂e/kg. Not the 0.17 for concrete or 0.14 for wood.

A calculation example: A 5-tonne mixed container with plastic in the mix:

• Mixed: 5,000 kg × 5.17 = 25,850 kg CO₂e
• Sorted (assume 80% concrete, 15% wood, 5% plastic): 4,000 × 0.17 + 750 × 0.14 + 250 × 5.17 = 680 + 105 + 1,293 = 2,078 kg CO₂e

The difference is over a factor of 12. Sorting is not just good environmental practice — it is a pure mathematical necessity for staying within the limit.

Energy accounts for approximately 27% of the total A4+A5 budget (electricity, heating, and fuel combined). The two largest individual energy items in A5 are often:

Construction drying

New construction during winter months requires drying of concrete structures, floors, and walls. Gas heaters, heat cannons, and dehumidifiers can run for weeks — with massive energy consumption. Drying alone can account for 15-25% of the entire A5 budget.

Site huts and temporary facilities

Heating of crew cabins, office containers, and drying rooms is a constant cost running from day one to project completion. On large projects with site camps for 50-100 workers, the heating consumption can be considerable — and it is easy to forget because it is not tied to a visible construction activity.

Both items must be documented with actual energy consumption (electricity and heating are mandatory measured data in BR18). Standard values cannot be used for these.

The good news: precisely because waste and energy make up such a large part of the budget, there are significant savings to be gained with relatively simple measures:

Waste

• Strict source sorting from day one. Set up dedicated containers for the heaviest fractions (concrete, wood, metal, gypsum, plastic). Monitor continuously.
• Minimize packaging. Agree with suppliers to deliver materials with minimal packaging — or have packaging returned.
• Training for everyone on site. Subcontractors, tradespeople, and apprentices need to know that mixed waste costs in the CO₂ budget.

Energy

• Connect permanent electricity and heating early. Avoid temporary diesel generators and gas heaters for as long as possible.
• Heat pumps in site huts instead of electric radiators — halves the heating consumption.
• Weather protection. Tent covering and temporary closure of the building envelope significantly reduces the need for drying.
• Electrification of machinery. Smaller machines (mini excavators, compressors) are available in electric versions. Eliminate diesel where possible.

The hidden CO₂ traps are only hidden if you don't measure them. The key is systematic tracking:

• Record waste weighing slips continuously — not at project completion. Receiving facilities issue weigh slips per fraction; use them.
• Read electricity meters monthly and document consumption. Ideally separate construction site vs. site huts.
• Keep fuel receipts separate for machines above and below 1 tonne.
• Use a tool with continuous compliance tracking. A static spreadsheet updated at project completion will not reveal overruns in time.

A45 lets you upload weigh slips, energy data, and fuel receipts continuously and see the current status against the limit in real time. See our practical guide to data collection for the full checklist.