A45 vs. LCAbyg: Two tools — two different jobs

When people ask "A45 or LCAbyg?" there is usually a misunderstanding at play. The two tools don't solve the same problem — they each cover a different part of BR18 requirements.

LCAbyg handles the full life cycle assessment (A1-A3, B4, B6, C3-C4): material production, replacements during use, and end-of-life disposal. A45 handles the construction process (A4-A5): transport to and from the site, and on-site energy and waste.

The confusion arises because both calculations appear in the same BR18 submission. But they are legally and methodologically separate budgets — requiring different data, different methods, and different expertise. See the article on the two separate CO₂ accounts and the BR18 A4-A5 guide for the full picture.

LCAbyg is a free desktop application developed by BUILD (Aalborg University). It is the most widely used LCA tool in Denmark and is broadly recognised by municipalities, consultants, and building owners for the full climate calculation.

What LCAbyg does well

• Covers the full LCA lifecycle: A1-A3 (material production), B4 (replacement), B6 (operational energy), C3-C4 (waste handling and disposal).
• Large library of Danish product data — easy to find familiar materials and building components.
• Free and publicly available to everyone.
• Recognised standard that municipalities expect to see in the full LCA documentation.

Limitations for A4-A5

• A4 transport cannot be calculated inside LCAbyg. This is not a flaw — it is a deliberate scope boundary. You need a separate Excel sheet or a dedicated A4-A5 tool for the transport calculations.
• A5 data (energy use and waste on site) must be entered manually via supplementary files. There is no automatic handling or validation.
• No AI, no invoice scanning, no continuous compliance tracking.
• Desktop-based — no real-time multi-user collaboration.

A note on funding

The Danish Housing Authority withdrew its support for LCAbyg in 2025 due to EU state aid rules. In 2026, LCAbyg is funded by foundations. From 2027, a new funding model must be established. This creates uncertainty about long-term development and support.

A45 is a SaaS platform built specifically for A4-A5 documentation under BR18. Its purpose is to automate the part of the climate calculation that LCAbyg does not handle: transport to and from the site and on-site construction activity.

What A45 does well

• AI invoice scanning: Upload invoices, delivery notes, and fuel receipts. AI extracts materials, weight, distance, and fuel type automatically.
• Automatic BR18 calculation: Calculates A4-A5 according to BR18 Tables 8, 10, and 11 — no manual formulas or cell references.
• Method comparison: Compare measured data, standard values, and EPD data per emission category and automatically select the lowest valid result.
• Real-time compliance tracking: See continuously whether the project complies with the 1.5 kg CO₂e/m²/year limit — and whether the trajectory holds for the 1.3 target in 2027.
• Team collaboration: Invite contractors, subcontractors, consultants, and building owners to the same project. Everyone works in the same data environment.
• Audit trail: Full traceability from data source to calculation result — ready for spot checks by the municipality.

Limitations

• Covers A4-A5 only. For the full LCA (A1-A3, B4, B6, C3-C4), you still need LCAbyg or equivalent.
• Requires a subscription — from 199 DKK/project/month. 14-day free trial, no credit card required.

LCAbyg is an excellent tool for what it was designed to do. But A4-A5 is not its core focus — and that shows in practice.

A4 transport: Calculating transport emissions (truck type, fuel consumption, distance, tonne-kilometres) requires data from invoices, weigh slips, and driver logs. This data cannot be imported into LCAbyg — you need to run the calculations in a separate Excel sheet and then feed the result back into LCAbyg. This creates an extra step with error risk and broken traceability.

A5 data: Energy use (electricity, diesel, natural gas) and waste volumes on site must be entered manually. There is no validation of reasonableness, no benchmarking against comparable projects, and no automatic accumulation as new data comes in over the course of the build.

No ongoing monitoring: You only see the final A4-A5 result when all data has been entered. Are you on track halfway through construction? LCAbyg cannot tell you. See the articles on calculation methods and data collection on site for practical approaches to A4-A5 specifically.

This is not a criticism of LCAbyg — it is a clarification of what it was designed for. For the full LCA, LCAbyg remains the best free choice.

A45 is built for a specific situation — and is especially strong when:

• You are a contractor with A4-A5 documentation responsibility and want to track compliance continuously — not just at handover.
• The project involves many subcontractors and coordinating transport data is a bottleneck.
• You receive large volumes of invoices and delivery notes and want to avoid manual data entry.
• You need an audit trail for spot checks — full traceability from invoice to calculation result.
• The building owner or consultant requires ongoing visibility into A4-A5 status throughout the project.

A45 is not the right choice if you need to produce the full LCA (A1-D). For that, LCAbyg remains the natural solution.

In practice, the most common answer is not "either/or" — it is "both".

The consultant uses LCAbyg to calculate A1-D: the climate footprint of materials, operational use, and end-of-life disposal. The contractor uses A45 to document A4-A5: transport and on-site energy. The two calculations are separate budgets under BR18 — the limits are independent, and neither side can offset the other.

The workflow typically looks like this:

1. The contractor sets up the project in A45 and invites subcontractors.
2. Invoices and delivery notes are uploaded on an ongoing basis — AI extracts and calculates.
3. Compliance is monitored in real time against the 1.5 kg CO₂e/m²/year limit.
4. The consultant exports A4-A5 results from A45 and includes them in the overall BR18 submission alongside the LCAbyg calculation for A1-D.

It is a clear division of labour that plays to each tool's strengths.

The question is not A45 or LCAbyg. It is which parts each tool handles best.

LCAbyg is the right choice for A1-D. It is free, broadly recognised, and covers materials, operations, and disposal in detail. A45 is the right choice for A4-A5. It automates data collection from invoices, calculates according to BR18, and keeps you updated in real time.

For most projects over 50 m² that fall within scope after 1 July 2025, the answer is: both. The consultant takes LCAbyg, the contractor takes A45. The result is a complete BR18 submission — without either party having to handle the part of the calculation they are least equipped for.

Read more in the BR18 A4-A5 guide or try A45 free for 14 days.