Calculating a BREEAM (Building Research Establishment Environmental Assessment Method) rating involves a systematic assessment of a building's environmental performance across various sustainability categories, culminating in a final percentage score that translates into a recognized sustainability rating.
What is BREEAM?
BREEAM is the world's leading sustainability assessment method for masterplanning projects, infrastructure, and buildings. It evaluates the environmental performance of buildings and aims to encourage best practice in sustainable design, construction, and operation. A BREEAM rating provides an independent measure of a building's environmental quality, offering valuable assurance to investors, developers, and occupants.
The BREEAM Calculation Process
The calculation of a BREEAM rating follows a clear, step-by-step methodology, moving from individual criteria to an overall building performance score.
1. Understanding BREEAM Categories and Credits
BREEAM assessments are structured around a series of environmental impact categories, each encompassing several specific criteria. These categories typically include:
- Management: Covering commissioning, site management, and responsible construction practices.
- Health & Wellbeing: Addressing indoor air quality, thermal comfort, lighting, and noise.
- Energy: Evaluating energy consumption, efficiency, and carbon emissions.
- Water: Assessing water consumption and efficiency within the building.
- Materials: Focusing on responsible sourcing and life-cycle impacts of materials.
- Waste: Promoting waste reduction, recycling, and responsible waste management.
- Land Use & Ecology: Considering the ecological value of the site and biodiversity enhancement.
- Pollution: Managing sources of pollution such as refrigerants, NOx emissions, and surface water runoff.
- Transport: Encouraging sustainable transport options and reducing car dependency.
- Innovation: Recognizing exemplary performance and innovative solutions beyond standard BREEAM requirements.
Within each of these categories, specific criteria are set, and for each criterion met, a building can earn a certain number of credits. For example, in the 'Energy' category, a building might earn credits for installing highly efficient lighting or utilizing renewable energy sources.
2. Achieving Credits
A certified BREEAM Assessor meticulously evaluates the building's design and construction (or operational performance for existing buildings) against the defined criteria within each category. Evidence is gathered to demonstrate compliance, and credits are awarded based on the extent to which these criteria are met. Each category has a maximum number of credits available.
3. Calculating Category Scores
Once the credits within each category have been determined, the assessor calculates the category score. This score reflects the percentage of available credits achieved within that specific category. For instance, if a category has a maximum of 10 credits and the building achieves 7, its raw score for that category would be 70%.
4. Applying Category Weightings
Not all environmental impacts are considered equal in their importance. To reflect this, each BREEAM category is assigned a specific weighting. These weightings can vary slightly depending on the specific BREEAM scheme (e.g., New Construction, Refurbishment, In-Use) and version, but they ensure that the final score prioritizes areas of greater environmental significance.
Here's an example of typical category weightings (these are illustrative and can vary):
| BREEAM Category | Illustrative Weighting (%) |
|---|---|
| Management | 12 |
| Health & Wellbeing | 15 |
| Energy | 19 |
| Water | 6 |
| Materials | 12.5 |
| Waste | 7.5 |
| Land Use & Ecology | 10 |
| Pollution | 10 |
| Transport | 8 |
| Total | 100 |
Note: Innovation credits are added to the final score after the weighted sum.
To arrive at the category's contribution to the overall building score, the category score is then calculated according to the number of credits achieved and its category weighting. This means the percentage of credits achieved in a category is multiplied by its respective weighting. For example, if a building achieved 70% of the credits in the 'Energy' category (which has a 19% weighting), its weighted score for Energy would be 0.70 * 0.19 = 0.133 or 13.3%.
5. Determining the Overall BREEAM Rating
The final performance rating is determined by summing the weighted category scores across all assessed categories. Any additional Innovation credits achieved are then added to this sum. This yields a total percentage score for the building.
For instance, if the sum of all weighted category scores (plus Innovation credits) totals 75%, the building receives a BREEAM rating corresponding to that percentage.
BREEAM Rating Tiers
The final percentage score directly correlates to one of the following BREEAM ratings:
| BREEAM Rating | Percentage Score |
|---|---|
| Pass | ≥ 30% |
| Good | ≥ 45% |
| Very Good | ≥ 55% |
| Excellent | ≥ 70% |
| Outstanding | ≥ 85% |
These ratings provide a clear benchmark of the building's environmental performance, ranging from a basic Pass to the highest standard of Outstanding.
The Role of the BREEAM Assessor
A BREEAM Assessor plays a crucial role throughout this entire process. They are trained and licensed professionals responsible for:
- Guiding project teams on BREEAM requirements.
- Collecting and verifying evidence of compliance.
- Performing the detailed assessment and calculation.
- Submitting the assessment report to BRE Global for quality assurance and certification.
Their expertise ensures the accuracy and integrity of the BREEAM rating. For more detailed guidance, refer to the official BREEAM website.
