Functional and Declared Units

Understanding Units in Building Life Cycle Assessment (LCA) and EPDs

In Life Cycle Assessment (LCA), the functional unit defines the core function of a product or system, while the declared unit represents the amount of the product being assessed. Essentially, the functional unit measures what a product does (its function), and the declared unit measures how much of the product is being considered.

Functional Unit

• This focuses on the performance or service a product provides.
• It answers the question: "What does this product do?"
• Functional units are typically used when the EPD includes the product's use phase, showing how it performs in its intended application.

Examples:

• For insulation, a functional unit might be "providing a thermal resistance of 1.5 m²K/W for 50 years over 1 m²." This tells us how well the insulation performs over its lifespan.

Declared Unit

• This focuses on the quantity of the product itself.
• It answers the question: "How much of this product are we talking about?"
• Declared units are used when the product's function in the building is unclear (it might have multiple uses), or when the LCA doesn't cover the entire product lifecycle (e.g., just manufacturing).

Example:

"1 kg of insulation" or "1 m² of 50 mm thick insulation."

In simpler term, think of the functional unit as measuring the effectiveness of the product and of the declared unit as measuring the amount of the product.

Which units does SustainCap LCA Support?

Product Level

You have flexibility. One Click LCA allows you to choose the unit that best suits your product and the lifecycle stages you're assessing.

Rules for Defining a Functional Unit (FU)

The FU must reflect the *primary function* of the product system in measurable terms. Key rules include: 

1. Based on Performance, Not Just Quantity

Must represent “what the product does”, not just its physical amount. 

   - ✅ Correct:   “One LED bulb "Providing 1,000 hours of light at 800 lumens." 

   - ❌ Incorrect: "One LED bulb" (does not account for performance). 

2. Quantifiable & Measurable** 

   - Must be expressed in clear, measurable units (e.g., km driven, m² covered, years of service). 

   - Example: 

     - Paint: "Coverage of 10 m² for 5 years with 95% opacity.

     - Washing Machine : Cleaning 5,000 kg of laundry at 30°C.

3. Comparable Across Alternatives

   - Enables fair comparison between competing products. 

   - Example: 

     - Beverage Containers: "Storage and delivery of 1 liter of liquid for 12 months. 

Rules for Defining a Declared Unit (DU)

The DU is a “fixed reference quantity” used for reporting impacts (e.g., in EPDs). Key rules include: 

1. Standardized & Consistent

   - Typically follows industry norms (e.g., per kg, per m², per unit). 

   - Example: 

     - Concrete: "1 cubic meter (m³) of C30/37 grade." 

     - Packaging: "1,000 units of 500 mL PET bottles." 

2. Clearly Defined Boundaries** 

   - Must specify if it includes: 

     - Only the product ("cradle-to-gate") 

     - Full lifecycle ("cradle-to-grave") 

   - Example: 

     - Steel Beam: 1 ton, cradle-to-gate (A1-A3).

 

 

Examples of Functional Units

1. Wall Paint: "To cover 1 m² of interior wall surface for 10 years with stain-resistant paint."
2. Thermal Insulation: "To prevent the loss of 1 kWh of heat through 1 m² of roof area over 50 years."
3. Packaging: "To package and transport 1 kg of apples over 100 km without damage."
4. Lighting: "To provide 1000 lumens of light for 10,000 hours using an indoor lighting system."
5. Passenger Transport: "To transport one person for 1 km in an urban area during peak traffic within one hour."

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Examples of Declared Units

1. Aluminum Sheets: "1 kg of aluminum sheet produced at Egyptalum facility."
2. Ceramic Tiles: "1 m² of ceramic tile with 10 mm thickness."
3. Plastic Pipe: "1 linear meter of PVC pipe with 50 mm diameter."
4. Ready-Mix Concrete: "1 m³ of ready-mix concrete grade C30/37 produced at Plant X."
5. Industrial Paint: "1 liter of acrylic paint for indoor use."