6.3 Windows, Insulation & Customized Materials
Key Takeaways
- Aluminum window frames without a thermal break have a high embodied energy (approx 700-1,000 MJ/m² of frame area) compared to thermally broken aluminum or uPVC frames (approx 315-420 MJ/m²).
- Secondary (recycled) aluminum production consumes only about 5% of the primary smelting energy, reducing frame embodied carbon by up to 95%.
- Stone wool (rockwool) insulation has an embodied energy of approximately 16-24 MJ/kg, while expanded polystyrene (EPS) ranges from 80-100 MJ/kg and extruded polystyrene (XPS) ranges from 90-110 MJ/kg.
- The EDGE App Customized Materials Workflow allows project teams to override default dataset values by submitting third-party verified EPDs or manufacturer-declared primary energy demand figures.
- In the EDGE App, customized materials require entering material density (kg/m³), thickness (m), and primary energy demand per unit mass (MJ/kg) into the software interface alongside audit evidence.
6.3 Windows, Insulation & Customized Materials
Exam Focus: Understanding the embodied energy trade-offs in glazing and insulation selection, and mastering the step-by-step EDGE App Customized Materials Workflow—including density, thickness, and EPD input parameters—is essential for passing the EDGE Expert exam and executing advanced project submissions.
While heavy structural elements dominate total material mass, specialized architectural components—such as window framing, glazing units, and thermal insulation materials—exhibit extremely high energy intensity per unit mass ($MJ/kg$). Optimizing these assemblies requires balancing their initial embodied energy against their operational energy performance over the building lifecycle.
Window Assemblies & Glazing Material Selection
Window performance is evaluated across two tabs in the EDGE App:
- Energy Tab: Evaluates thermal transmittance ($U\text{-value}$ in $W/m^2K$), Solar Heat Gain Coefficient ($SHGC$), and Visible Light Transmittance ($VLT$).
- Materials Tab: Evaluates the embodied energy ($MJ/m^2$) of the window framing material and glass pane configuration.
Window Framing Materials & Embodied Impact
Aluminum is widely specified due to its strength, durability, and narrow profile capability. However, primary aluminum smelting is extremely energy-intensive, consuming approximately 190 to 210 MJ of electrical energy per kg of primary metal.
| Frame Material Type | Primary Energy Demand ($MJ/kg$) | Frame Weight ($kg/m^2$ of window) | Total Frame Embodied Energy ($MJ/m^2$) | Recycled Content Impact |
|---|---|---|---|---|
| Standard Aluminum (No Thermal Break) | $\approx 200\ MJ/kg$ | $3.5 - 5.0\ kg/m^2$ | $\approx 700 - 1,000\ MJ/m^2$ | High baseline embodied energy. |
| Thermally Broken Aluminum Frame | $\approx 175\ MJ/kg$ | $4.0 - 5.5\ kg/m^2$ | $\approx 700 - 950\ MJ/m^2$ | Includes polyamide thermal barrier strip; slightly higher weight, lower thermal conductivity. |
| Recycled Aluminum Frame (80% Recycled) | $\approx 35\ MJ/kg$ | $3.5 - 5.0\ kg/m^2$ | $\approx 120 - 185\ MJ/m^2$ | Secondary aluminum uses 95% less energy than primary smelting. |
| uPVC (Unplasticized Polyvinyl Chloride) | $\approx 70\ MJ/kg$ | $4.5 - 6.0\ kg/m^2$ | $\approx 315 - 420\ MJ/m^2$ | Cuts frame embodied energy by 50-60% vs. primary aluminum. |
| Timber / Engineered Wood Frame | $\approx 15\ MJ/kg$ | $5.0 - 7.0\ kg/m^2$ | $\approx 75 - 105\ MJ/m^2$ | Lowest embodied energy; biogenic carbon storage. |
Glazing Configurations: Operational Savings vs. Embodied Energy
Transitioning from single clear glass to double or triple low-E glass increases the initial embodied energy of the glazing component:
- Single Clear Glass ($6\ mm$): Embodied energy $\approx 150 - 180\ MJ/m^2$.
- Double Glazed Unit (DGU, $6\text{mm} - 12\text{mm Air} - 6\text{mm Low-E}$): Embodied energy $\approx 320 - 380\ MJ/m^2$.
Lifecycle Trade-Off Analysis: Although DGU carries approximately double the embodied energy of single glazing, the operational energy savings achieved by reducing HVAC cooling/heating loads outweigh the embodied carbon penalty within 1 to 3 years of building operation in warm or cold climates.
Thermal Insulation Materials & Energy Intensity
Insulation materials reduce heat transfer through walls and roofs. In EDGE, selecting insulation requires evaluating both thermal resistance ($R\text{-value} = \frac{\text{Thickness}}{k}$) and primary embodied energy per kilogram ($MJ/kg$).
Insulation Material Comparison Table
| Insulation Material | Raw Material Source | Density ($kg/m^3$) | Thermal Conductivity ($\lambda, W/m\cdot K$) | Embodied Energy ($MJ/kg$) | Embodied Energy per $R=1$ ($MJ/m^2$) |
|---|---|---|---|---|---|
| Glass Wool (Fiberglass) | Recycled glass & sand | $15 - 30$ | $0.034 - 0.040$ | $\approx 28 - 35$ | $\approx 16 - 25\ MJ/m^2$ |
| Stone Wool (Rockwool) | Basalt rock & slag | $40 - 100$ | $0.035 - 0.042$ | $\approx 16 - 24$ | $\approx 22 - 38\ MJ/m^2$ |
| Expanded Polystyrene (EPS) | Petroleum monomer | $15 - 30$ | $0.033 - 0.038$ | $\approx 80 - 100$ | $\approx 40 - 60\ MJ/m^2$ |
| Extruded Polystyrene (XPS) | Petroleum monomer | $30 - 45$ | $0.028 - 0.034$ | $\approx 90 - 110$ | $\approx 75 - 105\ MJ/m^2$ |
| Polyurethane (PUR) / Polyisocyanurate (PIR) | Petrochemical foam | $30 - 40$ | $0.022 - 0.026$ | $\approx 100 - 120$ | $\approx 65 - 85\ MJ/m^2$ |
| Cellulose Fiber (Loose Fill) | Recycled newspaper | $30 - 60$ | $0.038 - 0.042$ | $\approx 5 - 8$ | $\approx 6 - 12\ MJ/m^2$ |
The EDGE App Customized Materials Workflow
When a project specifies a novel building material, a locally manufactured low-carbon block, or an assembly not present in the default EDGE dropdown menus, the project team must utilize the Customized Materials Workflow.
Step-by-Step Customization Procedure in the EDGE App
- Select Component Category: Navigate to the Materials tab and locate the target assembly (e.g., External Walls).
- Enable Custom Material Option: Select
"User Defined / Customized Material"from the dropdown list. - Input Physical & Energy Parameters:
- Material Density ($\rho$, in $kg/m^3$): Extracted from manufacturer technical datasheet or laboratory test report.
- Component Thickness ($t$, in meters, $m$): Specified from architectural detail drawings.
- Primary Energy Demand ($PED$, in $MJ/kg$): Extracted from an ISO 14025 / EN 15804 compliant EPD (Cradle-to-Gate Modules A1-A3).
- Calculated Output Verification: The EDGE App multiplies these parameters to determine the total embodied energy per unit floor/wall area:
- Upload Audit Documentation: Attach the verified EPD, product technical specs, and structural quantity takeoffs to the EDGE App project file for Auditor verification.
Secondary (recycled) aluminum production requires approximately what percentage of the energy consumed by primary aluminum smelting?
Which insulation material has the lowest primary embodied energy per kilogram (MJ/kg)?
In the EDGE App Customized Materials Workflow, what formula is used to calculate the embodied energy per square meter (MJ/m²) of a custom wall or insulation layer?
Why is double glazing (DGU) specified in green buildings despite carrying nearly twice the initial embodied energy of single clear glass?