Intention
To select a window frame specification with a lower embodied energy than the typical specification. The window frame specification matching the actual building design must be entered in the software.
Approach/Methodologies
The design team must select the specification that most closely resembles the windows specified. Where there are multiple specifications the predominant specification must be selected.
Potential Technologies/Strategies
The following is a list of the specifications included in EDGE. The user must always try to select the specification that most closely resembles that of the building design.
| Aluminum | The two metals typically used for window frames are aluminum or steel. Aluminum is lighter weight and does not rust like a ferrous metal such as steel, but the embodied energy is much higher. The advantage of using metal window frames is that they are strong, light and require less maintenance than other materials used for window frames. However as metal conducts heat very well, the thermal performance of metal windows is not as good as other materials. To reduce heat flow and U-Value, metal frames can include a thermal break between the inside and outside of the frame. |
| Steel | The two metals typically used for window frames are aluminum or steel. Aluminum is lighter weight and does not rust like a ferrous metal such as steel, but the embodied energy is much higher. The advantage of using metal window frames is that they are strong, light and require less maintenance than other materials used for window frames. However as metal conducts heat very well, the thermal performance of metal windows is not as good as other materials. To reduce heat flow and U-Value, metal frames can include a thermal break between the inside and outside of the frame. |
| Timber | Timber window frames insulate relatively well, but they also expand and contract in response to weather conditions. Timber frames can be made from either softwood or hardwood. Softwood frames are much cheaper, but are likely to require more regular maintenance. The maintenance required can be reduced by using aluminum or vinyl cladding. |
| uPVC | uPVC window frames are made of extruded polyvinyl chloride (PVC) with ultraviolet light (UV) stabilizers to keep sunlight from breaking down the material. uPVC window frames are low maintenance as they do not require painting. If the cavities of uPVC frames are filled with insulation, they have very good thermal performance. |
| Aluminum Clad Timber | Aluminum cladding is fixed to wooden framing members with a space for ventilation purposes. Timber and aluminum have high embodied energy. The extruded aluminum sections are designed for strength and rigidity, to prevent deformation at the fastening points. Often used in commercial applications, these windows are also suitable for residential applications where low maintenance is important, such as social housing and high-rise developments. |
| Re-Use of Existing Window Frames | Re-using an existing material avoids the use, and therefore embodied energy, of new materials. The re-use of existing materials option in EDGE is highly desirable and assigned an embodied energy value of zero. The material must be verifiably more than five years old to be classified as re-used. The material does not have to have been sourced from the project site. |
Relationship to Other Measures
The choice of window frame material will have an impact on thermal performance. EDGE does not directly take account of this as it is already reflected in the manufacturer’s calculation of the window U-value.
Assumptions
The default assumption is that window frames are aluminum.
Compliance Guidance
| Design Stage | Post-Construction Stage |
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At the design stage, the following must be used to demonstrate compliance:
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At the post-construction stage, the following must be used to demonstrate compliance:
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