Requirement Summary
This measure refers to U-value as the indicator of performance, in which the use of insulation improves the U-value. The measure can be claimed if the U-value of the external walls is lower than the base case U-value listed in the Key Assumptions for the Base Case in the Design section. The user must select the measure for ‘Insulation of the External Walls’ in the Energy tab in all cases except when the measure is not marked with an asterisk, or when the project U-value is better than the baseline and a project chooses not to take credit for it (an auditor must verify this).
The actual U-value of the wall should be entered in the software by selecting the measure for ‘Insulation of External Walls’ in the Energy tab. For multiple exterior wall types with different U-values, use an area-weighted average.
Note: The measure for ‘Wall Insulation’ should also be selected in the Materials tab, and the actual insulation type and thickness entered.
Intention
Insulation is used to prevent heat transmission from the external environment to the internal space (for warm climates) and from the internal space to the external environment (for cold climates). Insulation aids in the reduction of heat transmission by conduction, so more insulation implies a lower U-value and better performance. A well-insulated building has lower cooling and/or heating energy requirements.
Please note that many modern insulating materials, such as certain foam-based insulations, as well as air cavities that improve the sustainability and energy efficiency of buildings also spread fire more easily than traditional materials such as concrete and wood. The project team is encouraged to take proper fire safety precautions in the selection of these materials and the associated design details such as fire stops.
Approach/Methodologies
This measure uses U-value, which is defined as the quantity of heat that flows through unit area in unit time, per unit difference in temperature; it is expressed in Watts per square meter Kelvin (W/m²K). U-value is an indication of how much thermal energy (heat) is transmitted through a material (thermal transmittance). The U-value, which is the performance indicator of this measure, is the reciprocal of the total thermal resistance (1/∑R) of the external walls, which is calculated from the individual thermal resistance of each component/layer of each external wall.
If the default improved case is used (as shown in EDGE as the top insulation material in the dropdown), the design team must demonstrate that the U-value of the external walls does not exceed the U-value assumed by EDGE. This can be obtained by the manufacturer or by the “simple method” calculation, which is explained as follows. If a different U-value for the external walls is used, then it must be calculated with the following formula or in accordance with the “combined method” given in ISO 6946.
Simple method of calculating the U-value:
Where:
Rsi = Resistance of air layer on the inner side of the external wall (add constant of air)
Rso = Resistance of air layer on the external side of the external wall
R1, 2 etc. = Resistance of each layer material within the external wall
The resistance of a wall material is derived by the following formula:
Where:
d = Thickness of the layer of material (m)
= Thermal conductivity in W/m K
As seen in the formula above, the insulating capacity is a direct function of the thickness of the material. Table 22 demonstrates how to achieve a U-value of 0.45W/m² K for a certain thickness. The actual thickness required will depend on many other factors, including the fixing method, wall construction, and the position of the insulation within the material layers.
Table 22: Thickness of insulation required to achieve a U-value of 0.45 W/m² K
EDGE provides a built-in calculator for calculating the U-value of a wall with multiple layers of materials next to each other. For more complex assemblies, for example, if the materials are not in continuous layers or metal penetrations punctuate the wall, dedicated U-value calculation software or energy modeling software can also be used.
Potential Technologies/Strategies
Insulating the external walls is potentially the most cost-effective way to reduce the energy used for heating a building. Therefore, in cold or temperate climates a strong case can be made for maximizing the insulation before designing the heating ventilation and air conditioning equipment. In hot climates insulating the wall can reduce heat gain, but the effect is relatively minor.
Different types of insulation are available, and the appropriate type will depend on the application as well as cost and availability. Insulation types can be grouped into four main categories, as shown in Table 23:
Table 23. Insulation types and typical conductivity range
Auditors and reviewers can use the range of thermal conductivity to check for reasonableness of the project team’s claims about insulation properties. The range can also be applied as a substitute in the rare case when manufacturer data is not available.
Relationship to Other Measures
Selecting this measure will show an increase in the environmental impact in the materials section due to the addition of insulation material (reflected as a negative percentage impact).
By increasing the level of insulation, the heating and/or cooling loads will be reduced. Increasing the levels of insulation could therefore reduce the cost and environmental impact of the heating and cooling plant.
If this measure is not selected, which assigns the Wall a U-value, a U-value will be assigned to the wall via the selection of the Exterior Wall Material. Changing the wall material will change the heat transfer through the wall which will impact the building’s energy use.
Assumptions
The base case insulation assumed in the roof varies by building type and location. The base case U-value can be seen in the Advanced Settings: Key Assumptions for the Base Case in the Design tab. The default value for the improved case is that the actual U-value is better (lower) than the base case listed in the Key Assumptions.
Compliance Guidance
To claim this measure, it is necessary to demonstrate that the U-value of the complete external walls specification is better (lower) than the base case as listed in the Key Assumptions for the Base Case in the Design section. If the EDGE default for the improved case U-value is used, then it is only necessary to demonstrate that insulation has been or will be installed, and that the U-value of the External Walls does not exceed the base case.
If a user-input U-value exceeds the default improved case value, then it is necessary to confirm that the U-value has been calculated in accordance with the “simple” or “combined” method as shown in the Approach/Methodologies above.
| 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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Since the insulation material will not be visible at the post-construction stage, it must be demonstrated that the insulation material specified at the design stage was delivered to the site. The following must be used to demonstrate compliance:
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