Requirement Summary
This measure refers to the U-value or thermal conductivity of materials as the indicator of performance, in which the use of insulation improves the U-value. The user must select the measure for ‘Insulation of the Roof’ 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 U-value must be entered following the guidelines in the Approach/Methodologies section.
Note: The measure for ‘Roof insulation’ must also be selected in the Materials tab, and the actual insulation type and thickness entered.
Savings from the measure can be claimed if the U-value of the roof is lower than the base case U-value listed in the Key Assumptions for the Base Case in the Design section.
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 compared to 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 a 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 roof, which is calculated from the individual thermal resistance of each component/layer of the roof.
If the default improved case is used, the design team must demonstrate that the U-value of the roof does not exceed the U-value assumed by EDGE (see assumptions below). This can be obtained by the manufacturer or by the “simple method” calculation, explained as follows. If a different U-value for the roof is used, then it must be calculated with the following formula or in accordance with the “combined method” given in ISO 6946. For multiple roof types with different U-values, use an area-weighted average.
Simple method of calculating the U-value:
Where:
Rsi = Resistance of the air layer on the inner side of the roof (add constant of air)
Rso = Resistance of the air layer on the external side of the roof
R1,2 etc. = Resistance of each material layer within the roof
The resistance of a roof 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 20 demonstrates how to achieve a U-value of 0.45W/m² K, with the thickness of certain insulation materials indicated. The actual thickness required will depend on many other factors, including the fixing method, roof construction and position of the insulation within the material layers.
Table 20: Thickness of insulation required to achieve a U-value of 0.45 W/m² K
Source: Insulation Materials Chart, Energy Savings Trust, 2004.
EDGE provides a built-in calculator for calculating the U-value of a roof with multiple layers of materials layered on top of each other. For more complex assemblies, for example, if the materials are not in continuous layers or metal penetrations punctuate the roof, dedicated U-value calculation software or energy modeling software can also be used.
Potential Technologies/Strategies
Insulating the roof is potentially the most cost-effective way to reduce the energy used for heating a building. Therefore, in cold or temperate climates there is a strong case for maximizing the insulation before designing the heating ventilation and air conditioning equipment. In hot climates insulating the roof 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 21.
Table 21. Insulation types and typical conductivity range
The range of thermal conductivity can be used by auditors and reviewers to check for reasonableness of the project team’s claims about insulation properties. It can also be used 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 percent improvement).
However, 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, leading to energy savings that more than compensate for the negative impacts in the materials section.
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 savings from this measure, it is necessary to demonstrate that the U-value of the complete roof 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 its U-value does not exceed the default improved case value. The U-value is the reciprocal of the sum of the R-values for each component of the roof structure.
If a U-value has been entered that exceeds the improved case, then it is necessary to confirm that the U-value was calculated in accordance with the “combined method” given in ISO 6946 as shown in the Approach/Methodologies above.
| Design Stage | Post-Construction Stage |
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At the design stage, the following evidence 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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