Why do I fail the Criterion 2 U-value Check?
Why does my construction fail the U-value check? My constructions have U-values which meet or are superior to those within ADL2A.
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Clearly the first step is to double check the constructions in use are using an EN-ISO U-value within the limits of Table 4 in ADL2A.
However, the most common reason for failure is in fact due to the room type for each space being incorrectly assigned.
In Compliance there are 5 room types:
- Heated room.
- Unheated roof.
- Glazing cavity.
- Unheated buffer space.
- Internal void or warm roof.
In the case of unheated roof, glazing cavity and unheated buffer space, all representing types of unheated buffer spaces, then an external ventilation rate must also be defined for the purpose of the Criterion 2 U-value calculation.
Selection of these room types is critical. The unheated roof and buffer space require a layer of insulation to be present between them and the adjoining heated room. Commonly users forget to include this insulation layer and therefore they are using constructions which would be fine for use between heated rooms only.
An example is an internal partition which is still classified as this between an unheated buffer space and heated room but now requires insulation in order to pass the U-value check as it is a cold room adjoined to warm room.
The best way to think about which spaces should be assigned the unheated space options is to mark down all the spaces outside the insulation envelope. The insulation envelope can cross between floors, ceilings, roofs, external walls, internal partitions doors and windows so users must be aware of the correct assignment in all of these categories.
