Technical Booklet F2 Conservation of Fuel and Power in Buildings Other Than Dwellings·Page 54·3.35
High U-Value Windows and Doors Replacement
Existing windows (except display windows) or doors (except high usage entrance doors) with U-values greater than 3.3 W/(m2.K) that separate conditioned from unconditioned spaces must be replaced.
Where any existing window (excluding display windows but including roof windows or rooflights) or door (excluding high usage entrance doors) that separates a conditioned space from an unconditioned space (or the external environment) has a U-value greater than 3.3 W/(m2.K) it should be replaced in accordance with the provisions given in paragraphs 3.57 to 3.64.
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