Technical Booklet F1 Conservation of Fuel and Power in Dwellings·Page 30·2.43
Limiting External Doors and Glazed Openings
The total area of external doors and glazed openings in a dwelling should not exceed 25% of the floor area, to reduce heat losses and limit excessive heat gain.
To reduce heat losses and help limit excessive heat gain, the limiting extent of external doors and glazed openings in a dwelling should be no greater than 25% of the floor area of the dwelling.
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