Technical Booklet E Fire Safety·Page 45·2.29
Smoke and heat alarm positioning requirements
Alarms must be positioned either on ceilings at least 300 mm from walls or on walls 150-300 mm from the ceiling, at least 300 mm from heaters or air conditioning, on surfaces at ambient temperature, and easily accessible.
A smoke alarm or heat alarm should be located so that it is – (a) either on a ceiling and not less than 300 mm from a wall or light fitting, or where designed for wall mounting on a wall and not less than 150 mm, or more than 300 mm from the ceiling and the sensitive element should not be below the level of a door opening; (b) not less than 300 mm from, and not directly above, a heater or an air conditioning ventilator; (c) on a surface which is normally at the ambient temperature for the space it bounds; and (d) easily and safely accessible.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet E - Fire Safety.pdf