UK12• Avoid the angle at the top of a pitched ceiling:Horizontal distance from peak.Figure 6• Avoid ‘closed’ rooms or cupboards if you are only fitting one or a few detectors. Ifyou are going to fit several detectors then put one in each room where the door isnormally closed.• Avoid spaces where there is a lot of dust. Dust may accumulate on and within thedetector, and prevent smoke reaching the sensor.900mm

Eaton DET-RSMOKE Manual