Fire detector spacing calculator
Detector spacing and count for a room or corridor.
Inputs
Worked example with the default inputs. The live calculator replaces it when the page loads.
- Detector type
- Point-type smoke detector
- Room length
- 20 m
- Room width
- 12 m
- Corridor
- No
- Beams or joists on the ceiling
- No
Detectors, lines or beams
4
- Spacing along
- 10m
- Spacing across
- 10m
- Greatest distance from a wall
- 5m
- Setback from the wall used in the layout
- 5m
- Limit on the distance from a detector, line or beam
- 7m
- Worst distance this layout leaves
- 7.07m
- Grid
- 2 by 2
- Floor area
- 240m²
This result is a design aid. Verify it against the current standard.
Calculation steps
- Spacing along the room10mNZS 4512:2010 Cl 405.3
- Spacing across the room10mNZS 4512:2010 Cl 405.3
- Greatest distance from a wall5mNZS 4512:2010 Cl 405.3
- Setback from the wall used in the layout5mNZS 4512:2010 Cl 405.3
- Limit on the distance from a detector, line or beam7mNZS 4512:2010 Cl 405.3
- Worst distance this layout leaves7.07mNZS 4512:2010 Cl 405.3
- Floor area240m²
- Detectors, lines or beams4NZS 4512:2010 Cl 405.3
- Distance from the apex of a sloping roof500mmNZS 4512:2010 Cl 405.3
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
What does the detector spacing tool do?
The tool reports the spacing between detectors, the greatest distance from a wall where the clause states one, and the grid and count for a room or corridor. For point heat detectors it also applies the coverage rule of one detector for each 30 square metres of floor area.
What is the spacing for smoke and heat detectors?
NZS 4512:2010 Clause 405.3 gives 6 m between point heat detectors and 3 m from a wall, or 9 m and 4.5 m in a corridor. Point smoke detectors are 10 m apart and 5 m from a wall. Smoke beams are 14 m apart. Line heat detectors are 8 m apart.
Why does the tool say the spacing misses the 7 m rule?
Clause 405.3.3 gives 10 m between point smoke detectors and 5 m from a wall, and it also holds every point within 7 m of a detector. A full 10 m grid leaves a corner 7.072 m away, so AmpSize measures the layout and tells you to close the spacing.
How do beams and joists change the layout?
Clause 405.2.1(m) reduces the spacing across the beams to two thirds where the beams are 100 mm or deeper. Where the depth is over 460 mm and the spacing is over 2400 mm, each beam acts as a wall. The normal spacing then applies inside every bay.
How large can a zone be?
AmpSize compares the floor area with the 750 square metre zone limit of NZS 4512:2010 Clause 401.2.3 and warns you where the area is above it. Four cases in that clause raise the limit to 900 or 2000 square metres. Read the clause and check them.