Fire alarm system design follows a fixed sequence: collect the project inputs, decide the system type, select a detector for each space and lay it out, place manual call points and notification appliances, divide the building into zones and loops, calculate batteries and voltage drop, build the interface matrix with other systems, and finally prepare the drawings and documents submitted for approval. Each step depends on the result of the one before it. This article puts those steps into one workflow, points you to the detailed calculation article at each stage, and explains what the AZEIDK engineering design and calculations service delivers.
Key takeaways
- The mandatory reference in Saudi Arabia is the Saudi Fire Code SBC 801; the 2024 edition of the Saudi Building Code has been mandatory since 30 June 2025.
- NFPA 72 (current edition 2025) is the technical reference the designer adopts for layout, circuits, power and documentation details.
- Order matters: batteries cannot be sized before the device layout is complete, and loops cannot be allocated before zoning.
- Design outputs are layout drawings, a riser diagram, calculations, an interface matrix, specifications and a bill of quantities.
- Frequent review comments: calculations that do not match the drawings, or actual room use that differs from what the design assumed.
In this article
- What inputs does fire alarm system design need?
- Step 1: is a system required, and conventional or addressable?
- Steps 2 and 3: detector selection, then layout
- Step 4: call points, sounders and strobes
- Step 5: zones and loops
- Step 6: battery and voltage drop calculations
- Step 7: interfaces and the cause and effect matrix
- Step 8: drawings and documents for Civil Defense
- Fire alarm system design workflow and the output of each step
- What does the AZEIDK engineering design and calculations service deliver?
- Common fire alarm design mistakes
- Frequently asked questions
- Conclusion
What inputs does fire alarm system design need?
Before a single detector is drawn, the designer collects the data every later decision depends on. Missing any of it means rework later:
- Up-to-date architectural drawings for every floor, with room names and their real use.
- The building’s occupancy classification (business, residential, industrial, educational and so on), because it sets the SBC 801 requirements.
- Ceiling heights and profiles, suspended ceilings, beams and ceiling voids.
- HVAC drawings: supply diffusers and air handling units that may need duct detectors or shutdown on alarm.
- Systems that will interface with the alarm: sprinklers and flow switches, lifts, doors, smoke control and special suppression systems.
- The approval path the consultant requires: UL devices with NFPA 72, or EN 54 devices with BS 5839. Mixing the two is a common cause of submittal rejection.
Step 1: is a system required, and conventional or addressable?
Section 907 of SBC 801 (see When Is a Fire Alarm System Mandatory?) sets when and where a fire alarm system is required, based on occupancy type, area, occupant load and height. That is the legal starting point. The technical decision follows: a conventional system with zones, or an addressable system in which every device has its own address. A small building with few rooms may be served by a conventional system, while multi-storey buildings or projects with many interfaces usually favour addressable, because alarms and faults are located device by device.
Steps 2 and 3: detector selection, then layout
Each space gets a detector that suits the expected fire and the conditions in the room: optical smoke detectors for offices and corridors, heat detectors for kitchens and steamy or dusty areas, beam detectors for halls and high-ceiling warehouses, and flame detectors for specific industrial areas. A wrong choice at this stage is one of the main causes of false alarms after handover.
Layout comes next: the number of detectors and their spacing based on ceiling height and profile, beams and air movement, under Chapter 17 (Initiating Devices) of NFPA 72. We do not repeat the figures and examples here; they are worked through in Smoke and Heat Detector Spacing: How to Calculate a Layout to NFPA 72.
Step 4: call points, sounders and strobes
Manual call points go at exits and along escape routes, then audible and visual notification appliances are placed so the alarm reaches every occupied space. Chapter 18 of NFPA 72 (Notification Appliances) is the reference for sound and light levels. Where a building needs voice evacuation, Chapter 24 (Emergency Communications Systems) applies, which changes the power and battery calculation later, so decide it early.
Step 5: zones and loops
Alarm zones follow floors, fire compartments and evacuation routes, and the devices in each zone are then allocated to loops. This is where the circuit class is set (Class A, B or X under Chapter 12 of NFPA 72), isolator positions are chosen, and each loop is checked for device count, current and cable length against the panel datasheet. Details and practical limits are in Addressable Fire Alarm Loop Design.
Step 6: battery and voltage drop calculations
Only once the device list is complete can the standby and alarm current of each panel be worked out, and from that the battery capacity, under Chapter 10 of NFPA 72 or the BS 5839-1 method, depending on the project path. Voltage drop on sounder and strobe circuits is checked at the same time, to confirm the last device on the circuit still operates above the minimum voltage in its datasheet. Method and examples: Fire Alarm Battery Calculation and Secondary Power Supplies.
Step 7: interfaces and the cause and effect matrix
A fire alarm system does not work alone. On alarm it may need to shut down air handling units, recall lifts, release electrically locked doors on escape routes, start smoke extract fans, and supervise sprinkler flow switches and valve positions. Chapter 21 of NFPA 72 covers emergency control function interfaces. All of this goes into one table, the cause and effect matrix, which the panel is programmed from and tested against at handover.
Step 8: drawings and documents for Civil Defense
NFPA 72 dedicates Chapter 7 to documentation: design (layout) documents in Section 7.3, shop drawings in 7.4, and completion documentation, including record drawings, in 7.5. The minimum documentation is listed in 7.2.1 and includes:
- A written narrative describing the intent of the system and how it works.
- A riser diagram.
- Floor plans showing every device and control unit.
- The sequence of operation, as a matrix or narrative.
- Datasheets for each device and the manufacturer’s instructions.
- Battery calculations, and voltage drop calculations for notification circuits.
A symbol legend, technical specifications and a bill of quantities are normally added. The full package and how it relates to suppression systems is covered in Civil Defense Fire Design Drawings: What the Design Package Contains.
Fire alarm system design workflow and the output of each step
| Step | Output | Technical reference |
|---|---|---|
| Inputs and requirement check | Room schedule, occupancy classification, system type | SBC 801 Section 907 |
| Detector selection and layout | Detector layout for each floor | NFPA 72 Chapter 17 |
| Call points and notification | Call point, sounder and strobe locations | NFPA 72 Chapter 18 (Chapter 24 for voice evacuation) |
| Zones and loops | Loop and isolator schedule, riser diagram | NFPA 72 Chapter 12 and the panel datasheet |
| Batteries and voltage drop | Calculation sheets per panel and circuit | NFPA 72 Chapter 10 or BS 5839-1 |
| Interfaces | Cause and effect matrix | NFPA 72 Chapter 21 |
| Documentation | Drawings, specifications, bill of quantities | NFPA 72 Chapter 7 |
What does the AZEIDK engineering design and calculations service deliver?
As described on the service page, it covers analysis of the facility’s occupancy and safety system requirements, definition of the design basis and technical references, engineering calculations within the project scope, design drawings, specifications and equipment schedules, and a review of coordination between systems and other disciplines. For fire alarm systems specifically, the client receives device layout drawings, battery and load calculations, technical specifications and bills of quantities. Design follows SBC 801 and Civil Defense requirements, with NFPA 72 as the technical reference.
If the facility needs a technical report on the Salamah platform, that report is issued by engineering consultancy offices, not by AZEIDK. AZEIDK’s role in that process sits within its Civil Defense approval support service, which includes issuing the safety equipment installation certificate.
Common fire alarm design mistakes
- Designing on outdated architectural drawings, then changing partitions or ceilings without updating the detector layout.
- Specifying a smoke detector in a kitchen or laundry, which leads to repeated false alarms after handover.
- Sizing batteries before the device list is final, or with estimated currents instead of datasheet values.
- Loading a loop beyond its real capacity, or leaving out isolators at zone boundaries.
- No cause and effect matrix, so the panel is programmed by guesswork on site.
- Mixing UL and EN 54 devices on the same project.
Frequently asked questions
How do you design a fire alarm system for a new building?
Start with the architectural drawings, occupancy classification and SBC 801 requirements, then select and lay out detectors, divide zones and loops, calculate batteries and voltage drop, and prepare the interface matrix, drawings and specifications.
Which code governs fire alarm design in Saudi Arabia?
The mandatory reference is SBC 801 within the Saudi Building Code, together with Civil Defense requirements. NFPA 72 or BS 5839 is used as the technical reference for details, as the consultant specifies.
Should batteries be calculated before detector layout?
No. Battery sizing needs the complete device list and each device’s current from its datasheet, so it comes after layout and loop allocation.
What is the difference between a design drawing and a shop drawing?
The design drawing sets the system concept and device locations and is submitted for approval. The shop drawing is prepared by the contractor with the actual models supplied and cable routes, before installation.
Does AZEIDK issue the Salamah technical report?
No. The technical report is issued by engineering consultancy offices. AZEIDK provides design and calculations and issues the safety equipment installation certificate as part of its Civil Defense approval support.
When is an addressable system needed instead of conventional?
Usually in large or multi-storey buildings and where there are many interfaces with lifts, HVAC and doors, because an addressable system locates alarms and faults device by device.
Conclusion
Fire alarm system design is sequential work: correct inputs, then selection and layout, then loops, power and interfaces, then documentation. Keeping to that order reduces review comments, keeps drawings and calculations consistent, and makes installation and commissioning easier. Each detailed calculation has its own article linked above.
Have a project that needs a fire alarm design? Send the architectural drawings and occupancy type, and our team will define the design and calculation scope with you. Talk to the AZEIDK team
