A fire detection design lives or dies on spacing. Put a smoke detector too far from a wall, leave a bedroom uncovered, or forget a heat detector over the cooker, and the certificate is worth nothing. This guide shows how to plan smoke and heat detector coverage on a floor plan with RoomPlot, so every room is demonstrably protected before you ever climb a ladder.
Why spacing is the whole job
Detectors do not cover a room the way a light does. Each device has a nominal radius of protection, and the codes set out how far apart heads can sit and how close they must be to a wall. Sketching dots on a PDF tells you nothing about whether those circles actually overlap. The fix is to draw the coverage, not just the device, so the gaps show themselves.
Place the detector, see the circle
Drop a smoke or heat detector from the Fire Safety symbol library and RoomPlot draws the area it covers as a radial circle centred on the head. Coverage switches on automatically when you place the device, and a blue radio-wave handle lets you drag the radius to match your design. The defaults follow BS 5839 and NFPA 72 style nominal radii: roughly 7.5 m for a smoke detector and 5.3 m for a heat detector, and you can tune any head from 1 m to 15 m.
Build the design room by room
- Start from the real plan. Scan with LiDAR or draw the floor by hand, so walls and room sizes are accurate before you place a single head.
- Place heads to type. Smoke detectors in circulation spaces and bedrooms, heat detectors in kitchens and garages where smoke types would false-alarm.
- Check the overlap. Walk the plan and confirm neighbouring circles touch or overlap, with no room left outside a coverage area.
- Tune the edge cases. Drag a radius down in a small WC, or add a head where a long hallway runs past the nominal reach.
Tip. The nominal radii are a starting point, not a substitute for the standard. Always verify spacing against the current edition of BS 5839 or NFPA 72 for the building's category and ceiling height before you certify.
From plan to a zone document
Once coverage looks right, the same plan becomes the paperwork. Add the red Fire Alarm Zone Plan banner, switch on the multi-page report, and the Fire and Security preset forces coverage areas to print. You get a branded PDF that shows the head positions, the protected areas and the legend in one pass. For the zone-by-zone layout that sits alongside this, see our guide to the fire alarm zone plan.
Get it right on paper first
Coverage you can see is coverage you can defend. Drop your detectors, watch the circles fill the rooms, and hand the client a plan that proves the design. Browse the rest of our floor plan guides to take your survey from scan to signed-off report on the device in your hand.
