Fire alarm system design in London

What is in a design package

• Design brief and category: the category taken from your fire risk assessment, with the reasoning recorded rather than implied.
• Device layout drawings: every detector, call point, sounder, beacon and interface, positioned against the real floor plan.
• Zone plan: how the building is divided, and the plan that ends up mounted next to the panel for the fire service to read.
• Cause-and-effect matrix: every input against every output, which is also the document commissioning gets tested against.
• Equipment specification: panel, devices, cable type and battery standby, written so two contractors would price the same system.
• Variations schedule: any departure from the recommendations of the standard, stated openly with the reason for it.
• Design certificate: the signed record of who designed it, to which standard and to which category.

What changed in BS 5839-1:2025

BS 5839-1:2025 replaced the 2017 edition on 30 April 2025. It is not retrospective, so a system properly designed and certificated under the old edition does not become non-compliant by itself. New designs, extensions and significant alterations are worked to the current edition, and your fire risk assessment can reasonably conclude that a particular change ought to be applied to what you already have.

The changes that most often affect a design:

None of this replaces reading the standard, and we would not pretend a table on a website does. It is here because "which edition applies to me" is a fair question and the answer is rarely on the pages of the people selling the systems.

Design-only, if that is what you need

Not every design job ends with us installing it. We are asked for design on its own by architects and main contractors who need a fire alarm package inside a wider build, by owners who want a specification to tender against so the quotes are comparable, and by landlords who have been given a proposal by somebody else and want to know whether it is sound before they sign it.

Reviewing another company's design is the same discipline in reverse: does the category match what the risk assessment actually says, do the zones survive the compartment lines, and does the cause and effect describe a building anyone would want to be in during an alarm. We will tell you if the answer is that the design is fine, which it sometimes is.

Variations belong in writing, not in somebody's memory

BS 5839-1 is a code of practice, so departures from its recommendations are permitted. What it asks is that they are recorded as variations, with the reason, rather than quietly done. A period building where a cable route is genuinely impossible, a detector that cannot go where the geometry says it should, a category agreed down for a defensible reason, all legitimate, all fine, all problems only when they are undocumented.

An unrecorded variation is what turns into an argument at handover, or worse, at an insurance claim, because there is nothing to distinguish a considered engineering decision from a corner that was cut. Listing them is the cheapest part of the job and the part that protects you longest.

What a design costs

There is no calculator on this page, and that is deliberate. Every price on this site comes from one rate file, and a design is priced against the building rather than a device count: the floor area, how many storeys and compartments, whether usable drawings exist or the building has to be measured, and whether the work is a fresh design, an extension or a review of somebody else's. A figure invented for a website would be a figure we then had to contradict on the phone.

Tell us the building and roughly what you are trying to do and we will give you a real range in the conversation, including whether you actually need a full design or a smaller piece of work.