Fit a carbon monoxide alarm to a metal stud wall

Fit a carbon monoxide alarm to a metal stud wall safely, with the right fixing and no drilled cables.

CO-01Choose the spot and check the rules that applyFit the alarm in the room with the boiler, gas fire or wood burner, or in a hallway near bedrooms if it's covering the whole home. Follow the maker's siting guide for exact height and distance - typically 150-300mm down from the ceiling on a wall, and 1-3m from the appliance, not right beside it or tucked in a dead-air corner. Don't fit it above a door, window or extractor fan where draughts pull air away from it.

RULES

1 each · Carbon monoxide alarm (battery powered)

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KNOW THE RULES

If you rent the property out, the Smoke and Carbon Monoxide Alarm Regulations require a CO alarm in any room with a fixed combustion appliance - check your landlord duty. If your alarm is mains-wired rather than battery, connecting it to the electrics is notifiable work under Part P, so use a registered electrician.

CO-02Gather your tools and materialsGet everything together before you start so you're not hunting for a drill bit halfway through with a hole marked on the wall. Lay a dust sheet under the working area.

1 each · Cordless drill/driver

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1 set · Masonry/wood/HSS drill bit set

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1 each · Pencil

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1 each · Spirit level or small tape measure

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1 each · Dust sheet

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1 each · Small hand vacuum or brush and pan

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CO-03Find cables and pipes, and check your stopcock, before drilling anythingRun a cable and pipe detector over the marked spot before you drill. Cables and pipes can run almost anywhere, not just in the 'safe zones' - a detector can miss ones that are deep, in metal conduit, or behind metal-backed plasterboard, and a metal stud frame can confuse a cheap detector even more. Find your stopcock now, usually under the kitchen sink, and check it turns freely so you can shut the water off fast if you hit a pipe. If you have any doubt at all, isolate the relevant circuit at the consumer unit before drilling.

1 each · Cable and pipe detector

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CO-04Work out exactly what's behind the wallRun a magnet or detector across the wall to find the line of screw heads - that line tells you where the studs are. Tap between the marks: a hollow drum sound with metal studs feels sharper and thinner than the hollow sound of timber studs. Drill a small 3mm pilot hole at the marked spot - fine timber dust means a timber stud or plasterboard, shiny grey swarf means metal, and no give at all with dense grey dust means solid brick or block. A gap that feels hollow but the pilot goes through plaster then hits nothing solid for a while suggests dot-and-dab; slight bounce and thin horizontal ridges every 25-30mm suggest old lath and plaster.

CO-05Pick the right fixing for your wallA CO alarm is light, around 150-200g, so most fixings will hold it - but still match the fixing to the material. Into a timber stud, use a wood screw straight into the centre of the stud, no plug needed. Into a metal stud, use a self-drilling metal-stud screw or a self-drilling hollow-wall fixing - never a plain plastic plug and never a wood screw, both strip straight through 0.5mm steel. If your fixing lands on plasterboard between the studs rather than on a stud itself, use a small self-drilling plasterboard fixing (a spring or self-drilling toggle) - it's light enough that a basic one will do. On solid brick or block, drill a 6mm hole to about 35-40mm deep, fit a wall plug, and use a 4x30mm screw. Through dot-and-dab, use a fixing long enough to reach the solid masonry behind the dabs, usually 50-60mm. On lath and plaster, aim for a solid timber lath if you can find one, or use a proper plaster/lath toggle fixing rather than a plug, which just crumbles the old plaster.

1 pack · Self-drilling plasterboard fixings (pack)

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1 pack · Self-drilling metal-stud screws (pack)

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1 pack · Wood screws 4x30mm (pack)

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1 pack · Wall plugs and screws for masonry (pack)

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CO-06Mark and drill the fixing holesHold the alarm's mounting bracket against the wall at the height you chose, level it, and mark the screw holes with a pencil. Drill each hole to the size and depth needed for your chosen fixing - shallow for a self-drilling plasterboard or metal-stud fixing, deeper for a wall plug in masonry. Keep the drill straight and don't push too hard on plasterboard, it's easy to punch straight through.

CO-07Fit the wall fixings and screw on the bracketPush in the wall plug or self-drilling fixing until it sits flush with the wall. Line the bracket back up over the holes and drive the screws in until snug - stop as soon as the bracket sits firm, overtightening cracks the plastic or strips a hollow-wall fixing. Give the bracket a gentle tug to check it's solid before moving on.

CO-08Fit the battery and clip the alarm onto the bracketOpen the battery compartment and fit the battery the right way round, following the marks inside. Most alarms give a short beep or flash when they power up - listen for it. Clip the alarm body onto the bracket until it locks in place, usually with a quarter-turn twist.

1 each · Alarm battery (if not supplied)

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CO-09Test the alarmPress and hold the test button until the alarm sounds its full alert - this checks the sensor and sounder together, not just the battery. Check the status light shows normal operation once it stops. If nothing happens, check the battery orientation and the bracket connection before assuming the unit is faulty.

CO-10Tidy up and set a reminderVacuum up drilling dust and wipe down the wall and skirting below. Write the fitting date somewhere handy, and set a phone reminder to test the alarm monthly and check the manufacturer's date for when the whole unit needs replacing, usually every 5-10 years.

PART OF A BIGGER PROJECT

Make a home easier to live in as you get older · Get your home ready for winter

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