Mark the aperture with the template, drill and cut carefully, then fit and test the letterbox for a clean, snug finish.
AB-01Check the door and choose the right letterboxCheck the door edge and top for a coloured plug or label — this means it's a fire door. If it is, you must use a certified fire-rated letterbox with an intumescent lining; a standard letterbox breaks the door's fire seal. Also check if the door is solid or hollow-core (lightweight internal doors) — hollow doors need a letterbox with a sleeve kit, not a standard plate. Measure the door thickness with a tape measure; most letterboxes suit doors 40-50mm thick.
RULES1 each · Letterbox kit with paper template KNOW THE RULES
Building Regulations Approved Document B covers fire doors, common on flat entrance doors and doors to integral garages. Fitting a standard letterbox in a fire door invalidates its fire rating — use a certified fire-rated letterbox kit instead.
AB-02Mark the cutting positionTape the paper template to the door at the height given by the manufacturer, usually somewhere between 760mm and 1200mm from the floor. Use a spirit level to check the template is level and centred side to side. Mark the four corners and the centre lines of the cutout, plus any screw hole positions, in pencil.
AB-03Drill pilot holes at the cornersClamp the door securely or get someone to hold it steady. Drill a 6-8mm pilot hole at each marked corner, right through the door, to give the jigsaw blade a way in. Check first that the cutout doesn't overlap the lock mechanism or a hinge.
1 each · 6mm wood drill bit AB-04Cut the apertureFit a fine wood-cutting blade to the jigsaw. Starting from a pilot hole, cut just inside your pencil lines, working slowly around the rectangle. Support the cut-out piece with your free hand near the end of the cut so it doesn't tear away and splinter the face of the door.
1 each · Fine wood-cutting jigsaw blade AB-05Clean up the edges and test-fitOffer the letterbox front plate up to the hole to check it fits. Use sandpaper and a small file to true up rough edges and remove splinters or burrs. Vacuum the sawdust from the cut before fitting anything.
1 sheet · Sandpaper, medium grit AB-06Fit the letterboxPosition the outer plate over the aperture and mark the screw fixing holes through it. Drill 3mm pilot holes at these marks so the screws don't split the timber. Fix the outer plate with the screws provided, then fit the inner plate or sleeve and any brush or flap draught seal on the inside.
1 each · 3mm wood drill bit 1 set · Letterbox fixing screws (usually supplied) AB-07Check it works and tidy upOpen and close the flap several times to check it moves freely and doesn't catch on the door edge, lock, or letterbox surround. Post an envelope through to check letters pass without snagging. Vacuum any remaining sawdust and dispose of the offcut and waste.
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