How to fit a letterbox

Video by Ultimate Handyman. This walk-through is based on the video "How to fit a sleeved letter plate" from Ultimate Handyman, which covers the full process from measuring the existing hole through to fitting the inner sleeve and tightening up. Worth watching before you pick up the jigsaw — the bit on cutting the aperture carefully rather than at full speed is easy to overlook but makes a real difference to the finish.

1. Choose the right letterbox for your door

Most UK letterboxes follow a fairly standard plate size — around 280 mm wide by 35 mm tall for the opening — but do check the product spec before you buy. Sleeved letterboxes, where an inner and outer plate bolt together through the door, are by far the most common these days and suit both wooden and uPVC doors. The sleeve adjusts to fit different door thicknesses, which is handy given that front doors vary quite a bit.

If you have a composite or uPVC door, check whether the manufacturer specifies a particular letterbox geometry. Some composite doors have a foam core that crumbles if you cut at the wrong angle, and a few have reinforcing plates built in that affect where the bolts can go. To be fair, most replacement letterboxes will fit without any drama, but it is worth a quick look at the door spec first.

2. Mark the position carefully before cutting anything

The standard position is one-third of the way up from the bottom of the door, centred on the door width. On a typical 78-inch door, that puts the centre of the plate at around 600 mm from the bottom. Use a tape measure and a pencil, and double-check both the height and the horizontal centre before drawing any lines.

Hold the outer plate up against the door in the marked position and draw round the aperture opening in pencil — that is the actual slot you need to cut, not the outer plate itself. Then mark the bolt holes either side. If you are replacing an existing letterbox, remove it first and check whether the old hole is the right size for the new plate. Sometimes it is, sometimes it needs a small amount of cutting out. That said, if the old hole is already too big you may need a larger plate to cover it tidily.

3. Drill corner holes and cut the letterbox slot

Drill a hole in each corner of the marked slot, using a flat bit or spade bit large enough to get a jigsaw blade through comfortably — around 14 mm to 16 mm works well. The corner holes stop the cut from running past the line and give you clean corners rather than ragged ones.

Cut between the corner holes with a jigsaw, keeping the blade just inside the pencil line. Go slowly — a jigsaw will cut fast enough on a front door, and rushing it tends to leave a rough edge or a slight bow in the cut. Finish the corners with a sharp chisel or a file if needed. On a uPVC door, use a fine-tooth blade and keep the speed down; coarser blades tend to melt the plastic slightly and leave a messy edge.

4. Drill the fixing bolt holes

The letterbox is held together by two long bolts that pass right through the door from the inside. Mark the bolt hole positions from the plate template, then drill through with a bit that matches the bolt diameter — usually 8 mm or 10 mm. Drill straight and steady; a hole that wanders slightly will make lining the plates up awkward later.

On a uPVC door, take extra care not to crack the outer skin around the holes. Start with a smaller pilot drill and step up to the final size. Mind you, the bolt holes are usually tucked behind the plate flanges anyway, so a minor mark there will not show once the letterbox is fitted.

5. Assemble the sleeve and fit the letterbox

Sleeved letterboxes have a telescopic inner section that you set to match the thickness of your door before tightening. Slide the outer plate into the slot from the front of the door, then fit the brush seal section from inside and push the two halves together. On most designs the inner plate then covers the brush section from the inside of the door.

Thread the bolts through from the inside and start them finger-tight first to check everything is lining up squarely. The plate should sit flush against the door face on both sides without rocking. Once you are happy, tighten the bolts gradually and evenly, alternating sides, until the sleeve is clamped firmly against the door. Do not over-tighten on a uPVC door — the plastic can crack or distort if you really lean on it.

6. Test the action and check the draught seal

Open and close the flap a few times to make sure it swings freely and springs back to the closed position. A letterbox that sticks open even slightly will let in cold air and, in a house like most in Sandwich and East Kent, that draught goes straight down the hallway. Most modern letterboxes have an inner brush seal to deal with this, but make sure it has not been compressed or caught on the sleeve during fitting.

Step outside and push a piece of card through to check the opening is clean and unobstructed. Then check from the inside that you cannot see daylight around the edges of the plates — if you can, the outer sleeve may need adjusting or you may need a small bead of draught-excluding foam tape around the rebate. It is a small thing, but worth doing properly before the next cold snap rolls in off the Channel.

When to call a handyman

Call Richard if the old letterbox hole has been cut too large and needs a filler plate or re-routing, if your composite door has an unusual foam or reinforced core that makes cutting tricky, or if the front door is warped and the frame needs planing before a new plate will sit flush. Fitting a letterbox to a solid timber front door that has never had one is also more involved than it looks and is worth having done properly to avoid weakening the door.