How do I cut a letterplate opening into a door?
Choosing the position on a rail rather than a joint, setting out an aperture that is not the same size as the plate, and the finishing that stops a letterplate becoming the coldest hole in the house.
- Difficulty
- intermediate
- Time
- 1 hr 15 min
- Read
- 4 min
- Safety
- warning
Short answer
Cut into a solid rail, never across a joint or into a panel. Mark the aperture from the manufacturer's template, not from the plate. Drill all four corners first, then saw between the holes from the face that will show. Seal the raw edges and fit a brush or flap seal on the inside.
A letterplate is a large deliberate hole in an external door, so it has to be cut in the right place, cut cleanly, and finished properly. On a timber door this is straightforward carpentry. On a composite or uPVC door it is a different question entirely, and the honest answer for most people is that it belongs to the door manufacturer.
Safety
What you'll need
- The letterplate and its template
- A drill and a bit sized to the aperture corner radius
- A jigsaw with a fine down-cutting blade, or a padsaw
- A spirit level and a square
- Masking tape
- Exterior primer or a sealant for the cut edges
Step by step
- Decide whether you should be cutting this door at all.On a timber door, yes. On a composite or uPVC door, cutting an aperture may pass through an internal reinforcement and will very likely affect the guarantee, and a factory-cut aperture is properly sealed in a way a site cut is not. Ask the supplier first.
- Find the solid rail.On a panelled door the letterplate goes in the mid or lower rail, never across the joint between a rail and a stile and never into a panel. Tap along the door to find the solid areas, and measure the rail from both sides to confirm where its edges are.
- Check what else is inside.Mortice lock case, night latch backplate fixings, hinge bolts, glazing. Measure from a known reference on both faces. A letterplate cut through a lock case is unrecoverable.
- Set the height and centre it.Conventionally in the middle of the rail and centred on the door width, unless the door design says otherwise. Check it against the height of the mail slot on the inside if there is a cage or basket.
- Mark from the template, not from the plate.The aperture is smaller than the plate and the fixing bolt holes sit outside the aperture. Use the manufacturer's paper template, tape it down, and mark through it. Then check it with a level before anything is cut.
- Mask the cut line.Masking tape over the marked line on the face that will show reduces splintering and lets you re-mark on top of it. Cheap insurance on a painted or veneered door.
- Drill the four corners first.Use a bit matching the corner radius on the template. The holes give the corners a clean radius, stop the saw cut running on, and stop the corners splitting. Drill from the show face until the point breaks through, then finish from the back.
- Saw between the holes.A jigsaw with a fine down-cutting blade, or a padsaw for control. Work from the face that will show and support the offcut so it does not tear out as it drops. Keep to the waste side of the line and pare back to it.
- Test fit before finishing.Offer the plate up. Ease the aperture with a file or a chisel until the flap swings freely with a small clearance all round. A tight aperture makes a letterplate that sticks and rattles.
- Seal every raw edge.The inside of the aperture is end grain and it is where water gets in. On a timber door, prime and paint it or use an exterior sealer. On any door, this is the step that decides whether the door rots around the letterplate.
- Fit the plate and an internal seal.Bolt the plate through, then fit a brush or flap draught seal on the inside. A letterplate is often the single largest gap in the building envelope, and on a front door it is also an entry route worth thinking about.
- Consider the security fittings while you are there.A letterplate cowl or a restricted-aperture internal plate stops an arm or a tool reaching through to a thumbturn or a key. If the door has a thumbturn cylinder or keys kept nearby, this matters.
Common mistakes
- Cutting across a rail-to-stile joint — It removes the tenon that holds the door together at that point. The door will loosen and eventually rack.
- Cutting to the size of the plate — The plate overlaps the aperture on all sides. Cut to the plate size and you have a hole with nothing to fix through.
- Leaving the cut edges raw — End grain in the wettest, most exposed part of the door. It is the single most common origin of rot in a timber door and of skin lifting in a composite one.
Questions people ask
Where should a letterplate go, high or low?
Anywhere in a solid rail. Postal services generally prefer a plate at a height that does not require crouching, so a mid-rail position is usually better than the bottom rail if the door allows it.
Horizontal or vertical?
Vertical letterplates in the stile look neat but the stile is often too narrow to take one safely, and the same joint rules apply. Check the timber before choosing on looks.
Can I fit one to a glazed door?
Not into the glass. If the door is largely glazed, the letterplate has to go in a solid rail or a separate wall-mounted box is the alternative.