How to Fit a Letterbox in a Door: A UK Guide
Fit a letterbox in a UK front door with advice on height, door materials, cutting the aperture, draught protection and when to get a pro.
A letterbox seems like a simple fitting until you are holding a jigsaw next to a front door you cannot easily replace. Doors differ greatly in material and construction, and a clumsy cut cannot be undone. Measure carefully, choose the right fitting, and know when to hand the job to a joiner.
Check the door type
- Solid timber doors: the easiest to cut, with a jigsaw and drill.
- Hollow or veneered doors: have thin skins and a core that may include blocks, so find out where the solid sections lie.
- Composite and uPVC doors: often have a reinforced core or metal inserts, and cutting may affect strength or warranties. Many are best done by a specialist.
- Fire doors: letterboxes can affect fire resistance. Fire-rated doors need a fire-rated letterbox, and altering the door may breach regulations, particularly in flats and HMOs.
Choose the letterbox
Pick one that suits the door thickness and your post. Look at:
- Aperture size: a standard size covers letters, but larger parcels need a bigger opening.
- Draught seals: brush or flap seals reduce cold air and noise.
- Security features: restrictors and cowls reduce fishing for keys or locks through the opening.
- Finish: match the door furniture.
Check the manufacturer's template for the cut-out size and fixing holes.
Plan the position
Letterboxes are commonly fitted centrally in the door and around 70 to 100 cm from the floor, though your door layout may dictate otherwise. Check:
- That it will not clash with the lock, handle or glass panels.
- That there is room for the flap to open fully.
- That the inside of the door has a clear area for the back plate and any internal cage.
For homes with several occupants, consider a letterbox location that suits different heights.
Fitting steps for a typical timber door
- Mark the centre line of the opening, using a pencil and level.
- Tape the template and mark the cut-out.
- Drill a pilot hole in each corner.
- Cut with a jigsaw between the holes, supporting the door so it does not vibrate.
- Sand the edges and seal bare wood with paint or varnish.
- Insert the letterbox and mark fixing holes.
- Drill the holes and fix with the screws or bolts supplied.
- Add the internal flap or draught excluder.
Common mistakes
- Cutting where an internal lock block or reinforcement sits.
- Making the cut-out too large, which cannot be undone.
- Skipping a seal, leaving bare timber to take on water.
- Mixing up the template front and back.
Alternatives
If cutting the door is not an option, a wall-mounted or external post box, or a gate-mounted box, can be fitted without changing the door. A letter cage inside can catch post and stop it sliding on the floor. If you are installing other door hardware at the same time, see fitting door handles.
When to get help
Cutting a composite or fire door, or fitting in a rented or leasehold property, may need permission. Ask the landlord or managing agent first, and consider a joiner or door specialist where the door is high value. You can browse local installers for door and fitting work.
A worked example: a timber front door
You are fitting a standard letterbox to a 44 mm thick timber door. Mark the centre line so the opening sits around 70 to 100 cm from the bottom, check the position with a template, then drill pilot holes at each corner of the cut-out and join them with a jigsaw or a saw. Smooth the edges, fit the plate, and secure with the screws or bolts provided. Add a draught excluder or brush if the design allows.
Choosing the box
| Feature | Why it matters |
|---|---|
| Door thickness | Needs a through-fix or deep-flap design |
| Opening size | Needs to take your usual post |
| Draught protection | Brush or flap for energy savings |
| Fire rating | Required for some fire doors and flats |
Common mistakes
- Cutting before checking door thickness and internal frame.
- Using a template that is the wrong size.
- Leaving rough edges that snag the post.
- Drilling through a door lock or reinforcement.
Fire doors and flats
Flat entrance doors often have fire ratings, and cutting them can invalidate the rating. Check with the landlord or building manager before altering such a door. If your door is composite or uPVC, a specialist or locksmith may be the better route. See fitting door handles and furniture for related hardware.
Weather and draughts
A letterbox is an easy path for draughts and rain. Choose a model with a brush strip or a sprung flap, and fit it so the flap closes against a flat surface. Seal gaps between the plate and door with a thin bead of sealant if the manufacturer suggests it, and test with a piece of paper to see if it gets pulled through the gap.
Frequently asked questions
Can I fit a letterbox in a uPVC door myself?
It is possible with the right tools, but the door has a core and sometimes steel reinforcement, and cutting can affect weather sealing and warranty. Many people prefer a specialist.
How high should a letterbox be?
Commonly around 70 to 100 cm from the floor, but it depends on the door and who uses it. Avoid very low positions as they are inconvenient.
Do I need permission to cut a hole in a door?
In rented or leasehold homes, probably yes. Fire doors in shared buildings may be controlled, so check before making any changes.