There are three types of spring-operated door latch, operated by a door handle, used in the UK. You may be familiar with the first type, but the others are more obscure. As always, you will ignore these items - until they go wrong or you have to fit a new one!
Latches are only intended to keep the door from swinging open, although some have now been developed into locking devices. Remember that latches can also be found as part of an exterior door lock - then called a sashlock, i.e. a combination of a latch and a locking bolt housed within one metal case. A door lock with just a locking bolt is called a deadlock.
The kinds of latch typically found in the UK are:
The first probably accounts for 95% of the independent latches fitted in the UK today. The second is a much more substantial device and requires a little more skill to fit. The homeowner rarely fits the third type except as a replacement.
Despite your lack on interest in these devices, you will use them many times each day. Economising on something in constant use seems unwise. Fitting new door handles onto an old and worn sprung latch is false economy. Pay a few £ more, fit a new quality latch and enjoy a smoother experience(!) for years to come.
a) The tubular mortice latch is, surprisingly, round and tubular! Easy to fit, a reasonable quality tubular latch will give years of satisfactory service. Prices vary but you inevitably get what you pay for.
Available in a range of sizes, the latch is fitted into a round hole drilled into the door edge. The latch length then fixes the distance of the door handle from the door edge.
TIP: If fitting a door knob where knuckles may scrape on the door frame, fit a longer latch to give more space to turn the knob.
The latch length can also be chosen for what looks better, as handles tend to look "cramped" if fitted too close to the door edge. Of course, the length may be pre-fixed because you are replacing an existing latch that has failed.
Typical tubular latch lengths are 2½" (63mm) or 3" (75mm), but they are also available in 4", 5" and even 6" lengths for older panelled doors.
The spring inside the latch is important for two reasons. Firstly, it needs to be soft enough for the latch to engage into the frame with minimal effort - no one enjoys the sound of slammed doors! Secondly, the spring has to be strong enough to keep the door handle horizontal when not being turned. Balancing these two requirements means better latch manufacturers use two springs, of different strengths, to solve each problem.
Fitting involves drilling into the edge of the door, typically with a carpenter's brace and drill bit. Latch diameters vary so check before drilling. Most new doors have a large block of wood set at mid-height in one edge in order to take the latch and the handle fixings. The drilling depth is set by the latch length plus 3mm. This extra distance allows the rectangular face of the latch, known as the "forend", to be set into a recess chiselled in the door edge, leaving it flush with the edge of the door.
TIP: Look on the top edge or underside of the door for a mark indicating which edge of the door carries the block.
After drilling, hold the latch against the face of the door and mark the hole position for the handle spindle. Drill carefully through the door face - it is better to drill from each side separately - to form a hole which will clear the spindle bar as it turns. Now push in the new latch and secure with screws through the forend.
TIP: If you clamp a block of wood tightly to the opposite side of the door you should be able to drill straight through without it splintering.
Finally, fit the latchplate to the doorframe. Close the door temporarily and mark the position of the latch tongue against the frame, both for depth and for height. This shows where the latch plate must be fixed.
TIP: Chisel out a shallow recess in the frame to test the closed position of the latch, before screwing the metal latchplate in its final position. Any slight repositioning can then be covered by the latchplate.
Now fit/re-fit your handles and the job is done!
b) The box mortice latch is quite rare as it requires a rectangular mortice to be drilled and chiselled into the door edge - similar to that required for a mortice deadlock or mortice sashlock. The option of fitting a tubular latch is too easy for most people to resist. However, a box latch is a much stronger mechanism and, if the door is likely to be in constant use or even subject to abuse, then a box mortice latch is a better long term choice.
Fitting is along similar lines to the above, but involves a larger mortice recess to be cut into the door edge. If care is taken, this is no more difficult than for the tubular latch.
c) The rim latch is most commonly fitted to the very basic door constructions found on garden sheds, garages and certain internal doors. It sometimes incorporates a simple lock but, with its rather crude internal mechanism, it is rare to find it fitted as a new feature except for period interiors.
Fitting to the face/edge of the door (hence "rim") is easy, with the latch tongue locating into an enlarged latchplate. Rim latches are usually operated by knob furniture, rather than lever handles.