... it must of been at least 15 years ago so I'm not sure when the building regs were in place for fire doors
There have been building regs covering fire doors for far longer than I've been working... (so quite a few decades)
its no issue i can fit a casing and frame, I just didn't want to spend the money if it wasn't necessary that was all. Would you recommend a casing with a base as well or not?
A bigger concern is gapping around the door and the casing, and the casing and wall. At one time fire brigade assessment officers would sign off on fire door works (in public buildings) and (i found) they would be fairly flexible in their approach (i.e. pragmatic)
The main thing with the casing is to ensure that any gaps between the casing and the wall (i.e.just underneath the architraves) are filled with a non-flamable material. Up to 10mm the entire gap should be filled with intumescent caulk. Above that the gaps need to be filled with mineral wool to within 10mm of the surface of the casing and a 10mm deep layer of intumescenr caulk needs to be applied on top of the mineral wool
These are for 30 minute rating.1 hour requires a lot more. If the casi g has been foamed in the foam all needs to be removed - foam burns and some generates toxic fumes when burned. Even the old pink fire foam is a bit suspect (a lot of it decays with age and is no longer fire resistant agter 10 or 20 years). There is a modern blue fosm which some peoe use, but to date I am yet to work on a job which permits it
The doors are a different matter. They do need to be proper fire doors and FD30 doors are available in 35 and 44mm thicknesses. You need to hang them on fire door hinges with a gap of 2 to 4mm round the 3 sides and no more than 4mm st the bottom, although a drop seal on the bottom of the door can deal with that. The door needs an automatic closer and this must be fire rated. On new builds we often have to install intumescent pads beneath the hinges as well as wrap the lock or latch in intumescent (Intergraf), etc. Finally a replacement/upgraded door will need a groove (most likely 15mm wide x 4mm deep) routing around the three sides to accommodate a combinstion intumescenr/cold smoke seal strip (unless a new fire rated casing has been fitted, in which case tbe groove will already have been routed gor you in the casing).
The brush strip and drop seal are designed make it more difficult for smoke from a fire to get past the door opening still enough to set your alarm off, though) whilst the intumescent expands to fill gaps, thus slowing the progress of the fire snd giving the fire brigade a better chance of bringing the fire under control before it consumes the rest of the house. This is why fire doors and fire compartments are so important
My other concern is, my wall is only 76mm thick, is there a certain spec on how thick the fire door casing has to be?
Probably, but the immediate need is to stop smoke (which is the big killer) and after that to contain the fire for the specified period. On listed buildings the casings are often painted with intumescent paint as realistically there is no other option. If your door casing is a standard sort of thickness it shouldn't be an issue
Sorry for the long post