Check out page 30 of approved document part b fire safety.
Internal garage fire door regulations.
Only common walls between garage and house not perpendicular walls must meet this requirement.
You also need to check the floor of the garage which is detailed on the same page.
Internal doors to integral garages should be fd30 fire doors and include smoke seals and self closing devices.
If you are replacing internal doors like for like and do not currently have any fire doors then no standard doors are fine.
For a typical two storey domestic home the building regulations require that where the property has an integral garage the door between the main property and the garage normally kitchen or utility should be a fd30 fire door 30 minute fire resistant and include smoke seals and self closing device it is also recommended that the garage floor be at least 100mm lower than that of the property to prevent any fuel spillage entering the main property.
When there is a living area habitable space above the garage the ceiling requirement ramps up to 5 8 type x fire rated drywall.
This means a door with a two hour rating for example can be expected to resist combustion for two hours in the event of a fire.
Fire ratings measure the amount of time that a door is able to contain the spread of fire as tested according to nfpa guidelines.
However before doing so consider and check the following.
These are the only doors inside a dwelling that require self closing doors garage floors should also be sloping outwards or at least 100mm lower at these doors to prevent fuel spillage leaking in to the home.