I need advice on how to fit the new fire door casing 6" / 150mm around the stair case.

How much of the door frame can be cut at the bottom around the second step on the stair case without jeopardising the fire rating of the door set? if you look at the pictures you will see how the original door casing was wrapped around the stair tread and stair string, on the hinge side it's going over the stair string and on the latch side the door casing is cut around the stair string.

Can the new fire door casing be fit like the original door casing was fitted?

Or Can the new fire door frame be cut around the stair tread so not to damage the second step by leaving 70mm of the fire door frame at the bottom where the stair string and door frame meet? that way it will avoid the second step on staircase on both sides.

or does the whole door casing need to be continuous and go all the way down to the first step so would have to cut into the second stair tread and riser? like some bm trada installers have suggested.

thank you for your help.

In order to comply with the fire door manufacturer's evidence of fire resistance performance (and therefore BS 8214: 2026) the door framing sectional dimensions* must 'continuously' be at least that specified by the installation instructions or certification data sheet for the door leaf. Therefore, the door frame should not be interrupted at any point.

*commonly 32mm thick by 70mm wide as a minimum, but check the door leaf installation data.

Are you sure that this needs to be a fire door?

Building regs (part K) requires a safe, level, landing at the top and bottom of a flight of stairs and no door swing can encroach closer that 400mm to the front of any step.

The current situation creates an enormous tripping hazard

Hi Neil,

thank you for that information, so the 70mm width for the door casing would avoid both the stair tread and riser and the door frame can be cut around the staircase string with some fire mastic or fire foam between the fire door casing and staircase string.

Hi Mike,

yes i have been advised by council housing standard inspectors that i need to change this original staircase door for a FD30S door as it leads onto second and third floors of the terraced house.

Does this new building regulation (part k) apply to a untouched historic stair case / door that was constructed over 150 years old? thank you.

Not until you make a material alteration to the premises, like changing the door. 

The changing of the door must be done in compliance with building regulations which includes part K.

Would it be possible to create a small lobby at the foot of the stairs and turn the door 90deg?

Is this a single family dwelling house?

Why has FD30(s) been specified by "Council Housing" - rather than FD20?

And are the Regs being applied retrospectively?

Approved Document B Table C https://assets.publishing.service.gov.uk/media/67d2bb074702aacd2251cb94/Approved_Document_B_volume_1_Dwellings_2019_edition_incorporating_2020_2022_and_2025_amendments_collated_with_2026_and_2029_amendments.pdf

Whilst I agree that ADB calls for a FD20 door.

Unfortunately, FD20 doors are rarely manufactured or certified today, the current standard is now FD30

"Whilst I agree that ADB calls for a FD20 door". It was the restricted smoke spread requirement that struck me, notwithstanding that self-closing is not a requirement.