I'm part of a local charity that has had a number of FD30 doors fitted to existing frames. I'm looking for clarification/guidance on the thickness of the door check stops. At current the carpenter has fitted 19mm thick kiln dried timber. I've seen reference to 25mm stops. I was hoping to find clarification on this subject?

Thank you for your time.

Regards

25mm stops date back to the days before intumescent seals and smoke brushes existed and were a rudimentary way of forming a seal on a door  - if your doors are correctly fitted with intumescent seals (and if on an escape route smoke brushes) the 25mm stop is not required and a 19mm stop should suffice.

Is a 18 mm Mdf rebate ( slam strip )

sufficient on a new domestic fire door  ? 

or is pine  .this of course sjoupd be glued & pinned / screwed 

 

The new fire door will come with installation instructions or a technical data sheet. That information document will state door frame and planted stop requirements.

When would a frame with 25mm door stop need upgrading to include an intumescent strip if the the 25mm was a standard before?

Where the fire door is so critical to the fire strategy at the building that it is desirable to upgrade the fire performance of the door. Consider that all timber-based fire doors have had intumescent seals for around the past 30 years now.  So why wouldn't you fit them to a fire door?