The 3 mm to 1 mm Fire Door Gap: What the Geometry Is Telling You

The 3 mm to 1 mm Fire Door Gap: What the Geometry Is Telling You Related diagnostic: How Should You Measure Fire Door Gaps for Fault Finding? explores the connected frame-fixing or gap-measurement issue and helps compare the evidence before choosing a repair. A 3 mm to 1 mm change is useful because it is a pattern rather than a single measurement. It says the relationship between the leaf and frame is changing along the opening. The 3 mm to 1 mm example is a diagnostic geometry example, not a universal pass/fail limit. BWF generally gives 2–4 mm for the side and head gap, while the permitted bottom clearance is manufacturer- and doorset-dependent. I would not start by cutting the door simply because one point is tight. What the pattern is telling you Then measure the same edge at the…