How do you measure the gaps on a fire door?

What you need

A gap gauge or tester card is the usual tool. Government guidance mentions gap tester cards for this check. They are cheap and show the gap at a glance, and a set of feeler gauges does the same job. A pen and a way to record the numbers are the rest. The check is visual and needs no specialist equipment, though knowing what you are looking at helps.

Steps

1. Close the door fully. Let it shut on its own if it has a closer, so you measure how it really sits. Make sure the latch has caught. 2. Check the hinge side. Look for the gap between the leaf and the frame at the top, middle and bottom hinge. It is the hardest side to read, so look for an even line. 3. Measure the latch side. Take readings near the top, the middle and the bottom. This side shows a dropped door first. 4. Measure the top. Take a reading at each end and the middle. 5. Measure the bottom. Take readings at both corners and in the middle. Government guidance says to keep the bottom gap as small as practicable without the door snagging on the floor. Many doors can have a larger bottom gap, but the limit comes from the door's own test evidence and manufacturer, so check it. 6. On double doors, measure the meeting edge. Read the gap at the top, middle and bottom where the two leaves meet. 7. Write the numbers down. Note the door number, the position of each reading and the result in millimetres. Take a photograph of any gap that looks wrong.

Reading the results

The door's own certification or test evidence, and the manufacturer's fitting instructions, take precedence over general figures. If you have those, check them. Our guide to fire door gap tolerances goes into the figures, and our fire door repairs page covers fixing them.

Common mistakes

Measuring with the door open or on the latch. The gap changes once the door sits home. Measure shut.

One reading per side. A single reading hides a twist. Three points show the shape of the gap.

Using a ruler on a narrow gap. A ruler is hard to read at 3mm. A gauge is quicker and more accurate.

Ignoring the seals. A gap of 3mm is no use if the intumescent strip has been painted over or is missing. Look at the seal while you are there. See intumescent strips and smoke seals.

Not recording it. Gaps change over time. A record from last quarter tells you whether a door is slowly dropping.

When to call someone

In blocks of flats above 11 metres the responsible person has to check communal fire doors at least every 3 months and flat entrance doors at least every 12 months. Gap checks are part of those. A trained caretaker or housing officer can do the visual check. A detailed inspection measures every door and records the defects. See fire door inspections, or our fire door inspection checklist for the wider list.

Sources

• Fire Safety (England) Regulations 2022: fire door guidance (GOV.UK)