Is Your Fire Door Really Fitted Right? 7 Faults Installers Often Miss

Doors fitted by other trades fail inspection far more often than owners expect, and one fault is enough to fail. Our inspectors find them with a gap gauge, a torch, and a close look at the frame. Trust a measurement over a builder’s reassurance.

A fire door is a tested assembly. The leaf, frame, seals, hinges, closer and fixings must work together exactly as they did in the test. Get one part wrong, and your FD30 door behaves like an ordinary door when it matters most. Most builders and carpenters are skilled at their trade. Fire doors are a different trade.

Key takeaways

  • Seven faults turn up again and again.
  • Most are visible without tools.
  • A five-minute check catches many.
  • Any door on your escape route deserves a specialist’s eye.

Our Inspection Method

Our inspectors examine doors fitted by builders, carpenters and general contractors, not certified fire door installers. The doors come from flats, HMOs, houses and loft conversions, and include both FD30 and FD30S types. Each one is checked against its certification using a gap gauge, a torch and the handover paperwork. Any one of the faults below can fail a door, and how strictly it is judged depends on the inspector.

The Seven Most Common Fire Door Fitting Faults

1. Excessive Gaps Around the Door and Frame

The fault: The head and side gaps should be about 3mm, within an accepted range of 2mm to 4mm. The door’s certification has the final word. Oversized gaps let fire and smoke straight through.

How to identify it: A £1 coin is about 2.8mm thick, so it works as a rough screen. If it slides through with room to spare, the gap is too wide. A gap gauge gives the real answer. Measure at the top, then at the top, middle and bottom of each side. Gaps well beyond 4mm are a common sight on doors hung by eye, and any gap you can slide a finger into is a clear fail.

The bottom gap is where fitters slip most. A fire only FD30 door often allows 8mm to 10mm at the threshold, depending on the manufacturer. Where smoke control is required (FD30S), it drops to about 3mm. Many carpenters apply 3mm everywhere. Others leave the bigger gap on a door that needs the smaller one.

FD30 threshold gap: 8mm to 10mm, check the manufacturer.
FD30S threshold gap: about 3mm.

The remedy: Rehang the door to the certified gaps, or replace it.

2. Incorrect Intumescent Fire and Smoke Seals

The fault: Seals are fitted, but they are the wrong ones. Where smoke control is needed, the door requires combined fire and smoke seals. A fire only strip does half the job.

How to identify it: Check the seal markings against the door’s certification. Do not assume that any strip in the edge is the right strip.

Why it matters: Smoke reaches people before flames do.

The remedy: Replace the seals with the product named on the certificate.

3. Missing or Ineffective Door Closers

The fault: No closer has been fitted, or the one in place is too weak to shut the door.

How to identify it: Open the door halfway and let go. It must close fully and latch every time.

Why it matters: A door left ajar protects nobody. It is simply a door.

The remedy: Fit a correctly rated closer and adjust it so the door latches without a slam or a gap.

4. Non Compliant Hinges, Latches and Handles

The fault: Hardware is part of the tested assembly. Cheap hinges, the wrong number of them, or a latch that does not hold the door shut all count as faults.

How to identify it: Count the hinges, look for markings on them and check that the latch actually engages.

Why it matters: Hardware that softens in heat lets the door sag and open.

The remedy: Replace it with hardware that matches the certification.

5. A Frame Not Prepared for an FD30 Door

The fault: The frame is out of square or the wrong size, so the door gets planed or forced to suit it.

How to identify it: Look for uneven gaps, a door that rubs or a leaf that will not sit flush.

Why it matters: Trimming a fire door to fit a bad frame wrecks the tolerances the door was tested to.

The remedy: Correct the frame. Never fix a frame problem by cutting the door.

6. Inadequate Fire Stopping Around the Frame

The fault: Behind the architrave, the gap between frame and wall needs proper fire stopping. Ordinary sealant and expanding foam are not intumescent or fire rated. Gaps left unsealed are just as bad.

How to identify it: You cannot see it, and that is exactly why this fault survives. Ask what was used and ask for photographs.

Why it matters: Fire will go around a perfect door if the wall opening beside it is open.

The remedy: Remove the architrave, fire stop with the correct material, then refit.

7. Missing Documentation and Installation Photographs

The fault: Nothing was handed over at completion, and no photographs were taken during installation to show what is now hidden behind the architrave and plasterwork.

How to identify it: Ask for the door’s certificate, the installer’s declaration and the installation photographs. A builder’s word is not a sign off, because builders cannot sign off fire door work as compliant.

Why it matters: Without proof, nobody can say the job was done properly, and an inspector may fail it.

The remedy: Obtain the documents and photographs from the installer, or have the door independently inspected.

A Five Minute Visual Check You Can Carry Out Yourself

  1. Measure the head and side gaps with a gap gauge, or a £1 coin as a rough screen.
  2. Open the door halfway, let go, and check that it closes fully and latches.
  3. Run your eye along the seals and look for breaks, paint over them or missing sections.
  4. Count the hinges and look for a certification label on the door edge.
  5. Look for gaps between the frame and the wall.

This check cannot confirm that the door is certified or that its fire rating is genuine. Only the paperwork and a specialist can do that.

When to Instruct a Specialist

Call one if the door fails any step above, if nothing was supplied at handover, or if the door sits on an escape route. Every door on an escape route must be a compliant fire door. Landlords, insurers, Building Control and your fire risk assessment will all ask for proof. Our inspection service covers all of it, so get in touch before someone else asks the question.

Frequently Asked Questions

What size should the gap around a fire door be?

The gap around the head and sides should be about 3mm, with an accepted range of 2mm to 4mm. The door’s certification is the final authority, because tested gaps vary by manufacturer. Measure with a gap gauge at several points along each edge, not just one.

Only as a rough screen. A £1 coin is about 2.8mm thick, so it shows quickly whether a gap is roughly right. It cannot tell you whether a gap is 2mm or 4mm, and it says nothing about the threshold. A gap gauge gives the real measurement.

On a fire only FD30 door, the bottom gap is often 8mm to 10mm, depending on the manufacturer. Where smoke control is required (FD30S), it drops to about 3mm. Check the certification for your exact door before adjusting anything.

FD30 resists fire for 30 minutes. FD30S does the same and also limits smoke, using smoke seals and a tighter bottom gap. Your fire risk assessment or Building Control will tell you which one applies to each door in your building.

A carpenter can fit one, but the work must still match the door’s certification, and many trades do not know how. A certified installer or an independent inspection gives you proof. Builders cannot sign off their own fire door work, so a second pair of eyes matters.

Look for a label or plug on the door edge, then ask for the manufacturer’s certificate and installation documents. No label and no paperwork means you cannot prove the door is certified. Treat it as unverified until a specialist confirms otherwise.

Only within the limits set by the manufacturer, and only if the certification allows it. Planing too much removes strength and the space the seals need. If a door needs heavy trimming, the frame is probably wrong. Fix the frame, not the door.

It depends on the building and your fire risk assessment. Doors in communal areas are generally checked more often than doors inside a single home. Inspect after any building work, and any time a door sticks, rubs or fails to close.

The gap around the head and sides should be about 3mm, with an accepted range of 2mm to 4mm. The door’s certification is the final authority, because tested gaps vary by manufacturer. Measure with a gap gauge at several points along each edge, not just one.

Only as a rough screen. A £1 coin is about 2.8mm thick, so it shows quickly whether a gap is roughly right. It cannot tell you whether a gap is 2mm or 4mm, and it says nothing about the threshold. A gap gauge gives the real measurement.

On a fire only FD30 door, the bottom gap is often 8mm to 10mm, depending on the manufacturer. Where smoke control is required (FD30S), it drops to about 3mm. Check the certification for your exact door before adjusting anything.

FD30 resists fire for 30 minutes. FD30S does the same and also limits smoke, using smoke seals and a tighter bottom gap. Your fire risk assessment or Building Control will tell you which one applies to each door in your building.

A carpenter can fit one, but the work must still match the door’s certification, and many trades do not know how. A certified installer or an independent inspection gives you proof. Builders cannot sign off their own fire door work, so a second pair of eyes matters.

Look for a label or plug on the door edge, then ask for the manufacturer’s certificate and installation documents. No label and no paperwork means you cannot prove the door is certified. Treat it as unverified until a specialist confirms otherwise.

Only within the limits set by the manufacturer, and only if the certification allows it. Planing too much removes strength and the space the seals need. If a door needs heavy trimming, the frame is probably wrong. Fix the frame, not the door.

It depends on the building and your fire risk assessment. Doors in communal areas are generally checked more often than doors inside a single home. Inspect after any building work, and any time a door sticks, rubs or fails to close.

Conclusion

Most of these faults are small, visible and fixable. A wrong gap, a missing closer and a missing certificate are all easy to correct once someone spots them. The danger is that nobody looks. Doors fitted by other trades fail far more often than owners expect, and yours could be one of them. Book an inspection or request a quote from Fire Door Solutions, and find out before a fire does.

Fire door installer

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