3 Panel Oak Fire Door

You’re not buying a door. You’re buying time. Time to escape, time for the brigade to arrive, time to protect lives. That’s what a correctly installed fire door gives you. After 40+ years helping customers choose and supply internal fire doors across homes, flat entrance doors, schools and plant rooms, we’ve learned this: the products matter, but the installation matters more. 

This comprehensive guide blends manufacturer-backed steps from our current fire door range, the fire door regulations you must meet in the UK, and the real-world checks our team uses on site to ensure correct installation and reliable fire performance.

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A note on FENSA certificationIn England and Wales, replacing an external door (including patio doors, bifold doors, French doors, and glazed front or back doors) counts as notifiable work under Building Regulations. The simplest way to stay compliant is to use a FENSA-registered installer. FENSA (Fenestration Self-Assessment Scheme) is a government-authorised scheme that allows approved installers to self-certify the work on your behalf, so you won’t need to notify your Local Authority Building Control (LABC) separately.  Once complete, you’ll receive a FENSA certificate: an important document to keep safe, as you’ll need it if you ever sell your home. If your installer is not FENSA-registered, you or they must apply to LABC before work begins.

Fire door installation guide: what makes a compliant fire door work

A fire door is a tested system. The door leaf, fire door frame, hinges, seals, self closing device, latch, lock, and even the frame fixing method work together to provide adequate protection in a fire. Switch one component, trim the door leaf the wrong way, or fit the intumescent strips to the wrong surface, and the door’s performance can fail.

In the UK, fire door installation is regulated by the Building Regulations 2010, and fire door testing is carried out to British standards like BS 476 Part 22 or BS EN 1634 Part 1. For timber fire door sets, BS 8214:2016 gives practical guidance on installation. Your goal is simple: ensure correct installation in line with the specific product’s test evidence and the manufacturer’s instructions. That is how you protect lives and comply with the legal requirement.

From our current range:

• We stock internal fire doors from UK fire door suppliers who provide fire resistance rating (FD30/FD60) details, and installation instructions.
• Many of our FD30 door leaf options arrive pre-lipped on the door edge to limit on-site trimming. The acceptable trim size can differ by model, so check the data sheet on the product page before you cut.
• Frames may be supplied as part of a fire door set, or you may purchase a compatible fire door frame separately. Either way, the frame and leaf must match the certification.

Always read the fitting instructions for the exact model you buy. Fire door installation is not “all done the same way”.

Cobham Black Oak – Prefinished FD30 Fire Door

How to fit fire doors: the essentials we would always check

Here’s the practical flow fit for many of our products, recommended when installing fire doors. Treat it as a framework, then map each step to your specific model’s documentation.

1) Prepare the opening and frame

• Make the structural opening true and plumb. Installation should consider the site’s structural conditions to avoid distortion. A twisted wall will create unfixable gaps.
• Position the fire door frame square and plumb. Use appropriate frame fixing methods at the centres given in the installation instructions. Avoid packing right at fix points which can bow the jamb.
• Fill the frame to the wall gap as specified. Many timber sets allow mineral wool or a tested fire-resistant foam, then seal over with approved mastic. Follow the manufacturer’s instructions.

2) Hang the door leaf

• Use three CE marked, fire-rated hinges, with intumescent hinge pads where required by the test evidence. Hinge screws should be the specified size and length.
• Check the door leaf to frame the gap. Most internal fire doors call for 2 to 4 mm on the sides and head. The threshold gap is typically 8 to 10 mm unless a drop seal is specified. Verify your model.
• Never plane the hinge edge beyond the permitted trim. Over-trimming is a common incorrect installation error that can void certification.

3) Fit seals, hardware and closer

• Intumescent strips and smoke seals must be fitted exactly as specified. Some products place them in the frame, others in the door edge. Do not mix and match.
• Install a compliant self closing device and adjust it so the door latches from any open position without slamming. Fire doors must not be propped open.
• Fit the latch/lock listed for the door’s test. If your fire door allows air transfer grilles, they must be fire-rated types included in the door’s evidence set.

4) Final checks and documentation

• Test close several times. Confirm consistent latching and that seals make contact without dragging.
• Record the installation: product codes, fire rating, installer details, and any adjustments. Documentation of the installation is necessary for compliance.
• Book regular fire door inspection intervals, especially in multi-occupancy buildings.

NOTE: Installing a fire door is a specialised task requiring precision. If you’re unsure at any point, bring in a competent person who can demonstrate knowledge of fire door installation standards and product-specific test evidence.

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How to fit internal fire doors: model-specific cautions from our range

Across our internal fire doors, two themes cause most on-site issues: trimming and seals.

• Trimming allowances differ. For example, several FD30 timber fire door leaf models in our range permit limited trimming on the bottom only, while edges are factory-lipped and must not be reduced beyond a couple of millimetres. Exceed that and the door can be incorrectly installed against certification.
• Seals are not universal. Some ranges supply combined intumescent and smoke seals for the frame. Others expect separate intumescent strips in the door edge and smoke seals in the frame. Always use the specified size, position and brand where named.

Where we see clean installs, teams slow down for these three checks:

• Confirm the threshold gap with the actual floor finish, not the plan.
• Check the door leaf stamp and labels match the paperwork.
• Dry-fit the leaf on the hinges before routing for seals, then mark exact seal locations.

How to fit intumescent strips to fire doors

We get asked this every day, so here’s a practical overview that aligns with most of our current door sets. 

Your model’s data sheet takes priority.

Do fire doors need intumescent strips on the bottom?

Usually no. The bottom is managed by an approved threshold gap or a specific drop-down seal named in the door’s certification.

Do intumescent strips go on the door or frame?

Often the frame, but not always. Some fire resistant doors specify strips in the door edge, others in the frame. Follow the door set’s evidence. Mixing positions can compromise fire and smoke control.

Are intumescent strips easy to fit?

Yes, if you route the correct groove size and keep a continuous path around the head and jambs. Avoid gaps at the mitres. Press the strip in evenly and avoid stretching.

Steps we follow:

1. Mark the groove position per the instructions. Most call for a 10 to 15 mm wide groove, depth set for the strip thickness.
2. Rout clean, continuous grooves. Vacuum out dust so adhesive sticks.
3. Install intumescent strips or combined intumescent seals and smoke seals. Keep the carrier flush with the surface to achieve the correct door leaf clearance.
4. Check latch and hinge locations. Use intumescent hinge pads and lock protection kits where required.
5. Close the door and confirm uniform contact without excessive friction.

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Fire door installation tips from our technical team

• Treat the door as a tested system. Swap components only for those listed in the certification.
• Avoid over-packing behind hinges. It can twist the stile and create a tapering gap.
• Don’t paint over smoke seals. A painted fin can stick or tear, reducing smoke control.
• Verify substrate. Some fire door sets are tested into timber, others into block. Match the frame to the wall type as per the test evidence.
• Check floor clearance with carpets and underlay in place. That’s how you achieve the right threshold gap without rework.
• Label everything. Keep certification and installation records available for your fire risk assessment and future audits.

Fire door installation checklist

Use this quick on-site list to avoid the most common fire door installation errors:

• Opening plumb and square; frame fixing at specified centres
• Gaps 2 to 4 mm at head and sides; threshold gap as specified
• Three CE marked, fire-rated hinges fitted with correct screws
• Intumescent hinge pads fitted where required
• Intumescent strips and smoke seals installed to the correct surface
• Approved self closing device fitted and adjusted to latch reliably
• Lock and latch listed in the test evidence
• Frame to wall gap filled as specified, using approved materials such as mineral wool or tested foam and mastic
• Door closes and latches from any position; not binding on floor
• Documentation completed and stored for compliance

Black Heritage 3 Panel Fire Door

DIY fire door installation: can you fit a fire door yourself?

Short answer: you can, but you probably shouldn’t unless you’re confident with the standards and your model’s documentation. Fire door installation requires knowledge of building regulations, British standard guidance, and the specific fitting instructions for your door set. A competent person should carry out the work. Many responsible landlords require installers to be members of accredited schemes such as FIRAS. The reason is simple: incorrect installation puts people at risk and can void insurance.

Why customers choose DoorsDirect2U for fire doors

• We include VAT in our prices and offer free mainland UK delivery.
• Family-run with 40+ years of know-how. If you ask how to fit internal fire doors for a specific model, we’ll send the exact manufacturer’s instructions rather than guesswork.
• Wide range from recognised fire door suppliers, including options from Green & Taylor and ATT Fabrications, and compatible fire door accessories like intumescent seals, CE marked hinges and closers.
• 10-year warranty on many products and an excellent TrustSpot rating. Reliable products, backed by people who pick up the phone.

Summary and key takeaways

Fire door installation isn’t about hanging a heavy slab. It’s about building a tested system that can save lives when it matters most. Key takeaways:

• Match door leaf, fire door frame, seals, hinges, latch and self closing device to the certification. Mixing parts risks incorrect installation.
• Hold gaps to 2 to 4 mm at head and sides, and follow the specified threshold gap. Check with finished floor levels.
• Fit intumescent strips and smoke seals exactly where the manufacturer specifies. Use intumescent hinge pads when required.
• Budget around £250 to £300 for professional labour per internal fire door, with total supply and fit depending on design and fire rating.
• Keep records. Book regular fire door maintenance and inspection.

Next steps:

• Browse our fire resistant doors and internal fire doors range and choose your style and fire rating.
• Find specific installation instructions and test evidence for the exact product you’re buying, so you can ensure correct installation from day one.

Shop FD30 Internal Fire Doors