35mm Fire Doors

Despite being 9mm thinner than regular fire doors, 35mm internal fire doors still carry the same FD30 rating - meaning they’ve been fully tested and certified to the same standard to stop the spread of fire and smoke, giving you and your family up to 30 minutes of valuable time to get to safety. They’re made to strict safety standards using fire-resistant cores, so while they’re thinner, they don’t compromise on safety and you can rest assured your home is protected. Whether you want the natural beauty of oak fire doors or you'd prefer something white and bright, like their chunkier siblings, 35mm internal fire doors are available in a wide variety of designs, from period-inspired to sleek and modern, in finishes with matching standard internal doors so you can keep the style consistent throughout the whole of your home.

Why choose 35mm fire doors?

• FD30-rated: offers 30 minutes of fire protection
• Slimmer 35mm thickness fits standard internal door linings
• Same safety performance and solid construction as standard 44mm fire doors
• Ideal for retrofitting into existing frames
• Available in a selection of popular designs & finishes

Whether you’re updating a single room or carrying out a full renovation, our 35mm fire door range makes it easy to stay safe without a full door frame upgrade.

35mm Fire Door FAQs

What is a 35mm fire door?

A 35mm internal fire door is a thinner version of the standard 44mm fire door, offering the same 30-minute fire resistance while fitting into traditional 35mm frames of standard internal doors. It’s a practical solution when you want the added safety of a fire-rated door but don’t want to replace your existing frames.

How is a 35mm fire door different from a 44mm fire door?

The main difference is thickness - 35mm fire doors are slimmer, designed to fit older or standard-size internal door frames, while 44mm fire doors are typically used in new builds or where a chunkier door is desired. Both types can be FD30-rated, meaning they offer the same level of fire resistance when correctly installed with compatible hardware and intumescent strips.

Are 35mm fire doors compliant with UK building regulations?

Yes, as long as they are at least FD30-rated and installed according to the fitting instructions with certified fire door hardware, they can meet building regulations for 30-minute fire protection. They are especially useful for retrofitting older homes where existing frames are only 35mm deep.

Do 35mm fire doors need special hardware?

Yes. To meet safety standards, all fire doors should be fitted with fire-rated hardware such as intumescent strips, self-closing hinges and certified latches. These help maintain the door’s fire resistance by eliminating any gaps in the event of a fire.

Can I trim a 35mm fire door to size?

Most internal fire doors can be trimmed slightly, but there’s usually a limit - often around 3mm per edge. Over-trimming can affect fire performance, so always check the door’s specification before making any adjustments. If you feel the trim allowance isn’t sufficient enough and you need to take more from the top edge for example, then made to measure 35mm fire doors might be a better option.

Which is better, 44mm or 35mm fire doors?

Both 35mm and 44mm internal fire doors can be equally effective at providing FD30-rated fire protection. So in terms of performance, neither is inherently better, as long as they’re tested and fitted properly.

44mm fire doors:

• Most common FD30 spec in the UK
• More heavyweight option
• Often fitted in new builds or commercial properties
• Slightly better sound insulation and thermal efficiency due to thicker core
• Will need 44mm door linings or adjusted frames

35mm fire doors:

• Perfect for retrofit projects - they slot neatly into standard internal door frames
• Avoids the need for replacing linings or architraves
• Lighter and easier to handle/install
• Still fully FD30 rated when installed with the right hardware

Choose 44mm if you’re working on a new build, doing a full refit, or want a more heavyweight feel. Choose 35mm if you’re upgrading fire safety in an older home and want to keep your existing frames. Both are safe and compliant, it just depends on your project needs. Need help choosing the perfect fire door for a specific room or frame? We’ve got you! Just contact our knowledgeable team who are always happy to help.