Can I fit flush bolts to a fire door?

There are several aspects to be aware of, including intumescent protection, length and the material the bolt is made of.


The first thing you must be sure of is that the flush bolt you are proposing to use has been included in a successful fire test, and what intumescent was used in conjunction with the bolt in that test. Our BFA030 flush bolt was tested with a 2mm thick graphite-based intumescent behind both the bolt and the keep plate, for both FD30 and FD60 applications. With this in mind, we will always allow for 2mm intumescent when we quote, even though the fire test on your door core may allow for a 1mm thick intumescent instead.

In addition to this, (and these points and diagram below are specifically with regard to our BFA flush bolt) where the bolts are fitted in the meeting edge of doors, they can often interrupt the fire strip running up the edge of the door. In FD30 applications, at least 7mm of the strip should by-pass the flush bolt, whilst a full width strip of minimum 15mm wide should be fitted in the leading edge of the primary door leaf. The same applies in FD60 applications, except that in this case a minimum of 12mm of the fire strip should by-pass the flush bolt.

Also to be considered in FD60 applications is the keep plate positioning in the head of the frame. The fire strips in the head should by-pass the keep by a minimum of 9mm each side or 15mm to one side only (if the bolt is face fixed to the door).

The diagrams below may help to explain these points.


Often on a tall door, a longer top bolt is preferable to make operation easier. However whilst our Flush bolt is tested up to length of 609mm, it shouldn’t be automatically assumed that the door fire test will accommodate lengths like this.

For instance, the IFC Field of Application report IFCA/06166 Revision C for the Halspan Prima 30 door core stipulates a maximum dimension of 250mm long x 20mm wide x 19mm deep for flush bolts.

Other door cores have similar restrictions, so this should always be checked before fitting any flush bolts over 203mm long.


To ensure that the bolt doesn’t melt, many fire door tests will stipulate that it is made from steel. Lower grade materials should not therefore be used, nor any materials that are combustible – for obvious reasons!

Please do get in touch if we can help you further with fire compliance queries. We are trade only suppliers to commercial and refurbishment contractors, fire door manufacturers and installers, facilities management and maintenance companies.

Review of this page due November 2022. Please note that advice given is advisory only and to the best of our knowledge at time of writing. We cannot be held responsible for loss or damage incurred as a result of actions taken based on this article.

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