Architects and clients often request ‘hidden’ doors on higher specification projects. This generally involves concealed door hinges which are invisible when the door is shut. 

Traditionally ‘Soss’ hinges were the main type used to fulfil the ‘hidden door’ brief, and we still sell many of these. They are available in a wide range of sizes and can be used for everything from small cupboard doors right up to FD30 and FD60 doors.

However, they do have the disadvantage of not having any adjustment, so that once morticed out there is no easy way of adjusting the position of the door within the frame.

This is where other, more recent, types of concealed hinges come into play – most notably the ‘Tectus’ brand. These have the added benefit of 3 dimensions of adjustment within the hinge body, so that the door can be precisely positioned. They also come in larger sizes and can cope with doors of up to 300kg in weight!

Obviously installing concealed hinges involves quite a lot of morticing into the door leaf and frame – more so than a conventional butt hinge. This consequently has a greater impact on the fire integrity of the door. What aspects therefore do I need to consider when fitting such hinges to fire doors?

Firstly, it’s critical that any concealed hinge you are considering has been through a successful fire test in an accredited test house to the level you are requiring (FD30/FD60).

Secondly, and very importantly, you must check the fire test data for the door you are using. Because of the specialist nature of concealed hinges, the fire assessment is normally quite specific on what models of hinge can be used.

For instance, the Warrington Fire Field of Application report (Chilt/AO2066 Revision 0) for the standard Strebord 44mm door core specifies the following hinges that may be used;

Simonswerk Tectus TE340 3D FR, TE540 3D FR, TE540 3D A8 FR, TE640 3D FR and TE640 3D A80 FR

Various other stipulations are made re the installation, including;

Hinges must be fitted according to the manufacturers instructions including using the supplied hinge fixings.

The mortice for concealed hinges must be no closer than 50mm to any aperture or other mortice or recessed area within the door leaf.

The hinges must be used in conjunction with a twin strip perimeter intumescent arrangement where one of the seals remains continuous past the hinge blade in the frame reveal or leaf edge.

The timber based frames must be hardwood of minimum density 640kg/m3.

For doors of leaf height 1201 – 2400mm, the top hinge should be 150-200mm from head of leaf to top of hinge. Second hinge should be Minimum 200mm from top hinge and maximum centrally between top and bottom hinge. The Bottom hinge should be 150-300mm from the foot of the leaf to bottom of hinge.

It is not permitted to fit more than 3 hinges unless the door is over 2400mm high – different hinge spacing pertains in this circumstance!

I have included all the above detail to illustrate the importance of carefully studying the door’s fire test assessment. It’s not enough to simply fit one of the hinges specified – their positioning, fixings and the frame details are also critical.

It’s worth noting that many of the Tectus fire rated hinges come with intumescent pre-installed within the hinge which makes fitting them simple.

We keep a Tectus jig which we rent out if you are needing it to make installation simpler – just get in touch to discuss!

If you are wanting to fit another brand of concealed hinge, it would be worth checking to see if another fire assessment would cover this.

In conclusion, concealed hinges are aesthetically beautiful but need a lot of care installing in a fire door situation!