Architrave V’s Shadow Gap: A Commercial Perspective

Chris Robinson , Aug 12, 2021 4:29:38 PM

Architraves or Shadow Gaps. The aesthetic choice is tantamount to marmite. Love them or hate them, when installing doorsets, we need one of them.

For your consideration, we list the pros and cons of either option, and highlight the costs associated with both when installing typically rated FD30 and FD60 fire rated doorsets.


An architrave is a form of interior molding that is featured in most buildings. It is the strip of material that fits on either side of a doorset – covering the joint between the doorset and wall.

For an architrave to have purpose within fire certification, it must be at least 15mm thick. Furthermore, it must cover the frame by at least 15mm, as well as the entire gap between the frame and structural opening and the wall by 15mm. Gone are the days of buying 44mm wide architraves. Consider 57mm or even 68mm wide as a minimum.

diagram of fire stopping product

There is no specification regarding the timber materials used for architraves, but we would recommend a material of equal or greater density than the door frame. MDF makes for good architraves also.

Architrave has a small influence in a fire test. This gain is achieved when considering the fire stopping required to fill the gap between frame and structural opening. If architraves are used, then gaps up to 20mm may be filled with proprietary fire-stopping product (e.g. expanding PU foam or preformed compressible intumescent foam). Products must be tested for this application to BS 476: Part 22: 1987 or BS EN 1634-1.

This foam is by far the cheapest way to treat the fire stopping.

Commercially allow for:

-2 sets of architraves.

-One tube of PU foam will typically treat 2 to 3 single doorsets.

-15 minutes to apply foam and trim off. (Foam must be applied from both sides of the frame. Installing architraves to one side before foaming is bad practice)

-20 to 30 minutes to install architraves (x2)

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Advantages of Architraves

-They can mask architectural flaws such as uneven walls or workmanship flaws such as cracked plaster or imperfect finishing. (Consider the permitted tolerances between the two and gaps can vary significantly)

-They can hide that joint and any following shrinkage and movement between the structural opening and doorframe.

-They act as a barrier to protect the doorframe.

-They provide a defined line for decoration between the structural opening and doorframe that, if used in contrast, provides additional colour differentiation for DDA.

-They allow skirting board to finish neatly to the doorframe.

Shadow Gap

The shadow gap frame has a feature groove at the junction between the frame and the wall, creating a modern and minimalistic feel. Shadow gap profiles eliminate the requirement for architraves, allowing for a more contemporary design and feel.

Whilst eliminating the architrave, consideration must be given to the termination of the skirting board when it meets the doorframe.

Consideration must also be given to the continuation of fire certification. Compliance with fire certification is split between both doorset installer and dry liner. Risk, co-ordination, and compliance, therefore, become the responsibility of the main contractor.

For a shadow gap to have a purpose within fire certification, it must not exceed a maximum permitted size of 10 x 10mm.

There are strict rules regarding the treatment of the fire stopping between the doorframe and structural opening which incorporates some intensive fire stopping practice.

Shadow gap

Alternative 1. In its crudest form, a shadow gap can be created using a 10mm sold timber packing piece capped with a 2mm intumescent mastic capping or 10 x 4mm PVC encased intumescent seal. However, this is almost impossible to achieve as there is no tolerance between structural opening and doorframe. (Consider the permitted tolerances between the two and gaps can vary significantly)

Alternative 2 omits the solid timber packer and substitutes proprietary fire-stopping product (see architraves) capped with a 2mm intumescent mastic capping or 10 x 4mm PVC encased intumescent seal. Again tolerances are small and this practice involves filling the entire void with foam, allowing it to set before raking out the shadow gap and capping the shadow gap base with fire mastic.

Alternative 3 sets the doorframe into the studwork before boarding, treating the gap with proprietary fire-stopping product before double boarding with the second board forming the shadow gap. Certainly a neat solution, but with the cost of double boarding all the wall and inserting a proprietary plaster trim to finish the edge of the plasterboard.

Alternative 4 increases the thickness of the doorframe by 10mm and forming the shadow gap in the doorframe. The frame is installed before the single plaster board and the gap treated as above. The additional cost of a plasterboard trim and significant co-ordination (revisits) in labour is required.

For alternative 4, commercially allow for:

-Increased thickness of doorframe.

-2 sets of plasterboard trims

-One tube of PU foam will typically treat 2 to 3 single doorsets.

-One tube of fire mastic will typically treat 2 single doorsets.

-30 minutes to apply foam and rake out / trim off. (foam must be applied from both sides of the frame.

-20-30 minutes to apply fire mastic.

-20-30 minutes to apply plasterboard trim.

-Revisits from plaster boarders.

Advantages of Shadow Gaps

Excluding the aesthetic consideration (of which there are several) we see no advantage in choosing a shadow gap over an architrave.


RW Joinery has significant experience in the treatment of fire stopping between doorset and structural openings from both the certified manufacture of fire doorsets and the certified installation of the same. Outside “normal” fire certification, we have an extensive library of fire assessments covering interactions between veneered timber or cementitious wall paneling, steel cover trims and the like. Get in touch to find out more.

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