Upgrading doors in listed buildings presents some unique challenges because of the wide diversity of door construction in the UK’s historic building stock and the limitations placed on such work by the relevant authorities. The International Committee for Monuments, Statues and Historic Buildings (ICOMOS) insist on conservation directives that whatever methods are adopted, they be non-invasive and reversible. Our own English Heritage and National Trust similarly stress the importance of their own directives on non-invasive and reversible upgrading. In this article we highlight the issues involved in upgrading historic doors and identify ways in which intumescent materials can be used the meet these onerous requirements.
The Potential for Upgrading Panelled Doors
There are some basic issues to be addressed before embarking on an upgrading project, which centre on establishing if upgrading is a realistic option. If the property is not listed or of particular historical importance, the chances are that a replacement door is the most cost effective option. If upgrading is required for historic reasons or at the preference of the client than a careful survey of the door and frame is essential. There are no magic solutions that will turn an unsafe door into a safe one. There are, however, a fairly small number of failure mechanisms for doors in fire conditions.
Burn through of thin timber panels or around the edge of the panel under the beading.
Excessive distortion of the door leaf as it burns, creating large gaps between the door and frame. In extreme cases the door may even distort out of the frame.
Failure of non-fire rated glazing.
Structural joints in the door may fail.
Lock cavity burn through.
With all these cases, steps can be taken to prevent them becoming a major problem and a thorough inspection will help to identify the areas that require treatment.
Selection of materials for upgrading panelled doors
General Condition
The door leaf should be checked for visible damage. If upgrading is to be non-invasive then the door leaf must be sound, particularly at the edges. Intumescent strips can cope with some damage; it is possible that using more intumescent material will be satisfactory, supported by relevant test evidence.
Substance
The door must be substantial enough to be the subject of upgrading. Modern fire doors are usually al least 44mm thick and so careful evaluation will be required for any door less than this thickness. It may even be necessary to carry out tests on a replica to establish a satisfactory solution. The condition of the framing joints may also be a consideration and may require additional gluing or mechanical fixing. As a rough guide, a panelled door with 35mm thick and 75mm wide stiles and rails is likely to be satisfactory provided that suitable panel treatment is employed.
Panels
The type and condition of the panels will have bearing on the treatment method e.g. whether they are flat, raised and fielded or perhaps glazed. In the case of timber panels a minimum thickness of 6mm would normally be required for upgrading to be viable. The edge detail where the panel meets the stiles and rails is particularly important, as this is generally the most vulnerable area of the door. Upgrading methods using intumescent sheet material laminated with thin decorative plywood have been developed which, in combination with an appropriate intumescent sealant, can successfully upgrade timber panels in historic doors. The decorative plywood surface may be painted, varnished, stained or even veneered to reinstate the appearance of the door. In the case of glazed panels replacement with appropriate fire rated glass together with the relevant fixing details including intumescent seals will be required.
Ironmongery
This is another area requiring careful attention. Whilst the relevant code of practice in the area, BS 8214 states that intumescent protection is not required for FD30 rated door sets, in the case of existing ironmongery on an historic door such protection is certainly recommended. It may be necessary in some cases to install replacement or additional ironmongery. A self-closing device will also be required.
Frame Gaps
The aim should be to achieve a maximum leaf/frame gap of 3-4mm and for this to be even around the leaf perimeter. It is particularly important that the leaf to frame gap can be maintained. Most intumescent materials are designed to tolerate 3-4mm gaps so if larger gaps are unavoidable an intumescent seal with appropriate test evidence to satisfy the larger gap will be required.
Frames
For FD30 applications most existing frames will be sufficient however they must be checked for mortices cut to hold now-removed ironmongery. Perhaps of greater importance is the junction between the frame and the surrounding construction. This must be investigated by removing the architraves and any gaps sealed with an appropriate intumescent material such as a sealant, strip or flexible joint seal.
Finding the right solution for your doors
It is dangerous to consider a single “blanket” solution to upgrading all doors. Every door must be subject to a separate evaluation and the regime used must be tailored to the individual door set.
Many claims are made regarding the suitability of materials for upgrading but the individual nature of historic doors means that careful scrutiny of material claims must be made to ensure that they can be substantiated for the application under consideration.
Conclusions
To summarise, the following factors are worth considering to establish whether upgrading is a realist option:
Is the condition of the door and frame sufficiently substantial for upgrading to be an acceptable option?
Can the door set be maintained with acceptable leaf to frame gaps?
Are the panels sufficiently sound and of an acceptable thickness. If glazed panels, what changes will be necessary to improve the glazing detail?
Does the manufacturer of the door upgrade system provide test evidence relevant to the project in hand?
What changes or protection will be acceptable to improve the performance of existing ironmongery?
Will existing closers perform adequately and if no closers are fitted, can one be fitted?
Are the upgrading systems proven to be non invasive and reversible and can the upgrade system be treated to meet the aesthetic standards of the project?
Does the manufacturer of the upgrade system provide an initial survey?
Does the manufacturer provide a specialist contracting service, devoted to maintaining the door sets in a functional and safe manner, with resultant indemnity to the client in the event of claims arising out of the product’s performance?
Upgrading historic doors is not a simple matter but it is possible to have confidence in proven systems that can be effective and non-invasive.
Prepared by Bob Settle, Divisional Manager for Sealmaster, a founder member of the Intumescent Fire Seals Association, and a past Chairman of IFSA.
