From TRADA Wood Information Sheet 1-47, published March 2005
Timber external doors are attractive, durable and have the added advantage of being produced from one of the world’s few renewable resources. They are available in a wide range of types from solid timber to insulated components faced with wood-based board products, giving the designer a broad choice of colours and designs.
An external door has a demanding role to perform and is expected to maintain its level of performance over many decades. It is mechanically stressed throughout its life due to opening and closing. Its inner face is subjected to the heated dry interior of the building, whilst the outer face is often exposed directly to the elements, unless protected by a porch or generous canopy. It is often installed into a building which has not yet dried out, yet it is expected to remain flat and maintain the designed door-to-frame gaps both during and after the drying out period.
Expectations for external doors have increased over recent years with heightened emphasis on thermal performance, sound insulation and security, in addition to keeping out the weather. Whilst the door leaf itself may be designed to meet these criteria, it is only in conjunction with the frame, threshold and hardware that the full performance can be achieved. It is therefore always preferable that ‘doors’ are purchased as doorsets, complete with frame.
The architect, door designer, manufacturer, supplier, installer, user and maintenance contractor all have a part to play in the chain of responsibility that leads to long term satisfactory performance of timber external doorsets. This Wood Information Sheet discusses aspects of design and site practice which affect the performance of external doors, ie those on the outside face of a building, but it does not cover sliding patio doors, nor specialist industrial doors.
Legislative and performance requirements
External doors and frames have to be included in the calculations for the thermal performance of the external wall (or taken into account in whole building performance calculations). Hence manufacturers must be able to provide evidence of the U-value achieved by their doors. This can be measured by test or calculated by modelling in line with BS EN ISO 10077-1 or -2. Approved Document L for England and Wales gives a basic U-value of 3.0 W/m²K for a solid timber external door.
Building Regulation requirements relating to the passage of sound do not cover sound transmission from outside a building to the inside so external doors are not included. However, planning restrictions often place an obligation upon designers and developers to meet particular sound insulation requirements and this may affect the design and choice of external doorsets.
External doorsets, in some situations, may require fire resistance. Their width may be governed by the escape route provisions of the fire safety requirements laid down in Building Regulations. This may also affect the choice of locks and hardware and the direction of opening.
The requirements for accessible thresholds and for minimum widths of door openings for wheelchair access must also be taken into account in the design of entrances to buildings and choices of doorset.
The relevant parts of the Building Regulations for England and Wales, for Northern Ireland and the Building Standards for Scotland and their related documents should be consulted for further information.
There are no specific product standards relating to external doorsets. However, two documents give general guidance; Product Assessment Standard PAS 23-1 and Draft for Development DD 171: 1987. A second Product Assessment Standard PAS 24 relates specifically to enhanced security for door assemblies.
Some of the information in DD 171, published in 1987 has been superseded by more recent European Standards for performance testing and criteria (see references). Both PAS 23 and DD 171 address manufacturing and performance criteria for single-acting exterior doorsets, although double acting doorsets are soon to be added. These are the aspects which should be taken into consideration in the specification of all external doors and include:
Weather performance: air permeability, watertightness and wind resistance.
Mechanical performance: including operating forces, resistance to loads torsion etc, resistance to impact.
Performance in use: cyclic operation (opening and closing), effect of temperature and humidity variation, basic security considerations.
Secured By Design is a scheme launched by the Association of Chief Police Officers Crime Prevention Initiative Ltd. Doors are tested in line with PAS 23 for weathertightness, cycling and operational tests, and with PAS 24 which includes manual assault tests using hand tools, mechanical loading using a hydraulic ram and impact by hard and soft bodies.
Specifiers should satisfy themselves that the doors and frames they are selecting meet the level of performance required, taking into account the degree of exposure of the door, its level of use, the need for security etc. Manufacturers should be able to supply details of the tests carried out on their doors and the level of performance reached.
