What it costs: timber internal doors

The whole-life costs of internal doors should take into account the impact of damage, moisture or temperature, as well as decoration and servicing costs.

Specification is difficult because of the uncertainty of future use and environmental conditions. Over-specification may result in higher than necessary capital costs, but under-specifying could lead to higher costs for maintenance and replacement.

Standards

The British Standards Draft for Development DD171:1987 provides a series of performance tests and criteria for different duty categories. European Standards EN 1192 and EN 1294 refer to European use categories.

Four categories are:

• Light duty or class 1 – private dwellings
• Medium duty or class 2 – offices and dwellings with higher risk of damage
• Heavy duty or class 3 – shops, hospitals and public buildings
• Severe duty or class 4 – stockrooms or schools subject to frequent impact.

Hinges: Specification of a hinge for the weight of a door and its level of use is important. Single-axis hinges to BS EN 1935 include four duty categories. There are eight durability grades, based on operating cycles from 10,000 to 200,000.

Door hardware: A harmonised European standard for building hardware is in development. Lock cylinders in EN 1303 include three durability grades based on 25,000 to 100,00 cycles of operation. For advice, contact the Guild of Architectural Ironmongers or the Door and Hardware Federation.

Specification options

• Whole-life costs of internal timber doors are related to the form of construction and the finish. Common options include:
• Hollow-core doors, typically with a flush or moulded panel of MDF, hardwood or plywood.The core may be composed of polystyrene, card or plastic honeycomb grid.The edges may be timber-based
• Solid-core doors have a core of particleboard to BS EN 312 or flax board
• Engineered timber doors are constructed from laminated strips of solid timber.They offer a stable solution using modern fast-grown kiln-dried timbers
• Solid softwood or hardwood doors. BS EN 942 provides a classification of timber quality. Traditionally, softwood is painted and hardwood is polished or varnished.

• Finishes: Typical finishes are paint, varnish or stain. High-performance paints offer longer periods between maintenance. Reduced site time is possible with pre-finished doors.The performance of rea wood veneer is related to the adhesive, the species of timber and the thickness of veneer (typical range 0.6-3mm). Plastic foil veneers are a common alternative that rely on clear coating for protection. Damage to the foil may be costly and require repainting of the door.
• Doorsets offer a pre-assembled solution that minimise site installation. However, the door opening needs to be accurately formed and there is a risk of damage during construction.
• Adhesives should be at least type D3 to EN 204.
• Storage and conditioning are essential to protect doors from adverse construction activities and moisture.The building should be dried out and doors conditioned before hanging.