There are so many timber internal doors on the market,
it can be hard to see the wood for the trees.
Peter Mayer of Building LifePlan helps specifiers
pick the right product.
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 due 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.
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 use 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- stockroom or schools subject to frequent impact.
• Hinges: Specification of a suitable 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 threee durability grades based on 25,000 to 100,00 cycles of operation. For advice contact Guild of Architectural Ironmongers or the Door and Hardware Federation.
Whole-life costs of internal 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 polished or varnished.
Whole life cost issues
• Finishes: Typical finishes are paint, varnish or stain. High performance paints offer longer periods between maintenance. Reduced site time are possible with pre-finished doors. The performance of real wood is related to the adhesive, the species of timber and the thickness of the veneer (typical range 0.6 – 3mm). Plastics 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
Internal domestic doors
Net present value for 60 years £/door
Risk of damage
Hollow core doors: £40 – £140
Hollow core door, with timber edging and blocking for hardware, factory primed.
Hollow core door, with timber edging and blocking for hardware, factory finished.
Solid core doors: £100 – £300
Solid core door, particleboard to BS EN 312 grade P3, softwood edging.
Solid core door, particleboard to BS EN 312 grade P3, softwood edging, real wood veneer 2mm thick
Solid timber doors: £200 – £500+
Four panel softwood door. European Redwood to BS EN 942 Class J30, D3 adhesive to BS EN 204, assembled to BS 1186-2
Four panel hardwood door to BS EN 942 Class J2, D3 adhesive to BS EN 204, assembled to BS 1186-2. For varnished finish
• A discount rate of 3.5% is used to calculate net present values.
• An internal door assembly correctly specified for expected use in a dry internal environment should have an indefinite life with regular servicing and redecoration.
• However, usage and environments change and accidents happen. The whole life cost models are based on a risk of damage occurring as well as planned redecoration every 10 years, if applicable, with an allowance for servicing, replacement of hardware and minor repairs.
• The door cost range is indicative for a 2040 x 626–826 x 40mm door; lowest price for basic door unfinished, upper price for real veneer finish.
• Capital costs for the whole life cost examples include installation; frame and linings; hardware; decoration.