Lifetime costs: Entrance doors

Most clients are aiming for best value. When it comes to entrance doors we often hear clients asking for a robust, durable door with low maintenance. Whole-life costing provides a tool to determine best value and compare options by measuring capital costs and costs incurred during the life of the component.
A door specifier is faced with a bewildering range of options. Not only are there many material choices; softwood, hardwood, steel, aluminium, plastics – PVCu, pultruded glass fibre, and composite doors – but there are also variations of quality within each material type.
The distinctions between choices based on longevity and durability are not always transparent; nor does product literature help in many cases. However, durability is not just about the intrinsic qualities of doors; design, installation and ancillary components such as hinges can be equally important. Here, the key durability issues that impact on whole-life costs are considered for three commonly used entrance doors for housing: hardwood, PVCu, and composite.
In the table below, the whole-life costs of a commodity product and a high performance product are compared for each of three door types. This is, however, just the tip of the iceberg: the Housing Association Property Mutual's Component Life Manual defines nine durability classes of hardwood door alone.

Factors affecting durability

<B>Atmospheric conditions</b>
These can be viewed from the perspective of:

• The chemical environment – marine and industrial areas are more aggressive and promote corrosion in metals as well as deterioration in plastics.
• The climatic environment – particularly temperature and moisture changes. The co-efficient of expansion for plastics and metals is higher than timber so allowance must be made for expansion and contraction to prevent distortion of door members.

<B>Use</b>

• Heavy-handed use or abuse.
• Frequency of operation. Some door manufacturers have data relating to cycles of operation – this will provide confidence for particular uses.
• Maintenance. Typically annual lubrication and adjustment of hinges. Annual touch-up of paint for wooden doors or six-monthly cleaning of plastics doors.

<B>Quality: Materials, manufacture, installation </b>
Durability classes describe options available in terms of relative durability. Many standards relating to physical properties of door leaves are now covered by European Standards, such as BS EN 947 – resistance to vertical load. BS EN 1192 defines four strength classes for light, medium, heavy and severe duty conditions, which help the designer specify the correct door for the job.
The assumption is that installation is carried out to good practice – where this is not the case, a reduced service life is to be expected.

Durability and whole-life cost tips

• Although not common practice, outward opening doors offer greater weather resistance. Specify hinges that are non–corroding and secure.
• The current practice of designing entrance doors to be in the same plane as the external envelope of the building makes the door more vulnerable to weathering.
• Where heavy use is expected or vandalism or burglary is an issue, the whole door assembly should be of proven performance. Product Assessment Standards (PAS) 23–1 and 24–1 apply.
• Doors should suit the proposed exposure in terms of air permeability (BS 5368: Part 1) and watertightness (BS 5368: Part 2). European standards are BS EN 12207 for air permeability, BS EN 12210 for resistance to wind load and BS EN 12208 for watertightness.
• A door with effective weather-stripping, to BS 7386, should result in reduced energy cost for space heating (£10–40 a year for a three-bedroom house, according to the BRE Domestic Energy Research Model).
• Where the hinges do not hold the door in the correct position or are not lubricated or are misaligned, door failure may be premature because of the excessive force required. Specify single-axis metal hinges to BS EN 1935, ideally with a kitemark.
• Specifying doorsets rather than sourcing individual components of the door assembly separately can offer significant cost savings in installation and procurement.

<B>Hardwood</b>

• Cut-end grain should be sanded smooth and treated with two full brush applications of preservative. If it isn't, the service life will be significantly reduced.
• Robust glazing details can improve the service life. A vented and drained glazing detail is an alternative that should give an even better service life.
• Keep water off with weathered exposed horizontal surfaces - BS DD 171 recommends a slope of 15° for external ledges. External edges should be radiused.
• Avoid the risk of splitting timber at edges when screw-fixing ironmongery: screws should be at least five screw diameters away from edges.
• General timber quality should be defined in the job specification by reference to BS EN 942 classes J2– J50. This limits flaws in the timber such as knots, and fast-grown timber and grain slope, which both tend to decrease the performance of the timber.
• Use three hinges (half-pairs) and bolts (or equivalent) at top and bottom of door to restrain any tendency to twist.

<B>PVCu</b>

• Plated steel or ferritic stainless steel ironmongery in a marine environment are likely to have a reduced life. Specifying austenitic stainless steel ironmongery will enhance the durability of the doorset.
• Each door leaf should be hung on two pairs of hinges. Fixing should be into the reinforcement within sections.
• Reinforcement in PVCu doorsets is important to withstand imposed loads. Guidance is given in the British Plastics Federation and Glass and Glazing Federation's Code of practice for the reinforcement of high impact modified PVCu windows and doorsets.
• Solvent-based cleaners should not be used as there is a risk of chemical damage to the plastics.

<B>Composite: Glass-reinforced plastics or plastics-faced cored doors</b>

• Not all composite doors can be planed or trimmed to suit openings. Where fitting a door leaf that may require adjustment, use a door that the manufacturer describes as suitable for alteration.
• Door fixings should be made to the timber framing provided, not to the insulated cores.

Modes of failure

• Moisture levels above 20% promote conditions for decay and distortion of timber.
• Decay can be minimised by using preservative-treated or naturally durable species of timber.
• Regular recoating of timber doors is essential to protect the timber from the deteriorating effects of moisture and ultraviolet light. Most repainting programmes are based on three- to five-year cycles. Stains and varnish do not offer the same degree of protection as opaque finishes.
• Prompt repair or piecing-in of damaged or decayed sections of timber is essential to prevent further decay and expensive door replacement.

<b>PVCu</b>

• Distortion of members may be due to temperature variation, lack of fixings or inadequate allowance for movement.
• Prolonged exposure to ultraviolet light can lead to yellowing, pinking, embrittlement and loss of gloss finish. Self-coloured PVCu tends to fade when exposed to sunlight although where this happens evenly there will be no obvious change in colour.
• Ironmongery failure may cause complete replacement of PVCu where replacement hinges no longer have adequate fixing into the frame or leaf.
• Impact damage may cause plastics panels to crack. Although it is possible to repair cracked plastics, the resulting appearance may not be acceptable.

<B>Composite: Glass-reinforced plastics or plastics-faced cored doors</b>
The main modes of failure include:

• Impact damage
• Discolouration of surfaces
• Delamination of the covering surface with the inner core typically due to stresses caused by temperature variations and lack of adhesion between the surfaces.