PVC Life Cycle

While the debate of wood window frames versus PVC continues to rage on, scientific research has shown that PVC windows just keep on performing long after wood has reached the end of its usefulness.  Below are the conclusions of a recent research paper that should add ore fuel to the debate.

Advantages of PVC
The whole life costs of the wood and UPVC windows have been examined.  This has entailed a net present value (NPV) assessment, a representation of the total cost expressed as the investment required "today" to pay for the 25 year timescale.

Issues Addressed
The NPV is based on capital and maintenance costs for both the standard 25-year period and the whole life of the profiles of 30 years.  The discount rate in the investment appraisal table is six per cent, in accordance with normal government recommendations.  VAT is excluded.  Due to this long timescale, the NPV's provided are estimates and in some circumstances may not reflect the actual expenditure during the lifetimes since external factors such as the actual maintenance cost programme undertaken and the actual maintenance cost (labour and material costs) will affect whole life costs. The following analyses have been performed:

• 25-year NPV (standard NPV calculation period);
• NPV (to reflect the whole expected life of the profiles);
• Sensitivity analysis on painting frequency.

Following discussion with Manchester City Council, the following general assumptions were made for the analysis:

• Number of window per property:  11;
• Capital cost wood per profile:  Stg£265;
• Maintenance cost for wood per property (every five years) Stg£400;
• Maintenance cost UPVC per property:  Stg£0.

The capital costs quoted are current discounted prices available to Manchester City Council.  Local, undiscounted open market prices for the profiles were found to be higher at Stg£325 for wood and Stg£270 for UPVC.  Undiscounted prices used as part of the DETR 2000 study were Stg£375 for wood and Stg£297 for UPVC.  It is apparent the UPVC capital cost is consistently cheaper than wood by between 4% and 26%, the bulk purchase discounted prices exhibiting the smallest percentage difference.

Two rates of replacement were examined for each material, 500 properties per year for 10 years and 5,000 properties per year for 10 years.  Costs excluded at this stage are:

• Costs incurred due to the necessary repair/replacement of existing stock through the current practice;
• Disposal costs of the removed windows;
• Disposal/recycling costs at the end of life of the replaced window.

The following table presents the results of the 30-year, whole life NPV assessment.  The NPV for wood is 22% greater than that for UPVC for both Option A and B.  This is a result of both higher capital costs and maintenance costs.

30-YEAR WHOLE LIFE NPV RESULTS
OPTION	NPV WOOD	NPV UPVC
A: 10 year programme of 500 units per annum	Stg£13,281,300	Stg£10,899,100
B:  10 year progeamme of 5,000 units per annum	Stg£132,813,400	Stg£108,991,100