Solutions to the Problems
The external elements of concern to the system are the cladding and roof.
ROOF CONSTRUCTION
The Method used a flat lightweight roof construction and generally a three layer built up felt. It was accepted that a roof of this nature would have a limited life of about fifteen years and therefore require replacement under normal maintenance. In 1985 a manual produced by the Oxford Regional Health Authority and their specialist consultants Bickerdike Allen and the NAS Continuing Education Unit at York gave recommendations and specifications to satisfy the replacement of Oxford Method roof. In general this has worked. In some cases an alternative roof design has been used and pitched roofs introduced.
CLADDING
It has been the cladding which has given the most problems. Designed as a lightweight construction it did not require a foundation as a traditional building. Only a raised retaining wall to provide an undercroft and support the brackets to take the cladding cill. The photographs shown previously illustrate the point. The cladding is only 100mm thick and any alternative designs would have to meet the same dimensional discipline.
The decision to patch and mend the panels would extend their life and provide a serviceable building for a few more years.
In 1986 a detailed Manual was produced to tackle the problem. The approach was to identify each type of fault and using mastic paint and plates of metal prevent further deterioration. It was not until 1993 that an update of the Manual was produced which would still be effective today.
The following extract from the Manual should give guidance on the intended sequence of work.
INTRODUCTION
The 'Stelvetite Panel' is a manufactured unit consisting of a PVC coated steel sheet galvanised on both sides, with an approximate 50mm layer of 'U; foam and two layers of plaster board as in internal liner. The panels are mechanically fixed to the structure, relying upon compression gaskets between the preformed panels as a mechanically held water proof joint. These panels are to be found upon Oxford Method buildings erected between 1967 and 1976. See Appendix 'A' for details.
Minor defects have been apparent from an early stage, but over the years more serious defects have shown themselves, and the rate of deterioration has increased.
Previous guidance issued in 1980, and 1983 was superseded by a more detailed and specific analysis carried out at Northampton District Health Authority during 1985.
Following the experience gained on these trials, it has been found necessary to revise the guidance given at that time. The principal changes are related to the painting. The paint originally specified is required only for over coating the PVC but can be used universally, however, it is costly, has a very limited open tin life, is difficult to use, and there are difficulties with delivery, etc. …
The specification has now been changed so that normal paints can be used in the majority of cases. Additional specification clauses have been included for defects not previously experienced.
Before outline methods of repair it is necessary to restate the extent of the problems likely to be found i.e.:-
- The panels are showing rusting from the inside, due to the presence of water or water vapour between the foam infill and the outer Stelvetite sheet.
- The PVC outer covering of the panel, may be either coming away from the metal substrate or disintegrating due to normal weathering.
Since it is not a viable proposition to stop this continuing process then action must be taken to 'patch repair' the panel until such time as it becomes economically viable to completely repaint the external cladding. Therefore overall cosmetic treatment is to be deferred and repair and treatment should be directed to dealing with visible and actual defects only.
SURVEYS
Since the introduction of Oxford Method Construction surveys have been carried out to determine the rate of deterioration of the panels. From these, a methodology has been determined and it is recommended that a detailed panel survey is carried to determine the extent of the various types of repair work involved. A suggested example of this survey documentation complete with list of defects and photographs are indicated as follows:-
It was intended that a contractor produced prices against each item of fault and from this a quotation could be produced.
The general notes and paint recommendations were made nearly eight years ago and are therefore not detailed in this manual. It would be possible to update this information to current specification.
The metal plates suggested are illustrated to support the type of defect B, C, D, E. & F and a complete sheet replacement.
"Upon the completion of the detailed survey, the number and type of defects will have been recorded. The appropriate clauses can then be extracted from the following list and including into your standard specification documentation for going to tender, either upon a lump sum or measured term basis. From experience the most economical way of carrying out the work would appear to be by using your directly employed labour force if resources will allow.
It is not recommended that this document should be used in total as most sites will only exhibit a few of the defects shown.
In order to reduce unnecessary repetitive work it is to be anticipated that all buildings with Stelvetite panel defects with the Trust will be the subject of one contract only. It is suggested that a schedule of rates should be used as a basic rate for all sites within the Unit and that any additional items such as scaffolding, raveling, etc. should be covered in the preliminaries for each individual site.
©2004 Oxford Method Royalties Management Group