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Integrity Testing Plans
This week I would like to highlight a previous piece of work on ITP’s done within SPRA by Jim. The reason to draw attention to this issue again is to remind all of the continued importance of waterproofing integrity testing. Also, the issue is again on the agenda at SPRA for the development of a digitized Integrity Testing Plan (ITP) to enable efficient site work recording and transfer of information from the contractor’s standpoint. Using ITP’s is not only good practice but also assists in verification of work under the IRG competency agenda.
A digitized ITP is something that we hope can be developed in the not too distant future.
As a reminder I enclose below the key points and detail of any ITP
Testing for integrity may serve two different needs:
The specialist contractor’s own QA procedures: in this case, the contractor may purchase and use the testing equipment themselves, to keep a record of installer skill (testing of seams) and effectiveness of protection (identification of roof-field punctures and tears). Unfortunately, the latter is still an issue in spite of the industry’s best efforts to raise awareness and promote tidy work areas.
The client’s desire for a defect-free, continuous waterproof membrane over their building: in this case, an inspection and report by an independent, accredited service provider is essential.
All electrical testing complements traditional and effective practice, including membrane manufacturers’ own visual inspection. These are mandatory for SPRA Membrane Manufacturers where product warranty is offered on jobs above 100m2 and must be randomised on smaller jobs. The more enlightened main contractors also undertake inspections but neither of these can hope to be sufficiently frequent and/or thorough to be effective in many design circumstances.
SPRA’s concern is that the right test method is utilised, a customer will have confidence in its results and the roof finish will not have to be patched unnecessarily. Here are some of the conclusions, which enhance the existing SPRA Guidance document (available by download from www.spra.co.uk)
Low voltage earth leakage (LVEL) should continue to be the default method for use with single ply membrane. It is slow and requires a wet roof surface, but it is thorough and effective especially at welded or adhered seams. High voltage (HVEL) is useful where slopes or very dry conditions preclude LVEL and as a complementary technique, but calibration must be set carefully to (a) ensure the test if effective and (b) avoids damage.
Steel and concrete decks create a good electrical earth and so are suitable for both methods, but the need for an effective earth is greater for LVEL. That earth must be found rather than assumed, for example a metal perimeter capping or metal-framed access hatch set on timber kerbs may not be electrically connected to the deck. Plywood decks cannot be tested reliably using LVEL. At best, if the roof has been exposed to wet weather for a while it will likely detect a discontinuity but maybe not all of them. However, if a foil-faced cellular insulation board is used (default for mechanically fastening or – as is increasingly permitted by membrane manufacturers – for a fully adhered specification) the HVEL method is likely to be effective.
All thermoplastic membranes can be tested because they are not electrical conductors. Thus the necessary electric field can be created across the upper surface to enable electrical leakage to be detected. All EPDM elastomeric membranes cannot be tested reliably because they are electrical conductors. However, specific products which combine FPO coatings to the upper surface of the EPDM can be tested.
It is vital that the service provider has access to the as-built system specification, not the architect’s original design intention, which may have been minced by value engineering. Such matters as method of attachment, membrane thickness and insulation type will be important in checking the test will work.
BALLASTED AND GREEN ROOFS
Here again, the default method is LVEL, but great care is required to ensure that results accurately reflect the true condition of the single ply membrane. For example, a lightning conductor may not be visible yet will skew results. Generally, testing should be conducted on the exposed membrane. If investigation of an existing roof is required, it may be necessary to remove the ballast or green roof. Given that such action will be required locally to effect repairs, it would be sensible to bite the cost bullet in any case, at least in that part of the roof where there is some confidence regarding the location of ingress.
MEMBRANE-COVERED COMPOSITE PANELS
Water ingress through the single ply membrane due to damage in the field of the panel will not reach the liner (earth) because the PIR core is highly water resistant. Ingress at poorly welded seams to side laps or head lap cover strips is likely to reach the liner because the panels are butted along these edges. Hence any test will at best be partial and should be treated and reported as such. Generally, it is more cost-effective to probe laps and run a visual examination elsewhere.
PROBING OF LAPS
The test service provider is reporting on integrity and so anything potentially destructive should be done by parties to the roofing contract. Thus probing of laps should either be carried out by the SPRA contractor or by the testing operative provided the contractor is present. SPRA has investigated setting technical standards for probes, but the key is ‘never sharp and never used aggressively’.
CODE OF CONDUCT CHECKLIST
The service provider must submit the following information prior to the test:
A job-specific method statement and risk assessment, which demonstrates that the technique to be used is effective for the roof specification and construction circumstances. If there is any doubt as to the efficacy of the method, a sample test should be considered. It is recommended that the checklist below is completed.
A proforma test report.
Details of suitable insurance.
Evidence operative training in the use of the equipment to be used.
The roofing contractor should always be in attendance to arrange safe access and to conduct repairs immediately following the test. The test service provider must then re-test the repair so that a final certificate of integrity can be issued.
Services as required for repairs (e.g. a power supply for welding single ply) must be available.
All points of potential leakage should be marked on the roof surface with a waterproof marker that can subsequently be cleaned off if necessary once repairs are complete.
The report must include:
Explanation as to how the earth was created.
Details of any areas excluded from test, with reasons.
A schedule of defects with each term clearly defined (e.g. puncture, weak weld, cut etc.)
Hopefully the above is informative and we can take this framework forward into a Digitized Integrity Testing Plan (DITP) format in the near future.
As always, all comments welcomed.
Dr Ronan Brunton B.Sc MBA GMICE, Technical Manager
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