CSCS Roof Felting common mistakes
CSCS Roof Felting · Understand the traps and how to avoid them.
Treating a flat-roof felt job as a single generic activity and applying one set of controls (e.g. edge protection only) rather than working through the full hierarchy of falls risks for each stage of the work.
Candidates memorise 'use guardrails' as the answer to every height question and skip the sequence of assessing, avoiding, preventing and mitigating risk, including fragile surfaces and openings.
What to do instead
Practise writing a short risk-control ladder for a typical felt roof: eliminate work at edge where possible, use collective protection first (edge protection, covers, platforms), then personal fall protection as a last resort, and name the specific hazard each control addresses.
Selecting a felt membrane by product name or price without matching it to the substrate, slope, expected foot traffic and UV exposure stated in the specification.
Candidates learn products by brand or by 'torch-on versus self-adhesive' and ignore the performance criteria (service temperature, dimensional stability, tensile and tear strength, fire classification) that drive selection.
What to do instead
For each material type, build a one-page comparison of the properties that matter and rehearse matching them to scenario clues such as a warm roof, a low slope, a balcony or a plant room.
Failing to check and record substrate moisture, surface dryness and primer coverage before laying the first layer, then laying membrane over damp or dusty concrete.
Candidates focus on the visible installation steps and treat preparation as a formality, missing that trapped moisture and poor adhesion are the root cause of most blistering and debonding defects.
What to do instead
Learn the standard pre-cover checks as a fixed checklist (moisture test, cleanliness, primer cure, falls to outlets) and practise explaining what each check prevents and what evidence should be recorded.
Installing the waterproofing layer without confirming the required number of layers, overlap dimensions, direction of laps and stagger between layers for the specified system.
Candidates recall 'overlap the felt' but not the system-specific lap values or the rule that laps must be staggered and run with the fall, so they give a vague answer that does not meet the specification.
What to do instead
Memorise the lap and layering rules as a table per system type, and practise answering with the principle (water must run over, not into, a lap) plus how stagger and direction are verified on site.
Detailing an upstand or edge termination without specifying the height above the finished surface, the fixing method, and a drip or edge trim to discharge water clear of the wall.
Candidates draw or describe the general shape of the detail but omit the measurable requirements, so the answer cannot be shown to comply with the specification or good practice.
What to do instead
Rehearse each detail as a labelled sketch with dimensions, fixings, reinforcement and termination, and state why the height and the drip are needed rather than just that they are required.
Describing an outlet or penetration detail without reinforcement, without a suitable collar or flange, and without confirming the membrane is dressed and sealed in the correct sequence.
Candidates treat outlets and pipes as small items and answer in one line, missing that these are the highest-risk leak points and need specific components and sequence.
What to do instead
Build a detail card for each penetration type showing the order of work, the reinforcement layer, the clamping or sealing method and the test that proves it is watertight.
Answering a safe-working-at-height question by naming equipment without stating the pre-use inspection, anchorage or rescue arrangements that go with it.
Candidates equate naming a harness or a tower with a complete safe system of work and forget that equipment alone does not control the risk.
What to do instead
For each item of access equipment, practise giving a four-part answer: suitability and selection, inspection before use, competent user and anchoring, and rescue or recovery plan if someone falls.
Ignoring hot-work and fire risks when describing torch-applied systems, including combustible substrates, hidden materials and the need for a permit and fire watch.
Candidates concentrate on the technique of torching and overlook that the dominant hazard in torch-on work is fire in the structure or substrate beneath.
What to do instead
Link every torch-on answer to a hot-work permit, a check of what lies beneath the membrane, fire-fighting provision and a post-work fire watch, and state the alternative cold-applied option where risk is high.
Describing an inspection or test as 'check for leaks' rather than naming the method, timing and acceptance criteria, such as a flood test or electronic leak detection before the covering is completed.
Candidates know defects are found by looking but do not know that testing has defined procedures and that some tests must happen at specific stages.
What to do instead
Learn the main test methods, when each applies, and what counts as a pass, then practise writing an inspection sequence with hold points where work cannot proceed until a check is signed off.
Diagnosing a defect such as blistering, ridging or ponding by naming a single cause and a repair without first establishing the mechanism and extent.
Candidates jump to a familiar cause and a patch repair, missing that correct diagnosis requires identifying the failure mechanism and deciding whether local repair or replacement is appropriate.
What to do instead
Practise a diagnostic routine: describe the symptom, list plausible mechanisms, state the investigation needed to distinguish them, then choose repair or replacement and the acceptance check afterwards.