Installation of Felting Systems and Waterproofing Layers
Layering logic
Installation follows a defined sequence: vapour control layer, insulation (where specified), underlay(s), then cap sheet. Candidates must understand side laps and end laps, the staggering of laps between layers, and the direction of water flow so that laps shed water rather than trap it.
Fixing methods
Know torch-applied, hot bitumen, cold adhesive, and mechanical fixing. Torch work requires controlled heat, even pressure with a roller, and visible bitumen bleed at laps as evidence of fusion. Cold adhesive requires full contact and adequate cure. Mechanical fixing patterns depend on wind uplift calculations.
Traps to watch
- Laps running the wrong way relative to fall - water must run over, not into, a lap.
- Aligning laps in successive layers - they must be staggered.
- Insufficient heat (no bleed) or excessive heat (damaged carrier).
- Skipping the vapour control layer where the specification requires one.
Worked rule of thumb
For a warm-roof build-up, remember V-I-U-C: Vapour control, Insulation, Underlay, Cap. Laps always run down-slope so water flows over the lap edge. If you can see continuous bitumen bleed along a lap, fusion is likely adequate; if the lap peels back cleanly, it is not.