For a high-quality two-layer waterproofing system, the cap sheet is preferably installed with full-surface torch welding. Only then will the cap sheet and the underlayer form a seamless whole, resulting in excellent waterproofing and wind resistance.
General guidelines:
- The substrate must be smooth, dry, clean, and free of grease and dust.
- To ensure a good welded seam, a bitumen bead of ≥ 5 mm must always flow out at the overlap.
- Remove the protective wrappers from the rolls before installation.
- Always install the cap sheet in the same direction as the underlayer.
- T-joints at end overlaps should be avoided by trimming the corner.
- The cap sheet is laid in a staggered (half-bond) pattern with a minimum distance of 2 meters between transverse overlaps.
- Avoid cross joints at transverse and longitudinal overlaps to reduce water stagnation.
- Always position the cap sheet staggered relative to the underlayer, both longitudinally and transversely. The overlap of the cap sheet should preferably be offset by half a roll width from the underlayer overlap. This ensures the best waterproofing result.
- Roll width of the waterproofing membrane
- Staggered positioning of cap sheet relative to underlayer (half width)
- Minimum distance between end overlaps
- Chamfered corners to prevent capillarity
- Recommended drainage direction for this laying pattern (without cross joints in the overlap)
For more information, see our guide:
“This is how you choose and install the bituminous cap sheet”, available on the IKO website.