Torch welding a bituminous cap sheet is a widely used method to achieve durable waterproofing on flat roofs. This technique requires skill and adherence to technical guidelines.
Execution of torch welding
Bituminous rolls are always installed in the direction of water drainage in a staggered (half-bond) pattern, ensuring optimal stress distribution and strong overlaps.
The membrane is torch-welded with an 8 cm overlap longitudinally and a 15 cm overlap transversely, following Buildwise Technical Guidelines 215 and 244 (formerly WTCB).
During welding, the soft flame of the asphalt torch is directed approximately two thirds on the roll and one third on the substrate, creating a continuous bitumen bead in front of the roll to guarantee good adhesion.
Important considerations for single-layer systems
For single-layer bituminous waterproofing, seam joints must be executed with great care and thoroughly inspected.
Detailing and upstands
All gutter zones, roof details, edge finishes, expansion joints, pipe penetrations, rooflight upstands, etc. must always be executed in two layers for reliable waterproofing.
Upstands are provided with a two-layer waterproofing system using vertical strips 1 meter wide. The waterproofing on the upstand is staggered relative to the roof field membrane to avoid vulnerable joints.
The underlayer is fastened using a method suited to the substrate, while meeting wind uplift resistance requirements as specified in Buildwise Technical Guideline No. 280.
Want to learn more?
Find all practical tips in our guide:
👉“This is how you choose and install the bituminous cap sheet”, available on the IKO website.
Or try it yourself with your company or team in our IKO Experience Center.
The types of training we provide can be found here: IKO Experience Center | IKO.