When constructing an expansion joint on a flat roof using bituminous roofing membranes, and in addition to the specified roof build-up of the selected roofing system, the detail should be executed as follows:
Flexible insulation layer in the joint This layer absorbs movements between the roof sections.
First loose-laid base layer A strip of roofing membrane (e.g., IKO base P3 (Atelia) T/F), installed upside down with the film on the top side, at least 20 cm wider than the joint width. This strip is laid loose and serves as the first buffer layer.
Fully bonded base layer On top of that, a fully bonded strip of roofing membrane (e.g., IKO base P3 (Atelia) T/F, with the film on the underside) is applied. This strip must be at least 50 cm wider than the previously mentioned loose-laid strip.
Second loose-laid upper layer Next, another loose-laid strip of roofing membrane (e.g., IKO base P3 (Atelia) T/F, installed upside down with the film on the top side) is placed. This strip is at least 20 cm narrower than the fully bonded base layer and is centered above the joint.
Top layer and waterproofing The roof’s top layer is connected to the fully bonded base layer. A separate strip of top layer membrane is applied above the joint, with a minimum overlap of 15 cm on both sides. This strip ensures the final waterproofing.
Below is a visual representation of an expansion joint constructed using bituminous roofing membranes.
You can find more information about roof details and design your own roof build-up in our IKO Design Center.