Bituminous roofing sheet
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Bituminous roofing membranes with alternating bitumen and bitumen-free strips often experience leaks at the head joint due to misalignment during the butt joint connection process, especially when using cold-adhesive bitumen, as the bitumen strips on the underside may not fully fill the bitumen-free areas during pressing or welding.
Innovation Solution
The bitumen strips on the upper side are offset by one strip width in the transverse direction relative to those on the lower side, allowing them to interlock like a zipper between the bitumen-free strips, ensuring watertight connections even with less careful alignment, and incorporating spaced breaks in the strips for vapor pressure equalization without compromising the seal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bitumen strips on the underside are aligned with bitumen strips on the upper side, then the membrane structure is simple and easy to manufacture, but leaks occur at the head joint because bitumen-free strips are not completely filled with bitumen during pressing or welding
Solution Approach 1:
The bitumen strips on the upper side and lower side are intentionally offset by one strip width in the transverse direction, creating an asymmetric configuration. This asymmetry ensures that bitumen strips on the underside engage like a zipper between bitumen-free strips on the upper side, guaranteeing complete filling of bitumen-free areas and preventing leaks at the head joint.
2Ease of manufacture
If bitumen strips are made of cold-adhesive bitumen, then the installation process is simpler, but the risk of leaks increases because bitumen strips may not fully fill bitumen-free areas during pressing
Solution Approach 1:
The offset configuration of bitumen strips is predetermined in the membrane structure before installation. This preliminary design ensures that during the pressing or welding process, the bitumen strips on the underside will automatically engage with the bitumen-free strips on the upper side, compensating for the lower adhesion strength of cold-adhesive bitumen and ensuring complete filling of bitumen-free areas.
3Reliability
If bitumen strips are offset by one strip width in the transverse direction, then watertightness at head joints is improved, but the manufacturing and alignment process becomes more complex
Solution Approach 1:
The membrane is divided into alternating bitumen strips and bitumen-free strips running in the longitudinal direction. This segmentation creates a modular structure where the offset by one strip width becomes a straightforward manufacturing specification, reducing the complexity of achieving precise alignment compared to a continuous bitumen coating.
Data Source
Figure 1~2
AI summary
The roof sheet (I-III) has ply carrier layer such as insert (1) and coatings (2,3) and upper side and lower side bitumen strips (4,5) with equal width that are extended in longitudinal direction of sheet. The bitumen-free strips (6,7) are separated, such that upper-side bitumen strip is offset from lower side bitumen strip in transverse direction of sheet for cold or heat sealing of end of sheet (I) with an overlapping end of next sheet (II). The lower-side bitumen strip is connected with bitumen-free strips (6).