Lengthwise joint of D roof panels — types of undercuts

Junction function

Lengthwise joining of roof panels = when the hall roof is longer than the available factory lengths (typically max 13-16 m). The joint requires:

1. 200-250 mm overlap of the upper panel over the lower one.
2. Joint over a purlin (NOT between purlins!) — the fastener anchors both panels + the purlin.
3. Butyl sealing within the overlap.
4. PUR assembly foam filling the gap between the panels.

Two types of factory undercuts:

• Standard undercut = parallel — faster, less tight.
• Stepped undercut = labyrinth — slower, more airtight.

Critical installation aspects

• Joint OVER the purlin is mandatory — between purlins the panel will deflect under the weight of people/snow.
• Fasteners within the overlap = long self-drilling screws, through both panels into the purlin.
• Butyl mastic 30-40 mm wide along the entire length of the overlap.
• PUR assembly foam fills the 2-5 mm gap between panels; trim excess after curing.
• Avoid lengthwise joints whenever possible — design the roof with single-length panels.

Documentation

Technical Catalogue insPIRe S/U + GS PIR D (Gór-Stal 2025), page 102 — Lengthwise joining of D panels, types of undercuts. Scale 1:5.

Components in this junction