In-line lean-to junction detail

The roof-to-wall junction detail where the side of a lean-to finishes in line with the main building is tricky. We work through some options.

Topics include

Cladding systems
In-line lean-to junction detail
By
Trevor Pringle
Last updated 20 May 2026
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Acceptable Solution E2/AS1 doesn’t include details for roof-to-wall junctions where the side of a lean-to finishes in line with the main building and the roof slopes away from the upper wall (Figure 1).

Diagram showing the junction location between a two‑storey roof and a lean‑to roof, with fall directions marked
Figure 1 Junction detail location.

Sequencing for installation

Figures 2–5 illustrate the steps for the construction of the detail where a sheet cladding is installed over a drained and vented cavity.

Step 1 – Complete all wall and roof framing.

Step 2 – Install wall underlay to lower-level walls.

Step 3 – Lay roof underlay to lean-to roof turned up higher wall and down face of wall.

Step 4 – Fit cavity battens to continuous side wall. Set horizontal batten to suit location of horizontal timber trim and flashing.

Step 5 – Fit flexible flashing tape to the corner at top of lean-to and dress over cavity battens.

Diagram showing steps one to five for installing a roof‑to‑wall junction at an in‑line lean‑to roof
Figure 2 Steps 1–5 – Roof to-wall junction for in-line lean-to.

Step 6 – Install roofing to lean-to.

Step 7 – Install cladding to lower level.

Step 8 – Fix bargeboard to side of lean-to and the horizontal timber trim.

Diagram showing steps six to eight for installing a roof‑to‑wall junction at an in‑line lean‑to roof
Figure 3 Steps 6–8 – Roof to-wall junction for in-line lean-to.

Step 9 – Barge flashing installed.

Step 10 – Fit horizontal flashing to cladding break

Step 11 – Install wall underlay to upper side wall. Lap over flashing upstand.

Step 12 – Begin cavity closure, battens and cladding to side wall but don’t complete to corner. Complete horizontal z flashing to side wall.

Diagram showing steps nine to twelve for installing a roof‑to‑wall junction at an in‑line lean‑to roof
Figure 4 Steps 9–12 – Roof to-wall junction for in-line lean-to.

Step 13 – Install horizontal apron flashing.

Step 14 – Install fabricated corner flashing over apron, barge and horizontal break flashing.

Step 15 – Install wall underlay to upper return wall, lap over apron flashing upturn.

Step 16 – Complete cavity closures, cavity battens and cladding installation on upper wall.

Diagram showing steps thirteen to sixteen for installing a roof‑to‑wall junction at an in‑line lean‑to roof
Figure 5 Steps 13–16 – Roof to-wall junction for in-line lean-to.

Some specifics from E2/AS1

Specific requirements of Acceptable Solution E2/AS1 include that there must be:

  • a 75 mm minimum wall cladding cover over the upstand
  • a gap between the wall cladding and the roofing as per E2/AS1 Table 7
  • cover over the roofing as per E2/AS1 Table 7 depending on wind zone and roof pitch.

Option to make this detail easier

Figure 6 provides a step at the lower wall junction so that the barge simply butts to the wall at right angles.

Diagram showing a simplified lean‑to roof junction with a stepped lower wall and indicated roof falls
Figure 6 A simpler option – a step at the lower wall junction means the barge simply butts to the wall at right angles