🔒 Factory Welded. Permanent Frame Seal.

Welded Upstands That Stop Water at the Frame No Sealant. No Maintenance. No Failure.

Name: Welded Upstands for Aluminium Window Sills
Brand: Cills.ie
Availability: InStock
Rating: 4.9 (82 reviews)

The junction between sill and window frame is where most water ingress occurs. A welded upstand creates a raised lip along the rear edge that forms a permanent barrier. No sealant required. No maintenance. A factory-welded solution that lasts the life of the building.

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Sealant at the frame junction always fails

If the gap between sill and frame relies on silicone, it will crack and allow water behind the frame. Welded upstands eliminate this weak point permanently.

What Is a Welded Upstand and Why Does It Matter?

An upstand is a raised lip along the back edge of a window sill — the edge that sits against the window frame or wall. Its purpose is to prevent water from flowing over the rear edge of the sill and running behind the frame into the wall cavity.

Most sill suppliers form upstands by folding. This works, but the fold creates a gap between the upstand and the sill body that can collect moisture and debris. A welded upstand is fused to the sill, creating a solid, sealed junction with no gap, no crevice, and no place for water to sit.

Raised rear lip prevents water tracking behind the window frame
Factory-welded — solid junction with no gaps or crevices
Essential on exposed elevations where wind-driven rain is common
Critical for deep EWI sills where water pressure is highest
Eliminates the need for silicone at the sill-to-frame junction
Powder coated after welding for seamless colour consistency

Welded upstand detail on aluminium window sill showing raised rear lip at frame junction

Where Welded Upstands Are Critical

Any sill installation where the rear edge is exposed to water pressure benefits from a welded upstand. These are the most common applications.

External Wall Insulation

Deep projection sills on EWI projects collect and channel more water. The upstand prevents water from running behind the insulation board at the frame junction — the single most common failure point on EWI sill installations.

Exposed and Coastal Elevations

Wind-driven rain on west-facing and coastal elevations pushes water upward against the sill-to-frame junction. A welded upstand provides the physical barrier that sealant alone cannot maintain long term.

Recessed Window Positions

When windows are set back into deep reveals, the sill channel concentrates water flow. An upstand at the back edge directs all water forward to the drip edge, keeping the frame junction dry.

Passive House and Airtight Buildings

Airtightness testing on passive house and NZEB projects requires every junction to be sealed. A welded upstand eliminates a potential air leakage and moisture path at the window sill.

Commercial Curtain Wall Interfaces

Where aluminium sills interface with curtain wall systems, the upstand provides a weathertight detail that integrates with the glazing system's drainage plane.

Heritage and Conservation Projects

On sensitive renovation projects, the upstand hides behind the frame and provides invisible weather protection without altering the visible sill profile or architectural character.

Welded Upstands vs Folded Upstands vs No Upstands

Not all upstands are equal. Here is how the three approaches compare on performance, longevity, and maintenance.

✓ Welded Upstand (Best)

Fused to the sill body. No gap. No crevice. No maintenance. Permanent weathertight seal at the frame junction. Powder coated after welding for seamless finish.

△ Folded Upstand (Acceptable)

Formed by bending the sill material. Creates a functional barrier but may have a small gap at the fold line that can collect debris and moisture over time.

✗ No Upstand (Risk)

Relies entirely on silicone or mastic to seal the rear edge. Fails in Irish weather within 2 to 5 years. Water tracks behind the frame and into the wall structure.

Aluminium window sill with welded upstand installed showing clean frame junction