U-PVC Window Head Drip Bead

Water on a façade does not only run straight down. At the bottom edge of the window head it turns the corner, follows the underside of the reveal and reaches the window frame. Over time the render, the insulation and the joint around the window all get damp. The drip nose breaks this path, so the water falls clear of the wall.

The bead sits on the outer edge of the head, where the face of the façade turns into the top reveal. On this edge it also replaces a standard corner bead, so the corner is protected against knocks as well. The joint between the render and the window frame is handled by a different profile, the window connection bead. A good detail uses both, each in its own place.

The bead is part of the external thermal insulation composite system (ETICS, often called external wall insulation). It should come from the same supplier as the adhesive, mesh and render, or at least be approved by the system supplier.

The beads are made of PVC, which copes with moisture, the alkaline conditions of fresh mortar and sunlight. Most have glass fibre mesh already attached to the wings. They usually come in lengths of about 2 or 2.5 metres. There are two basic types, depending on how the nose looks once the render is on:

• Visible drip bead. The nose stays visible after rendering. It sheds water reliably and forgives slightly less precise work by the renderer. It suits most houses and blocks of flats.
• Concealed drip bead. The nose is hidden and the façade looks cleaner, without a visible edge. People choose it for a modern, minimal look. It needs more accurate fixing and careful rendering, otherwise the edge will not be straight.

Decide on the type in advance, ideally together with the colour and texture of the render. It should not be a choice made on the scaffold.

The bead goes on once the insulation boards are bonded, anchored and the reveals are insulated, but before the full base coat with mesh. The usual sequence is:

1. Rasp the edge of the head flat and to a sharp corner, then remove the dust.
2. Measure the width of the opening and cut the bead with a fine-toothed saw. The cut must be clean and square.
3. On wider openings, join lengths with a connector or butt them tightly as the manufacturer specifies, never with a gap.
4. Apply base coat mortar to both faces of the edge.
5. Press the bead onto the edge and line it up with a spirit level, with the nose pointing down and out.
6. Embed the mesh wings in the mortar and smooth them over.
7. Place diagonal strips of mesh at the corners of the opening so cracks do not start there later.
8. When laying the full base coat, overlap the façade mesh over the bead mesh, usually by roughly 10 cm.
9. Once dry, apply primer and render up to the nose of the bead, not over it.

Mortars and renders are usually not applied below about 5 °C, in strong direct sun or in rain. The exact conditions are in the system manufacturer's technical data sheet.

The simplest case is a new build or a full insulation job with scaffolding around the whole house, straight reveals and ordinary windows. The beads then go on smoothly along with the other corner profiles.

More time is needed for:

• Uneven or crooked window heads that have to be straightened first
• Very wide openings, sliding doors and garage doors, where several lengths must be joined
• Arched windows, which need flexible profiles
• Retrofitting into a finished façade, where old render has to be cut back, the bead fitted and the edge re-coated and rendered
• Poor access, for example upper-floor windows without scaffolding

In blocks of flats, insulation and façade repairs are the responsibility of the building management or owners' association, not the individual flat owner. If the bead is part of a larger façade renovation, check with your local building authority what the work requires under local building regulations.

This is work at height and on scaffolding, so it belongs with a professional contractor rather than a DIY project.

Mistakes at this detail often only appear after the first heavy rain or the first winter. Fixing them then means breaking out a section of finished render.

• Nose covered with render. The renderer pulls the render over the nose and water runs down the reveal again. Hardened render cannot be cleanly removed from the nose.
• Bead left out. Sometimes it is skipped to save effort or out of ignorance. Dark patches, algae and cracks appear under the head over time.
• Short mesh overlap. Hairline cracks form at the joint, and frost gradually widens them.
• Bead not seated on the edge. On an uneven surface a void remains underneath. The bead can work loose or crack later.
• Gaps at joints. Two lengths simply placed next to each other by eye give water a way in.
• Bead from outside the system. A profile that does not belong to the chosen system can put the manufacturer's warranty on the whole insulation at risk.

When you accept the façade, go round each window separately, ideally while the scaffolding is still up:

• A bead is fitted above every recessed window and door
• The nose is clear along its full length and not covered with render
• The edge is straight, without waves or sagging
• Joints between lengths are tight with no visible gap
• The bead does not sound hollow when tapped and does not move
• There are no cracks in the render at the corners of the opening
• The render meets the window frame with a separate connection bead
• The contractor can tell you which system the beads come from and has stated the warranty in the contract