What is a wood roll (verheven kraalnaad)?

A wood roll, known in Dutch as a “verheven kraalnaad” (raised bead seam), is a joint between two lead sheets on a roof in which the seam is raised on a timber roll and the lead is dressed over it into a rounded bead. It is how the longitudinal joints, running with the fall, are made on a lead batten roll roof. On zinc or copper roofs a separate roll cap covers the joint; with lead, the lead itself forms the capping.

Note: despite the Dutch word “naad” (seam), this has nothing to do with pointing in brickwork. It is a leadwork and roofing technique.

Why do it this way?

A wood roll solves two problems at once:

Keeping water out: because the joint sits higher than the roof surface, water cannot simply run into it, even when strong wind drives water up the roof.
Preventing cracks: lead expands and contracts with temperature changes. Dressing the lead in a rounded bead over the timber lets it slide gradually over the wood instead of tearing.

Build-up

A timber roll with a rounded top is fixed to the roof boarding in the direction of the fall. One lead sheet (the undercloak) is dressed up against and over the roll; the other (the overcloak) is laid over it and formed around the roll into the bead.

Application

You find wood rolls on lead roofs of dormers, bay windows, turrets and historic buildings, and in the restoration of traditional leadwork. It is specialist work for a plumber or roofer experienced in leadwork.

Tips and points of attention

Do not nail through the roll: a fixing through the joint stops the lead from moving and causes cracking.
Use treated, rot-resistant timber for the roll: it sits under the metal for many years.
Cracks along the roll: often a sign that the lead is fixed too tightly or that the sheets are too large. Have a specialist look at it before it starts to leak.

Related terms

Bead
Roll cap
Batten roll roof
Roll batten
Sheet lead
Standing seam

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