Roof flashings
Roofs do not leak in the middle but at the edges and details. This sheet goes through every sheet-metal component of a pitched roof from eaves to ridge, with the figures for each from the installation guides of roofing manufacturers and suppliers in Slovakia.
- Sheet
- Roof flashings
- Revision
- Sources
- 7 items
- Type
- information guide
The eaves
- rafter
- fascia board
- underlay drip flashing (odkvapnica) at the rafter ends
- roofing underlay
- counter-batten and batten
- eaves flashing under the covering
- roof covering, overhanging the gutter
- gutter bracket (rafter type)
- half-round gutter with a bead on the outer edge
- Drawing no.
- KV-04
- Title
- Eaves with gutter, section
- Scale
- diagram
- Revision
- 14 October 2026
Three components meet at the eaves, and people often confuse them:
| Component | Where it sits | Function |
|---|---|---|
| underlay drip flashing (odkvapnica) | at the rafter ends, under the roofing underlay | carries condensation and water from the underlay into the gutter, so it does not drip onto the rafters and soffit |
| eaves flashing (drip edge) | on the first batten, usually doubled, under the covering | directs water from the covering straight into the gutter |
| gutter on brackets | below the edge of the covering | collects water and carries it to the downpipes |
Ruukki’s installation guide says the underlay drip flashing should project about 3 cm beyond the end of the rafter so that the soffit can be fitted beneath it. MASLEN says the covering should overhang the edge of the roof by 1/3 to 1/2 of the width of the gutter.
Eaves flashing
According to Ruukki’s guide for standing seam roofing, the eaves flashing is laid in a straight line, fixed with flat-head screws or nails at 300 mm centres, and the pieces lap by 100 mm. Gutter brackets and the gutter must go up first, because once the covering is on you can no longer reach rafter-type brackets.
On a roof without a gutter (for example over a terrace with a free-draining eaves), the eaves flashing has to project far enough beyond the facade that water does not run down the wall.
The verge
The gable is finished with a verge flashing. It stops the wind lifting the covering and carries water from the edge into the gutter. Details, the difference between under-covering and over-covering trims, and fixings are on the Verge flashings sheet.
Valleys
Water from two slopes runs into a valley, which makes it the most heavily loaded part of the roof. MASLEN gives a 200 mm lap between lengths of valley (against 100 mm for other flashings); Ruukki gives an exposed valley width of 200–300 mm once the covering is on. The full detail is on the Valleys sheet.
Ridge and hips
Ridge caps are laid on a ventilated ridge strip. MASLEN specifies fixing with 4.8 × 20 mm stitching screws at roughly 300 mm centres, a ridge cap lap of at least 100 mm, and that the ridge caps are not fixed to one another, so as not to restrict expansion. At the gable end the ridge is closed with an end piece, and at a hip with a hip cap.
Wall junctions and penetrations
Where the roof meets a wall, a dormer or a chimney, the junction is dealt with by flashing. According to MASLEN, a side flashing under the covering is fixed into the wall and the joint with the wall is sealed. At a chimney the back also has to be dealt with, where water and snow collect – see Chimney flashing and Flashing trims.
Expansion and fixing
Metals change length with temperature. For rainwater systems KJG gives coefficients of linear expansion of 0.12 / 0.17 / 0.22 / 0.24 mm per metre for a 10 K change, for galvanised steel, copper, titanium-zinc and aluminium respectively. A ten-metre titanium-zinc component will therefore change length by about 17.6 mm over an 80 K temperature range (for example −20 °C in winter and +60 °C in summer sun). So:
- long components are divided and joined so that they can slide,
- fixing is with clips or through vertical legs, not with a screw through a horizontal surface,
- ridge caps and trims only lap over one another and are not fixed rigidly together.
The most common mistakes
| Mistake | Consequence |
|---|---|
| no underlay drip flashing | condensation from the underlay drips onto the rafters and soffit; the rafter ends rot |
| covering does not overhang into the gutter far enough | in a downpour water runs behind the gutter and down the facade |
| valley pierced by a nail in the middle | leaks at the most heavily loaded point |
| sheet cut with an angle grinder | burnt paint and zinc around the cut, rapid corrosion; Lindab and Ruukki both exclude this in their warranty conditions |
| metal swarf left on the roof | rust spots on the paint |
| flashing fixed rigidly with no allowance for expansion | buckling, torn joints |
More mistakes and how to spot them: Common roof flashing mistakes.
Technical sources
The sources this sheet draws on. We checked prices and values from standards on the date shown; for prices, whatever the source currently states always applies. Sources marked “in Slovak” or “in Czech” are only available in that language.
- Prepared by
- KlampiarskeVýrobky.sk
- Revision
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