Ridge cap: how the top of a roof is closed
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A ridge cap is the folded strip of metal, or row of shaped tiles, that covers the peak where two roof slopes meet and keeps rain out of the joint. ALAF, the Tanzanian sheet maker, sells 325 mm and 407 mm ridges in 28 and 30 gauge, coloured to match its roofing sheets.
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What a ridge cap does
On a pitched roof the sheets on each slope stop short of each other at the top, leaving a gap along the ridge line. A ridge cap — also called ridge capping, roof capping or ridge flashing — bridges that gap. The Australian roofing supplier Metal Roofing Online describes its job: it seals the highest point of the roof against rain, dust and debris, and so protects the roof timbers underneath from moisture.
Ridge cap profiles
The cap is shaped to suit the roof covering. Metal Roofing Online lists these common forms for metal roofs:
| Profile | Suits | Example sizes from the supplier |
|---|---|---|
| Roll top | corrugated sheets | — |
| Corrugated ridge capping | corrugated sheets | 190 mm |
| Flat ridge flashing | box (trapezoidal) sheets | 140 mm |
| Ridge capping for a box profile | box (trapezoidal) sheets | 170 mm and 220 mm for its Trimdek profile, 210 mm and 260 mm for Klip-Lok |
The supplier makes them from coated steel 0.42 mm or 0.55 mm thick, and advises choosing the type by roof pitch as well as by sheet profile. Tile-profile sheets take a ridge shaped to match, as ALAF’s range below shows.
ALAF ridges and valleys
In Tanzania, ALAF sells ridges through its online shop to match its own sheets:
- 325 mm ridge for coloured roofing sheets, in 28 and 30 gauge; the 28-gauge version is 0.32 mm thick and sold by the piece.
- 407 mm ridge for coloured roofing sheets, in 28 and 30 gauge.
- 407 mm tile ridge, 28 gauge, in matte and textured finishes, for its tile-profile sheets.
- Valleys in 325 mm and 407 mm, for the inside corner where two slopes meet.
All come in the six colours of its coloured sheets: charcoal grey, brick red, dark green, sky blue, maroon and tile red. Ridge prices sit with the sheet prices in ALAF’s shop; sheet prices from two sellers are compared on the roofing sheets price page.
Matching the ridge to the sheet
ALAF’s flashings page sets out the rule: flashings are made for a particular position on the roof and a particular sheet profile, and they are usually made of the same material as the roof so the colours match. ALAF makes them in aluminium-zinc coated steel and in aluminium, and its branches take orders for custom flashings.
In practice that means four things to match when buying roof capping: the sheet profile (corrugated, box or tile), the gauge, the coating and the colour. The roofing sheets page explains profiles and gauges; the full set of roof parts is on the roofing page.
Fixing a ridge cap on a roof
Metal Roofing Online advises fixing the cap with suitable roofing fasteners so that the peak holds against wind-driven rain. Air movement at the top of the roof is a separate question, covered under roof ventilation.