Summary

The 2014 amendment to BS 5534 (the British Standard for slating and tiling) effectively ended mortar-only ridge bedding in the UK. Until then, the convention was mortar-bedded ridges over a sand/cement bed, occasionally with a clip or wire to hold the end tiles. That method failed too often in high winds — entire ridge runs would lift off, taking tiles and creating safety hazards. Dry ridge systems use a continuous mechanical fixing (screws into a batten or clamp) with a ventilation strip underneath, eliminating the failure mode.

For a roofer, the question is rarely "which is better" — the question is "what does the job require?" New build or re-roof = dry ridge. Repair to an existing mortar ridge = either re-mortar with supplementary mechanical fixing (BS 5534 minimum) or upgrade the whole ridge to dry. NHBC won't sign off a new build with a mortar-only ridge, and insurance assessors increasingly note mortar ridge failure as "below current standard" on claim assessments.

This article covers when each method is acceptable, the BS 5534 fixing rules, ridge ventilation requirements (Part F + NHBC), system components, and the cost difference per metre.

Key Facts

Quick Reference Table

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Scenario Method BS 5534 NHBC
New build Dry ridge Required Required
Full re-roof (new battens, full re-tile) Dry ridge Required N/A (not new build)
Strip-and-recover (battens kept) Dry ridge strongly preferred Mechanical fixing required either way N/A
Partial repair < 25% of ridge Mortar + mechanical clip acceptable Mechanical fixing still required N/A
One or two cracked ridges, rest sound Re-bed with mortar + clip Acceptable N/A
Listed building / heritage Mortar may be required by conservation officer Mechanical fixing still required N/A
Component Spec
Ridge batten 50mm × 25mm or 50mm × 38mm BS 5534-compliant treated softwood
Batten bracket spacing One per ridge tile (typically 450–500mm centres)
Ventilation roll width 250–300mm to span ridge plus 50mm each side onto tiles
Free vent area 5mm continuous (≈ 5,000mm²/m) per Part F2
Screw type A2 stainless or galvanised — manufacturer-supplied
Standard ridge tile lengths 450mm or 500mm

Detailed Guidance

When dry ridge is required

Any of the following triggers dry ridge:

When mortar is acceptable

Mortar-bedded ridges remain acceptable in the BS 5534 framework ONLY for:

Even in these cases, the BS 5534 mechanical-fixing rule still applies — every repaired ridge tile must have a stainless steel clip or wire fixing in addition to the mortar bed.

Dry ridge installation procedure

  1. Strip existing ridge tiles and mortar back to the rafters or original timber.
  2. Fix a ridge batten centrally over the apex, packing as required to achieve a true line.
  3. Lay the ventilation roll over the batten, dressed onto both tile sides — fix with the manufacturer's clips or stainless nails.
  4. Position each ridge tile dry along the run, marking bracket positions on the batten.
  5. Lift each tile and screw its bracket through the vent roll into the batten.
  6. Drop the tile onto the bracket, ensuring the union sleeve overlaps the next tile in the run.
  7. Cap ends with the manufacturer's end-cap (or close with a mortar end-stop on heritage jobs).
  8. At hip junctions, use a hip-to-ridge transition fitting from the same manufacturer.

Ventilation requirements

Approved Document F2 requires roof ventilation where the insulation is at ceiling level (a cold roof). For a typical UK pitched roof, this is a continuous 5mm gap at the ridge (or 10mm if no eaves vent is present). Dry ridge systems include a vent roll designed to give exactly this free area. A mortar-bedded ridge gives ZERO ventilation — this is one of the underlying reasons for the BS 5534 change, since post-2010 thermal-efficiency requirements push more moisture into cold roof voids and the ridge is the natural escape.

Hips and verges follow the same rules

Hip tiles and verge tiles are subject to the same BS 5534 mechanical-fixing requirement as ridges. Dry hip systems use a hip-batten with bracket fixings; dry verge systems use clip-on plastic or metal end caps that hook over the tile and screw into the gable edge. Mortar-bedded hips and verges should be upgraded to dry whenever the roof is opened up.

Common faults on dry ridge installs

Frequently Asked Questions

Can I leave the existing mortar ridge if I'm just replacing tiles?

If you're doing a substantial re-roof, no — upgrade to dry ridge. If you're replacing one or two slipped ridge tiles only, you can rebed with mortar and add a clip (BS 5534 minimum). Document the decision in your job notes and quote so there's a paper trail for any future warranty or insurance claim.

How much more does dry ridge cost than mortar?

Materials roughly £15–25/m for dry ridge components vs £3–5/m for mortar. Labour is comparable — dry ridge installs faster once you're set up. Net cost difference on a typical 12m terrace ridge is around £150–250 — usually included in any modern re-roof quote without itemising separately.

What about ridges on listed buildings?

Conservation officers vary. Some require mortar-only to maintain visual authenticity; others accept a dry system with appropriate ridge tiles (handmade clay, lime mortar end-stops). Always ask before specifying. The BS 5534 mechanical-fixing requirement still applies regardless — clips can be hidden under mortar end-stops.

Does dry ridge need maintenance?

Less than mortar. The vent roll and brackets should last 50+ years; the screws are stainless. Inspect every 5–10 years for any tile rocking or weather penetration around end caps. Mortar ridges typically need re-bedding within 20–30 years; dry ridges effectively don't.

Regulations & Standards