How to specify dry ridge and verge systems
What a dry verge and dry ridge clause has to cover, from BS 8612 and wind to tile compatibility, gable staining and ventilation, and how to write it in CAWS and in Uniclass.
Photo: Mr Ignavy, CC BY-SA 2.0, via Wikimedia Commons.
How do you specify dry ridge and verge systems?
To specify a dry verge or dry ridge, call for a system that conforms to BS 8612, is made for the specific tile or slate and headlap, and has test data showing it suits the wind exposure of the site. Every ridge, hip and verge unit must be mechanically fixed, as BS 5534 has required since 2014. State how the verge sheds water clear of the gable, any ridge ventilation needed by the condensation design, and the colour.
Dry-fixed ridges and verges replaced mortar on most new roofs after BS 5534 was revised in 2014 to require mechanical fixing at the perimeter. The early products were uneven: some did not hold the tiles in high wind, and some verges directed rain down the gable wall, leaving black streaks on render. BS 8612, published in 2018, was written to deal with both problems, and BS 5534 now refers to it.
This guide covers dry verges, ridges and hips on tiled and slated roofs. In Uniclass the verge is Pr_35_90_93_30 Dry fixing verges, with neighbouring codes Pr_35_90_93_29 Dry fixing ridges and Pr_35_90_93_28 Dry fixing hips. The roof covering itself is written separately, as in our guides to concrete and clay tiles and natural slate.
What does a dry verge system clause need to cover?
Some properties are specific to dry ridge and verge systems. Others belong in every product clause. A clause that leaves either out gives the contractor room to substitute.
Properties of dry ridge and verge systems
- FixingsMechanical fixing of every unit and ridge tile, to BS 5534.
- CompatibilitySame system as the tile, left and right handed units.
- Free ventilation areaFor ventilated dry ridges, from the condensation design.
- FinishColour to match the tile or ridge.
- Weather resistanceRain resistance and water shedding clear of the gable.
- AccessoriesBatten end clips, end caps, ridge unions and brackets.
What every product clause needs
- Manufacturer and product referenceUsually the tile manufacturer's own system for that tile.
- Product standardBS 8612, with test evidence for mechanical resistance.
- Installation methodManufacturer's instructions with BS 5534 and BS 8000-6.
- Technical submittalsBS 8612 test data and suitability for the site wind exposure.
- Operation and maintenance informationInspection of units and clips after storms; replacement parts.
- MaterialPlastic units, ridge rolls and metal clips.
- ProfileMade for a specific tile profile and headlap range.
Uniclass Pr_35_90_93_30 Dry ridge and verge. Not every property applies to every project; where one does not, say so rather than leaving it blank.
Which decisions does the clause depend on?
Most properties follow from the product you choose. These depend on the project, so they need a decision from the designer before the clause is written.
- 01
Mechanical resistance and the site's wind exposure
WindSince 2014 BS 5534 has required ridge, hip and verge tiles to be mechanically fixed whether or not mortar is used. BS 8612 then set out tests for the mechanical resistance of dry-fixed systems and how to use the results against the wind exposure of the site. That means the question to ask a supplier is not "is it dry fix" but "what does the BS 8612 test data show, and does it cover this site". On exposed coastal or upland sites the answer can differ between products that look the same.
How to decide
- Get the site wind exposure from the tile manufacturer's BS 5534 fixing calculation.
- Ask for the system's BS 8612 test data and the supplier's confirmation that it suits that exposure.
- Make sure every unit and every ridge tile is fixed, including at ridge ends and hip bottoms.
Write it asDry verge: System to BS 8612, every unit mechanically fixed. Submit BS 8612 test data and confirmation of suitability for the site wind exposure. - 02
Matched to the tile, its profile and headlap
FitDry verge units are shaped for particular tile profiles and only seal within a range of headlap and gauge. Fit the wrong unit, or the right unit at the wrong gauge, and the units ride up, leave gaps or fail to clip together. Tile manufacturers make their own verge and ridge systems for each range, and the guarantee on the roof often depends on using them. Universal systems exist, but check that the tile you have specified is on the list. Left-hand and right-hand verges are different units, so both must be specified.
How to decide
- Prefer the tile manufacturer's own dry verge and ridge for the specified tile.
- Check the headlap and gauge range for the unit against the tile clause.
- On re-roofing, check the existing tile is on the system's compatibility list.
Write it asVerge units: Left and right hand units from the tile manufacturer's dry verge system for the specified tile, within the system's stated headlap range. - 03
Shedding water clear of the gable
WaterA dry verge replaces the mortar bed and undercloak that used to throw water off the edge of the roof. Some early systems channelled water down the face of the gable instead, leaving streaks on render and brick. BS 8612 includes a test for how a verge sheds water away from the wall, and the detail at the gable matters too: battens projecting the right amount beyond the brickwork or bargeboard, and underlay carried across the verge. The clause should require both the tested product and the setting out.
How to decide
- Require a system tested to BS 8612 for water shedding at the verge.
- Set batten projection and underlay at the verge to the manufacturer's instructions.
- On rendered or pale gables, look at the run-off path on the gable detail.
Write it asVerge setting out: Battens projecting beyond face of gable or bargeboard as manufacturer's instructions; underlay carried over full width of verge. - 04
Ventilated ridges and the condensation design
VentilationA dry ridge can be solid or ventilated. A ventilated ridge roll is one way of providing high-level roof ventilation, but it only works if the underlay is cut back at the apex as the manufacturer requires and the stated free area is enough for the roof. Some vapour-permeable underlays and warm roof build-ups do not need ridge ventilation at all. Decide from the condensation risk assessment, not by default, and state the free area if one is needed.
How to decide
- Take the ventilation need from the BS 5250 condensation risk assessment and the underlay's certificate.
- If ventilation is needed, state the free area per metre and the underlay detail at the apex.
- Seal the ridge either side of gas flue or soil vent terminals as the manufacturer requires.
Write it asRidge: Dry ventilated ridge system to BS 8612, free ventilation area as condensation risk assessment to BS 5250. Underlay gap at apex as manufacturer's instructions. - 05
Mortar, dry or both on traditional roofs
AppearanceDry verge units are visible from the street, and on some roofs, particularly in conservation areas or on listed buildings, a planning officer may want the traditional look of a mortar-bedded verge. That is allowed, but BS 5534 still requires the tiles to be mechanically fixed, so a mortar-bedded verge becomes mortar plus clips or nails. The clause should say which is used where and, for dry systems, the colour of the units, because black plastic on a red clay roof is a common complaint.
How to decide
- Ask early whether planning or conservation will accept dry verge units.
- Where mortar is used, still specify mechanical fixing of the verge tiles.
- Choose a unit colour that matches the tile and approve a sample.
Write it asVerge, front elevation gables: Mortar bedded on undercloak, every verge tile also mechanically fixed with manufacturer's verge clips, to BS 5534.
The values under "Write it as" are examples. The right value depends on the location, the use and the fire strategy.
Which standards should the clause cite?
Cite the product standard the declaration of performance refers to, the code of practice for installation, and the test method behind each value you set. A value without its test method cannot be checked against a submittal.
- BS 8612
- Dry-fixed ridge, hip and verge systems for slating and tiling. Specification
Requirements and tests for dry-fixed systems: mechanical resistance to wind, rain resistance, water shedding at verges, material durability and ventilation performance of ridge rolls.
In the clause "Dry verge: system to BS 8612".
- BS 5534
- Slating and tiling for pitched roofs and vertical cladding. Code of practice
Roof tiling design including fixing for wind. It requires ridge, hip and verge tiles to be mechanically fixed, and refers to BS 8612 for dry-fixed systems.
In the clause "Ridge, hip and verge tiles: mechanically fixed to BS 5534".
- BS 8000-6
- Workmanship on construction sites. Slating and tiling of roofs and walls. Code of practice
Site workmanship for tiling, including setting out at verges and ridges.
In the clause "Workmanship: to BS 8000-6".
- BS 5250
- Management of moisture in buildings. Code of practice
Condensation risk and roof ventilation, which decides whether a ventilated ridge is needed and how much free area it must give.
In the clause "Ridge ventilation: as condensation risk assessment to BS 5250".
- BS EN 490
- Concrete roofing tiles and fittings for roof covering and wall cladding. Product specifications
The product standard for concrete tiles and their fittings, which the dry system has to match.
In the clause Cite it in the tile clause; the verge clause refers to "the specified tile".
- BS EN 1304
- Clay roofing tiles and fittings. Product definitions and specifications
The product standard for clay tiles and fittings, including ridge tiles used with dry ridge systems.
In the clause "Ridge tiles: clay, to BS EN 1304, from the tile manufacturer's range".
- BS EN 1991-1-4
- Eurocode 1. Actions on structures. General actions. Wind actions
The wind actions behind the BS 5534 fixing calculation that sets the exposure the dry system must resist.
In the clause "Fixing: to the manufacturer's BS 5534 calculation for the site".
Confirm the current edition of each standard at every issue. Avoice's State of UK Specifications 2026 found a withdrawn standard cited in 40% of specifications at contract issue.
How do you write it in CAWS?
Dry verges and ridges are not a CAWS section of their own. They are written as edge and junction clauses within the tiling or slating section: H65 for single lap tiles, H60 for plain tiles and H62 for natural slate. In manufacturers' NBS-format specifications the verge sits in the 400s, for example 411 for a dry verge and 440 for a mortar-bedded alternative, and dry ridges sit later in the same section.
The type clause for the roof, in the 100s, says which verge and ridge clauses apply. Those edge clauses then lean on the general tiling clauses: basic workmanship, underlay, battens, tile fixing, local and general fixing areas, and the generally clause for edges and junctions that forbids improvised fittings.
- Gable
- Masonry gable with timber bargeboard, brought up level to underside of battens
- Underlay
- Carried over full width of verge, as clause 240
- Battens
- Projected beyond face of bargeboard as manufacturer's instructions, as clause 245
- Batten end clips
- Manufacturer's clips, securely fixed to end of each batten
- Verge units
- Left and right hand units for the specified tile
- Manufacturer
- Tile manufacturer's dry verge system
- Product reference
- Submit proposals
- Standard
- BS 8612
- Headlap
- Within the system's stated range for the tile
- Colour
- TBC Unit colour to match tile is reserved for approval by the planning authority. Resolve before ordering.
- Fixing
- Every unit mechanically fixed with the fixings supplied, to BS 8612 and BS 5534
- Verge tiles
- Fixed twice, as clause 275
- Ridge end
- Manufacturer's ridge end cap
- Submittals
- BS 8612 test data and suitability for the site wind exposure
Illustrative, not from a real project. One property is left as a TBC with a reason so it can be tracked and closed before issue.
Clauses the type clause relies on
- H65/210
- Basic workmanship Tiling to BS 5534 and BS 8000-6, true lines, neat edges.
- H65/240
- Underlay Laps, tautness and not obstructing ventilation paths.
- H65/245
- Battens/ counterbattens Grade and size to BS 5534; ends that take the batten end clips.
- H65/275
- Tile fixing Perimeter tiles at verges and ridges fixed twice.
- H65/280
- Local and general fixing areas Perimeter bands that need extra fixing for wind.
- H65/305
- Generally Recommended fittings only; do not improvise at edges.
Clause numbers vary between NBS versions and practice masters; the numbers here follow a tile manufacturer's NBS-format H65 specification.
How do you write it in Uniclass?
In Uniclass the verge belongs to the roof it finishes, for example Ss_30_40_95_40 Interlocking tile roofing systems. The system clause lists the tile, the underlay and battens, and the edge details, and calls up the dry verge and dry ridge as products by type mark.
The verge units are a product clause under Pr_35_90_93_30 Dry fixing verges, and a dry ridge under Pr_35_90_93_29 Dry fixing ridges. Writing them as products makes it clear they must be compatible with the tile product clause, which is the main thing that goes wrong.
- Description
- Interlocking concrete tile roof with dry-fixed ridge and verges
- Tiles
- Pr_25_93_72_17 Concrete interlocking tiles (T01)
- Verges
- Pr_35_90_93_30 Dry fixing verges (DV01)
- Ridge
- Pr_35_90_93_29 Dry fixing ridges (DR01), ventilated as condensation risk assessment
- Fixing
- All tiles and ridge, hip and verge units mechanically fixed to BS 5534
- Verge setting out
- Battens projecting and underlay carried over verge as manufacturer's instructions
- Manufacturer
- Tile manufacturer's dry verge system
- Product reference
- Submit proposals
- Standard
- BS 8612
- Compatibility
- For tile T01, within the system's stated headlap range
- Units
- Left and right hand
- Accessories
- Batten end clips, ridge end caps, fixings supplied
- Colour
- TBC Unit colour to match tile is reserved for approval by the planning authority. Resolve before ordering.
- Mechanical resistance
- BS 8612 test data showing suitability for the site wind exposure
Illustrative. Performance of the finished system sits in the system clause; properties of the product sit in the product clause.
In NBS Chorus the Uniclass product clause also carries the NBS reference 45-80-90/378 for dry fixing verges; use one referencing system throughout the specification.
What goes in the spec, and what goes in the schedule?
The specification defines each type once. The schedule and drawings say where each type goes.
In the specification
What the product is and how it performs and is installed. Written once per type.
In the schedule or drawings
Where each type goes and how much of it. Changes with every plan revision.
Write the verge and ridge types once and show which gables get which on the roof plan and elevations. Planning-driven mortar verges are usually only on some elevations, so mark them on the drawings.
What are the common mistakes?
Most problems are a missing property, a property filled with the wrong kind of value, or a decision left silently open.
- "Dry verge" with no standard. Ask for a system conforming to BS 8612 with test data. Products that look alike perform differently in wind.
- A universal verge on a tile it was not tested with. Check the tile and headlap are on the system's list, or use the tile manufacturer's own system.
- Mortar verge with no mechanical fixing. BS 5534 requires mechanical fixing whether or not mortar is used. Write the clips or nails into the mortar verge clause.
- A ventilated ridge with the underlay run over the apex. The vent does nothing if the underlay is not cut back. Write the apex detail in.
- Only one hand of verge unit. Left and right verges use different units. Specify both, or the supplier sends the wrong quantity.
- Black units on a red roof. Unit colour is visible from the street. Specify it and approve a sample.
How Avoice helps
Avoice drafts verge and ridge clauses alongside the tiling clause, so the two refer to the same tile and the same fixing rules.
- Drafts from your drawings and schedules
It reads gable and ridge details from your roof plans and elevations, picks the H65 edge clauses or the Uniclass dry fixing products, and links them to the tile type clause.
- Leaves a TBC where the information is not there
If the planning authority has not agreed dry verge units on the front gables, or the unit colour is open, the clause says TBC with that reason, and it goes into the project TBC register.
- Writes in your format and your style
Choose CAWS or Uniclass. Avoice adapts your own tiling master, so your verge and ridge clauses keep your practice's wording.
- Checks the clause against everything else
QA/QC flags a dry verge clause that names a different tile from the roof type clause, a mortar verge with no mechanical fixing, or an outdated edition of BS 5534.
- Keeps product data in one place
BS 8612 test data and compatibility lists sit in the Product Room, linked to the verge clause, so a proposed alternative can be checked against the tile and the site exposure.
Related guides: How to specify concrete roof tiles, How to specify clay roof tiles, How to specify fascias and soffits.
Software can draft and check. The designer still chooses the product and is responsible for the specification.
Draft your dry verge system clause in Avoice
Upload your drawings and schedules. Avoice drafts the clause in CAWS or Uniclass, cites the standards and flags anything your information does not settle.
This guide is for general education and is not professional advice. Check current editions of standards and Approved Documents, the manufacturer's data, and the requirements of your project before relying on any clause.