Two Quotes, One Cracked Ridge
The homeowner has half a metre of ridge mortar on the drive and a photograph of the gap it came out of. Two roofers have been up the ladder since. The first quote says rake out and re-bed the ridge, make good the verge pointing, twelve metres of ridge and two rakes. The second says strip the ridge, fit a dry ridge system with unions and stop ends, dry verge to both rakes, and it is close to twice the first. Both roofers were standing on the same roof. Neither of them is being dishonest.
What separates the quotes is not the mortar. Mortar is a bed, and a bed is a good thing to have under a ridge tile — it keeps the unit level, it closes an irregular gap over a cambered tile profile, and on a roof where the ridge line wanders it is the only practical way to make the run look straight. What separates them is what is holding the tile down when the bed lets go, and on a roof built before the middle of the last decade the answer is usually nothing at all. The mortar was the bed and the fixing in one, which meant a bond failure and a fixing failure were the same event.
So the useful question is not whether to re-bed. It is which of three separate lines you are pricing — the ridge along the apex, the hips down the corners, the verge up each rake — because they take different products, they are measured in different ways, and only one of them is a horizontal dimension you can scale off a plan. Everything below is arranged around those three lines and the one revision to a British Standard that changed what each of them has to do.
What the 2014 Revision Removed
BS 5534, Slating and Tiling for Pitched Roofs and Vertical Cladding — Code of Practice, is the document that sets UK practice for a tiled or slated roof. Its 2014 revision is the one that matters here: it removed reliance on mortar as the sole means of fixing ridge, hip and verge units. Under it, those units are mechanically fixed, and they are mechanically fixed whether or not they are also bedded. Mortar was not banned and has not gone away. It was demoted from a fixing to a bedding and weathering material, with something made of metal doing the holding behind it.
That change did not arrive from nowhere. A mortar bed is a rigid material joining two rigid materials that move at different rates, sitting in the most exposed line on the building, and it is asked to bond to a tile surface which on a modern concrete or glazed clay unit is not especially keen to be bonded to. It cracks, the crack lets water into the bed, frost opens the crack, and the failure runs along the whole run rather than appearing at one tile. Anyone who has swept a driveway after a gale has seen the result, and it is a falling-object problem before it is a leak.
The same revision tightened the fixing of the roof generally, so a re-roof quoted today is not the roof next door from 1994. Uplift is calculated rather than assumed, using wind actions from BS EN 1991-1-4 Eurocode 1: Actions on Structures — General Actions — Wind Actions with its UK National Annex, brought together with site altitude, terrain, building height and the position of the tile in the roof's edge and corner zones. Perimeter tiles at eaves, verge, ridge and abutment are mechanically fixed as a matter of course. The underlay is part of the calculation too, and it is a specified product under BS EN 13859-1 rather than whatever is on the van.
Four years later BS 8612, Dry-Fixed Ridge, Hip and Verge Systems for Slating and Tiling — Specification, gave the products themselves something to be measured against. Before it existed, the phrase dry fix covered an engineered kit with published wind performance and also a length of extruded plastic with a screw through it, and a specifier had no common ground on which to compare them. A system that conforms to BS 8612 has been assessed for wind resistance, for weathertightness, for the ventilation performance it claims where it claims any, and for the durability of its own components, and it comes with fixing instructions that are part of the specification rather than a leaflet in the box. Asking which standard a system is offered against is a fair question to put in writing, and it is the single most useful line in a quote comparison.
One thing the standard does not do is make an existing roof retrospectively unlawful. A ninety-year-old bedded ridge that is sound is a sound ridge. The trigger is the work: once you strip and re-form that line, you are forming it to current practice, and a warranty provider will look at it that way too — NHBC Standards Chapter 7.2, Pitched Roofs, sets what a builder has to achieve on a plot the warranty covers. Outside the UK the arithmetic is the same and the paperwork is different: Chapter 9 of the International Residential Code and the tile manufacturer's published fixing instructions carry the equivalent requirements where that code is adopted.
| Line | What a pre-2014 detail relied on | What a re-formed line has to have |
|---|---|---|
| Ridge | Mortar bed to the top courses, bonding to two tile surfaces | A mechanical fixing per unit — screw to a ridge batten, or clamp — bedded or not |
| Hip | Mortar bed, plus a hip iron at the foot on better work | Mechanical fixing per unit, restraint at the foot, and each cut tile fixed |
| Verge | Mortar fillet over an undercloak, pointing renewed periodically | Dry verge units, a cloaked verge tile, or a bedded fillet with the tiles fixed |
| Cut tiles at hips and valleys | Held by the bed they were pushed into | Clipped or nailed in their own right — the bed is not a fixing |
Six Things Stacked Over One Apex
A dry ridge looks like one component from the pavement and is six from the loft. Working up from the structure: rafters or truss chords, then the underlay and the battens carrying the courses, then the top course of tiles on each slope, then a ridge batten held above the apex on brackets or straps, then a roll that seals and often ventilates the gap between that batten line and the tile profile, and finally the ridge unit itself screwed down through the roll into the batten. Every one of those is a separate delivery item and three of them are separate suppliers.
The height of the ridge batten is the number the whole detail hangs on, and it is the one most often got wrong on a first dry-fix installation. Set it too low and the ridge unit sits down onto the top course, rocks on the tile nibs and will not pull tight; set it too high and there is a shadow gap under the unit that the roll is being asked to bridge without support. It is set from a string line down the run, against the profile of the tile actually on the roof and the system manufacturer's stated dimension for that combination, and it is checked at both ends and in the middle before a single ridge unit is offered up.
A dry-fixed ridge, taken apart
- Ridge unit — screwed down through a pre-formed hole into the ridge batten, one fixing per unit, with a union at every joint and a stop end at each run end Roof Ridge Cap Calculator
- Sealing and ventilating roll — closes the gap between the batten line and the tile camber, and on a ventilating product carries the free area the roof is relying on Ridge Vent Linear Footage Calculator
- Ridge batten and brackets — held above the apex at the height the system states for that tile profile, and levelled on a string line before any unit is offered up
- Top course of tiles — cut to the ridge line on each slope and fixed in its own right, since the bed it used to sit in is no longer counted as holding it Clay Barrel Roof Tile Calculator
- Underlay and battens — the secondary weather barrier and the gauge that every course above is set out from, both specified rather than chosen on site Roof Batten Spacing Calculator (Tile Roofing)
- Rafters or truss chords — what the brackets and straps ultimately fix back to, and what decides whether the ridge line is straight before anyone tries to make it look straight Roof Truss Spacing & Count Calculator
Three Lines, Measured Three Different Ways
Ridge is the easy one: a horizontal length along the apex, taken with a tape or a laser from gable to gable, and on a roof with more than one ridge height taken run by run. Hips are where takeoffs go wrong. A hip runs on the rake of two slopes at once, so the distance you scale between two corners on a plan is shorter than the timber it follows, and on a common domestic pitch the difference is enough to leave you a unit or two short on every hip. Take hips on the slope, or take the plan dimension and apply the pitch factor deliberately rather than forgetting it exists. Verge is measured up the rake as well, both rakes, both ends of the building, and it is the line people leave off the sheet entirely because it is vertical on the elevation and therefore invisible on the plan.
Then the run becomes units, and units are not the same thing as metres. A ridge tile has a cover length rather than an overall length, because consecutive units either lap or butt against a union piece depending on the system, and the difference between overall and cover across a twelve-metre run is a whole tile. Junctions eat stock too: every point where a ridge meets a hip takes a purpose-made junction or a mitred and sealed detail, every run end takes a stop end or a block end, and a hipped roof has more of these small manufactured pieces than the estimate ever allows. Count the junctions off the roof plan before you count the metres.
The last item on the list is the one that halts a crew: fixings. A dry-fix screw is a specified length for the system, the roll, the tile profile and the batten it has to bite, and it is not the box on the van. Its durability grade is part of the specification as well, because the standard treats the life of a fixing at the ridge as part of the life of the roof, and a fastener that corrodes in a decade has made the mechanical fixing decorative.
- Walk the roof plan and mark every ridge run, every hip and every rake, then number them.
- Measure ridge runs horizontally; measure hips and rakes on the slope, or convert the plan dimension with the pitch factor.
- Total the ridge and hip lines together — that combined figure is what cap and ridge material is ordered against.
- Count junctions, run ends and changes of direction separately; they are manufactured pieces, not offcuts.
- Convert each run to units at the system's cover length, not its overall length, and round up per run rather than across the roof.
- Confirm the fixing length against the tile profile, the roll and the batten depth before the order is placed.
The combined ridge-and-hip run is the figure every capping product is bought against. This one turns that length into bundles of asphalt cap for a shingle roof; on tile, take the same measured length to the ridge unit's cover length and add the junctions separately.
SettingsSettings for this calculation
The standard allowance most suppliers and estimating guides assume for ordinary work.
The total length of ridge and hip lines needing cap shingles.
Extra cap for the pieces cut where hips meet the ridge and at the end of each run.
Ridge cap bundles needed
2 bundles
- Ridge/hip length (with waste)
- 42.9 linear ft
They open the calculator with your figures already in it
Roof Ridge Cap Calculator: 2 bundles — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- Every bundle is counted as 33 linear feet (10 m) laid at the exposure the maker intends, the single coverage figure the source gives; there is no field for the rating printed on your own wrapper, and no way to tell the arithmetic you plan to lay the caps tighter or wider than that.
- Hip lines have to be measured along the slope and added into the one total yourself — no pitch is asked for anywhere, so a hip scaled off a plan-view drawing goes in short and the bundle count follows it down.
- The allowance is one percentage of whatever total you type, so at the same setting three short hips adding up to sixty feet and one unbroken sixty-foot ridge return exactly the same figure, even though each extra run adds two more cut ends; raise it for a roof of many hips.
- Bundles are rounded up to whole packs, so a 35-foot run and a 59-foot one both come back as two, with the first leaving well over half of the second bundle unused and no remainder reported anywhere in the output.
- Fixings and sealant sit outside the result entirely: the calculation returns a bundle count and nothing else, so nails for the caps still have to be worked out from the same ridge length.
A Hip Is Not a Short Ridge
Gravity acts along a hip run and not just across it, which is why a bedded hip has always needed a hip iron at the foot to stop the whole run creeping down the slope over thirty winters. Take the bedding away and the restraint problem does not go with it: a dry hip system carries the load through its own fixings back into a hip batten fixed along the hip rafter, and there is still a defined restraint at the bottom unit. Bonnet and arris hips, which are bedded units by their nature and often the only ones that suit the roof they sit on, get bedded and mechanically fixed — the two are not alternatives any more.
The other hip problem is the tiles nobody counts. Every course on both slopes arrives at the hip as a raking cut, and a narrow cut tile has lost most of the nib and interlock that was holding it. Those pieces used to be pushed into the hip bed and left to it. They are now fixed in their own right, with a clip or a nail into the batten, and a cut too narrow to take a fixing is a cut that should not have been made — the course is re-set so the cut lands wider. That is a setting-out decision taken at the start of the slope, not a repair made at the hip.
The Verge Is Where the Wind Gets a Grip
Uplift is not uniform across a roof. It concentrates at edges and corners, which is exactly where the verge is, and a verge is also the one perimeter line with an unsupported tile edge presented to the weather. A mortar fillet at the verge is therefore doing the hardest job on the roof with the least help, and when it goes it goes along a run rather than at a point, taking the pointing, then the bed, then the edge tiles.
There are three honest answers and they are not equally good on every roof. A dry verge system clips over the projecting batten ends and the outer edge of the tile, running as a continuous line of units with a starter at the eave and a cap at the ridge. A cloaked verge tile — a purpose-made unit with the return already formed — gives the cleanest appearance and is a decision taken when the tile is chosen, not afterwards. Or the traditional detail: an undercloak board set to the correct projection, tiles bedded on a mortar fillet over it, with every verge tile mechanically fixed so the fillet is weathering and appearance rather than structure. That last one is often the right answer on a conservation roof where the first two would be refused.
Dry verge failures are nearly always upstream of the verge. The units clip to the batten ends, so the batten ends have to project by the amount the system states and be cut square and to a line — and that was done weeks earlier by a different pair of hands, before anyone had read the verge system's instructions. Short battens give a unit nothing to grip; long battens hold it proud and let wind under it. Check a sample run of batten projection before the tiling gang leaves the roof, because correcting it afterwards means lifting courses.
The undercloak deserves the same scrutiny on a bedded verge. It is a specified board, a fibre cement undercloak on modern work, laid on the bedding to a stated projection past the wall face so the tile overhang discharges clear rather than running back down the gable. Timber and slate undercloaks appear on older roofs and are still repaired in kind on the right building. What none of them are is a strip of whatever came off the last job, cut to fit and buried under a fillet that will hide the decision for fifteen years.
Ventilation Arrives Attached to the Fix
A mortared ridge is a sealed ridge. Swap it for a ventilating dry ridge roll and you have not just changed a fixing, you have opened a continuous high-level path out of the roof space along the whole apex — and that is a moisture decision, not an ironmongery decision. Sometimes it is exactly what the roof needed and it quietly fixes a condensation complaint the homeowner had stopped mentioning. Sometimes it is the wrong move on a warm roof or a sarking-boarded roof where the moisture strategy was never meant to run through the ridge at all. BS 5250, Management of Moisture in Buildings — Code of Practice, is the document that decides which of those you have.
Not every dry ridge roll ventilates, and the ones that do publish a free area per linear metre that is well below the size of the physical gap, because baffles and insect mesh sit in the airway. Size against the published figure and against the requirement for that roof, never against the slot you can see. That is the same trap the site's ridge vent calculator warns about on its own page, and it is worth repeating here because on a dry-fix job the ventilation figure is buried in a system data sheet rather than printed on a vent.
The balance matters more than the total. Exhaust at the ridge needs matched intake at the eaves, and a roof given a new ventilating ridge over eaves that are stuffed solid with blown insulation will draw its make-up air through the ceiling from the heated house below. That is warm, wet air arriving in a cold roof space, which is the precise fault the ventilation was installed to cure. Look into the eaves before quoting the ridge, and if the intake is not there, price the trays and the vents with it rather than discovering the problem on the callback.
Ridge roll and ventilated ridge are bought by the linear metre off the same run you measured for the units, with a waste allowance that rises with the number of hip and ridge intersections — each one is an offcut.
SettingsSettings for this calculation
Waste is set to 5% by hand. Pick a tier above to replace it, or keep your own figure.
The combined length of all ridge lines to receive ridge vent.
Extra material to allow for cut waste at ridge ends and intersections.
Ridge vent needed
51.45 ft
They open the calculator with your figures already in it
Ridge Vent Linear Footage Calculator: 51.45 ft — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- Buys vent, not the slot it sits over. A continuous ridge vent only works if the deck is cut back each side of the ridge board — typically 25 to 38 mm (1.5 in) a side — and that slot stops short of the ridge ends, of hips, and of any wall the ridge dies into, with the ridge board itself left uncut. Vent laid over unbroken decking looks exactly like vent laid over a slot and moves no air at all.
- Leaves out everything that finishes the run. Hip-and-ridge cap runs over the top of the vent as a separate quantity, and because the vent lifts the cap, coverage per bundle is a little less than over a bare ridge. End plugs, the connectors between vent sections and the longer nails that reach through the vent into the deck are all separate line items.
What Mortar Is Still For, and What It Weighs
Mortar survives this change in three places on a pitched roof: bedding a verge fillet over an undercloak, bedding bonnet and arris hips that have no dry equivalent worth having, and bedding a ridge on a building where the appearance of a bedded ridge is a planning condition rather than a preference. In all three it is a bed with a mechanical fixing behind it. A quote that says re-bed and stops there is quoting the pre-2014 detail, and the fix is not to argue about mortar but to ask what is holding the tile when the bed cracks.
The mix is trade practice rather than a code clause, and it should be described that way. The bedding mortar traditionally used for ridge and verge work is a cement-to-sand mix in the order of one to three by volume, made with a sand suitable for mortar under BS EN 13139, and the figure that actually governs your job is the one in the tile manufacturer's fixing instructions. Factory-made and site-made masonry mortars are specified under BS EN 998-2, Specification for Mortar for Masonry — Masonry Mortar, which is the document to name when a specification asks what the material is rather than how it is proportioned. Colour consistency is worth a sentence in the quote too, because a ridge re-bedded in two batches of different sand shows as banding from the pavement for the life of the roof.
Getting from a bedding job to a quantity is straightforward arithmetic that almost nobody does. A bed is a prism: a cross-section repeated along a run. On a ridge there are two of them, one under each edge of the unit, each about as wide as the tile bears and as deep as the gap the camber of the top course leaves. Take the cross-section off the actual tiles rather than from memory, multiply by the run length from your takeoff, and do it separately for the ridge, each hip and each rake, because a bonnet hip bed and a verge fillet are nothing like the same section.
That volume is then worth converting into a weight, for two unglamorous reasons. The first is ordering: mortar volume tells you nothing at the merchant, who sells sand by the bulk bag and cement by the 25 kg bag, and a weight is the honest bridge between the two. The second is handling. Bedding mortar goes up a scaffold in buckets, and a run of ridge and two rakes is a great deal more material than it looks like on the drawing — knowing the tonnage before the day tells you whether that is an afternoon or a hoist.
Two constraints have nothing to do with quantity and will still ruin the work. Mortar has a working life, and retempering a stiffening batch with more water to stretch it out weakens it materially — batch to the pace of the bedding, not to the size of the mixer. And bedding in frost, or where frost will arrive before the mix has gained strength, produces a bed that looks right in November and is on the drive in February. Both of those are reasons a re-bed gets programmed rather than squeezed in, and both are reasons the mechanical fixing behind the bed is not a formality.
| Where the bed is | What sets its cross-section | What sets its length |
|---|---|---|
| Under each edge of a ridge unit | The bearing width of the unit and the gap the top course camber leaves | The ridge run, taken horizontally along the apex |
| Under a bonnet or arris hip | The bedding face of the hip unit and the cut tiles it laps | The hip run, taken on the slope and not scaled off the plan |
| The verge fillet over an undercloak | The undercloak projection and the tile overhang past the wall face | The rake, both rakes, at both ends of the building |
Once the beds are a volume, this converts it to a weight for ordering sand and cement and for judging how much is going up the scaffold. It takes cubic yards and answers in short tons with no metric switch, so convert a metric bed volume going in and read the answer as short tons rather than tonnes — a tonne is about ten per cent heavier. The density behind it is a planning figure for sand-cement mortar; the merchant's ticket governs.
The volume of mortar in cubic yards.
Approximate weight
18 short tons
About 1.8 short tons per cubic yard for sand-cement mortar; close to concrete but without coarse aggregate. A planning figure, not a specification. Confirm the density with your supplier before ordering by weight.
- Conversion factor applied
- 1.8 short tons per cu yd
They open the calculator with your figures already in it
Mortar Cubic Yards to Tons Calculator: 18 short tons — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- This weight is a total for the elevation, summed from joints that go in over days or weeks. Site-mixed mortar is batched to the pace of laying and carried up in tubs, so nothing — platform, hoist or floor — holds this figure at once. Where the work runs off retarded ready-to-use mortar, which arrives wet, or off a site silo of dry preblended material with the mixer at its outlet, the opposite is true: that stock stands on site in bulk, and a charged silo puts a concentrated load on whatever base it was sited on.
- A small mortar tonnage does not turn straight into an order. Site-mixed work is bought as sand and cement in units that do not subdivide — sand by the ton or the yard, cement by the bag — so a job of a yard or two rounds up to the next whole unit of each, and at that scale the rounding moves what arrives more than the density does. On a job several times that size it disappears into the total, and what the mix ratio does to the density matters more.
- The volume converted here is joint volume, and mortar in a wall is not confined to the joints. Hollow units bedded full rather than on their face shells take mortar into the cores, and a collar joint between wythes is solid mortar that no take-off of beds and perpends counts. Where either applies, this tonnage is a lower bound on what to buy.
Mortar volume is worked out from the joint dimensions across a wall, and converting it to weight matters mainly for ordering the sand and cement that make it. The density sits below concrete because there is no coarse aggregate, only sand and binder. The figure most often underestimated is not the density but the volume itself: joints look thin, but across a full elevation the mortar in a single-wythe wall amounts to a substantial proportion of the wall's volume, and perpends consume as much as beds.
Answering the Homeowner
Write the three lines separately in the quote and the argument mostly ends. Ridge: system name, the standard it is offered against, fixing per unit, junctions and stop ends counted. Hips: same, plus the restraint at the foot and the fixing of the cut tiles. Verge: which of the three details is being used and why, and if it is a bedded fillet, the words mechanically fixed somewhere in the same sentence. A homeowner comparing two quotes cannot judge workmanship, but they can absolutely see which quote knows what it is doing.
Do not sell dry fix as maintenance-free, because it is not and the claim will be quoted back. Polymer components sit in full ultraviolet for decades, clips and unions are the parts that go, and a system guarantee is conditional on the system being installed to its own published instructions — which is another reason those instructions are worth having on site rather than in an email. What dry fix genuinely offers is a fixing that does not depend on a bond to a smooth tile face, and a failure mode that announces itself as a loose unit rather than as a length of mortar arriving on a car roof.
None of this is worth doing off a ladder. A ridge line is the full height of the building, at the point where the roof gives least, and the whole run has to be reached from a working platform — the Work at Height Regulations 2005 are the law in the UK, and OSHA 29 CFR 1926 Subpart M does the same job where that applies. Price the scaffold into the ridge quote openly. It is usually the honest reason the second quote was twice the first, and saying so out loud is more persuasive than any amount of argument about mortar.
The sheet to fill in before pricing a perimeter
Three lines, measured three ways, each turning into a different manufactured product. Fill this in on the roof rather than off the elevation, because two of the three do not appear on a plan at their true length.
- Ridge runs, horizontal, run by run — Gable to gable along each apex, kept separate where ridge heights change, and converted to units at the system's cover length rather than its overall length.
- Hip runs, taken on the slope — Scaled from the plan and left unconverted, a hip is short every time. Take it on the rake or apply the pitch factor deliberately.
- Rakes for verge, both ends — The line most often missed entirely, because it reads as vertical on the elevation. Decide dry verge, cloaked tile or bedded fillet before pricing it.
- Junctions, stop ends and starters — Manufactured pieces counted off the roof plan, not offcuts absorbed by waste. A hipped roof carries far more of them than a plain gable.
- Fixings, to the system's stated length and grade — Sized through the unit, the roll and the batten, with a durability grade that outlives the covering. Not the box already on the van.
- Bedding mortar, where a bed is still being used — Cross-section off the actual tiles, multiplied by each run separately, then converted to a weight for ordering and for carrying it up.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.