A slate re-roof in Thanet, step by step

01

The survey, before anything is decided

Every re-roof starts on the roof, not at a desk. We go up, look at the slates, the ridge, the valleys and the lead, and look at the underside from the loft where we can get in. Two terms are worth knowing. The valley is the inside corner at which two slopes join, and a flashing is lead dressed over a joint, for example the line between a slope and a chimney or wall. Photos of your own roof come back to you, so what we saw is on record for you too.

The survey answers the first question, which is whether a re-roof is needed at all. A few slipped slates, a tired ridge or one failed valley can usually be put right on their own. Stripping the whole slope becomes the right answer when slates are failing across it, when the nails have corroded through, or when the battens and underlay beneath are worn out.

HomeBuilding gives typical lives for natural slate of "100+ years" for Welsh slate, 75 to 100 years for Spanish and 50 to 80 years for reclaimed Welsh. Those are typical ranges, never a promise for a particular roof. A slate can still be sound when the nails, battens or underlay holding it have given out, which is why the survey looks underneath as well as on top.

What the survey records:

• the slate type, and whether sound slates can be saved for reuse
• the pitch of each slope, which limits the slate size and lap
• every chimney, valley, parapet and dormer, and the lead each one carries
• where the scaffold will stand, and whether it sits on the highway
• the council district, which sets the building control route

02

Kent County Council's scaffold licence

Scaffolding that occupies a highway, or hangs above one, falls under section 169 of the Highways Act 1980. Whether the house is in Thanet, Canterbury, Dover, Swale, Folkestone & Hythe or Ashford, the licensing body is Kent County Council, acting as highway authority. No district council has a say in it.

Kent County Council asks the scaffolders to put in the application, so you have no forms to fill in. Its conditions are these:

• Notice: 5 working days, counted back from the first day of the licence, and renewals follow the same rule.
• Fee: Kent County Council charges £52 per week for 2026 to 2027 for scaffolding placed on the highway.
• Insurance: a firm cannot register to apply until it holds public liability insurance worth £5 million or more.
• Inspection: a site inspection, if Kent County Council deems one necessary, costs £78.
• On the street: the scaffold keeps a minimum distance of 1.2 metre from the carriageway; its vertical tubes carry white paint for 2.5 metres or more above the pavement; and lamps burn overnight if the scaffold reaches the carriageway or comes within 45 cm of it.

Skips are treated on their own. Kent County Council charges £45 per week for 2026 to 2027 for a skip on the road, wants the application in 5 working days before delivery, and sets limits of 5 metres in length and 2 metres in width. For a skip on the footway, express permission is required and a 1.5 metre pedestrian walkway stays clear.

Where a front wall opens straight onto the pavement, the scaffold and skip dates are booked early so the 5 working days are covered. For a question before the application goes in, Kent County Council's highways line is 03000 41 81 81. Our answer on the Kent scaffold licence goes into who applies.

03

Building control: which council, which route

Building Regulations apply to re-roofing, and the Planning Portal sets the national test. The usual exemption applies only if "Less than 25 per cent of the total 'building envelope' (walls, floor, roof, windows, door, roof windows and roof-lights) is affected" and also "Less than 50 per cent of the roof is affected." Re-roofing the whole house works on every slope, so that exemption is out of reach here, and we confirm the right one with the council's building control team before the strip starts.

The second test is weight. Approval is called for under Planning Portal guidance when the covering going on is 15 per cent or more heavier than the covering coming off, and past that point it advises bringing in a structural engineer or a surveyor before work begins.

On Dover District Council's building control page, swapping pitched or flat roof coverings counts as work needing approval, even when the new one matches the old; that applies to houses across the Dover district. Folkestone & Hythe District Council is less firm, saying approval may be needed when roof coverings are replaced.

A private option exists beside the council team: the registered building control approver. Registration began on 6 April 2024, though private building control existed long before.

04

The strip, the battens and the underlay

With the scaffold up and the route settled, the old roof comes off one slope at a time. Sound slates are stacked on the scaffold for reuse and broken ones go down to the skip. The old battens and underlay follow, and that is the first time the rafters can be seen in full. A soft or rotten rafter goes on your photos, and you hear about it before any timber repair begins.

Battens are the horizontal timber strips the slates are nailed to. Their spacing, called the gauge, follows from the slate length and the headlap, the amount each slate overlaps the courses below it. A gauge set wrong at the eaves, the lowest edge of the roof over the gutter, throws out every course above it.

Underlay is the sheet laid across the rafters under the battens. It catches wind-driven rain that gets past the slates and runs it down to the gutter. There are two broad kinds, and the choice changes how the roof space is ventilated:

• HR underlay is non-breathable. For a cold roof with HR underlay, Marley gives a continuous 10mm eaves gap on pitches steeper than 15°, and 25 mm along the eaves at 15° or less.
• A breathable membrane is the other kind. Its maker's data and BS 5250:2021, which governs moisture management in buildings, set how the roof space is ventilated with it.

In a cold roof the insulation sits across the loft floor at ceiling level, so the void above it stays unheated. Our guide to underlay and battens compares the two kinds side by side.

05

Slating to BS 5534 on an exposed slope

BS 5534:2014+A2:2018 is the slating and tiling code of practice in force today. It is not the law: Marley says "Installing to BS 5534 isn't required by law". Even so, a re-roof ought to be built to it, and Marley notes the 2018 amendment updated its scope to include normal re-roofing work, repairs included.

Pitch comes first. Cupa, the slate maker, says BS 5534 puts the lowest pitch for natural slate at 20 degrees, for moderate exposure with a 500 mm slate and a 115 mm lap. Cupa also rules out hook fixings on anything shallower than 25°. A shallow back addition or dormer roof can sit close to those lines, so every slope is measured at the survey.

Exposure comes next. Cupa grades tall buildings, and those on hills, slopes or the coast, as more exposed, while Marley notes that the wind uplift formulas sit in BS 5534, together with the means to derive a fixing specification. Under BS 5534 we work the fixings out for your own site's exposure, so a high villa on the clifftop and a sheltered back street get the fixings each one needs.

The slating then runs in a set order:

1. Mark out each slope so the courses run true and the side margins match.
2. Fix the eaves course, then the first full course over it.
3. Work up the slope course by course, holding the gauge and the lap.
4. Cut slates into the valleys and around each chimney, with lead soakers where a slope meets a wall.
5. Close the top course under the ridge line.

Our page on BS 5534 fixing explains how the fixing calculation is worked out.

06

Ridge, hips, verges and the lead to finish

The ridge capping runs the full length of the roof's top. Where two slopes form an outward corner you get a hip, in effect a ridge set at a slant, and a verge is the finished edge against a gable wall. These are the parts the wind works hardest at, so they are finished with care.

Mortar is not banned. Marley says the 2015 amendments to BS 5534 settled that a bed of mortar was no longer enough by itself to secure the roof covering. Dry-fix kits for the ridge, hips and verges are specified under BS 8612:2018. Dry-fix means those parts are held by mechanical fixings rather than by a bed of mortar alone.

Lead goes on as the slating reaches each joint. A soaker is a small sheet of lead slipped between slates where a slope meets a wall, with a flashing dressed over it. Lead is sold in codes by thickness, and the Royston Lead table runs from Code 3 at 1.32 mm to Code 8 at 3.55 mm. Code 3 is for soakers only, and each other detail takes whichever code the specification names. MyJobQuote puts the life of lead flashing at over 80 years.

Before the scaffold comes down:

• you see photos of the finished ridge, valleys and flashings
• the gutters are cleared of anything the job dropped into them
• the skip goes and the pavement is swept
• any building control completion paperwork the route needed is in hand

Then the scaffold is struck, and the street looks as it did before the job started, apart from the roof.