How to Slate a Roof

Re-Slating Process

  • Erect scaffolding for access and Health and Safety of roofers
  • Strip and store existing slates - Random slates are sorted by length, size and thickness
  • Re-felt the roof - Underlays are 'breathable membranes' which allow water vapour without air movement to move through and watertight and airtight to protect from rain and dirt blown between the slates and to protect against wind pressure on the underside of the slates.
  • Re-batton to roof rafters using softwood cut to dimensions that prevent bounce when driving in the slate nails. Secured wood batten boards at each and at points along their length to a minimum of three rafters. Battons should be square sawn and butt-jointed at rafter centres, not spliced between supports or allowed to cantilever
  • Re-slate - verge overhang, eaves up, overhang, top & ridge tiles. hole replacement slates to the correct gauge with the thicker end as the tail. The first course begins at the eaves and at the verges. Lay slates with broken bond up to the ridge, being aware of verges and abutments to reduce redressing or cutting of slates. Use thicker slates to the eaves and thinner to the ridge to minimise dead loading. Alternatively when creating a diminishing random effect use the smallest slates nearest to the ridge. Neighbouring slates are affixed with a 3-4 mm gap between them and two slanting slating nails that do not protrude above the face of the slate.
  • Quality: position courses and laps along true and regular lines with slating nails that do not protrude above slate face. This allows overlying slates to sit snugly - so preventing wind chatter and reduced weather resistance. Ensure sufficient type of each slate before work begins. Remove debris to keep site and membranes clean. Keep mortar off slate face. Use patination oil on new lead work.
  • Re-fix lead flashing's & chimney aprons
  • Dry fix - replace any dry verges, hips, ridges
  • Wet fix - verge pointing and fair ends - bedding and pointing of slates on gable ends and ridges with mortar

Nail and Bib Repair

  • Identify the slate of slates that need replacing
  • Use a 'slate ripper' that slides under the slate and hooks the retaining slate nail.
  • Hit the 'slate ripper' on the handle to loosen the nail, and pull to extracted it.
  • Remove the slate and match its characteristics with a replacement slate.
  • Slide the replacement slate into place. Fasten it using a roofing nail in the slot between the two slates above it.
  • Tap the roofing nail down and slide the bib flashing under the slate but over the nail head.

Slate Hook Repair

  • Nail a copper or stainless steel hook in the slot between the under slates and if required push the hook into the slot.
  • Slide the replacement slate in and over the hook.

DIY Problems

  • Insecure fastening of slates so they blow off
  • Poor selection of slate to match environmental characteristics of a site
  • Poor selection of replacement slates so they don't blend with existing covering
  • Selecting the wrong shape thickness or size of replacement slates
  • Incorrect form of valley between roof sides
  • Face nailed slates
  • Tarred slates
  • Using chipped or broken slates
  • Using steel nails
  • Weatherproofing chimney stacks with tar instead of lead

How to Slate/Tile/Flash A Roof Valley

Conical Slate Roofs

How to install flat slates onto a curved roof.

  • Use 'shouldered slates' - with the corners cut off to allow them to sit without such obvious corners
  • Felts applied and battened or ply base
  • Insert an anchor point to the top of the turret and attach a line so the trimming lines can be set.
  • To make it easy to align the slates on the curved roof lay as many slates as possible onto a straight board so the bottom edges align. Mark the outer slates and then snap a line across the slates to mark the bottom of the overlying course. This will ensure successive layers of overlaying slates are level.
  • Set the overhang for the first slates with a measure, usually about 3 - 7 cm.
  • Drill and screw in a cant strip or fascia board (cut into small strips to allow for curvature)
  • Calculate the height and widths of the slates so they take account of the exposure area of each slate and head lap at the bottom.
  • Use the anchor point line to snap mark a line. This is the correct angle up to the turret and trim the slate accordingly with a slate cutter. A slate can be used as a template for each course of slates. Slates ma then be cut out in advance and given a final trim at installation.
  • Punch holes in the slates (from the slate back prior to trimming (to avoid wasted effort).
  • Slates become progressively narrower towards the turret and atop the top wrung, a ridge of lead is often applied.
  • Installation of a slate roof needs to be on top of structural materials with a similar lifespan
  • Roofing contractors do not usually recommend use of plywood under slate as it can delaminate under adverse conditions.
  • Use Thick rough sawn timber
  • Never use galvanised nails, as their life span is usually less than slate. Copper or stainless steel nails should always be used.
  • Always use adequate head lap.
  • Always use appropriate tools for slate roofing to avoid wasted time and damage to the slates and roof.
  • Use high quality (lead) flashing's in the valleys and chimney aprons.

How to Choose a Roofing Contractor

  • Know to the best of your ability what you want doing, how and by when.
  • Many roofing contractors are not Slater's or experienced in state roofing. Many do not conduct research into the techniques, material choices and tools to adequately quote and complete a job.
  • Choose the appropriate quality slate for your location and roof type.
  • Not all slates are top grades of Welsh and English slate. Some are imported and the lack of a UK standard can make comparison difficult.
  • D&C-Roofing contractors are dedicated to finding the most appropriate slate for your new or refurbished roof. We understand the differences in slate specification grades and colour and will advise you honestly and accurately on the slate we believe will match your roof type, location and budget.
  • Have a detailed contract
  • Contract documents should specify details such as the type, size and origin of the slate to be used - its type, length and gauge of the nails; the type and installation style of underlayment; the type and size of cant strip; the head lap; flashing specifications; number of squares to be installed and slate installation style.
  • Adequate head lap
  • The head lap helps to protect your slates. Each slate must overlap 2 courses below it to maximise roof protection. Head lap is measured as the distance between the nail hole in a slate and area covered by the overlaying slate. To calculated the correct head lap: set the head lap required (often 7.5cm) and subtract this from slate length. Halve the remainder to give the exposed area.
  • Poor flashing's installation
  • Use the correct Code rating for roof flashing's for maximum weather and waterproofing service.
  • Human traffic causing roof damage
  • First slate - starter slate - upside down so beveled edges merge

Build Up Felt Flat Roof

How to Mend Cracked or Peeled Flat Roofs

The cause of cracks in felt roofs include where the bonded layers tear due to joint movement within the insulation, roof deck or roof structure. Roof design should allow for some differential movement. Once damage occurs, a simple DIY fix is to:

  1. Ensure the damaged area is clean and dry
  2. Identify the extent of the cracked felt and cut out this and any peeling felt using a strong, very sharp knife. To make the patch easier to make use a straight edge to cut a uniform shape.
  3. The cut out piece is the template for replacement felt
  4. You'll need a similar number to number of layers as those initially removed to ensure the roof is brought up to the same level
  5. The top felt layer needs a larger area (about 5cm greater on each edge) to cover the patched area
  6. In the damaged section, use a blunt knife to lift roofing cement under the lowest felt edges to create a watertight seal and a base
  7. Cover the remainder of the base with roofing cement and apply the bottom felt patch into place. Secure with roofing nails. Subsequent layers do not require roofing cement, just roofing nails as the bond accommodates better minor movements which may have caused the initial crack
  8. Apply the largest top patch over the 'damaged section' and nail it down, apply roofing cement around the edges to form a waterproof seal

Mending Blistered, Bubble Felt

Inadequately protected of the felt membrane from UV radiation generally causes blistering . Small blisters may form between the cap sheet and the underlay and are usually safe to leave, but need to be inspected periodically.

Blisters may also be caused by full bonding of layers when part bonding was required. Again, they might be left if intact. However, if a roof is to be overlaid then cut and reseal then.

  1. Ensure the damaged area is clean and dry
  2. Cut a straight line in the top layer
  3. Lift and force roofing cement under the felt edges to make a watertight seal
  4. Create a felt layer about 5cm greater on each edge to cover the patched area
  5. Tack down using roofing nails
  6. Create a larger top patch and nail it down.
  7. Apply roofing cement around the edges to form a waterproof seal


Ponding on a flat roof may become a problem if water can rise above the waterproof layer. Ponding may result from poor roof design, a roof structure that has deflected due to rotting of the timbers, or failure of the insulation or deck causing a depression.

D&C-Roofing investigates and assesses flat roof ponding problems and provides appropriate professional solutions to these.

Pitched Roofs

Leaking Roof

Sources of roof leaks can include:

  • Water ingress through the membrane. If caused by a local, isolated membrane failure, repair holes, cracks, tears and splits. If a larger problem then an overlay may be required.
  • Water ingress through associated roof details such as skylights, window flashing's, copings, damaged or degraded rendering or damp courses. K-Roofing investigates and assesses flat roof ponding problems and provides appropriate professional solutions to these.

Roof Tiles

  • Shaling is the splitting and crumbling of tiles caused by weathering. Evidence shows up as partial tiles and voids.
  • Cracked tiles - tiles crack due to weathering and frost damage. Initially corners break off and work backwards which can allow water ingress into the roof.


Condensation can cause problems within the roof structure, reduce heat retention and cause material degradation. Evidence of condensation may indicate:

  • Poor or inadequate insulation between living space and membrane
  • Excessive humidity in the living environment
  • No of ventilation in a 'cold roof' - convert to a warm roof or add ventilation system
  • Poorly sealed or inadequate vapour control layer - refit this layer, the saturated insulation and membrane

Repairing a Roof

repairing a roofing

Repairing a roof is not particularly easy, particularly if you need to remove tiles first. If you are aware of tiles needing replacement, you may be able to fix the problem yourself.

If you need to remove a roof tile, you should be able to lift the two tiles above it with a piece of thin wood. This will allow you to move the problem tile, lifting the nib away from the batten. If the tile is nailed into place, you may need to use a slate ripper tool. A slate ripper is a flat tool with barbs at one end. It is slipped underneath the tile. The shaped barb hooks around the nail. With this engaged, pull down on the slate ripper (or hit the handle with a hammer) and the nail should come loose from the batten.

Once a tile has been removed, it should be replaced as soon as possible, to prevent moisture entering the space in the roof and becoming trapped beneath the new tile, as this can cause damage to the felt beneath the tiles. To replace a tile, the two tiles above the gap should be lifted, and be propped by blocks of wood. Replace the tile, and ensure it is centred correctly, checking against tiles immediately beneath it. If the tile is a one off replacement, this should be simple as the tile will fit into its new location. If more than one tile requires replacement, they should be checked against the tiles directly above, ensuring the gaps between the tiles on the higher course line up with the centre of the new tile.

Should the new tiles require nailing, use aluminium alloy or galvanised nails to secure the tile to the batten. If nailing roof tiles, aim to secure alternative courses of tiles, moving from top to bottom, using blocks of wood to lift tiles above the highest course.

If fitting single-lap tiles, work left to right as this allows for easier fixing of interlocking sections.


repairing a roofing

While a chimney may not be hugely important structurally, it is still an important part of the roof, as almost every house will have one. They are essential for removing gas and smoke from the home. It is important that the chimney and its lining is well maintained, else fumes and smoke from a fire may escape into the home. It is also possible for fires to start in poorly maintained chimneys, which can cause damage to the chimney stack as well as the home if not noticed.

There are three main areas to check when looking for potential issues around the roof and chimney - inside the roof (the loft or attic), outside at ground level, and outside at roof level.

Inside the loft or attic, look for evidence of water staining, as this can indicate dampness. If dampness is in evidence, it usually indicates problems with the flashing around the chimneys. Dampness can also cause structural issues around the home. Also, check the brickwork and mortar around the chimney to ensure it is solid, with no large gaps or cracks.

From ground level, you can scan the chimney stack to ensure there is no mortar missing or any other structural issues. Levels higher up can be checked using binoculars, and the entire surface of the chimney should be checked. Check for missing, cracked or damaged chimney pots, and for any visible deterioration in the mortar holding the pots on the chimney stack. Also, check the stack is not leaning to one side, and that any masonry is free from bulges.

If possible, you may wish to gain access to the roof to inspect the chimney and chimney pots in greater detail. The chimney pot should be accessed only by using a roof ladder, which can be hired from most hire shops. The ladder has wheels, allowing it to be rolled up the roof, to avoid damaging tiles. Once it is at the top, it can be turned over to allow it to hook onto the ridge of the roof. It is also possible to buy adaptors for a standard ladder in order to allow it to hook onto the ridge.

When examining the chimney, look for the same issues you are searching for from the ground level. If anything needs repairing, it is possible to buy or hire a special scaffolding rig, to enable safe access to the chimney when performing maintenance on it.


Flashing is used around the base of a chimney stack in order to seal and weatherproof the stack around the roof surface. Flashing is also used where a roof meets a wall, or around a dormer window. The flashing can be made from mortar, or it can be tiled. Alternatively, it can be made from metal, the most common examples being made from lead, zinc or copper. Metal flashing can be purchased in pre-cut lengths made for use around a chimney stack. It may also be bought in rolls of varying width and length, which can be cut to your specific requirements.


It is also important to ensure the guttering around the roof is well maintained; else it could potentially get a blockage and cause water to overflow from the gutter pipe, from where it may seep beneath the roof surface, or cause dampness in the walls.

Guttering will usually have a gutter pipe, of a 'half pipe' profile, which leads to a downpipe, which will be a fully enclosed pipe. The downpipe will drain into the local sewerage system.

For free estimates and advice call the best roofers in blackpool         07837980512 or 01253692110 or email blackpoolroofer@gmail.com

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