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Unlike a tiled roof where the tiles are nibbed,
and most tiles are not fully nailed and clipped, double lap slates
should all be either twice centre nailed, twice centre nailed and tail
riveted, once or twice head nailed, or once hooked with slate hooks; in
other words, fully fixed. This can make replacing a slate more
difficult, but not impossible.
Head nailed slates
For once head nailed slates that have been shouldered (had the top
corners cut off) it is quite easy to swing the slates above the affected
slate sideways and expose the head of the affected slate, and after
removing the nail and the affected slate, replace it with a new slate,
re-fix the head nail, and swing the slates above back into position.
If the head nails are slack the wind will make
them rattle in high winds, which may make them vulnerable to breakage.
If the slates are not shouldered and the nail is tight, or the slate is
twice head nailed, then the slates will be almost impossible to swing
sideways, in which case the nails will need to be ripped out with a
slate ripper and the slate reinstated using a slate hook fixing.
Centre nailed slates
Where the slates are twice centre nailed there are two acceptable repair
methods. For both methods the affected slate should be removed along
with the nails, using a slate ripper.
Centre nailed slates Where the slates are twice centre
nailed there are two acceptable repair methods. For both methods the
affected slate should be removed along with the nails, using a slate
The first method is to install a slate hook of the
right length, dependent upon the head-lap of the slates used. Before
cutting two notches in the head of the new slate where the nail fixings
of the slates above occur, allow the new slate to be slid into position
over the slate hook and then pulled down into the hook, to locate it.
Provided the side lap gap between the lower slates is sufficient to take
the shaft of the slate hook the new slate should lay flat. This method
is ideal for both natural and fibre cement slates.
The second method is to install two Jenny Twin fixings
to the new slate just above the normal nail hole position, such that
each clip, which has a hinged gate that flaps down and rests against the
head of the batten, is correct for the alignment of the bottom edge of
the slate. With Jenny Twin fixings it is important to slightly recess
the side of the slate to accommodate the thickness of the clip,
otherwise it will interfere with the adjacent slate, also the hole
through the slate needs to be accurately positioned and punched to
ensure there is no slack in the clip once installed.
With Jenny twin fixings it is possible to use
one clip and one nail fixing when stitching in up the edge of a
patch, with the final slate having two Jenny Twin fixings. Jenny Twin
fixings can be used with fibre cement slates provided a copper disc
rivet is also used at the tail of the slate.
Jenny Twin fixings
are not suitable for re-fixing slates where there are no battens,
and therefore not suitable for Scottish practice where the slates
are fixed directly to the rigid timber sarking.
Repairing hooked slates is the easiest of all methods. In many instances
the slate hook can be reused, provided the metal is not bent or damaged.
The broken slate is pushed up and over the hook holding the slate and
slid out, and a new slate slid back in, and pulled down into the hook.
If the hook is damaged in any way it should be removed and replaced.
There are two types of slate hook; the type that nails
into the face of the batten and the type that wraps around the head of
the batten. The wrap hook type is simple to install as long as the
batten thickness and the wrap clip depth are the same. Where a rafter
interferes with the installation of the wrap hook type, a nail fixed
slate hook should be used.
practice, where the slates are fixed directly to the rigid timber sarking, only the nail type slate hooks should be used. With the
nail type slate hooks the nail portion of the fixing must be fully
driven into the batten or sarking, which can be difficult if the
slate hook is installed after the slates in the lower row have been
installed. Therefore it is best to set out the roof and install the
hooks in bays prior to the slates being installed.
Slate hooks are manufactured in a range of metals, but
only stainless steel slate hooks should be used in the UK. There are two
grades of stainless steel that are commonly available, Grades 304 and
316. Grade 304 material is very common, and therefore the cost is a lot
lower than for grade 316. However BS5534, The Code of Practice for
Slating and Tiling, only recommends the use of Grade 316S11 and 316S19
stainless steel nail fixed slate hooks. Therefore if grade 304 stainless
steel slate hooks, or wrap type slate hooks are used they will not
comply with specifications that require compliance with BS5534.
If the broken slate to be replaced is close to a top edge, or there are
several broken slates in the same vicinity, it may be easier to strip
down in a V from the top edge and replace the broken slates and re-fix
them securely to match the adjacent slates, rather than use slate hooks
or Jenny Twin fixings, that may not be readily available on site.
While there are other temporary slate fixing methods,
they are just that, temporary. Lead tingles straighten out, anything
made of plastic will age harden and break under load and is unlikely to
last as long as the slate. Wire will not be strong enough to resist the
wind suction, and mastic will only stick to the outer layer of the slate
which is formed of many thin layers and will pull away when put under
- When replacing a slate
into a centre nailed slate roof always cut two Vs in the head of the
slate to correspond with the nails of the course above, to allow the
slate to be pushed up higher than normal and then pulled back down
into the slate hook, or onto the gate section of Jenny Twin fixings.
- To install a slate into a slate hook, do not straighten and rebend
the hook section of the slate hook, as it weakens the slate hook
- Never use Jenny twin fixings or batten clip slate hooks
where slates are nailed directly onto rigid timber sarking with no
by Chris Thomas, The Tiled Roofing Consultancy, 2 Ridlands Grove,
Limpsfield Chart, Oxted, Surrey, RH8 0ST, tel 01883 724774