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It is the little things that make all the
difference in our lives. They are the things that are difficult to see
and are therefore easy to forget, and the untrained eye is not aware of
their existence, or importance. For interlocking roof tiles, the
important little things are the tile clips.
With interlocking tiles, there are three main types of
clip: eaves clips for eaves tiles; verge clips for verge tiles; and tile
clips for every other tile on the roof. This first article will not be
dealing with the eaves and verge clips, although many of the issues
covered will be the same as for tile clips.
Tile clips are the most efficient method of preventing interlocking roof
tiles from being sucked off of a roof by hurricane force winds, and they
should also help to prevent tiles from chattering at lower wind speeds,
(but that may vary from one clip design to another).
Each design of tile clip will have a slightly different
performance figure with each design of tile. The performance is called
wind uplift resistance and is measured in Newtons (N). In very general
terms, a tile’s uplift resistance is the sum of its dead weight
resistance plus the resistance of the fixings.
The dead weight of a tile will resist (depending upon
the rafter pitch) approximately 1,000N of wind suction force. One head
nail fixing will provide approximately 500N resistance, while a well
designed clip could add between 2,000N and 6,000N resistance; making
clip fixings between four and 12 times better than a single head nail
Almost every design of interlocking tile will have a clip specifically
designed and made for it. Some are good and some are not so good, but
regardless, there is almost no alternative tile clip for each roof tile.
Most roof tile manufacturers have tried to design a
universal tile clip, but so far nobody has succeeded. Some clips will
fit a few tiles that are similar, but nobody has ever made a clip that
works adequately for all interlocking roof tiles, whatever they may
There are three basic designs of tile clip:
tile-to-tile clips; batten nail clips; and batten hook clips. Some clips
have features that make them both batten nail and tile-to-tile, or
batten hook and tile-to-tile, but nobody has ever produced a clip that
could be classified in all three categories.
Tile clips are also manufactured from a range of materials,
from aluminium and stainless steel to plastic. Galvanised steel clips
are popular in dry countries like Australia, but would not last long in
our climate. Of the metal clips, most are manufactured from strip or
sheet material, while some are made from spring wire.
The rigidity of some sheet metal clips can resist
uplift loads with little or no movement of the tiles. This is good as it
prevents the tiles from lifting and rattling. However, those made with
spring wire have a varying rate of resistance: the greater the suction,
the more the tiles lift, the more the clip bends and the greater the
Therefore, a spring wire clip will allow the tile to
lift before the maximum resistance value is achieved; then the spring
forces the tile back into position, which may cause tile breakage.
Spring type clips are not ideal for single pantiles, as the spring pulls
the left-hand side of the tile down and out of its normal laying
Plastic clips are the most complicated to look at, but often the
easiest to install, as injection moulded plastic allows the designer to
include stiffening ribs and features that would be impossible to
reproduce in any other material.
In contrast, metal clips have to be punched
and bent to shape, and are therefore limited by the production process.
They can also be bent onsite to fit, if needs be.
To perform its function, the tile clip has to hold the tail of the tile
down by fitting into the left-hand interlock, pass down the head of the
lower tile, and either lock under the head of the lower tile
(tile-to-tile clip), or allow a nail to be passed through the clip into
the narrow face of the batten (batten nail clip), or pass around the
underside of the batten, so that any upward movement of the tile will
cause the clip to grip the batten (batten hook clip).
The end of the clip that locates into the side
interlock must be as thin as possible and shaped to suit the shape and
size of the interlock edge, to ensure it does not interfere with the
tile above. The portion of the clip that passes down the top edge of the
lower tile needs to be as vertical as possible, to give a straight pull.
The greater the horizontal distance from the interlock to the nail
fixing, the less effective the clip will be. The distance from the top
of the interlock to the underside of the tile below is critical for
tile-to-tile clips, and to the underside of the batten for the batten
hook clips and batten nail clips. Generally, flat tiles have a shorter
distance to the top of the batten than profiled tiles.
Once below the top face of the lower tile, the clip must not
interfere or clash with the tile nib, especially if the clip is nailed
to the batten. This can become a problem with some flat tiles when the
perpendicular joints drift out of alignment. Where tile-to-tile clips
are used, the lower tile should be head nailed to transfer the wind
uplift force from the clip, via the tile, to the batten below.
Where the tile clip is nailed to the batten, the nail should be
driven into the centre of the narrow batten face. With a 25mm-thick
batten, the distance to either edge will be, on average, 11mm. While
this is 4mm less than the minimum recommended by BS5268, it has been
found over many years not to be a problem and, therefore, is acceptable.
However, if the nail fixing is into a 19mm batten, or is off centre of
the 25mm batten, then the distance of the nail fixing to the edge of the
batten will be less than 11mm, and the risk of splitting the timber is
higher. Once the batten splits, the grip of the nail will be affected,
along with the resistance value of the tile clip.
Batten hook clips are mostly designed to fit
specific batten sizes, and may be a slack fit for smaller batten sizes,
or may not work at all if the batten is too large. Often the clip
position will clash with the rafter or counter batten position and make
it impossible or difficult to fit the clip.
- Always use the tile clip recommended
by the tile manufacturer.
- Metal clips are generally stronger
and will last longer than plastic clips.
- All tile clip designs have a better
uplift resistance than head nail fixings.
by Chris Thomas, The Tiled Roofing Consultancy, 2 Ridlands Grove,
Limpsfield Chart, Oxted, Surrey, RH8 0ST, tel 01883 724774