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According to the British Standard for
slating and tiling BS5534 it is not until a tile or slate is sucked off
the roof that it has failed. However before a tile or slate reaches that
point, it can rattle and chatter, especially if the tile or slate is
nailed or clipped, and this is a nuisance to the building occupier, but
is not a measurable failure.
During windy weather a tile or slate will be subject to wind uplift
forces caused by the wind blowing over the roof and creating vortices as
it passes over the edges. Long before the wind force is strong enough to
rip the tile off the roof it will be lifted and dropped with each wind
gust, making an impact noise, which may result in breakage.
With a tile that is not nailed or clipped it is the dead weight of the
tile that is holding it down. Once the wind uplift force is just greater
than the force generated by the dead weight, the tile will be sucked up
and off the tile batten, and will slide off down the roof.
If the tile is head nailed, once the wind uplift
force is just greater than the force generated by the dead weight, the
tile will be sucked up until the slack in the nail fixing is taken up
and the tile will not rise any higher, and will drop back into position
making an impact noise. There will always be a small amount of slack in
a nail fixing as the battens deflect when the nail is punched in and the
nail shank will bend before it takes the full strain. The wind uplift
force may be enough to raise the tile just a few millimetres, but this
is enough to make the noise. If the wind gets stronger the wind uplift
force will increase and the amount a tile lifts will increase. There
will be a point at which the leverage on the surface of the tile will
raise the tile to the point where it will either pull the head off the
nail or pull the nail out of the batten. The same principle will also
apply to head and centre nailed slates.
The next level of tile fixing for interlocking tiles is
to clip the bottom left hand corner of the tile. A tile clip is a very
efficient fixing as it is so far away from the batten about which the
tile will try and rotate. Tile clips come in many shapes and materials
and only the very best will hold the two tiles together tightly and
secure them to the batten below. If there is any slack in the clip, or
the clip has an ability to rotate or flex, then there is the risk that
the tile will be able to lift, even a few millimetres, and drop back
down making an impact noise. A tile that is head nailed and clipped will
be less vulnerable to the tile lifting even a small amount, but again it
will be dependent upon the design of the tile clip and how it is
installed. With fibre cement slates that are tail riveted the same thing
applies. It is the installation of the rivet that is critical and needs
to be installed correctly and tightly to stop any movement.
In many instances it is not until the roof has been installed and a year
or more of weather has been experienced that the problems of tiles or
slates chattering are discovered, and chattering may only happen on
certain properties and certain parts of a property, on a big
development. It is difficult to predict exactly where chattering will
occur; often this results in an over specification of the fixings for
the total development.
Firstly small heavy roof tiles or slates are less
affected by rattling. This explains why plain tiles and small thick
slates survive in some windy parts of Scotland while large and
relatively light roof tiles or slates present a problem. Local
traditions should not be ignored without a good understanding of the
materials being used.
Secondly screw fixing tiles or slates in
place will allow the tiler or slater to control and reduce the amount of
slack in the fixing. This is especially true of vertical plain tiles
which are prone to rattling at the corners.
Thirdly look at the clip fixings for the interlocking
tiles and choose one with a clip that is both a tile to tile clip and
has a straight pull down between the interlock hook and the fixing to
the batten. The greater the sideways distance, the lower the resistance
Fourthly flat tiles are more vulnerable to wind
suction but are more resistant to overturning about a tile clip than a
single pantile, which can roll sideways along the batten.
If having followed all the guidelines you can end up with some tiles
that just refuse to play ball, there are two options. The first is to
inject a blob of silicone mastic in under the two bottom corners of each
tile to act as a shock absorber (not an adhesive) to cushion the tile
dropping, such that it does not make any impact noise on the lower tile.
The other is to drill through the lower edge of the tile that is lifting
and making the noise, and screw the tile down into the batten below.
This is not as easy as it sounds, as you must not break the tile in the
process, and you need to do it directly above the nail hole of the tile
below (if it has one) so that the screw passes easily through the tile
below and into the batten. It is always better to position the screw on
the right hand side of the tile as often there will be a clip on the
left hand side. The screw hole will need to be protected with a sealing
washer and sealed cap. Also the screw should not be over tightened
otherwise this could result in the interlock breaking.
In windy conditions, as soon as the wind uplift force is greater than
the dead weight resistance the tile will start to lift until it is
restrained by a nail or clip. Once the wind gust has passed, the tile
drops and makes an impact noise on the tile below. The more secure the
tile fixing and the less slack in the fixings, the less lift can be
achieved and so the less impact when it drops. Lightweight, large format
tiles or slates will be more vulnerable to rattling and chattering than
small heavy tiles or slates. There is no substitute for the correct
specification of materials and good workmanship to overcome the problems
before they become an issue. Whatever you do, do not glue and fix
everything down so tight that there is no movement in the roof covering,
as this will result in cracked tiles and slates, due to the natural
thermal movement of the roof structure taking place and affecting the
- Avoid large format interlocking
tiles and slates, especially if they are light in weight, in windy
- Choose a screw fixing in place of a
nail fixing for plain tiles and natural slates in windy locations.
- Choose an interlocking tile with a
very secure clipping system that has no slack or flexing in the clip
in windy locations.
by Chris Thomas, The Tiled Roofing Consultancy, 2 Ridlands Grove,
Limpsfield Chart, Oxted, Surrey, RH8 0ST, tel 01883 724774