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Rain is not the only thing that a good roof needs to keep out; it should
also keep out birds, rodents and large insects, as they like to nest in
the eaves, verge or other spaces, to protect themselves from the
elements and predators.
At the ridge, hip, verge and valley, mortar
bedding acts as a very effective means of filling in all the gaps. While
with clay pantiles, the eaves course was traditionally filled with
mortar, this has never been popular with other types of tiles or slates.
For all other high profile interlocking tiles, eaves comb fillers should
be used where the gaps are larger than 16mm.
Having watched blue tits squeeze between louvre only 20mm apart on an
extract fan grill, and bats fly into gaps between a soffit and a wall
only 15mm wide, very little space is needed to let them into a roof.
Where a high profiled tile sits on a fascia board,
birds and mice can use the guttering as a route to reach the open
doorways of each tile corrugation, and allow access to the corridors of
the batten cavity that can lead to other useful nesting and roosting
places – like the cavities in the external brick walls. The British
Standard BS5534: the code of practice for slating and tiling, recommends
that if it were possible to pass a 16mm diameter ball through an
opening, it should be protected with a closer to keep out small birds
BS5250: the code of practice for the control of
condensation, goes further and states that where ventilation grills are
installed to ventilate the loft, or cavity below the underlay, the width
of each opening in the grill should not be wider than 4mm, to prevent
large insects getting through. This will keep out large flies, bees,
wasps, moths and bats. You will never be able to keep out all insects
like midges, spiders and storm flies, unless you hermetically seal the
total external envelope of the building, which is impractical.
Flat tiles and slates
Generally, all flat tiles and slates should not need any form of eaves
closure unless the side-lap gaps are excessive, or a rigid underlay and
counter battens have been used below a roof cover. In such situations
the batten cavity will be exposed, and a mesh should be used to close
off the eaves opening, but not restrict the water draining off the
underlay into the gutters. A special eaves closure or an eaves comb
filler unit fixed upside down from the tilt fillet is usually adequate.
Interlocking tiles with a low corrugation – like the Redland 49 and
Sandtoft Standard Pattern – have eaves gaps less than the 16mm threshold
when laid, and will not need an eave closer.
The tiles with a more pronounced corrugation – such as the
Bold Roll, double pantile and single pantile, along with unders and
overs and the old Redland Delta tiles – will all need some form of eaves
The practice of mortar-bedding the eaves course of clay pantiles and
unders and overs, does more than stop birds getting into the roof; it
also helps the eaves tiles to resist wind uplift.
Those clay pantiles that do not have eaves clips should
be started with one or more courses of plain tiles that are fully
nailed, and then the first course of clay pantiles should be
mortar-bedded onto the plain tiles. This allows any water on the
underlay to drain under the plain tiles and into the gutter.
Mortar-bedding onto two or more courses of
plain tiles means that the minimum rafter pitch for the roof slope
should not be less than 35º.
But if a single course is used, and fully covered
by the eaves course of pantiles, then the pitch can be taken down to
30º. Mortar should never be laid directly onto the underlay as it will
block the drainage path from the underlay into the gutter.
Solid eaves closers
In the past, eaves closers were made of wood or aluminium – now plastic
– cut to the profile of the underside of the tiles.
They were nailed one per tile to the top of the fascia
board and angled out to meet the tiles. As rafter pitches vary and the
angle of the closer was fixed, the fit was generally good but not
perfect. Lafarge Roofing still manufactures the solid eaves closers
(Reform Eaves Filler Units), while all other manufacturers have moved
over to a comb filler unit.
Eaves comb filler units
Eaves comb filler units (sometimes call ‘bird stops’) are 1m-long
plastic strips that are either incorporated into the eaves vent grill,
or form a separate unit that is nailed to the top of the fascia board
with the fingers angled out towards the tiles.
The fingers are generally 50mm-70mm long, 4mm
wide and have a 4mm gap between them, such that each finger can bend
independently of its neighbour to accommodate any shape of tile. Where
the height of the corrugation is more than the length of the fingers,
the corrugations will not be fully protected and the tile manufacturer
should be consulted, as they may have an alternative detail.
Over the last 20 years eaves comb filler units have demonstrated that
they can keep out birds and small rodents; however they are not as
effective as mortar bedding.
The fingers of the comb allow air to circulate, and
lower the level of humidity in the batten cavity. Mortar bedding should
be used with clay pantiles that have no eaves clip, as it helps to
resist wind uplift, but it is not as good as a strong metal eaves clip.
Almost all concrete interlocking tiles (and a few
modern clay pantiles) have eaves clips, and these need to be nail-fixed
directly to the fascia board. Where eaves clips are available, eaves
closers should be used and mortar bedding is not recommended.
- Where roof tile manufacturers
recommend the use of eaves filler, it should be installed.
- Mortar-bedding onto a single plain
tile course should only be used with clay pantiles that have no
eaves clip system.
- With high profile tiles, check that
the fingers of an eaves comb are long enough to reach into the top
of the profile.
by Chris Thomas, The Tiled Roofing Consultancy, 2 Ridlands Grove,
Limpsfield Chart, Oxted, Surrey, RH8 0ST, tel 01883 724774