Retaining tab for standing-seam trays on supports made
of wood or wood derivatives
This invention relates to roofing systems, in
particular systems employing trays made of zinc or a
zinc alloy for standing-seam crimping.
Such trays are normally fastened to the roof support
using fixed and sliding metal tabs. The function of the
fixed tabs is to secure the standing-seam tray to the
support, which normally is made of wood or wood
derivative, by blocking the thermal expansion movements
of the zinc. The sliding tabs are designed to take up
the expansion movements of the zinc caused by
temperature variations, while still securing the
standing-seam tray to the support. The present
invention relates to the fixed tabs.
Existing fixed tabs are for example represented in the
rules of the art as described in France in the document
DTU 40.41 (DTU standing for Document Technique Unifie)
[Unified Technical Document] ) entitled "Couverture par
elements metalliques en feuilles et longues feuilles en
zinc" [Roofing with sheet-metal elements and long
sheets made of zinc]". These fastening tabs have two
holes, with or without a surround, whether staggered or
not, and are fastened using ribbed nails or wood screws
4 mm in diameter. They are normally installed along the
joint, every 33 cm.
However, we have found that ribbed nails, and also
small-diameter screws, smaller than 4 mm, may lift up
because of wood drying cycles and repetitive wind
forces. Also, many roofers use automatic nailers to
save fitting time, which however creates greater
difficulty in implementation because of the size of the
machine. In addition, the nails are often struck hard
and they deform the tabs, or are struck beside the
holes in the tab, thereby running the risk of
insufficient performance in terms of tear strength. A
poorly installed tab creates a risk of poor cramping of
the joint and therefore a lack of sealing and of
attractiveness.
Although switching to a single large-diameter screw
seems a priori to be advantageous, it does however pose
a specific problem that has to be solved. Such a tab is
mounted in fact by aligning it and attaching it along
the tray to be fastened. However, when the single screw
is tightened, a rotational torque is transmitted to the
tab, this being greater the larger the diameter of the
screw. Such screws are also very often provided, on
their head, with lugs initially designed for
countersinking and thus better penetrating the wood.
These generate additional frictional forces which
further increase the torque transmitted to the tab
during tightening. This torque makes the tab pivot to
the point that one of its ends bears on the tray to be
fastened with a sufficient blocking force. It
transpires that this blocking force may deform the tab
and the tray, something which it is desired to avoid.
The subject of the present invention is a fastening tab
using a single screw, and therefore simpler and quicker
to fit than conventional tabs. This tab is especially
designed to prevent it from being deformed and to
prevent it deforming the tray to be fastened while the
single screw is being tightened. The tab therefore
provides greater security of implementation and better
mechanical performance.
Figure 1 illustrates the invention in a three-
dimensional isometric view. Figure 2 shows a tab seen
from above.
The invention relates in particular to a metal
fastening tab for securing a standing-seam tray on a
support made of wood or wood derivative, comprising a
first surface (1) provided with a perforation (2) for
receiving a screw for fastening onto the support, a
second surface (3) generally perpendicular to said
first surface and including a hook (4) for engaging
with the edge of the tray to be secured, these two
surfaces defining a line of intersection (5) of length
L, characterized in that said first surface has a
single perforation (2) for receiving a single screw and
in that the center (6) of said perforation (2) does not
lie on the mid-perpendicular (7) to the line of
intersection (5) so as to reduce the force felt on the
tab and on the tray by the torque caused when said
screw is being tightened.
This tab is more particularly characterized in that the
center (6) of the perforation (2) lies off-center by a
distance D greater than 10% of L in relation to the
mid-perpendicular (7) to the line of intersection (5)
so as to reduce the force felt on the tab and on the
tray by the torque caused when said screw is being
tightened.
The off-center distance may be adjusted according to
the forces resulting from the tightening torque. These
forces essentially vary according to the size of the
screw heads used.
It will be understood that, to reduce the force felt on
the tab and on the tray by the torque caused by
tightening said screw, it is necessary to off-center
the center (6) of the perforation (2) by shifting it
away from the end (9) of the tab intended to reflect,
onto the tray, the torque transmitted when the screw is
being tightened, and not in the opposite direction. It
is therefore clear that figures 1 and 2 correspond to a
part designed for a fastening screw with a right-handed
thread, that is to say the usual case in which the
tightening direction is clockwise. In the
representation shown in figure 2, the perforation
therefore has to be off-centered to the right.
It is useful to provide reinforcements (10) along the
line of intersection (5). These also contribute to
reducing the deformations of the tab during tightening,
by blocking the angle formed by the surfaces (1) and
(3).
The perforation (2) for receiving the fastening screw
will preferably be provided with a surround (11), the
opening angle of which is usefully greater than 100°.
This makes it possible to reduce the area of contact
with the head of the screw and therefore to reduce the
frictional forces and thereby also the torque
transmitted to the tab during tightening. There are
solutions for reducing friction by lubricating or by
the use of interfacial materials, but these have the
drawback of complicating the work of the operator and
of increasing the cost of the solution.
It is preferred to use an AISI 304 stainless steel
sheet to produce the part by stamping. A thickness of
0.4 mm is suitable.
The novel tab is fixed using a single screw of 5 mm or
6 mm diameter. Such a screw no longer lifts up under
the effects of vibrations caused by the wind and by the
dimensional variations of the supports. Its superior
tear strength permits the tabs to be installed with a
maximum spacing of 75 cm instead of the usual maximum
spacing of 33 cm. The novel tab therefore significantly
improves installation comfort, while at the same time
making fitting easier and saving a significant amount
of fitting time by the reduction in the number of tabs
and the number of fastening operations. Moreover, these
tabs are particularly compact, with no superfluous use
of metal.
Claims
1. A metal fastening tab for securing a standing-seam
tray on a support made of wood or wood derivative,
comprising a first surface (1) provided with a
perforation (2) for receiving a screw for fastening
onto the support, a second surface (3) generally
perpendicular to said first surface and including a
hook (4) for engaging with the edge of the tray to be
secured, these two surfaces defining a line of
intersection (5) of length L, characterized in that
said first surface has a single perforation (2) for
receiving a single screw and in that the center (6) of
said perforation (2) does not lie on the
mid-perpendicular (7) to the line of intersection (5)
so as to reduce the force felt on the tab and on the
tray by the torque caused when said screw is being
tightened.
2. The tab as claimed in claim 1, characterized in
that the center (6) of the perforation (2) lies
off-center by a distance D greater than 10% of L in
relation to the mid-perpendicular (7) to the line of
intersection (5) so as to reduce the force felt on the
tab and on the tray by the torque caused when said
screw is being tightened.
3. The tab as claimed in either of claims 1 and 2,
characterized in that reinforcements (10) produced by
stamping are provided along the line of intersection
(5).
4. The tab as claimed in any one of claims 1 to 3,
characterized in that the perforation (2) for receiving
the screw for fastening to the support is provided with
a surround (11).
5. The tab as claimed in claim 4, characterized in
that said surround (11) has an opening angle of greater
than 100°.
6. The tab as claimed in any one of claims 1 to 5,
produced by stamping a sheet of AISI 304 stainless
steel.

In roof covering systems using zinc or zinc-alloy
trays with standing-seam crimping, the use of tabs
secured by two screws is well known. The invention
particularly relates to a metal fastening tab for securing a
standing-seam tray on a wood or wood-derivative carrier,
which comprises a first surface (1) with a perforation (2)
for receiving a screw for attachment onto the carrier, a
second surface (3) generally perpendicular to said first
surface and including a hook (4) for engaging with the
ridge of the tray to be secured, the two surfaces defining an
edge (5), characterised in that the first surface includes a
single perforation (2) for receiving a single screw, and in
that the centre (6) of said perforation (2) is not included in
the mediator (7) of the edge (5) in order to reduce the force
applied on the tab and on the (ray by the torque induced
when tightening said screw. Such a tab, with a single large-
diameter screw, is easier and quicker to place than
traditional tabs. The tab is specially designed to limit its
own torsion and to avoid any buckling of the tray to be
secured when tightening the single screw.