Window
flashings are most often required where windows are fixed into walls that are
covered with tiles or slates but are also used with other cladding e.g timber or
PVC weatherboarding. In all cases the detailing of the flashings is similar and
as with all lead flashings the maximum length when using Code 4 lead sheet is
1.5m.
Diagram
13 shows the detailing at a sill corner. Although the corner can be dressed or
bossed to shape it is more practical to introduce a gusset as shown which can be leadwelded or
soldered
Before
the sill flashing is placed in position. For windows that are wider than 1.5m,
100 – 150mm laps should be used between sill flashing pieces depending on the
exposure. Diagram 14 shows the window in position.
In
cases where the window is set back from the wall covering a jamb, flashing will
be required to prevent water from penetrating down behind the sill upstand.
Diagram 15 shows sill and jamb flashing in position. The length of flashing
pieces should not exceed 1.5m.
Laps
between pieces of jamb flashing and where the jamb flashing laps over the sill
flashing, should not be less than 75mm. Diagram 16 shows the finished detail.
The apron extends 150mm down the face of the wall covering and this is often cut to a scalloped pattern to suit the spacing of the tiles or slates.
Lead sheet is often used for covering small flat roofs on porches, door hoods and bay windows. Examples are shown in Diagrams 17 and 18.
Note that the down-stand of
these weatherings is often cut to a feature pattern – see diagram 18. To
achieve long life it is important with all leadwork to limit the maximum size
and this is governed by the thickness of the lead used. Diagram 19 shows the
recommended maximum sizes when using Codes 4-7.
Although
it is practical to cover a 2.5m long by 600mm wide area with Code 4 lead it
would require the use of joints- usually wood cored rolls. Using Code 4 it may
be possible for a do-it-yourselfer to fit these joints but it is usually
necessary to use a skilled leadworker. The upstand against the wall should not
be less than 100mm and cover flashings over the Upstand – previously
described
– should not exceed 1.5m in length.
Don’t
use an underlay which could cause adhesion to the sub-strate during hot weather.
Use a building paper or a geotextile underlay.
Don’t
nail or tack the edges to prevent wind lift. Use clips.
Never
oversize the bays. Divide them with wood – cored roll or, alternatively, use a
thicker sheet.
SMALL
EXTENSIONS AND CONSERVATIONS
Diagram 20 shows diagrammatically the type of extension or conservatory that is often added to a building. Where the structure abuts the wall a flashing will be required to prevent water from penetrating between the wall and the top of the tiles or other roofing material. Several types of lean-to conservatories also require a flashing where the polycarbonate roofing sheets abut the wall. Code 4 lead sheet should be used for these flashings with lengths not exceeding 1.5m and end laps between pieces not less than 100mm.
The
upstand against the wall should be not less than 75mm and the top edge is turned
25mm into the brickwork and fixed with lead wedges and lead sheet sealant as
previously described.
The
extension over the roofing material should not be less than 150mm and the
clipped to suit the exposure of the building.