Civil Engineering Reference
In-Depth Information
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Figure 10.3
A side flashing for a timber window. Note that the sill flashing is to envelope the side flashing at
their junction
window (see Figure 10.4). At the sides and top of the window it is important that the
render form a good seal to the timber, as this too will inhibit water penetration. This can
best be achieved by painting on a mixture of sand and adhesive to the surface of the
window that will be covered with render. This might be as little as 10mm of the face of
the window. I have found a mixture of Bondcrete
®
and coarse sand works well. It is ideal
if this is applied to timber windows prior to painting them, however it will hold to
painted surfaces. I have even found that it will hold to metal surfaces. Alternatively, use
construction adhesive and sand.
Water can flow uphill
The window sill has a groove cut into its underside approximately 6 mm from the front
edge of the window sill (see Figure 10.4). This is known as a drip line. This is to prevent
water flowing back uphill under the window sill which would cause the window sill to rot
out prematurely. Most people think that
water doesn't flow uphill, but I assure you
it does, as I will demonstrate shortly. For
this reason, you should also ensure that
the sill flashing is shaped to cause the
water to discharge. If the end of the
flashing is not turned down, the water
may run back below the flashing, much
the same way as it would the window.
This method of flashing has some serious
shortfalls as it leaves the cavity between
the window and the window buck or
frame open to condensation, which was
covered earlier, and will definitely cause
Figure 10.4
Sill flashing fixed to facilitate water discharge
onto the external face of the rendered wall below the window
