Manual of Purpose-Made Woodworking Joinery

Weathering features 63

features – already shown here in places – need to be

explained. Although common sense perhaps tells us

that the slope on the exterior surface of window- and

doorframe- sills is to allow rainwater to run off, it

will not tell us the most satisfactory angle required.

Traditionally, this was reckoned to be about 9° or

10° (1 in 6) or (1 in 5.5), but BS 644: 2003: Timber

Windows – Factory assembled windows of various types,

recommends that such weathering slopes should be

After the sashes are cleaned up, the grooves for sash
cord or chain are routered out and the sashes are fitted
into the boxframes, ready to be hung on site after they
have been glazed. Although not the domain of bench
joiners, knowledge- wise, the counterbalancing of the
glazed sashes involves obtaining separate pairs of sash
weights, theoretically with a combined pair- weight
equal to the weight of each sash. This is done by
weighing each sash with a hooked spring balance and
dividing by two. However, in practice, this does not
always work and usually each weight for the top sash
has to be increased by 0.25 to 0.5 kg – and each weight
for the bottom sash has to be decreased by 0.25 to 0.5
kg. Weighting problems on existing hung- sashes
can be caused by re- glazing with lighter- or heavier-
weight glass or through a build- up of paint over many
years.

DOUBLE- HUNG SASHES ON

SPIRAL BALANCES

Figures 4.10(a)(b)(c)(d): Spiral balances for vertically-
sliding sashes were introduced into the industry in the
1940s and a range of these fittings (to suit different
sash- weights) are still available from various manu-
facturers. Their demand exists for the replacement of
existing balances and for use with new sash windows.
If using these fittings on sashes in new frames, the
frames – as illustrated at (a) and (d) – are usually of
solid construction, as opposed to boxframes.
The tubular spiral balances, as shown at (b), can
be housed in semi- circular shaped grooves either in
the sashes (c) or in the solid jambs of the frame (d).
Either way, each of the four tubes containing the
spiral balances is fixed to the top of the frame with
a drive screw and, after being tensioned with 3 to 5
turns of the fixing plate at the base, is screwed into a
7mm housing on the underside of the sash. Note the
top and bottom limit- stops fixed in the channels in
view (a).
In the case of top sashes with joggles protruding
down below the meeting rail (inhibiting the fitting
and fixing of the fixing plates at the base of the sash),
additional channel fittings are available for an alterna-
tive fixing.

WEATHERING FEATURES

Sloping sills

Figure 4.11(a): Before completing this chapter with
details of other window- types, certain weathering

(a)

(b)

(c)

(d)

Figure 4.10 (a) Double- hung sashes operating on

spiral balances in a solid- type frame; (b) One of a pair

of spiral balances, showing the fixing hole at the top

of the tube; (c) Part of a sash stile grooved on its side

to house a spiral balance tube; and (d) Part of a solid

window jamb grooved in its sash channels to house spiral

balances.