70 Making traditional and modern windows
new weights (as described above, under Making and
Fitting the Sashes). Although new lead weights are
sometimes used to increase the weight, if they need
to be longer than the originals, the length of cord is
shorter and lessens the amount of travel and opening
area.
Alternatively, the sashes could be modified to
receive patent spiral- balances; but this would involve
them being removed, de- glazed, grooved on their
side- edges, re- glazed with stepped sealed- units, then
weighed to determine the weight- type of balances
required. To overcome the logistics of such a task
(brought about by retaining the existing boxframes),
the Ventrolla Sash- Window Renovation Company
takes site measurements and makes and installs new
sashes with pre- glazed sealed units. The replacement
sashes are grooved and fitted with pile- carriers and
Weatherfin pile on the abutting edges of the top-
and bottom- rails and between the meeting rails, on
the splayed edge of the bottom sash. On site, their
installers renew the parting- and staff- beads – the
latter grooved and fitted on the inner edges with poly-
propylene pile- carriers containing Weatherfin pile –
and the parting beads being plastic replicas with a
strip of Weatherfin pile fitted on one side, which must
face towards the exterior. A ‘U’ shaped polypropyl-
ene section is screwed into the original parting- bead
groove and, as illustrated at (b), the detachable pile-
carrier bead snaps into this and allows future removal
for sash and cord maintenance.local- authority and does not have to comply with Part
L’s standards regarding the WER of the whole window
and frame. Even so, the energy rating of existing
windows can be improved by removing the single-
thickness glass and re- glazing the sashes with double-
glazed sealed units with made- to- measure stepped
edges. Also, it is usually possible to fit weather- seals
around a sash, although this involves forming very
narrow grooves in the edges of purpose- made timber
beading; this can be done with special weather- seal
router cutters (on full- width boards, before cutting
to bead- thickness). The beading is mitred and – as
illustrated – surface- fixed around the frame’s interface
with the sash.
UPGRADING TRADITIONAL
BOXFRAME WINDOWS AND
DOUBLE- HUNG SASHES
Figures 4.17(a)(b)(c): The upgrading of weighted
double- hung sashes presents more problems than
upgrading traditional casement windows. This is
because the sashes are counterbalanced with the
corded sash- weights in the boxframes – and when
the single- thickness glass in the sashes is replaced
with double- glazed, stepped sealed- units, the sashes
are heavier and have to be re- counterbalanced with
(a)(b)(c)Figure 4.17 (a) Critical parts of the Ventrolla Perimeter
Sealing System (VPSS), showing a carrier channel and
Weatherfin pile fitted into the inner edges of their ‘small’
staff bead; and (b) a uPVC replica parting- bead fitted
with a Weatherfin pile, poised to snap into the modified
channel in the pulley stile below; and (c) the meeting rail
of a bottom sash also fitted with a carrier channel and
Weatherfin pile. Note that the polypropylene fin protrud-
ing in the centre of the silicone- treated pile, flexes over to
an ‘L’ shape when compressed between the normal sash
movements.Figure 4.16 (b) Part vertical section through the sill and
bottom rail of an upgraded, traditional stormproof- type
casement window, showing a 16mm stepped, sealed- unit
and splay- beaded AquaMac 109 or 63 compression
weather- seals mitred around the inner splayed faces of the
frame; all similar to Figure 4.16(a), except the front timber
glazing- beads – the inner- edges of which are either faced
with double- sided butyl glazing tape, or butyl glazing
compound.