Manual of Purpose-Made Woodworking Joinery

Upgrading traditional- type casement windows 69

Figure 4.14 (e)

Isometric view of an

assembled comb joint

between a top rail and

a sash stile, highlight-

ing the minimum waste

projections that should

be achieved.

given much wider rebates to accommodate double-

glazed sealed units, are made air- and water- tight with

AquaMac- type weather- seals and are either hinged

traditionally, or are more sophisticated with concealed,

side- fixed geometry friction hinges. Some designs allow

the sash to be fully reversible for interior maintenance

and window- cleaning. And, because of the more

substantial timber sections required to accommodate

the double- glazed sealed units, even open- and- shut

trickle vents can be fitted in the sash’s top rail or the

casement frame’s head.

The timber- beaded, sealed- unit rebates can be

internal or external – I prefer the former, but the

latter seem to predominate. External beads are

usually pinned and internal beads can be pinned or

screwed – if the windows are made of hardwood and

internally beaded, they should be cup- screwed. A

local glazing company in my hometown recommend

bedding sealed units into timber sashes with butyl

glazing-compound in preference to double- sided

glazing- tape methods – but, again, the latter seem to

predominate.

UPGRADING TRADITIONAL- TYPE

CASEMENT WINDOWS

Figures 4.16(a)(b): As per paragraph 4.18 of Part

L1B’s Guidance notes, the upgrading of exist-

ing windows is not notifiable to any accredited- or

Figure 4.15 Part vertical section through the sill and
bottom sash- rail of a StormSure casement window
manufactured by JELD- WEN to meet the new Building
Regulations Part L. The StormSure achieves a range of
Window Energy Ratings (WERs) from A to C and whole
window U- values of 1.2 to 1.6W/m^2 K. Note that the
24mm sealed unit uses low- E (emissions) glass; the sill is
68 × 67mm par and the bottom rail is 67 × 55mm par.
The un- portrayed jambs and sash stile/top- rail are 67 ×
56 and 67 × 55mm par respectively. The weather- seals –
as seen in the vertical face of the weathered rebate above

• are Schlegel’s AquaMac 109.

a coping saw then chisel- finished. As illustrated at
(c) (d) and (e), at least 6mm (square- ended) waste
material should be allowed on each of these jointing
methods. After the glue is set, this is easily sawn- off
and cleaned- up.

MODERN CASEMENT

WINDOW DETAILS

Figure 4.15: Modern casement windows with
stormproof- type sashes and related weathering details
are similar in design to the original Timber- windows
specification in BS 644 (Figure 4.12(b)), but they are

Figure 4.16 (a) Part vertical section through the sill and

bottom sash rail of an upgraded, traditional casement

window, showing a 16mm double- glazed sealed unit

with stepped edges resting on 2mm- thick plastic ‘setting

blocks’. The unit is held with glazing sprigs and bedded

and face- pointed in butyl glazing compound. Additional

upgrading is achieved by setting a Schlegel’s AquaMac

109 or 63 compression weather- seal into the narrow-

grooved 20 × 10mm ovolo- moulded beading, mitred and

fixed around the inner faces of the frame.