Civil Engineering Reference
In-Depth Information
wall into which it is set. Clearly the
first demands adequate resistance to
impacts and wear, while the second,
being protected, can be more flexible.
The former does need to be in the
right place, however, and BRE
investigators on site have on several
occasions seen it placed too far
forward, so that leakage running
down the rebates in the door frame
falls inside and not outside the bar.
Some laboratory experiments were
carried out by BRE in the 1970s
involving a variety of sections of
stainless steel, aluminium, neoprene
and PVC waterbars cast into concrete
beams.
The tests were severe, the first
creating a 10 mm pond of water
adjacent to the bar continuously for
24 hours, and the second a
conventional pressure box test.
Only seven out of 34 cases showed
any degree of leakage in the ponding
test; the pressure box tests however,
showed, as expected, that the height
of the waterbar to a large extent
governed its performance. None were
of sufficient height to entirely resist
the flow of water carried in the air
stream, emphasising the importance
of an effective air barrier in resisting
water penetration
(Figure 5.20).
It was noted that some of the
neoprene and PVC waterbars had
Figure 5.21
An open cavity at a threshold in new construction inevitably attracts detritus
developed a kink at one end after a
period of hot weather, since they had
been cast in tightly. The kink (caused
by expansion in the bar) remained
after cooling. In the case of the
aluminium and steel sections, the
expansion had taken place without
apparent distortion. It is good
practice, therefore, that the built-in
ends of non-metallic waterbars are
wrapped in a compressible material
to provide some degree of protection
against kinking, particularly when
cast into concrete which shrinks on
curing.
Work on site
Inspection
The problems to look for are:
◊
upstands greater than 13 mm where
wheel chair access is provided
◊
no drainage channel on level access
doorways
◊
condensation on thermal bridge at sills
◊
rain penetration
◊
frost attack on subsills
Thermal properties
Many thresholds seen in common use
present problems with thermal
bridging and do not conform to
current thermal insulation
requirements. One tendency noted on
construction sites was that often a gap
was left at the threshold during
construction which would be filled by
detritus. This compromises the
function of the cavity in respect of
both rain penetration and thermal
insulation (Figure 5.21).
Air seal
Upper waterbar set inside
jamb rebate
Maintenance
Regular checking is needed that the
weatherproofing or seal at the foot of
the door is working effectively and
not jamming the door.
Lower waterbar interrupts
the capillary path
Figure 5.20
Alternative positions and functions for
waterbars incorporated into door
thresholds
