Civil Engineering Reference
In-Depth Information
Chapter 5.2
Thresholds
DPCs etc). However, most cases of
rain penetration have proved to be in
the more exposed areas of the UK.
Nevertheless, it is anticipated that,
following proposals to make flat
thresholds obligatory for new
housing also, there will be more
attempts to convert existing
thresholds. It should be appreciated
that there will inevitably need to be
compromises, and what is best for
access will not necessarily be
best, or even adequate,
for other
functions.
Characteristic details
Basic design
The basic requirements for a flat
threshold are summarised in
Figure 5.13.
Four typical solutions in principle
are shown for providing flat access
for wheelchairs to these basic
requirements and at the same time
reducing the risk of rain penetration
Cheeked porch or recess projecting not less than 750 mm
beyond door way
Figure 5.12
'Danger of tripping, rain penetration and
thermal bridging'
Weatherboard with drip not less
than 40 mm in front of air seal
The external door threshold has
always been one of the problem items
in the external envelope so far as
danger of tripping, rain penetration
and thermal bridging are concerned
(Figure 5.12).
On the other hand, many doorways
throughout the ages have been
protected by porticoes and canopies,
and, for the favoured few, by
portes
cochères
, where rain penetration of
the actual door of course does not
occur.
Since standards for access by
disabled people were introduced for
public buildings, there have been
many attempts to provide so-called
'flat' thresholds at entrances.
Examples of flat thresholds in use
which were examined by BRE
investigators showed a wide range of
solutions, nearly all of which could
be criticised on construction grounds
(eg thermal bridges, inadequate
Wheelchair users need a
1200 mm x 1200 mm flat
space inside the doorway
Shielded drainage (to cope with 50 mm per hour),
porch or recess
Difference in level between floor
finish and top of water bar not
greater than 13 mm
Air seal between
door and thr eshold
13 mm
Ramp to wheelchair
requirements, including
level landing area not less
than 1200 mm x 1200 mm
and a slope at 1 in 80
gradient (for drainage) away
from the threshold
Durable threshold
Optional mat well
Wall:
damp-proofing to Part C
thermal insulation to Part L
Non-deformable bridge to
thermal insulation
Figure 5.13
Basic requirements for a flat access threshold
