Civil Engineering Reference
In-Depth Information
●
Balloon frame: two-storey height
or eaves-height external wall
panels with the studs continuous
from ground floor to roof (Figure
3.31a)
●
Platform frame: storey-height
external wall panels which are
erected upon platforms formed by
the ground and upper floor
construction (Figure 3.31b). This
is by far the most common form in
the UK
●
Post-and-beam: a structural frame
of widely spaced timber posts and
beams. Planked, joisted or
panelled floor and roof units span
between the beams, and non-
loadbearing infill panels span
between the posts to form the
external wall claddings
●
Volumetric box: assembled from
room-sized prefabricated boxed
accommodation units
insulation between the studs (Figure
3.32).
The dwellings built between 1945
and 1965 were clad wholly or mainly
in single leaf brickwork, with the
brickwork separated from the timber
frame by a cavity and connected to
the frame by metal wall ties.
Most systems used between 1966
and 1975 had an external sheathing
on studs and a separate cladding of
brick. Some systems were directly
clad with timber boarding or plywood
claddings fixed directly to the frame
or tile-hung panels on the front and
rear walls.
To meet the revised thermal
insulation requirements introduced in
1966, most timber frame systems
incorporated thermal insulation
between the frame studs of the
external wall panels. The increased
temperature gradients meant that
there was more chance of
condensation within the external
walls. To counter this threat, vapour
control layers were incorporated into
many of the timber frame dwellings
built during this period. The layer
was usually of aluminium foil-backed
plasterboard, never very effective, or
was a separate layer of polyethylene
film positioned on the warm
(internal) side of the frame. The
breather membrane was either of
building paper or of light bituminous
felt and was intended to project below
the sole plate to protect it, as well as
performing its main function of
keeping liquid water from reaching
the panel, and releasing internal
water vapour (Figure 3.33). At this
time there was no insulation under the
floor finish, and there was
consequently a risk of a thermal
bridge at the perimeter under the sole
plate.
Towards the end of the period, the
timber sole plates of some systems
were treated with preservative. There
were also a few instances of the
timber frame itself being treated.
Most separately clad systems have
single leaf brickwork cladding
connected to the timber frame with
metal wall ties through a nominal
2 inch cavity. Other separate
claddings, such as horizontal or
vertical timber boarding, are fixed to
The external walls of timber frame
dwellings built between the wars are
typically either timber framed panels
with large-section studs, or panels of
virtually solid timber planking. Both
alternatives are directly clad with
timber boarding. The timber was
rarely preservative-treated, excepting
the occasional brush application of
creosote. Generally there was no
a
b
Figure 3.31
Balloon frame (a) and platform frame (b)
