Civil Engineering Reference
In-Depth Information
thermal insulation, this is not easy to
achieve. Perhaps the best way, where
there is room, is to put an extra lining
internally after installing a vapour
control layer, making sure there is no
existing vapour control layer since
this could trap moisture (Figure
3.42). Removal of the original outer
cladding and re-cladding is a more
expensive solution, and, moreover,
one which destroys the original
appearance of a dwelling.
A small amount of thermal
insulation was incorporated into
some later dwellings. Where systems
have stout board linings over studs, it
may be possible to inject thermal
insulation into the closed cavity
between each pair of studs, although
care must be taken to avoid cavities
carrying electric cables. The cavities
between the sheathing and the brick
cladding should not be filled.
under construction. Defects included
cavity barriers omitted or removed
during construction, not positioned or
not fixed properly, not fully closing
the cavity, not tightly lapped or butted
(Figure 3.43), and imperfections of fit
not made good by fire stopping.
Examination by optical probe may be
required, or a stiff wire can be used to
check the existence of paths between
the wall cavities of adjacent
dwellings.
Durability
General comments
Timber decay is the principal
potential danger to older timber
frame dwellings, and sapwood even
in allegedly durable hardwoods may
deteriorate (Figure 3.44).
However, where the timber has
been kept dry, long life is normal.
Timber in any structure is
potentially vulnerable to decay if
the moisture content remains high
(that is to say, more than 22%) for
sustained periods and the timber
species is non-durable. Sapwood is
Noise and sound insulation
See Chapter 1.9 and the same section
in Chapter 2.1.
Original inner lining
Fire
Most timber frame construction has
been faced with an external leaf of
brick masonry, and therefore there
has been little difficulty in complying
with requirements. However, fire can
spread rapidly in timber frame
dwellings once the wall cavity is
breached, particularly where the
ceiling or wall linings are flammable.
Some Swedish Timber Houses and
Scottwoods had fibreboard linings
with poor spread of flame
characteristics. Since 1965, there
have been statutory requirements for
the standard fire performance of
linings of wood based materials.
Where these requirements were not
achieved by the original linings used,
many building owners have replaced
the linings.
A timber framed wall consisting of
an external skin of at least 100 mm of
brickwork or blockwork, covering
studs at least 37 mm wide spaced at
not more than 600 mm centres, either
sheathed or not sheathed, and lined
internally with 12.5 mm plasterboard
skimmed with 10 mm lightweight
plaster will give half an hour's fire
resistance.
Spread of fire within wall cavities
and into wall cavities of adjoining
houses was identified as a risk in site
inspections of timber frame housing
New inner lining
New vapour control layer
Figure 3.42
Adding thermal insulation to an existing
timber frame dwelling
Figure 3.44
Decay in a medieval sole plate
Figure 3.43
Cavity barriers being installed incorrectly. They should be tight butted, not lapped. Lapping
as shown leaves gaps
