This structure of this timber framed porch
extension was constructed some time ago but the weather
proof cladding was not completed, leaving the structure
exposed to the elements. The aim of the project was to
provide an weatherproof finish to the structure that was
durable, attractive and economically viable. Pre-painted
cement board cladding was chosen, it is relatively
inexpensive and weather resistant, its main weakness being
vulnerable to impact damage that is difficult to repair.
The first step was to strip off the incompleted
cladding to expose all the structural elements for a
thorough inspection to see that their exposure to the
weather had not reduced their strength and so be unable to
perform their function adequately.
The roof had sagged slightly due to a
number of roof support beams losing their strength from
exposure to dampness and so needed to be replaced. Apart
from that most of the weathering was purely cosmetic,
would not effect the structural stability and would be
covered by the cladding.
Fortunately, polystyrene boards had been used for
insulation between the framing timbers which is fairly
weather resistant and although exposed to the elements,
survived with minimal damage.
missing areas of polystyrene board were filled with the same
with smaller areas and gaps around the tiles being filled
with freeze-resistant foam, providing an effective
barrier against the cold.
Apply Building Paper
To provide an
effective barrier against external moisture, whilst at
the same time allowing internal moisture to escape (so
that it will not get trapped in the wall structure
and cause rot), a layer of building paper was applied to
the entire wall surface area, fixed to the timber
framing with large, flat, plastic headed pins so as to
reduce the possibility of moisture getting in through
the holes made by fixings. A generous overlap was
provided at joins in the paper and special attention
paid to detailing around openings to insure an effective
moisture proof barrier.
purpose of boarding over the timber framework is to
provide a consistent solid surface to attach the
external cladding to, it should also provide an
additional barrier against the weather without
preventing the walls from being able to breath.
After we have gone to the trouble of applying
building paper, it would be pointless to put an
impermeable barrier outside this for internal
moisture to get trapped behind. The reason we use
external quality plywood is to provide durability
because it is effectively outside the moisture
barrier (building paper), it will be exposed to
moisture vapor but will be protected from rain and
snow by the external cladding. That is why the
slight gaps between the boards are not sealed so as
to allow moisture to escape from the inside. This is
especially important in countries that get very cold
in the winter because all external openings are
rarely opened and effectively sealed, preventing
heat loss but minimizing ventilation, this is not
good for the building structure or our health.
Narrow shafted pins or screws with large flat
heads are again used to minimize moisture
penetration where the fixings pierce the building
The cement cladding
boards were then cut and attached to the plywood boarding
and underside of the roof verge overhang with a generous
overlap for added weather protection. Narrow shafted, wide
headed screws were employed again as fixings, it is
important to pre-drill and countersink cement boards as the
are brittle and unforgiving. As can be seen below, the
building paper protrudes over the window frame, this will
eventually be fixed behind the window surround, when fitted.
The fixing heads and bare patches on the cement boards where
they were cut are then painted with weather resistant paint
of the same colour for corrosion resistance and aesthetics.