Importance of Weep Holes
Weepholes are the gaps left between some bricks in
external masonry walls. They serve two important
purposes:
Ventilation of the internal wall cavity - Without
ventilation, mildew, dry rot and damp reduce the life of
the internal wall studs and other building materials
within the cavity. Inadequate ventilation is the main cause of "Leaky Building
Syndrome".
Drainage - Water that enters the cavity due to capillary action, condensation,
damage, or accidental flooding needs to escape somewhere. In tropical and subtropical areas of Australia it is not unusual to see water flowing from the weep holes
on the prevailing side of well-constructed houses after a 'gully raker' or monsoonal
storm.
The problems with weep holes
Weep holes also provide access to the wall cavity for rodents and
insects. Swarming bees and European wasps love cavities. Field mice make a track
through the weep holes looking for warmth. Snakes, cockroaches and spiders find
refuge in the cavity. Down lights, extractor fans and holes for plumbing or electronics
become the internal entry point for these unwelcome visitors.
In desperation many occupants resort to blocking weepholes with any number of
materials such as silicon sealants, rolled up paper, plastic, scourer pads, steel wool.
Unfortunately some manufactured weep hole covers, guards and barriers have also
been designed with holes too small to allow adequate ventilation.
These 'solutions' obstruct airflow to the cavity setting up moisture problems. The
resulting "Leaky Building Syndrome" can be difficult and very costly to fix later.
Why Ventilation?
Advances in building construction techniques have led to a structure which is
significantly more energy efficient and air-tight than in years past. As a result,
moisture is no longer allowed to migrate freely throughout the building
envelope. Trapped moisture in masonry construction, if not addressed, can lead to
problems such as spalling, efflorescence, mild, and deterioration of the building
components. Moisture control that involves proper ventilation is the key to
eliminating these problems.
The importance of proper ventilation as an important element of moisture control is
recognized by experts throughout the building industry. As industry leaders have
called for additional ventilation, the shortcomings of current and past moisture control
strategies have been exposed. Other systems provide minimal ventilation through
very small weep openings. Common types of weep openings are drilled holes or
tubes, hollowed joints, and weep inserts…
The open tubes and hollow joints may create additional problems because they
provide an open pathway to the interior of the structure. Pests such as rodents or
insects can take advantage of this vulnerability and enter the building
unimpeded. All weep openings are also susceptible to trash mortar. Trash mortar is
comprised of the droppings of mortar that fall behind the wall as mortar is squeezed
out from between successive courses of brick. This accumulation is significant as
layer upon layer is added. The weep openings will become partially, if not totally,
blocked by trash mortar. Measures that involve installation of mortar collection
devices have proven to be modestly effective in blocking the mortar. However, the
very small size of these weep openings does not provide for the necessary flow of air
to properly ventilate brick structures.