Dampness in buildings

DAMPNESS IN
BUILDINGS
Civil Engineering Drawing & Graphics (Theory)
10/27/2014 Pepared by Engr Fazal-E-Jalal

DAMPNESS IN BUILDINGS
1. Rising damp
Rising damp is the result of water rising
through the walls by means of capillary action.
Moisture may stem from the soil around the
outside of walls or from moisture rising through
the floor construction. As a result of the
capillary ‘lift’ through the fine pores in
brickwork and masonry, moisture reaches a
maximum height up the wall of about 1 metre.

To counter this effect in walls, the path of
water up walls is blocked by builders
incorporating an impervious layer into the wall
at low level. These ‘damp roof courses’ (dpc’s)
have been made of various materials over the
years including such things as slates,
engineering bricks and bitumen felt.

Deterioration of the dpc material leads to
failure in the barrier and allows moisture to
rise, and if the dpc is bridged, for example by
external soil being placed against the wall
above the dpc level, then the dpc is rendered
ineffective.

TREATMENT
Where a rising damp problem is caused by a
lack of a damp-proof course (common in
buildings over approximately 100 years old) or
by a failed damp-proof course (comparatively
rare) there are a wide range of possible
solutions available.

These include:
Replacement physical damp proof course
Injection of a liquid or cream chemical damp
proof course (DPC Injection)
Porous tubes
Electrical-osmotic systems
Land drainage

2. Hygroscopic salts
An additional problem is that the water
absorbed into walls in this way contains
dissolved salts in the form of nitrates,
sulphates and chlorides. These are left on the
wall surfaces as the water evaporates. The
problem is that some of the salts attract
moisture (what is known as hygroscopic).

As a result, if the salts aren’t removed, they
continue to attract moisture into the wall
surface which remains damp, even though
other repair works have been completed.
.

Some current thinking has questioned the
extent of genuine rising dampness in property
and before that is given as the ultimate cause,
therefore, a good surveyor/damp specialist will
eliminate other potential causes of moisture,
such as condensation, water penetration or
plumbing leaks

Replastering will often be carried out as part of
a rising damp treatment. Where plaster has
become severely damaged by ground salts
there is little argument about the need to
replaster.

However there is considerable debate about:
The extent of replastering required
 The use of hard sand: cement renders to
replaster as part of a rising damp treatment.

3. Penetrating dampness
Penetrating dampness is where water gains access to the
building through its external fabric (wall or roof) and it is not as
simple as its name first implies. For example, water can
penetrate a solid wall due to a number of factors: the high
porosity or degradation of the brickwork, for example, or
failure in a protective render (perhaps due to cracks or poor
application), or even due to the orientation of the wall (south
westerly elevations often face the fiercest moisture-laden
winds). Each possible cause needs to be assessed and
eliminated before an effective repair programme can be
specified.

Water will find any gap through which to travel
and all surrounds to openings and junctions of
the building fabric are potential areas of
weakness in resisting moisture. Doors, window
and often skylights are vulnerable and need to
be sealed as do joints between chimneys and
roof coverings which are protected by
flashings and soakers.

Water needs to be safely discharged away
from walls as it drops from high level and a
failure to do so may lead to water penetrating
the external walls. So, guttering and
downpipes that are leaking are a potential
problem and even small detailing such as
‘drips’ formed on the underside of window sills,
door thresholds and the base of render need
to function properly to ensure that water
doesn’t run down the face of external walls.

4. Bridging of Cavity Walls
In cavity walls, water will penetrate if the
cavity is improperly ‘bridged’ by mortar
droppings resting on cavity ties or by rubble
dropped into the base of the cavity during
construction. Both are examples of routes for
external rainwater to find a way to soak the
internal leaf.

5. Condensation
Condensation is a very common source of
dampness in buildings. The fact is that the air
around us and in our homes holds moisture
(water vapour). The amount it holds increases
with higher temperatures and when the
temperature is cooled and it has more water
vapour than it can bear, moisture is dropped
onto the surfaces that have cooled the air
close to them in the form of condensation.

To add to the problem, however, our lifestyles
tend to create extra water vapour which enters
the atmosphere within our homes when we
shower or wash clothes and at the same time,
our desire to reduce heat loss means that we
have sealed our houses which keeps water
vapour trapped and makes condensation more
likely.

Condensation is more likely in areas where air
flow is restricted such as behind furniture and it is
common to discover mould growth in these
places.
Condensation occurs, then, when a coincidence
of contributory factors occurs at a critical level.
Temperature is one factor (affected by heating
and insulation); water vapor discharged into the
air is another; and ventilation (management of
moisture laden air) is another.

Dampness tends to cause secondary damage
to a building. The unwanted moisture enables
the growth of various fungi in wood, causing
rot or mold health issues and may eventually
lead to sick building
syndrome. Plaster and paint deteriorate
and wallpaper loosens. Stains, from the water,
salts and from mold, mar surfaces.

The highest airborne mold concentrations are
found in buildings where significant mold
infestation has occurred, usually as a result of
severe water intrusion or flood damage. Molds
can grow on almost any surface and occurs
where there is a lot of moisture from structural
problems such as leaky roofs or high humidity
levels. Airborne mold concentrations have the
potential to be inhaled and cause serious
health effects in humans.

ASSIGNMENT # 02 (Part A)
Give brief short answers.
1. What is role of drainability of soil in causing dampness in a
building.
2. Why it is essential to provide a DPC in a brick masonry wall.
3. How dampness can be prevented in a building by surface
treatment.
4. Which cement concrete / mortar is used for laying horizontal DPC
/ vertical DPC.
5. What is the thickness of horizontal and vertical DPC when laid
with concrete or mortar.
6. What is the quantity of bitumen required for laying a DPC.
7. What are the ill effects of dampness on various components and
materials in a building.
8. Why the DPC is not provided within a door or verandah openings.
9. Why are the lead sheets not laid in cement mortar as a DPC.

ASSIGNMENT # 02 (Part B)
What are (at least 06) causes of dampness,
write down explaining them.
Write in detail the methods of preventing
dampness.
Drawing neat sketches, do explain the
methods of providing DPC under different
situations.
Q# 16 to Q#21 (Page 6-11, Dampness &
Damp proofing; in “BUILDING
CONSTRUCTION” by N.L Arora & B.R Gupta)

Dampness in buildings

More Related Content

What's hot

Similar to Dampness in buildings

More from Fazal-E- Jalal

Recently uploaded

Dampness in buildings