Biscoe
& Stanton
Chartered
Surveyors
Common
defects in buildings
Dampness
Dampness may be
due to several causes but can be categorized as following:-
-
Condensation
-
Penetrating dampness
-
Plumbing leaks
-
Rising dampness
Rising dampness whilst
probably the least common cause for dampness is one of the most treated
ailments. True rising dampness relates to the breakdown or deterioration
of the damp proof course. One of the major reasons why this is so often
misdiagnosed is that the bridging of the damp proof course by soil or pavings
gives a similar reading on an electric moisture meter.
High
ground levels
-
Paving and soil levels
should be at a minimum depth of 150 mm (6") lower than the damp proof course.
-
It is all too common
to find that paving and soil levels are within 150 mm (6") of the damp
proof course and in some cases even bridge the damp proof course.
-
This generally happens
when a patio or path is laid or when flower beds are created.
-
A damp proof course
is an impervious material usually in slate, hot laid bitumen or bituminous
felt in older type and 1930's houses. It is intended to stop
moisture within the ground from rising up the wall due to capillary action.
-
It can be seen therefore
if soil or pavings bridge the damp proof course it is inevitable that dampness
will occur within a building having walls of solid construction.
-
If soil and pavings
are lower than the damp proof course but are within 150 mm (6") of the
damp proof course, rainwater can, during heavy rain, "bounce" over the
damp proof course and again cause dampness to the interior of the building.
-
High soil levels and
pavings can also obstruct air vents to the base of walls. Vents are provided
for suspended timber floors in order to prevent dampness developing to
the sub-floor void.
-
It can be seen therefore
if pavings are too high they can create ideal conditions for rot to develop
to the floors.
In
addition to the high level of pavings note the considerable damp staining
due to defective gutters. Note also the fact the air vents have been ducted
in order to provide airflow to the sub floor void.
(The
above sketch shows the correct position for a damp proof course)
Horizontal damp proof
courses come in a variety of materials. For older type properties the damp
proof course is usually in two courses of slates. For 1930's built houses
it is normal for the damp proof course to be in bituminous felt although
could also be in two courses of slates, hot laid bitumen, courses of engineering
bricks or in lead.
Whilst slates form
an excellent damp proof course they can be damaged if the building suffers
from some settlement whereas the other materials generally will tolerate
some movement occurring.
Bituminous felt
damp proof courses do however deteriorate over a period of time.
Some typical
photographs taken on surveys
Loose
and slipped slates adjacent to valley gutter. Note several past slipped
slates held in place by tingles |
Cracking
to wall at the junction with the front bay and the main wall. This occurred
during the installation of double glazing. |
Cracking
to main wall below the window opening. Caused by settlement of the
foundations. Rebuilding will be necessary. |
A
felt covered flat roof nearing the end of its life. Note considerable moss
growth. |
Some
movement has occurred to an external wall. The wall leans outwards. |
Considerable
damp staining to base of wall due to defective guttering. |
Shaling
plain tiles and shaling half round hip tiles. Considerable overhaul is
required.
|
Loose
half round concrete ridge tile. Moss growth to upper surfaces of the concrete
plain tiles. |
Testing
for dampness and rot to the sub floor timbers within the cupboard under
the staircase.
|
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