Surveying for Damp Issues with Historic Buildings
Buildings fall into two categories for the purposes of surveying for damp:
I. Modern buildings built with a damp proof course and barriers to rainwater penetration.
II. Old buildings built prior to mid to late 19th century depending upon the region of the country. Old buildings relied on the walls breathing and shedding moisture before damp became a problem.
Because lime and earth mortars are so porous, timber in contact with these mortars is less prone to decay than when bedded in cement mortar.
Historic houses, when built, were able to breathe and shed water. They were also heated by coal or log fires in an open fireplace which promoted rapid air changes by way of air being drawn out through the chimney. Windows and doors were not sealed as they are today allowing air movement into and out of the building
Internal finishes were lime washed which allowed surfaces to breathe and, although it would discolour when damp, it would not peal off the wall like wall paper nor blister like modern paint.
Over the years most of these houses and buildings have been altered to suit our modern lifestyle, nearly always to the detriment of the building.
The heating has been changed and the windows and doors have been sealed and draught proofed. Consequently, we now no longer have the same amount of air movement.
From the day they were built many of these buildings have had moisture from the ground, rising into the walls by of capillary action. This moisture contains salts in solution. Initially for many years the moisture in the walls would evaporate harmlessly, outside during fine dry weather and inside, as a result of the rapid air changes induced by the heat from the open fire drawing air rapidly up the chimney.
When this moisture in the walls evaporates, the soluble salts it contains are left in the walls at the point of evaporation which would be within the surface of the masonry or plaster finishes.
Salts block the pores and cause moisture to rise further up the walls to a point where evaporation can continue. A proportion of salts are also hydroscopic (moisture attracting) and in humid conditions (modern living, no open fire, etc) will attract moisture to the wall causing a damp area or band even when there is no capillary moisture.
In many buildings the floors have been concreted on top of a plastic damp proof membrane which reduces the area of evaporation of moisture from the floor possibly causing more moisture to rise into the walls. Hard cementitious internal plaster finishes have been applied, which are far less porous than lime wash.
Ground levels are often higher than the original, either above the height of the masonry plinth in earth structures and/or sometimes above the level of the internal floors.
These problems along with defective roofing, joinery, rainwater goods, chimneys, pointing etc., can cause excessive damp in old properties. Also to consider, as Graham Coleman, a well respected expert from BRE wrote:
“Another factor to consider is that, all things being equal, rising damp tends to rise higher in thick walls than thin walls; this is due to the lower surface to volume ratio of thicker walls, evaporation being mostly subject to surface area. This is an important feature to consider when dealing with properties with larger dimensioned walls - simply the so-called 'allowing walls to breathe' syndrome to stop the rising water may prove of little effect in such cases”.
G.R.Coleman. 2000
To compound this problem houses were often externally
decorated with
non-breathable paint
or rendered with
hard dense cement
rich finishes. These
applications reduce
evaporation
significantly from
the outside surface
which then cause
damp to rise further
up within the wall
with the resultant
internal damp
staining.
When renders crack
they allow water to
penetrate through,
either by capillary
action into fine
cracks, or directly
into larger cracks
and debonded areas.
The water is then
trapped behind the
render and can
penetrate to the
inside face of the
wall structure.
Consequently, by the
21st century a great
many old
traditionally built
houses now have damp
problems often
caused over the last
100 years, by
changes in heating,
ventilation and wall
finishes.
Due to a lack of
knowledge and
understanding of
older buildings,
traditional
materials and the
way they work
together, these damp
problems have not
been addressed
correctly.
People buying houses
do, for the most
part, expect them to
be weather proof
with a dry interior.
Conservation of
houses means that
they have to be
owned and lived in
to be cared for.
They have to be fit
for this purpose.
How to conserve
these properties and
make them fit for
purpose is driven by
two opposed camps.
Some
conservationists
want the very least
intervention into
the property, so
that the historic
fabric and features
of the property can
be preserved for
future generations,
which is laudable.
However, many firmly
believe that when a
property is damp the
application of lime
plasters and lime
wash can reverse the
problem, by allowing
the walls to
”breathe”, even when
the way the whole
building functions
(i.e. modern heating
and ventilation) has
changed since it’s
original
construction.
At the other end of
the scale some
Preservation
companies consider
any visual damp, or
damp recorded on a
meter around ground
floor walls, to be
indicative of a
rising damp problem.
This, they will
recommend can be
cured by insertion
of a chemical damp
proof course,
followed by hard
moisture resistant
sand cement render.
This is often
detrimental to the
older traditionally
built buildings.
Given that there are
probably 3000
trading preservation
“specialist
companies” (and many
more builders who
will have a go at
it) and that there
are only a few
hundred with any
qualifications (and
far less who
genuinely understand
older buildings)
this leads to
unnecessary and
often damaging work
to historic
buildings.
Then there is the
middle ground:
Experienced building
professionals in
both the
conservation and
preservation
industries who
understand the
importance of
keeping older
properties in good
condition so they
can be preserved and
who can also
identify
historically
important elements
and features, which
must be conserved.
However they also
realise the
practical issues of
carrying out
effective long term
repairs and
treatments, so that
the occupants can
enjoy living/working
in these buildings
and therefore
continue to look
after them.
There are a number
of basic
environmental health
requirements for
occupying a
property, or
bringing up children
and housing the
elderly, the most
basic is that it
must be dry and
warm.
Some people not in
these groups may
decide to tolerate
some damp in a house
because they
consider the well
being of the house
to be more important
than their own
creature comforts.
However these people
are few and far
between. There is a
far larger group of
people who would
impose damp
conditions on people
living in old
properties due to a
lack of
understanding of the
problems.
the
house at the best price.
The Royal Institute of Chartered Surveyors, Trading Standards, and even The Estate Agents professional bodies, all state that surveys should be carried out by a qualified CSRT surveyor, and any work should be carried out by a BWPDA member company. This is often in the terms of the mortgage company instruction. However, many Estate Agents will try and use a cheaper unqualified company for a free survey. It is these companies who, through a lack of training and understanding, will usually in an effort to provide the cheapest quickest fix, recommend an injected chemical damp proof course and associated cementitious re-plastering.
Given that the survey is free there is some pressure to find some work. It costs on average £70 to attend a property write a report and send it. These costs have to be recovered somewhere.
In the ideal world, surveys would be commissioned by Building Surveyors or Architects who would undoubtedly use a surveyor or company that they knew to have the relevant experience , knowledge and qualifications. If Solicitors had a better understanding of guarantees they would insist that work was carried out by qualified companies, guarantees issued were meaningful, enforceable, and underwritten by insurance (and not by chemical companies) for the protection of their clients. This would ensure that companies do not use chemicals unnecessarily, just to comply with the terms of the guarantee.
MACLENNAN-LSE is the trading name for LSE Building Preservation Ltd
