Page 26 - The Constructor 2017

The Company

Some types of cavity wall insulation retain moisture within the cavity wall void increasing the risk of
dampness into the habitable space. A high proportion of cavity walls contain physical blockages
from the original construction and where interventions have been made to walls and alterations
which results in debris dropping into and blocking the cavity wall void creating obstruction when the
cavity walls are filled with insulation material.
Different genres of buildings give rise to specific constructional problems which result in endemic
dampness problems which often go undetected for example moisture transfer through a suspended
solid floor where there is no vapour barrier or from solid floors to many inter war homes where they
lack an adequate damp proof membrane.
To simply apply broad brush stroke retro-fit solutions to existing buildings that reduce heat loss
without considering the consequences of doing so is proving to be a huge mistake. For example,
how many cavity wall voids get optically checked before retro-fit wall insulation is inserted? And yet
we find a very high proportion of cavity wall voids physically blocked from rubble and arisings due to
the original construction processes and from alterations to the building subsequent to construction.
The Society for the Protection of Ancient Buildings commissioned a study a few years ago to
properly measure and monitor the U values of different types of wall construction in older buildings
where the results of actual thermal resistivity were found to be far better than many software
programmes, that calculate U values could produce. This was found to be due to a lack of adequate
or accurate data in the software programmes that recognises the different types of external walls in
ancient or much older structures. The result was that many of our older and ancient structures were
performing far better with significantly lower rates of heat loss than had previously been
understood.
The Public Health Act of 1875 and the Model Building Bye-laws of 1877 marked the introduction of
physical horizontal damp proof courses in walls. However, solid floors and fender walls to the fire
hearth were yet to receive a damp proof course or membrane for a number of decades following.
Some more modern practices of solid floor and suspended solid floor construction were still not
receiving damp proof membranes even through to the late 1970’s and early 1980’s. Many of these
types of constructions through past genres have suffered widely from ground moisture permeation.
No fines concrete panel walled buildings have been very problematic due to rapid heat loss and
inherent higher costs of heating and higher incidents of condensation dampness and mould. These
buildings were very popular to address the requirement for mass housing following World War II,
which resulted in a high number of houses and multi-storey blocks being rapidly constructed during
the late 1940’s, 1950’s into the 1960’s with wall thickness reducing from around 300mm to 200mm
over the same number of decades. Many have been subsequently improved with external wall
insulation and despite this, in a number of cases; condensation dampness and mould persist within
the habitable spaces.
If we are to avoid the pitfalls of creating damp, mouldy and albeit warm homes at the expense often
of occupiers health, what is required is an in-depth understanding of building pathology
incorporating the methods and application of different forms of measurement and monitoring
before determining the most appropriate remedial solution to either manage or cure the dampness
problems integrated with retro-fit energy saving solutions – It must be an interdisciplinary approach
driven by independence.”

26 | Autumn 2017 | The Journal of the Worshipful Company of Constructors