Heritage Retrofit

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BCD SPECIAL REPORT ON HERITAGE RETROFIT FIRST ANNUAL EDITION 33
such vernacular and humble houses,
some terrible 20th-century replastering,
painting, patch rebuilds and hard cement
pointing had been carried out. There
were even areas of glistening moisture on
interior wall surfaces and large areas were
black with mould. Also, the ground floor
skirting boards had rotted through. At
this point, some basic humidity readings
were taken in June 2015 (Figure 2).
The work began with internal faces of
the exterior walls being stripped of their
coatings and then relined with insulating
and humidity-buffering mineralised
woodchip panels created especially for the
project, and then plaster finished with a
Vivus plaster skim.
Outside, the walls were depointed of
cement and repointed with Vivus mortar
and lime-washed.
It was clearly demonstrated that the
material can be applied quickly. Pure
lime skims were applied and finished
in the same day. The skims contained
no aggregate of any kind nor any other
additive – they were pure air lime. In some
rooms, purely for the experiment, panels
were fitted to the walls and then skimmed
and finished on the same day without issue.
The north- and south-facing external
walls were also finished in the same
timescale, repointing and initial coat
of limewash completed on day one and
subsequent coats applied on day two,
completing the work, front and back –
sunshine with wind (south front) and cold
damp shade (north rear). The two walls
were completed in the same manner,
clearly demonstrating the setting property
of the materials used.
Inside, the walls were paper lined
and then decorated with a modern ‘fully
breathable’ soft paint. Although this will
not affect the insulation per se, it will
undoubtedly reduce the ability of the
walls to absorb humidity. However, many
owners and tenants will expect to be able
to use these finishes, so this was added as
part of the experiment. It is expected that
the house will remain humidity free, even
with the walls lined with paper.
A key element of the demonstration
lay in showing the effect of humidity,
contained within a structure, on the
insulation performance. This moisture can
reduce the effectiveness of any insulation
by up to 30 per cent depending on the
levels. Successfully dry out a building and
maintain that humidity, then it will be
warmer. Take an insulation that buffers
humidity while also helping to equalise
the humidity by being diffusive, and apply
it to a wall that because of its manner
of construction, acts in the same way,
then we will have achieved many things
simultaneously.
The insulation and humidity control
abilities are now being monitored with
sensors installed at the property. The data
taken thus far has shown a very beneficial
effect. The average humidity levels recorded
in the building had dropped 24 per cent
from June 2015 to April 2016, and it is
estimated that the energy efficiency of the
walls has increased by more than 30 per
cent. Empirically, the house is now warm
and dry, even though the building was not
inhabited all winter following the works.
The temperature remains fairly constant,
feeling cool on hot summer days and
warm and dry on damp cold days.
The monitoring will continue for
another two years to show the long term
effect over winters and summers with
the building being regularly used and
inhabited. Feedback from the occupants
will also be sought.
HARRY CURSHAM s)
has spent the past 27 years working with,
experimenting with and learning about
air lime materials. He is a director of Vivus
Solutions Ltd (see page 34). The full Welsh
Government SBRI report is available from
the author on request.
FIGURE 2: Humidity readings – June 2015
AREA POSITION
HUMIDITY(%RH)
Ground floor First floor
Internal west wall
Low level 96.35% 88.50%
High level 88.99% 88.50%
Internal north wall
Low level 94.89% 79.50%
High level 78.56% 79.50%
Internal east wall
Low level 93.02% 89.99%
High level 89.90% 89.55%
Internal south wall
Low level 89.95% 88.70%
High level 87.05% 88.70%
Mill Cottage on completion of repointing and lime-washing using Vivus materials Fireplace and window details, with insulated walls, plastered and finished
Sample data recorded following the work at Mill
Cottage showing a marked fall in dewpoint (black)
and relative humidity (green) from December 2015 to
April 2016, while temperatures (blue) rose. During this
period the house was uninhabited and the weather in
this exposed location was particularly cold and wet.
FIGURE 3