Heritage Retrofit

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30 BCD SPECIAL REPORT ON HERITAGE RETROFIT FIRST ANNUAL EDITION
UNHEATED AREAS
It is important that ventilation
requirements are also assessed and
addressed for unheated areas of a
building such as roof and sub-floor
spaces. Where insulation or airtightness
are improved in a home, this can make
unheated areas colder and less well
ventilated, particularly if measures are
applied incorrectly (sub-floor vents being
blocked by insulation, for example, or
loft hatches being left uninsulated).
For unused roof spaces, adding
significant levels of ceiling-level insulation
will make the roof space colder, increasing
the likelihood of condensation and
associated problems, and increasing
the risk of water tanks and pipework
freezing unless these are also adequately
insulated. Moisture-related problems are
exacerbated where gaps in the insulation
and airtightness layer (such as loft hatches
or spotlight openings) allow warm,
moisture-laden air to enter the roof space,
and where insulation blocks existing
vents. While such problems may be
minimised by good practice and attention
to detail, additional ventilation may be
needed in any case, typically in the form
of eaves, ridge or slate vents, for example.
It should also be borne in mind that
in the UK’s temperate climate, external
ventilation often admits warm moisture-
laden air. As warm air can carry more
moisture than cool air, condensation
may occur in a void cooled by high
levels of insulation. So, increasing
ventilation levels can bring its own
issues, and uncontrolled ventilation may
simply add to the problem. Ventilation
paths must be carefully thought
through to ensure that the overall
strategy is effective and appropriate,
and avoids stagnant pockets of air.
Ventilation in sub-floor spaces can
already be compromised by the build-up
of debris in the floor void and/or in and
around vents, which again presents risks
of condensation and associated issues.
Any such blockages should be removed
as part of a retrofit project, and care must
be taken to avoid blocking up ventilation
routes with insulation, and to increase
ventilation provision if necessary.
Where the building is in an area
with high levels of radon, strategies for
ventilation (both sub-floor and for the
main building), airtightness and insulation
will require particular consideration.
SAFEGUARDING PERFORMANCE
‘Despite all efforts made in its provision,
ventilation is still one of the most difficult
aspects to safeguard in use.’ (Designing
Out Unintended Consequences, see
Further Information)
Once a ventilation system has
been chosen, the key question is: how
can its operation and performance
be maintained in the long term? Or,
more simply, how much risk can be
designed out? This is a vital question,
and covers the following considerations:
• Design – is the designer experienced
in traditional building retrofit and do
they understand the systems under
consideration?
• Installation and commissioning
(particularly for higher-end
ventilation systems) – is a specialist
installer being used, or at the
very least is the installer familiar
with the selected system? Leading
on from this, will the system be
commissioned by an expert?
• Control and use – are the end-
users engaged? How simple can the
system and its controls be made?
How foolproof is the system? How
will users know if it fails? Are the
maintenance needs clear? What are
the consequences of failure?
• Supplementing ventilation provision
(leading on from the previous
question) – is supplementary
ventilation available (use of windows,
for example) in case of system failure?
To maximise chances of success,
insulation must be considered alongside
airtightness and ventilation, following
a whole-building approach to retrofit.
Worst-case scenarios must be anticipated
and risk designed out accordingly – this
will often lead to simpler, more foolproof
solutions rather than overly-complicated
designs. The building must be considered
in the context of its users and their
behaviours. Experienced designers,
installers and commissioners must be
used, and occupants must be involved
from the outset and be made fully
aware of any behavioural impacts and
maintenance needs in the future.
At the heart of all this lies
understanding: ‘Regardless of your
reasons for retrofitting, the key to success
is understanding. Understand your home,
your lifestyle, your environment, your
priorities, the upgrade measures available,
the importance of careful planning and
detailing, and the whole-house approach
and joined-up process’. (A Bristolian’s
Guide to Solid Wall Insulation)
Further Information
Bristol City Council/STBA, A Bristolian’s
Guide to Solid Wall Insulation, BCC, 2015
)
C King and C Weeks, Designing Out
Unintended Consequences When Applying
Solid Wall Insulation, BRE, 2016
)
N May and N Griffiths, Planning Responsible
Retrofit of Traditional Buildings, STBA, 2015
)
Royal College of Physicians, Every Breath We
Take: The lifelong impact of air pollution, 2016
T Sharpe et al, Characteristics and Performance
of MVHR Systems, Innovate UK, 2016
R Sharpe et al, ‘Higher Energy Efficiency
Homes are Associated with Increased
Risk of Doctor-diagnosed Asthma in a UK
Sub-population’, Environment International,
Vol 75, 2015
Zero Carbon Hub, Ventilation in New Homes,
2016
NICHOLAS HEATH is an independent
sustainable energy consultant specialising
in traditional and historic building retrofit.
He is director of NDM Heath Ltd, associate
technical director of the Sustainable
Traditional Buildings Alliance, a qualified
SAP and BREEAM energy assessor and the
author of numerous research publications
and technical guides.
Condensation on a window pane is often a good
indicator of inadequate ventilation.
A 1930s copper cupola providing passive stack
ventilation on a former school building in Bath