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BCD SPECIAL REPORT ON
HERITAGE RETROFIT
FIRST ANNUAL EDITION
15
THE STANDARD ASSESSMENT
PROCEDURE – RDSAP and SAP
The most common detrimental tool
imposed on domestic traditional buildings
is RdSAP – the reduced data standard
assessment procedure – which was the
basis for advice provided under the UK
government’s failed financial incentive
scheme, the Green Deal. Today its most
common use is in producing energy
performance certificates (EPCs) when
a dwelling is being let or sold, unless
it is listed. RdSAP will almost always
underestimate the current energy
efficiency of a traditional building and
therefore make recommendations for
works which are not necessary and which
may not make a building more energy
efficient. There are a number of reasons
why this is the case, but the main one
concerns the standardisation of U-values
which normally results in the thermal
performance of traditional construction
being underestimated. It becomes a
serious concern when this results in
inappropriate measures being deployed.
Despite these well-known flaws, the
imposition of RdSAP is being taken a
stage further. The
Private Rented Sector
Energy Efficiency Regulations (Domestic)
dictate that by April 2018 residential
properties cannot be let unless they
reach energy performance rating band E.
Property owners may have to undertake
works which deliver SAP points
determined by RdSAP. There is no reward,
however, for maintaining buildings
properly and appropriately and keeping
building fabric dry, all of which help to
make buildings far more energy efficient
and sustainable.
BREEAM and BREDEM
The Building Research Establishment’s
environmental assessment method
(BREEAM) for the refurbishment of
domestic buildings contains some very
good practice in considering a range of
issues, but where energy is concerned
it is flawed in using RdSAP for the
reasons stated above. Another version
of BREEAM has been developed for the
refurbishment of non-domestic buildings
where research by BRE has established
that heritage buildings do relatively well.
However, while RdSAP is not part of this
process, the full version of SAP is, and
again the standardisation of performance
data (such as the U-values of existing
walls) results in inevitable inaccuracy
where energy performance is concerned.
The BREDEM (BRE Domestic Energy
Model) is also based on SAP, hence its
potential unreliability in some areas, but
it could nevertheless provide some good
advice. Again, caution is needed and it
would be sensible to refer to
BS 7913: 2013
in order to reduce risks and take a more
robust approach.
PASSIVHAUS and ENERPHIT
Passivhaus is defined as: ‘… a building for
which thermal comfort can be achieved
solely by post-heating or post-cooling
of the fresh air mass, which is required
to achieve sufficient indoor air quality
conditions – without the need for
additional recirculation of air’. A version
has also been developed for retrofit and
refurbishment called EnerPHit which
Proposals are sometimes put forward for external wall insulation to be applied intermittently to the front elevation of individual houses in a terrace, despite there being
features of architectural interest. A heritage impact assessment may prevent alterations like this from happening. Aesthetics are not the only consideration under the
significance umbrella, but assessing significance will inevitably mean a greater likelihood of external wall insulation being applied to plain rendered elevations than to
very ornate elevations with bay windows. This terrace is somewhere between the two, which is where the more difficult decisions lie. (Photo: Historic Environment Scotland)
An EPC gives a property an energy efficiency rating
from A (most efficient) to G (least efficient). Figures
on the left give the SAP points required for each
rating band.