February Refurb and Renew magazine

Building Envelope |
Refurbs offer flexible opportunities
to focus on fabric to meet Part L
Successive revisions to Part L of the Building Regulations have raised the bar on energy efficiency for refurbishment projects. Such
schemes present an opportunity to focus on improvements to the building fabric which mitigate the need to incorporate renewable
technologies, and which can be more straightforward to achieve than in new builds. Graham Suttill, Energy Assessor at Darren Evans
Assessments reports.
Graham
Suttill
Aircrete wall
with brickwork
22
The revision to Part L of the Building Regulations
in 2013 raised the bar for the industry
significantly, requiring an additional 6%
improvement required on CO2 emissions over
that required by 2010 Part L. However for
domestic refurbishment projects there is no
Building Regulation requirement to meet the
Target Emission Rate (TER) which is required for
new builds, although depending on the Part L1B
route to compliance followed the emissions can
play an important role.
The most straightforward way to achieve Part L1B
compliance is to meet the U-value requirements
for retained and new thermal elements of the
dwelling. The U-values for new thermal elements
under Part L1B are in line with the requirements
for a new build house with the exception of the
external wall which requires a slight improvement
under L1B.
The retained thermal elements are slightly
different, having a ‘threshold’ U-value. If the
element U-value is below that of the threshold
before any work begins, then improvement is not
required. However if the retained element is
above the threshold the thermal efficiency must
refurb| RENEW Jan / Feb 2O16 issue 8955
be improved. The improved U-values required are
again almost in line with new build standards with
the exception of cavity walls where a target U-
value of 0.55 is required; this can normally be
achieved through retrofitting blown cavity
insulation.
The challenge in meeting the target U-values can
arise in the refurbishment of historic buildings. A
common issue that arises is the solid walls of
these period buildings should be insulated to
achieve a U value of 0.30 - typically achieved with
60mm+ insulated plasterboard. Where original
features are required to be retained this is not an
option. In this instance there are two options
available: a 15 year payback calculation or a
notional and proposed SAP calculation. The
payback calculation involves a feasibility study to
see if cost savings from the proposed measure
would cover the cost of purchase and installation
within 15 years.
The second and most preferred option in our
experience is to provide a notional and proposed
calculation to demonstrate a CO2 reduction is
being achieved. The notional calculation is of a
Building Regulations-compliant dwelling which is
modelled in SAP with the CO2 emissions
calculated. Then the proposed dwelling is
calculated which might for example have an
external wall U-value which is failing Part L but
other improvements elsewhere which go beyond
the Building Regulations standard, for example
improved heating efficiencies or controls. If the
CO2 emissions are less on the proposed
calculation than the notional, the building passes
Part L. In effect, this allows the extra CO2
emissions from a failing element to be offset
elsewhere in the calculation.
In addition to the targets on U-values for the
building fabric which are required to be met by
for Part L when undertaking a refurbishment,
there are also minimum efficiencies required for
heating systems and certain standards for heating
controls. These are outlined in the Government’s
Domestic Building Services Compliance Guide.
In essence it is much easier to achieve
compliance for a refurbishment than a new build
property, primarily due to the lack of CO2
emissions targets but also the degree of flexibility
in offsetting emissions that Part L1B allows.
www.darren-evans.co.uk