Following a lengthy review process with considerable industry involvement,
including comments from NES Ltd, the government have finally published a consultation
paper (1) that sets out proposals for changes to Part L of the Building Regulations
which deals with energy efficiency. A significant general change from the existing
regulations is the recognition of the need to improve the energy efficiency of
existing buildings. Thus, in future, changes such as replacing glazing and upgrading
of boilers will have to meet the same requirements as for new buildings. Allowances
will be made for dwellings that have efficient gas or oil fired heating systems
installed. Electric, solid fuel and inefficient gas or oil boilers will require
higher levels of insulation.
A further requirement will be the certification of heating and hot water
systems to show that they have been correctly installed and commissioned, and
the provision of operating and maintenance instructions for users.
Dr. Mark Gorgolwski, Architect and Environmental Consultant, has out lined
the key changes in a paper written for the NHER's September technical bulletin.
The aim of the proposals is to reduce carbon dioxide emissions from buildings
by up to 25%. It is predicted that the changes will lead to savings of 1.3 million
tonnes of carbon emissions per annum by 2010.
At the launch of the consultation document the construction minister, Nick
Raynsford, said
"Average building performance is poor by comparison with best practice
If implemented, the proposals would yield significant improvements in the energy
efficiency of new buildings and also in existing buildings when they are renovated."
The consultation paper sets out specific proposals for changes that, if accepted,
will be introduced in late 2001. Further improvements will be implemented 18 months
later. Proposals for possible future changes in 2005 and 2007 are also discussed
in the document.
A significant general change from the existing regulations is a widening of
the definition of a "material alteration" to bring more work on existing
buildings within the definition of "building work" in the Regulations.
This recognises the need to improve the energy efficiency of existing buildings.
Thus, in future, changes such as replacing glazing and upgrading of boilers will
have to meet the same requirements as for new buildings. Furthermore, work such
as substantial alterations to cladding, will have to meet the new air-tightness
and insulation requirements.
For new dwellings the main changes include
Significantly improved U-values in the elemental method, which will require
considerably higher levels of insulation. These will be introduced in two stages
the first probably in late 2001 and the second 18 months later.
A requirement for higher standards of envelope insulation for dwellings with
electric or poor efficiency gas and oil heating systems.
Adjustment of the target method to provide broadly similar overall performance
to the new elemental method U-values but with greater flexibility.
The inclusion of a "Carbon Index" method in place of the SAP energy
rating (but based on the SAP calculation) as an alternative method of demonstrating
compliance.
The use of the more rigorous and potentially accurate (but cumbersome) "Combined'
U-value calculation method as set out in BS 6946:19972 for U-value calculations.
Certification of heating and hot water systems to show that they have been
correctly installed and commissioned, and the provision of operating and maintenance
instructions for users.
A requirement for increased standards of detail design and site workmanship
to improve real building performance and to reduce the incidence of gaps in the
insulation, thermal bridging and poor air-tightness.
It is not proposed to introduce mandatory air-tightness testing of dwellings
at this stage. However, it will be necessary to demonstrate that air-tightness
has been addressed, and either "robust details" will need to be adopted,
or an air-tightness test carried out. The proposed air-tightness standard (10
m3/m2lhr @ 50 Pa) is not particularly demanding, though more attention to detailing
and site practice will be needed. It is likely that air-tightness testing will
become mandatory for dwellings within 4 to 5 years, and more demanding targets
will be set.
Overall, these are considerable improvements over the current Part L, and they
do take a significant step in the direction of those countries that have considerably
higher thermal standards than the UK. Furthermore, it is likely that the proposals,
along with other initiatives such as the Egan Report, will result in a move away
from the ubiquitous cavity wall construction. A variety of alternative construction
methods such as timber and steel framing, and others may become more attractive.
Framing provides a cost effectively solution that offers potentially high levels
of insulation and good air-tightness.
However, as is often the case, the details of how the proposals are implemented
are very important. There are a number of issues that are disappointing or are
currently still unclear. These will make a significant difference to the impact
of the final proposals. They include:
The large trade-offs that are still allowed between envelope elements and
heating system. Thus, it is still possible to specify external walls with a U-value
of 0.7 W/m2K and windows with U-values of 3.3 W/m2K as long as these are compensated
for by better standards in other elements or with an improved heating system specification.
It should not be necessary to put up with such poor performing elements, which
once built are difficult and expensive to upgrade.
Poorer U-values are allowed in return for smaller windows. This will tend
to lead to increased electrical use for lighting and reduce passive solar gains.
The energy performance of many dwellings would worsen if they go from 25% to 15%
glazing ratio and the wall U-value is increased to 0.45 W/m2K.
As currently set out; the "Combined" U-value calculation method
is unclear and ambiguous. There are various possible interpretations about how
to carry out calculations and clear guidance is needed. In particular it is important
that realistic values are laid down for the proportion of regular cold bridge
area in an element. The example calculation for a timber-frame wall in the consultation
paper assumes that the timber framing forms only 9.5% of the wall area. This is
unrealistic, as it does not include the wall plates, cripple studs and uninsulated
first floor areas. TRADA research in the UK suggests a figure of 15% while in
North America 19% is often used and figures of 25% to 40% have been found.
The air tightness standards are not very demanding and represent average air
infiltration standards for new UK housing. Thus, unfortunately, in the short term
the proposals are unlikely to lead to a serious reappraisal of construction practice
to improve air tightness, which would lead to the inclusion of an unbroken air
barrier next to the insulation as is required in other countries. It is likely
that for the time being, many poor practices, such as plasterboard on dabs without
any effective air barrier, and cold air penetrating to the warm side of the insulation
will continue to be seen.
1 Building Regulations - Proposals for Amending the Energy Efficiency
Provisions - A Consultation Paper issued by the Building Regulations Division,
DETR, June 2000 (available from DETR literature service 0870 1226-236)
2Building
Components and Building Elements Thermal resistance and thermal Transmittance
Calculation Method, BS EN ISO 6946:1997 (Available from the British Standards
Institute, 0181 9967000)
