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AD-L2
(2006) Regulations –
introduction
and compliance.
There is still a wide lack of understanding about the
full implications of the new Part L, yet it is essential for anybody
involved in the construction industry to have a firm grasp of what is
required, and to know what options are available to them in order to
achieve compliance.
The new England & Wales Part L regulations for conservation of fuel
and power (2006) edition came into force on 6th April 2006. Part F in
Northern Ireland which is similar to Part L for England & Wales
was implemented in November 2006. The implementation date for
the Section 6 requirements for Scotland is May 2007.
The focus for this
initial guidance is the new Part L2A (2006) for England & Wales,
which covers non-domestic new build. This amendment contains the greatest
changes. Assessment and compliance is no longer based round a simple
elemental approach to the building envelope together with controls on
air tightness and the efficiency of services. Instead compliance is now
based on a whole
building carbon emissions method, representing a wholesale change
in the method of assessing a building.
All previous compliance options
are withdrawn and what has to be used now is a software package – the SBEM (Simplified
Building Energy Model), or an approved alternative.
Despite its title SBEM is time-consuming and requires careful entry
of data and a considerable amount of organisation and pre planning
especially relating to the division of the building into distinct energy
zones.
Complexities of SBEM
In the first place, compliance
can only be achieved by assessing the whole
building, i.e. apart from the obvious elements such as the building
envelope and accessories such as windows, doors, rooflights etc aspects
such as lighting and controls; HVAC systems; domestic hot water systems
and other services that may require pumps or other users of electrical
input; and automated controls for the building in general, together
with the benefits of using renewable energy sources all have to be
considered.
So ultimately, whatever software
tool is being used will require inputs of the following parameters
– |
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Detailed thermal characteristics
of envelope – including
geometry, elements and junction details. |
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Design value for airtightness. |
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Heating installation details. |
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Air conditioning details. |
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Ventilation – i.e. Naturally
or mechanically ventilated. |
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Fixed lighting. |
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Occupancy type. |
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Provision of renewable energy sources. |
There are two stages to calculating compliance – first, the target
carbon dioxide emission rate (TER) needs to be ascertained.
The TER is defined in the Regulations as: “the minimum energy
performance requirement specified in Regulation 17B. It is the mass of
CO2 emitted per year per square metre of the total useful floor
area of the building(kg/m²/year)”.
It is calculated using a notional building model based on the 2002 standards,
then building in an improvement of 28% for air conditioned or mechanically
ventilated buildings, or 23.5% in the case of naturally ventilated buildings.
The
next stage is that the building carbon dioxide emission rate (BER,
which is the actual, as built performance of the building) must be calculated
using the same tool and must be no worse than the designed TER.
Achieving compliance
With so many options available
for carbon dioxide savings, the key question for any designer is ‘how
do I achieve the most reliable and cost effective compliance?’ It
is important that designers have an appreciation of what contribution
changing the specification of components and services can make towards
the target saving. It is of prime importance to adopt that way of thinking
and get used to a far more holistic approach to building energy design.
Increasing
U-values is not cost-effective
Consultants have conducted trials with the SBEM model for EPIC that indicate
that the contribution from increasing the thickness of a cladding system
(U-value) is only around 1% towards the BER figure. This compares with
a potential gain of as much as 11% by improving the airtightness. Greater
thicknesses increase cost, reduce design space and flexibility, and
introduce potential construction difficulties and costs both at junctions
and in relation to windows, doors and other accessories.
The
new regulations require some contribution to be made by improving U-values
but the effect is limited by the law of diminishing return. In light of
this, EPIC’s recommendation is to design to the default values set
out in AD-L2A (2006) or to a maximum thickness equivalent to 0.20 W/m²K
for roofs and 0.30W/m²K for walls.
Areas of greatest cost savings
In
view of the difficulties with the current version of SBEM it is
not yet possible to be precise about the benefits gained from improvements
in other areas, but the following general advice does give a strong
indication of where the most effective savings could be achieved: |
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Designing for low air permeability
will be a very important element of cost effective compliance.
The maximum allowable value is 10 m³/hour/m². Designing to
an air permeability of 5 m³/hour/m² could
make a significant contribution to achieving the TER. |
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Designing to reduce electricity
consumption can play a key role in achieving compliance. The use
of photoelectric dimming and occupancy light switching can achieve
significant savings. Optimisation of lighting controls in conjunction
with rooflight/glazing areas is critical. |
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Use of efficient building services, particularly in respect
of high boiler efficiencies can make a key contribution to achieving
the TER. |
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The use of thermally efficient junction details plays a significant role in compliance, particularly for smaller buildings where the proportion of detailing to main roof / wall area is high. The panel manufacturer’s recommended details should be used and the thermal transmittance data used in the calculations. |
The items above are the key areas to look at to achieve the most cost
effective compliance. Meanwhile, the release of an amended SBEM will
enable clearer design guidance to be published. The latest SBEM program
and user guide can be downloaded from the following link: www.ncm.bre.co.uk.
Whole life performance – the benefit of insulated
panels
The next big step change to take into account is the fact that
the new Regulations, in line with the Energy Performance of Buildings
Directive (EPBD), require that buildings perform as designed and retain
that defined level of performance throughout the life of the building.
The whole purpose of both the EPBD and the new Regulations is to encourage
the conservation of energy and thereby control environmental emissions
from the building. It is essential therefore, that the building in terms
of its fabric and services works at a high level of efficiency, not only
meeting these requirements on day one, but over the life of the building.
Insulated
panels are a major contributor to achieving this objective and enable
the designer to retain control of the building and the
building services by offering a guaranteed performance and high
level of security. Panels not only ensure a building fabric
of excellent and controlled thermal performance but, together with a
range of approved details, a level of air tightness that exceeds the
regulatory requirements. Having absolute surety of these main characteristics
means that the building HVAC services can be designed to work at maximum
efficiency. Control of services that are major users of energy and are
the primary source of emissions means easier compliance with AD-L2 (2006).
One
of the key characteristics of insulated panels is the build quality.
Panels are a one-piece component that are subject to factory controls
and constant checks, thereby ensuring that quality is built-in and can
be guaranteed. The metal facings in combination with the closed cell
nature of the insulation component mean that the designed properties
are retained for the life of the product. The highly engineered panel-to-panel
joint detail also helps to ensure the quality of the system on site.
Building energy costs
Although the main focus is currently
on how to achieve compliance in meeting the requirements of AD-L2 (2006)
for both new build and refurbishment, the continuing rise in the cost
of energy has placed renewed emphasis on the pure thermal performance
of buildings This is separate from the total building assessment for
which the main emissions producer is electricity. Under AD-L2(2006) and
the EPBD, energy audits will be conducted during the life of a building
and details on operational heat energy costs will be readily available
to the building owner or occupier as part of the asset rating of the
building.
Numerous studies over the past 20+ years
have shown the substantial benefits that can be achieved in heating energy
costs by moving to an insulated panel clad building. In certain cases
payback periods as low as 18 months have been achieved for the re-cladding
of buildings.
Footnote:
EPIC has been a leading member of the Working Group advising ODPM on
the development of the new AD as it affects lightweight industrial
framed buildings and the use of metal cladding systems.
EPIC has been a
leading member of the advisory committee working with BRE on the development
of the calculation methodology and has been involved in all the trials
of the SBEM programme.
EPIC together with MCRMA (Metal
Roofing and Cladding Manufacturers Association) has prepared Technical Paper TP17 (see link below) as a 2nd
tier guidance document on metal roofing cladding systems that is integral
to the new regional Regulations. This document gives guidance on the calculation
methodology, thermal performance, approved detailing and associated transmittance values and air tightness of buildings and aspects
relating to compliance.
EPIC is a leading authority
on building envelope issues for the important industrial, retail, distribution
and leisure sectors of the construction industry.
EPIC will continue to stay well informed about developments
in the industry, and will make that information publicly available.
References:
Approved Document L2A: Conservation of Fuel and Power
(New Buildings
Other Than Dwellings) (2006 Edition)
Download:
MCRMA/EPIC Guide
– Technical Paper TP17
Links:
Department for Communities
and Local Government (DCLG)
AD-L2A
AD-L2B
SBEM
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Also in this section:
Building regulations | Air
tightness testing | Sustainability |
