Part L2B and F2
Thermal Regulations for existing buildings other than dwellings
(England, Wales and Northern Ireland) 2006
Approved Document L2B
The new edition of the Approved Document
retains an elemental method of demonstrating compliance, although
in some cases, there is an option to use the SBEM calculation
method to show that the overall energy performance of the whole new
or altered building is no worse than it would be if the elemental
method were used. In addition, for extensions, it is possible to
use a weighted U-value calculation to trade-off between different
elements of the construction.
Technical Standard F2
The regulations for Northern Ireland are
identical to those for England and Wales. The information on pages
82-95 will therefore also apply.
- The guidance is set out in relation to three
classes of building work:
- Extensions to existing buildings, including
conservatories
- Buildings created as a result of a material
change of use
- Thermal upgrading as part of material
alterations.
For each of these classes of work the Approved Document gives
relevant energy efficiency standards for:
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new thermal elements |
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replacement thermal elements |
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renovated thermal elements |
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retained thermal elements |
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controlled fittings (glazed elements) |
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controlled services |
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New thermal elements
When creating new thermal elements (eg in an
extension), reasonable provision should be made for energy
efficiency. The building fabric should also be constructed so that
there are no reasonably avoidable thermal bridges, nor is there
unreasonable unwanted air leakage.
Newly constructed thermal elements need to
meet the highest thermal insulation standards (see Table 18 on page
84).
Note: A thermal element is a wall, floor
or roof that separates the internal conditioned space from the
external environment. New thermal elements are mainly constructed
in extensions, but also occur when a building has a change of
use.
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Replacement thermal elements
When replacing thermal elements, reasonable
provision should be made for energy efficiency. The building fabric
should also be constructed so that there are no reasonably
avoidable thermal bridges, nor is there unreasonable unwanted air
leakage.
Replacement thermal elements are replacements
for existing elements in an existing building. For pitched roofs,
the U-value standards are the same as for new thermal elements, but
for flat roofs, walls and floors, the standards are not as
demanding (see Table 18 on page 84). As for newly constructed
thermal elements, steps need to be taken to demonstrate compliance
in respect of thermal bridging and unwanted air leakage.
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Renovated thermal elements
When more than 25% of the surface area of an
existing element is to be renovated, reasonable provision should be
made for energy efficiency.
Renovation means the provision of a new
physical layer in the element, or the replacement of an existing
layer, but excludes paintwork. Examples of renovation include:
- Addition of a new insulating/ weatherproofing
layer
- Replacement of a slate roof covering
- Removal of plaster on a masonry wall and
replacement with dry lining
- Replacement of felt on a flat roof
- Removal of lath and plaster ceilings and
replacement with plasterboard.
Renovated thermal elements have the same basic
standards as replacement elements, but there is the possibility of
a lesser standard being acceptable if the required U-value cannot
be achieved without compromising technical, functional or economic
feasibility (see notes to Table 18 on page 84).
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Retained thermal elements
When part of the existing opaque fabric
becomes part of the thermal envelope when it was not before, it is
categorised as a retained thermal element and reasonable provision
should be made for energy efficiency.
A retained thermal element is an element which
in the existing building has no thermal insulation requirement but,
as a result of the improvement work, becomes an element bounding a
conditioned space.
Retained thermal elements need to meet the
same basic thermal insulation standards as renovated or replacement
thermal elements, where their existing U-values are worse than what
are called “threshold values”, see page 84.
However, there is an exception for existing
cavity walls, where it is thought reasonable for an existing
masonry cavity wall with a nominal 50mm air space to be upgraded to
a less stringent standard, ie by using retrofit cavity insulation.
Another circumstance where a lesser provision might be acceptable
is where the weight of the additional insulation might not be
supported by the existing structure.
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Controlled fittings
When a controlled fitting is to be provided
either as a new or replacement item, reasonable provision should be
made for energy efficiency.
Overview
Controlled fittings, defined as windows, roof
windows, rooflights or glazed doors, should be draught-proofed
units whose weighted-average performance is no worse than is shown
in Table 19 on page 85, where column (a) applies to new extensions
and column (b) to replacement fittings or new fittings installed in
an existing dwelling. Unless otherwise stated, the U-values are for
the whole unit, including the frame. Although not shown in the
table, the upper or threshold limit when calculating an overall
weighted U-value, or the limit above which fittings need to be
replaced in a building subject to a change of use, is 3.3
W/m2K.
It should be noted that slightly less
demanding U-values may be used for buildings subject to high
internal heat gains and that high usage entrance doors are excluded
from the requirements when being replaced as part of consequential
improvements or as a result of a change of use.
The U-values of controlled fittings can be
taken as standard values from the SBEM database. Alternatively, use
the manufacturer’s data, or failing that refer to Table 6e of SAP
2005, which has a comprehensive list of domestic window
constructions.
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Controlled services
When controlled services are to be provided,
replaced or extended, reasonable provision should be made for them
to be energy efficient and to have effective controls.
Building services need to comply with the
detailed guidance in paragraphs 38 to 68 of the Approved
Document.
Provisions are included for:
- Central plant including boilers, chillers and
air handing plant, which need to be effectively controlled, metered
and commissioned
- The insulation of pipes and ducts (a
specialist area of Knauf Insulation)
- Fixed internal lighting.
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How to comply
The options that the designer or builder needs
to work through to demonstrate compliance are described below.
Table 18 summarising the required thermal insulation standards is
on page 84.
This section concentrates principally on
standards for the building fabric.
Providing information
Provide operating and maintenance instructions
to enable the building and its services to be operated in an energy
efficient manner. When the work is completed, the owner of the
building should be provided with an updated Log Book with details,
in summary form, of:
- New, renovated or upgraded thermal
elements
- New fixed building services, their method of
operation and maintenance
- New energy metering
- Other details to help control and
monitor energy consumption.
Thermal bridging and air leakage
The avoidance of thermal bridging and
minimising unwanted air leakage is most easily achieved by using
accredited details or by showing that details achieve an equivalent
level of performance. A suitable way of demonstrating compliance
would be to submit a report by a qualified person that the
specified construction is appropriate and that the work has been
carried out to that specification.
Possible U-value relaxation
If a solution cannot meet the U-value
requirement for technical, functional or economic reasons, a
solution with the best possible U-value which has a simple payback
of less more than 15 years should be chosen. The U-value should not
be worse than the Threshold U-values in the table A below.
Table 18: U-values for thermal elements and
controlled fittings
| Application |
Cavity walls |
Other external
walls |
Warm pitched
roofs |
Cold pitched roofs |
Flat roofs |
Floors |
Notes |
| New elements in an extension (Table
6 (a) in AD L2B) |
0.30 |
0.30 |
0.20 |
0.16 |
0.20 |
0.22 |
Confirmation required that the
construction avoids thermal bridging and minimises air leakage Ð
see above |
| Replacement elements in the
existing building (Table 6 (b) in AD L2B) |
0.351 |
0.351 |
0.20 |
0.16 |
0.25 |
0.252 |
Confirmation required that the
construction avoids thermal bridging and minimises air leakage Ð
see above |
| Renovated elements in the existing
building (Table 7 (b) in AD L2B) |
0.551 |
0.351 |
0.20 |
0.16 |
0.25 |
0.252 |
Applies where more than 25% of the
element is to be renovated. Possible U-value relaxation for
technical, functional or economic reasons Ð see above |
| Retained elements in the existing
building (Table 7 (b) in AD L2B) |
0.553 |
0.35 |
0.20 |
0.16 |
0.25 |
0.25 |
Applies to an element that becomes
a thermal element when previously it was not. Possible U-value
relaxation for technical, functional or economic reasons Ð see
above |
| Threshold U-values Tables 3 and 7
(a) in AD L2B |
0.70 |
0.70 |
0.35 |
0.35 |
0.35 |
0.70 |
Absolute upper limits when
calculating an overall weighted U-value as an alternative way of
complying with the requirements for extensions. Upper limits when
seeking a U-value relaxation. The upper limits at which retained
thermal elements need to be upgraded |
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1 A lesser provision may be appropriate where meeting
such a standard would result in a reduction of more than 5% in the
internal floor area of the room bounded by the wall.
2 A lesser provision may be appropriate where meeting
such a standard would create significant problems in relation to
adjoining floor lev
1 A lesser provision may be
appropriate where meeting such a standard would result in a
reduction of more than 5% in the internal floor area of the room
bounded by the wall.
2 A lesser provision may be
appropriate where meeting such a standard would create significant
problems in relation to adjoining floor levels.
3 This only applies if the wall is
suitable for filling with cavity insulation. Where this is not the
case, treat as ‘Other external walls’.
els.
3 This only applies if the wall is suitable for
filling with cavity insulation. Where this is not the case, treat
as ‘Other external walls’.
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Table 19: Standards for controlled
fittings
| Fitting |
(a) Standard for new
fittings in extensions (U-value Wm2K) |
(b) Standard for new or
replacement fittings in an existing dwelling |
| Window, roof window or
rooflight* |
1.8 (whole unit) or 1.2
(centre-pane) |
2.2 (whole unit) or 1.2
(centre-pane) |
| Plastic rooflights |
2.2 |
2.2 |
| Alternative option for windows in
buildings that are essentially domestic in character** |
Window energy rating or Band D |
Window energy rating of Band E |
| Entrance doors for people where the
door has more than 50% of its internal face area glazed |
2.2 |
2.2 (whole unit) or 1.2
(centre-pane) |
| Entrance doors for people where the
door has no more than 50% of its internal face area glazed |
3.0 |
3.0 |
| Vehicle access and similar large
doors |
1.5 |
1.5 |
| Roof ventilators (including smoke
extract ventilators) |
6.0 |
6.0 |
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* Display windows are not required to meet the standard
given in this table.
** For example, student accommodation, care homes and
similar uses where the occupancy levels and internal gains are
essentially domestic in character.
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Extensions
An extension is a new enclosure created either
completely outside the existing building or by enclosing a space
that is already partially enclosed, for example by adding a roof to
a courtyard or adding enclosing walls to the area below an
overhanging roof. It can be a conventional construction with
external walls, windows and a roof or it can be a conservatory.
However, if a conservatory is no more than 30m2 in area, it need
not to comply with Part L of the Building Regulations, although any
glazing needs to comply with Part N.
The definition of a conservatory is an
extension to a building that:
- has not less than three quarters of its roof
area and not less than one half of its external wall area, made
from translucent material, and
- is thermally separated from the building by
walls, windows and doors with the same U-value and draught
stripping provisions as provided elsewhere in the building.
If the extension is a conservatory, there are
standards for:
- the elements between the existing building
and the conservatory
- independent controls for any heating to the
conservatory
- the glazed elements of the conservatory
(U-values in column (b) of Table 19 on page 85)
- the opaque elements of the conservatory
(U-values as for renovated thermal elements in Table 18 on page
84).
The majority of the work for extensions will
be constructing new thermal elements. However, depending on the
design of the building, retained and/or replacement elements may
also occur in the existing part of the building. For the new
thermal elements of the extension, it is possible to comply by
meeting the U-value standards of Table 18 on page 84 and to limit
the area of glazed elements to the percentages shown in Table 20,
below.
Table 20: Opening areas in the
extension
| Building type |
Windows and personnel
doors as % of exposed wall |
Rooflights as % of area
of roof |
| Residential buildings where people
temporarily or permanently reside |
30 |
20 |
| Places of assembly, offices and
shops |
40 |
20 |
| Industrial and storage
buildings |
15 |
20 |
| Vehicle access doors and display
windows and similar glazing |
As required |
n/a |
Greater design flexibility
There are two alternative ways of complying
with Part L2B that offer greater design flexibility than adopting
the Elemental U-values:
a) Benefit from greater design flexibility by
ensuring that the areaweighted U-value of all elements in the
extension is no greater than that obtained by applying the relevant
U-values in Table 18 on page 84, provided that no element has a
worse U-value than the threshold values on page 84 and the glazed
area limits in Table 20 are not exceeded.
b) Use SBEM (see page 80) to demonstrate that
the calculated CO2 emission rate for the building with its
extension is no greater than the emission rate obtained by applying
the fabric insulation standards for the extension and the
insulation standards for the existing part of the building, taking
into account any consequential improvements.
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The Approved Document gives relevant energy
efficiency standards for:
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new thermal elements |
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replacement thermal elements |
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renovated thermal elements |
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retained thermal elements |
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controlled fittings (glazed elements) |
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controlled services |
A
flowchart to assess the insulation requirements for extensions can
be downloaded here
Consequential improvements
When constructing a new extension or when a
fixed building service is being installed or extended,
consequential improvements need to be carried out to increase the
energy efficiency of the existing buildings.
The aim is to ensure that when work is carried
out on large buildings the resulting development (as a whole) is as
energy efficient as possible within the constraints of technical,
functional and economic viability.
There are two aspects to consider in relation
to consequential improvements:
- Assessing the potential need to carry out
consequential improvements
- Determining the extent of the
improvements.
The assessment of the need for such
improvements relates to the floor area of the existing building and
whether new plant is to be installed or its existing capacity (per
unit area) is to be increased (see the flow diagram opposite).
The requirement for consequential improvements
results from the application of Article 6 of the European Energy
Performance of Buildings Directive (EPBD), which states that
“Member States shall take the necessary measures to ensure that
when buildings with a total useful floor area of over 1000m2
undergo major renovation, their energy performance is upgraded in
order to meet minimum requirements in so far as is technically,
functionally and economically feasible.”
Consequential improvements relate to:
- the opaque building fabric (thermal
elements)
- glazed elements such as windows, rooflights
and glazed doors (controlled fittings)
- if necessary, additional building
service improvements.
A
flowchart to assess the insulation requirements
for consequential improvements can be downloaded
here
The extent of consequential improvements
The extent of consequential improvements for
extensions is less demanding than where a new building service
(heating or cooling) is being installed, or where the installed
capacity (as measured in capacity per unit area) of an existing
service is increased.
Extensions
The cost of consequential improvements is
limited to 10% of the cost of the Principle works (ie the cost of
building the extension). The improvements should be selected from
those listed on the opposite page. The reason for consequential
improvements is to ensure that the opportunity is taken to upgrade
the existing part of the building when the new extension is
built.
Building services
Consequential improvements are triggered
when:
- A new fixed building service, such as air
conditioning, is installed for the first time
- The installed capacity of an existing service
is increased, as measured in capacity per unit area, such as when a
full heating system is installed during refurbishment
There is no limit on the cost of consequential
improvements when building services are installed. The flow chart
opposite sets out the degree of improvements that are required if
heating or cooling services are installed.
Where a scheme involves an increase in the
installed capacity of a heating system, it may be more
cost-effective to carry out some improvement to the thermal
performance of the building such that the heat loss is reduced to
the level that an increase in installed capacity is no longer
necessary - and therefore consequential improvements do not come
into play.
Similarly, rather than be forced to carry out
extensive consequential improvements if a new cooling system is
proposed, it may be more cost-effective to carry out sufficient
improvement measures that a cooling system is no longer needed.
The ‘threat’ of consequential improvements is
likely to cause designers and building owners to carry out more of
these kind of assessments, the end result being an improvement in
the thermal performance of the existing building stock.
Table 21: Upgrading retained thermal
elements
| Element |
(a) Threshold U-value
(W/m2K) |
(b) Improved U-value
(W/m2K) |
| Cavity wall |
0.70 |
0.55 |
| Other wall type |
0.70 |
0.35 |
| Floor |
0.35 |
0.25 |
| Pitched roof – insulation at
ceiling level |
0.35 |
0.16 |
| Pitched roof – insulation between
rafters |
0.35 |
0.20 |
| Flat roof or roof with integral
insulation |
0.35 |
0.25 |
| Note: this only applies if the wall is suitable for
filling with cavity insulation. Where this is not the case, treat
as ‘Other wall type’. |
A
flowchart to find out the extent of consequential
improvements can be downloaded here
Material change of use
Under recent amendments to the Building
Regulations, a change of use is material when a building (or part
of a building) is used as a hotel or boarding house, an
institution, a public building or a shop when previously it was
not.
A “shop” includes a restaurant, bar or public
house. A public building is generally a place of “public resort”,
such as a theatre, library, educational establishment or
church.
However, not every change of use of a building
is subject to the Regulations. For example, a change from domestic
use to office use is not subject to Building Regulations unless the
change includes a material alteration - in other words, someone can
use a room at home as an office without needing Building
Regulations approval, but if the change of use involves building
work, then Building Regulations approval is required.
When a building is subject to a change of use,
it is likely to involve renovating or upgrading existing thermal
elements and/or creating new thermal elements.
Any glazed units that have a worse U-value
that the threshold value of 3.3 W/m2K need to be brought up to the
standard for new or replacement fittings in an existing building –
see column (b) of Table 19 on page 85.
As for extensions, an alternative option is to
use the SBEM calculation method to demonstrate compliance. The
choices for complying with the Regulations, as well as details of
how to comply, are shown in the flow diagram opposite.
Greater design flexibility
There are two alternative ways of complying
with Part L2B that offer greater design flexibility than adopting
the Elemental U-values:
a) Benefit from
greater design flexibility by ensuring that the areaweighted
U-value of all elements in the extension is no greater than that
obtained by applying the relevant U-values in Table 18 on page 84,
provided that no element has a worse U-value than the threshold
values on Table 21 on page 90 and the glazed area limits in Table
20 on page 86 are not exceeded.
b) Use SBEM (see
opposite) to demonstrate that the calculated CO2 emission rate for
the building with its extension is no greater than the emission
rate obtained by applying the fabric insulation standards for the
extension and the insulation standards for the existing part of the
building, taking into account any consequential improvements.
The SBEM
The SBEM (Simplified Building Energy Method)
is a computer programme that provides an analysis of a building's
energy consumption. It has been developed by BRE for the ODPM and
is based on a set of CEN standards in order to comply with the EPBD
requirement for a National Calculation Method. It is accompanied by
a basic user interface - iSBEM.
The procedure for demonstrating compliance
with the Building Regulations for buildings other than dwellings is
by calculating the annual energy use for a proposed building and
comparing it with the energy use of a comparable 'notional'
building. The calculation makes use of standard sets of data for
different activity areas and calls on databases of construction and
service elements.
The SBEM calculates monthly energy use and
carbon dioxide emissions for a building and uses the building
geometry, construction, use, HVAC and lighting equipment. The SBEM
can be downloaded free from:
http://www.ncm.bre.co.uk/.
A
flowchart to find out the requirements for material change of
use can be downloaded here
Material alterations
Alterations are considered to be “material” if
during the period of the works, and on completion, they would
affect the existing building in respect of the “relevant
requirements” in the following parts of the Building
Regulations:
- Part A (structure)
- paragraph B1 (means of warning and
escape)
- paragraph B3 (internal fire spread –
structure)
- paragraph B4 (external fire spread)
- paragraph B5 (access and facilities for the
fire service)
- Part M (access to and use of buildings).
Thus, where work is done to an existing
building, the work itself must comply with all the current relevant
requirements of the Building Regulations, but the existing building
must also not be adversely affected.
Examples of material alterations are:
- Removing part of a load-bearing wall that
consequently requires the insertion of a beam to carry the
load.
- Adding partitions in an open-plan office in
such a way that additional work is necessary to maintain the means
of escape.
- Removing part of a wall that is not
loadbearing but which is necessary for fire resistance.
- Re-covering a roof with tiles that are
heavier than the originals such that there are structural
implications.
In respect of alterations that relate to
improved thermal insulation measures, the following examples
illustrate how the “relevant requirements” might be affected:
- Laying a new inverted (ballasted) roof as
part of the refurbishment of a multistorey building (A1 –
Structure)
- Adding rainscreen cladding while refurbishing
an office block (A1 – Structure, B4 – External fire spread).
- In respect of Part L2B, if any part of the
proposed work is designated as being “material”, it triggers the
need to upgrade thermal elements and glazed elements (controlled
fittings) to a standard, which depends on whether the elements are
to be replaced or renovated, or whether they are retained thermal
elements.
The choices for complying with the
Regulations, as well as details of how to comply, are shown in the
flow diagram opposite.
Note: Where a building is being renovated,
but none of the work is designated as being “material”, the work
should still meet the U-values for ‘Renovated elements’ listed in
Table 18 on page 84.
Approved Design Details
When creating new, or replacing old, thermal
elements, the Regulations require that reasonable provision be made
to minimise thermal bridging and reduce unwanted air leakage. For
non-domestic buildings of domestic-style construction, Accredited
construction details are best practice details for minimising
thermal bridging and air leakage.
For other forms of construction, the Approved
Document refers the reader to guidance in MCRMA technical reports†
for metal clad buildings.
† Downloadable from: www.mcrma.co.uk/papers.htm
Renovated thermal elements
When more than 25% of the surface area of an
existing element is to be renovated, (e.g. when carrying out a
material alteration and/or the work is as a result of a change of
use), reasonable provision should be made for energy
efficiency.
Renovation means the provision of a new
physical layer in the element, or the replacement of an existing
layer, but excludes paintwork. Examples of renovation include:
- Addition of a new insulating/weather-proofing
layer
- Replacement of a slate/tile roof
covering
- Removal of plaster on a masonry wall and
replacement with a dry lining
- Replacement of felt on a flat roof
- Removal of lath and plaster ceilings and
replacement with plasterboard.
Renovated thermal elements have the same basic
standards as replacement elements, but there is the possibility of
a lesser standard being acceptable if the required U-value cannot
be achieved without compromising technical, functional or economic
feasibility.
A
flowchart to find out the requirements for material
alterations can be downloaded here