Part L1B & F1
Thermal Regulations for new dwellings (England, Wales &
Northern Ireland) 2006
Approved Document L1B
The new edition of the Approved Document for
existing dwellings keeps an elemental method of demonstrating
compliance, although in some cases, there is an option to use the
2005 edition of the SAP calculation method. This will show that the
overall energy performance of the whole extended or altered
building is no worse than it would be if the elemental method were
used.
There is also more emphasis than before on
ensuring that the construction meets the thermal standards
established at the design stage and that the heating and hot water
systems are correctly commissioned.
Technical Document F1 Section 3
The Regulations for Northern Ireland are
identical to those for England and Wales. The information on pages
52-61 will therefore also apply.
The guidance is set out in relation to three
classes of building work:
- Extensions to existing dwellings, including
conservatories
- Dwellings 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 air leakage.
Newly constructed thermal elements need to
meet the highest thermal insulation standards (see Table 7 on page
54).
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 can 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 describe existing elements in an
existing building that need to be rebuilt. 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 7 on page 54). |
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Renovated thermal elements
When more than 25% of the surface area of an
existing element is to be renovated, (eg 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/weatherproofing
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 (see notes to Table 7 on page 54). |
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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.
An example of a retained thermal element is
where a party wall within a loft space of a terraced or
semi-detached house, which has no thermal insulation requirement,
becomes an element bounding a heated space once a new habitable
room is created within the loft 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 Table 7 on page 54. 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.
Controlled fittings, defined as windows, roof
windows, rooflights or glazed doors, should be draught-proofed
units whose area-weighted average performance is no worse than is
shown in Table 2 from AD L1B (reproduced as Table 8 on page 55),
where column (a) applies to new extensions and column (b) to
replacement fittings or new fittings installed in an existing
dwelling.
The U-values of controlled fittings can be
taken either as standard values from BRE Report BR 443, or as
specific values relating to the particular size and configuration
of the actual fitting. In the absence of other data, refer to Table
6e of SAP 2005.
The window energy rating designation is from the publication
Windows for New and Existing Housing, CE 66, published by the
Energy Saving Trust. |
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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.
Heating and hot water systems need to meet
certain standards of efficiency as recommended in the Domestic
Heating Compliance Guide and commissioned correctly with a
declaration to this effect being supplied to the local authority by
a suitably qualified person. It is envisaged that this declaration
will eventually become part of the Home Information Pack (see
Providing information, above).
Pipes and ducts need to be insulated at least
to the standards set out in the compliance guide referred to
above.
Knauf Insulation provides a wide range of
insulation products to meet this standard.
Mechanical ventilation systems need to perform
no worse than those described in the BRE Good Building Guide GBG
268 and any fixed household air conditioning system needs to have a
certain minimum efficiency.
In general, fixed lighting fittings should only be able to
receive fluorescent or compact fluorescent lamps, although halogen
lamps rated no more than 150W are acceptable as security
lamps. |
How to comply
An explanation of the different thermal
elements and controlled fittings are outlined below. Table 6
summarising the required thermal insulation standards is on page
51.
Providing information
Provide operating and maintenance instructions
to enable the building and its services to be operated in an energy
efficient manner.
The owner of the building should be provided
with a set of simple operating and maintenance instructions
explaining how to use the installed heating and hot water system to
achieve economy in use. The aim is that this information will
eventually form part of the Home Information Pack.
Windows and doors
In the table below, the heading ‘windows and
rooflights’ includes roof windows and the heading ‘glazed doors’ is
for doors that have more than half of their internal face area
glazed.
The U-value shown is the overall U-value when
the frame is included. Other acceptable standards are given in the
table below.
Thermal bridging and air leakage
The avoidance of thermal bridging and
minimising unwanted air leakage is most easily achieved by using
accredited details (see page 60) 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 Table 7.
Table 7: U-values for
thermal elements and controlled fittings
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Application
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Cavity walls
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Other external walls
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Warm pitched roofs
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Cold pitched roofs
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Flat roofs
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Floors
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Windows and rooflights
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Glazed doors
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Other doors
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Notes
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| New elements in an extension (Table
3 (a) in AD L1B) |
0.3 |
0.3 |
0.2 |
0.16 |
0.2 |
0.22 |
1.8 |
2.2 |
3 |
Confirmation
also required that the construction avoids thermal bridging and
minimises air leakage |
| Replacement elements in the
existing building (Table 3 (b) in AD L1B) |
0.351 |
0.351 |
0.2 |
0.16 |
0.25 |
0.252 |
2 |
2.2 |
3 |
Confirmation
also required that the construction avoids thermal bridging and
minimises air leakage |
| Renovated elements in the existing
building (Table 3 (b) in AD L1B) |
0.351 |
0.351 |
0.2 |
0.16 |
0.25 |
0.252 |
- |
- |
- |
Applies
where more that 25% of the element is to be renovated. Possible
U-value relaxation for technical, functional or economic
reasons |
| Retained elements in the existing
building Table 4 (b) in AD L1B) |
0.553 |
0.35 |
0.2 |
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 |
| Threshold U-values Tables 1 and 4
(a) in AD L1B |
0.7 |
0.7 |
0.35 |
0.35 |
0.35 |
0.7 |
3.3 |
3.3 |
3.3 |
Absolute
upper limits when calculating an area-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.
For controlled fittings, the upper limit above which windows, roof
windows and doors need to be replaced in a building subject to a
change of use. |
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
Table 8: Reasonable provision when
working on controlled fittings
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Fitting
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(a) Standard for new fittings in
extensions
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(b) Standard for new or replacement
fittings in an existing dwelling
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Window, roof window or rooflight
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U-value =1.8 W/m2K
OR
Window energy rating = Band D
OR
Centre-pane U-value =1.2
W/m2K
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U-value =2.0 W/m2K
OR
Window energy rating = Band E
OR
Centre-pane U-value =1.2
W/m2K
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Doors with more than 50% of their
internal face area glazed
|
2.2 W/m2K |
2.2 W/m2K |
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Other doors
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3.0 W/m2K |
3.0 W/m2K |
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. 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
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 with:
- 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 (as
column (b) in Table 8 on page 55)
- the opaque elements of the conservatory (as
replacement elements in Table 7 on page 54)
Clearly, the majority of the work for
extensions will be constructing new thermal elements. However,
depending on the design of the building, renovated, retained and/or
replacement thermal elements may also occur in the existing part of
the building – use the flow chart opposite to determine if this is
the case.
A flowchart to
assess the insulation requirements for extensions can be downloaded
here
New thermal elements
For the new thermal elements of the extension,
it is possible to comply by meeting the U-value standards (see
Table 7 on page 54) and by limiting the area of glazed
elements.
Alternatively, in order to benefit from
greater design flexibility it is possible either to use an
area-weighted average U-value calculation for the extension or use
SAP 2005 to demonstrate compliance for the existing building, plus
the extension.
If the area-weighted average U-value
calculation method is chosen the Threshold U-values should not be
exceeded (see page 54).
The choices for complying with the
regulations, as well as details of how to comply, are shown in the
flow chart opposite.
Greater design flexibility
There are two alternative ways of complying
with Part L1B that offer greater design flexibility than adopting
the Elemental U-values:
- Ensure that the area-weighted U-value of all
elements in the extension is no greater than that obtained by
applying the relevant U-values from Table 7 on page 54, provided
that no element has a worse U-value than the Threshold U-values in
Table 6 on page 51 and the glazed area limits are not
exceeded.
- Use SAP 2005 to demonstrate that the calculated CO2
emission rate for the dwelling with its extension is no greater
than the emission rate obtained by applying the fabric insulation
standards for the extension and the estimated standards for the
existing part of the building.
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 dwelling, or a series of dwellings when
previously it was not.
Typically, for housing, this could mean
creating a dwelling (or dwellings) from a building with a previous
non-domestic use, eg a shop or industrial building. It can also
mean converting a single dwelling into flats, or increasing (or
reducing) the number of dwellings in a building. When a building is
subject to a change of use, it is likely to involve creating new
thermal elements, renovating or replacing existing thermal elements
or upgrading other existing elements to be thermal elements.
Any glazed units that have a worse U-value
than the threshold value of 3.3 W/m2K need to be brought up to the
standard for new or replacement fittings in existing buildings, see
column (b) in Table 8 on page 55.
The choices for complying with the
regulations, as well as details of how to comply, are shown in the
flow chart opposite.
Greater design flexibility
There are two alternative ways of complying
with Part L1B that offer greater design flexibility than adopting
the Elemental U-values:
- Ensure that the area-weighted U-value of all
elements in the extension is no greater than that obtained by
applying the relevant U-values from Table 7 on page 54, provided
that no element has a worse U-value than the Threshold U-values in
Table 6 on page 51 and the glazed area limits are not
exceeded.
- Use SAP 2005 to demonstrate that the
calculated CO2 emission rate for the dwelling with its extension is
no greater than the emission rate obtained by applying the fabric
insulation standards for the extension and the estimated standards
for the existing part of the building.
A
flowchart to assess 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, t
he 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
- Altering a three-storey house in such a way
that additional work is necessary to maintain the means of escape
from the third storey
- 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. Inrespect of alterations that relate to improved
thermal insulation measures, the following examples illustrate how
the “relevant requirements” might be affected:
- Creating a dormer window for a
room-in-the-roof loft conversion (A1 – Structure, B1 – means of
escape)
- Adding rainscreen cladding while refurbishing
a block of flats (A1 – Structure, B4 – external fire spread)
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 chart opposite
A
flowchart to assess the requirements for material alterations can
be downloaded here
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.