Accredited Construction Details
Accredited Construction Details (ACDs) have been developed to help the construction industry achieve the performance standards required to comply with the energy efficiency requirements (Part L) of the Building Regulations.
The details and introductory section of this document focus on the issues of insulation continuity (minimising cold bridging) and airtightness. They are not intended to provide any detailed guidance on other performance aspects such as vapour control and ventilation, which must also be considered by the design and construction team.
The details contain checklists which should be used by the designer, constructor and building control body to demonstrate compliance. The details have been grouped by generic construction type. It is strongly recommended that the introductory section ‘Accredited Construction Details’ is read in conjunction with the particular set of ACDs, in order to better understand the principles underpinning the details themselves.
Above information is from the Planning Portal website.
However since the 2010 & 2014 Part L changes have been in force the methods of achieving compliance have changed.
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Accredited Construction Details
Before the 2010 changes, it was commonly assumed that new dwellings followed the guidance for Accredited Construction Details which can be found on the Planning Portal website. In addition for a higher specification dwelling, designers would use guidance on the Energy Saving Trust website. These are known as Enhanced Construction Details.
Since the 2010 changes and more so the 2014 changes, Thermal modelling has been introduced as a way of achieving compliance along with the Planning Portal, Enhanced and manufacturers details.
The details that need to be justified under the new changes are as follows.
Came into force 6th April 2014 – Applicable to new dwellings application on or after that date.
| External Wall Junctions | Ref | Junction Detail | Accredited Ψ (W/m·K) |
Default Ψ (W/m·K) |
|---|---|---|---|---|
| External Wall Junctions | E1 | Steel lintel with perforated steel base plate | 0.50 | 1.00 |
| External Wall Junctions | E2 | Other lintels (including other steel lintels) | 0.30 | 1.00 |
| External Wall Junctions | E3 | Sill | 0.04 | 0.08 |
| External Wall Junctions | E4 | Jamb | 0.05 | 0.10 |
| External Wall Junctions | E5 | Ground floor (normal) | 0.16 | 0.32 |
| External Wall Junctions | E19 | Ground floor (inverted) | 0.07 | |
| External Wall Junctions | E20 | Exposed floor (normal) | 0.32 | |
| External Wall Junctions | E21 | Exposed floor (inverted) | 0.32 | |
| External Wall Junctions | E22 | Basement floor | 0.07 | |
| External Wall Junctions | E6 | Intermediate floor within a dwelling | 0.07 | 0.14 |
| External Wall Junctions | E7 | Party floor between dwellings (in blocks of flats) a) | 0.07 | 0.14 |
| External Wall Junctions | E8 | Balcony within a dwelling, wall insulation continuous b) | 0.00 | 0.00 |
| External Wall Junctions | E9 | Balcony between dwellings, wall insulation continuous b) c) | 0.02 | 0.04 |
| External Wall Junctions | E23 | Balcony within or between dwellings, balcony support penetrates wall insulation |
1.00 | |
| External Wall Junctions | E10 | Eaves (insulation at ceiling level) | 0.06 | 0.12 |
| External Wall Junctions | E24 | Eaves (insulation at ceiling level - inverted) | 0.24 | |
| External Wall Junctions | E11 | Eaves (insulation at rafter level) | 0.04 | 0.08 |
| External Wall Junctions | E12 | Gable (insulation at ceiling level) | 0.24 | 0.48 |
| External Wall Junctions | E13 | Gable (insulation at rafter level) | 0.04 | 0.08 |
| External Wall Junctions | E14 | Flat roof | 0.08 | |
| External Wall Junctions | E15 | Flat roof with parapet | 0.56 | |
| External Wall Junctions | E16 | Corner (normal) | 0.09 | 0.18 |
| External Wall Junctions | E17 | Corner (inverted – internal area greater than external area) | -0.09 | 0.00 |
| External Wall Junctions | E18 | Party wall between dwellings c) | ..0.06 | 0.12 |
| External Wall Junctions | E25 | Staggered party wall between dwellings c) | 0.12 |
| Junctions with party wall | Ref | Junction Detail | Accredited Ψ (W/m·K) |
Default Ψ (W/m·K) |
|---|---|---|---|---|
| Junctions with party wall | P1 | Ground floor | 0.16 | |
| Junctions with party wall | P6 | Ground floor (inverted) | 0.07 | |
| Junctions with party wall | P6 | Intermediate floor within a dwelling | 0.00 | |
| Junctions with party wall | P3 | Intermediate floor between dwellings (in blocks of flats) | 0.00 | |
| Junctions with party wall | P7 | Exposed floor (normal) | 0.16 | |
| Junctions with party wall | P8 | Exposed floor (inverted) | 0.24 | |
| Junctions with party wall | P4 | Roof (insulation at ceiling level) | 0.24 | |
| Junctions with party wall | P5 | Roof (insulation at rafter level) | 0.08 |
| Junctions within a roof or with a room in roof | Ref | Junction Detail | Accredited Ψ (W/m·K) |
Default Ψ (W/m·K) |
|---|---|---|---|---|
| Junctions within a roof or with a room in roof | R1 | Head of roof window | 0.08 | |
| Junctions within a roof or with a room in roof | R2 | Sill of roof window | 0.06 | |
| Junctions within a roof or with a room in roof | R3 | Jamb of roof window | 0.08 | |
| Junctions within a roof or with a room in roof | R4 | Ridge (vaulted ceiling) | 0.08 | |
| Junctions within a roof or with a room in roof | R5 | Ridge (inverted) | 0.04 | |
| Junctions within a roof or with a room in roof | R6 | Flat ceiling | 0.06 | |
| Junctions within a roof or with a room in roof | R7 | Flat ceiling (inverted) | 0.04 | |
| Junctions within a roof or with a room in roof | R8 | Roof to wall (rafter) | 0.06 | |
| Junctions within a roof or with a room in roof | R9 | Roof to wall (flat ceiling) | 0.04 |
Came into force 1st October – Applicable to new dwellings application on or after that date.
| External Wall Junctions | Ref | Junction Detail | Accredited Ψ (W/m·K) |
Default Ψ (W/m·K) |
|---|---|---|---|---|
| External Wall Junctions | E1 | Steel lintel with perforated steel base plate | 0.50 | 1.00 |
| External Wall Junctions | E2 | Other lintels (including other steel lintels) | 0.30 | 1.00 |
| External Wall Junctions | E3 | Sill | 0.04 | 0.08 |
| External Wall Junctions | E4 | Jamb | 0.05 | 0.10 |
| External Wall Junctions | E5 | Ground floor | 0.16 | 0.32 |
| External Wall Junctions | E6 | Intermediate floor within a dwelling | 0.07 | 0.14 |
| External Wall Junctions | E7 | Intermediate floor between dwellings (in blocks of flats) a) | 0.07 | 0.14 |
| External Wall Junctions | E8 | Balcony within a dwelling b) | 0.00 | 0.00* |
| External Wall Junctions | E9 | Balcony between dwellings a) b) | 0.02 | 0.04* |
| External Wall Junctions | E10 | Eaves (insulation at ceiling level) | 0.06 | 0.12 |
| External Wall Junctions | E11 | Eaves (insulation at rafter level) | 0.04 | 0.08 |
| External Wall Junctions | E12 | Gable (insulation at ceiling level) | 0.24 | 0.48 |
| External Wall Junctions | E13 | Gable (insulation at rafter level) | 0.04 | 0.08 |
| External Wall Junctions | E14 | Flat roof | 0.04 | 0.08 |
| External Wall Junctions | E15 | Flat roof with parapet | 0.28 | 0.56 |
| External Wall Junctions | E16 | Corner (normal) | 0.09 | 0.18 |
| External Wall Junctions | E17 | Corner (inverted – internal area greater than external area) | -0.09 | 0.00 |
| External Wall Junctions | E18 | Party wall between dwellings a) | 0.06 | 0.12 |
| Junctions with a Party Wall a) | P1 | Ground floor | 0.08 | 0.16 |
| Junctions with a Party Wall a) | P2 | Intermediate floor within a dwelling | 0.00 | 0.04 |
| Junctions with a Party Wall a) | P3 | Intermediate floor between dwellings (in blocks of flats) | 0.00 | 0.04 |
| Junctions with a Party Wall a) | P4 | Roof (insulation at ceiling level) | 0.12 | 0.24 |
| Junctions with a Party Wall a) | P5 | Roof (insulation at rafter level) | 0.02 | 0.04 |
Click the links to the below to see typical junction details. The Accredited Ψ values in the above table are from the Planning Portal website. These are standard details that apply to a lot of typical construction. The Enhanced details link will take take you to the Energy Saving Trust website and are a higher spec of details but help the DER/TER calculations a great deal.
a) Value of Ψ is applied to each dwelling
b) This is an externally supported balcony (the balcony slab is not a continuation of the floor
slab) where the wall insulation is continuous and not bridged by the balcony slab
* Value valid only if balcony support does not penetrate the wall insulation. If it does so
penetrate, either a Y-value must be calculated for the junction, or the SAP calculation uses
the default overall thermal bridging of y = 0.15
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