[NOTE: For other updates to the "Technical Guidance" document, please view the following posts:
- This post for the January 2013 updates.
- This post and this post for the October 2013 updates.
- This post for the April 2014 updates.
- This post for the April 2016 updates.
- This post for the April 2017 updates.
- This post for the September 2019 updates.]

Introduction:

The Department for Communities and Local Government (DCLG) has updated its "Permitted development rights for householders - Technical Guidance" document (note: this document provides advice relating to Part 1 of the GPDO). As such, the current and previous versions of the "Technical Guidance" document are now as follows:

• April 2017: Permitted development rights for householders - Technical Guidance (pdf) (link).
• April 2016: Permitted development rights for householders - Technical Guidance (pdf).
• April 2014: Permitted Development for Householders - Technical Guidance (pdf).
• October 2013: Permitted Development for Householders - Technical Guidance (as amended on 17/12/2013) (pdf).
• October 2013: Permitted Development for Householders - Technical Guidance (as amended on 20/11/2013) (pdf).
• October 2013: Permitted Development for Householders - Technical Guidance (as amended on 29/10/2013) (pdf).
• January 2013: Permitted Development for Householders - Technical Guidance (pdf).
• August 2010: Permitted Development for Householders - Technical Guidance (pdf).

The main differences between the current version (April 2017) and the previous version (April 2016) of the "Technical Guidance" document are as follows:

The phrases "the enlarged part of the dwellinghouse" and "[the] total enlargement" (pages 7, 16, 18-19, 21-24, 28-29, and 31):

Since the previous version of the "Technical Guidance" document was published in April 2016, limitations A.1(ja) and A.2(d) have been inserted, and conditions A.3(c), A.4(2), and A.4(5) have been amended, by SI 2017 No. 391 (link) on 06/04/2017. For info, these amendments mean that where a proposed extension would be joined to an existing extension, then some limitations and conditions apply to only the proposed extension, whereas other limitations and conditions apply to the combined structure (note: for more information, please view this previous post).

As such, a number of corresponding amendments have been made to the "Technical Guidance" document, as shown below.

On page 7 of the "Technical Guidance" document, in the section titled "General issues", the following definitions of the phrases "enlarged part of the house" [sic] and "total enlargement" have been inserted:

""Enlarged part of the house" - is the enlargement which is proposed to be carried out under Class A (pages 10-33)."

""Total enlargement" – is the proposed enlargement together with any existing enlargement of the original dwelling house to which it will be joined."

In other words, where a proposed extension would be joined to an existing extension, the above advice sets out that the phrase "the enlarged part of the dwellinghouse" applies to only the proposed extension, whereas the phrase "[the] total enlargement" applies to the combined structure.

For reference, the previous version of the "Technical Guidance" document set out that the phrase "the enlarged part of the dwellinghouse" applied to the combined structure, which was found to be incorrect by the "Hilton" High Court judgment (note: for more information, please view this previous post).

On page 16 of the "Technical Guidance" document, in the section relating to limitation A.1(e), a new paragraph has been added about how limitation A.1(ja) relates to limitation A.1(e). In my opinion, this new paragraph doesn't directly provide any new information (albeit see the note below about the sentence "Where a new extension is joined to an existing extension ...").

On page 18 of the "Technical Guidance" document, in the section relating to limitation A.1(f), a new paragraph and diagram have been added about how limitation A.1(ja) relates to limitation A.1(f). In my opinion, this new advice is confusing. The new diagram shows a proposed extension for which (in my opinion) 1) "the enlarged part of the dwellinghouse" would be contrary to limitation A.1(f), and 2) "[the] total enlargement" would be contrary to limitation A.1(ja). However, the new paragraph, which primarily relates to limitation A.1(ja), only states that the proposed extension would fail because of "the enlarged part of the dwellinghouse" (i.e. limitation A.1(f)). Furthermore, this new paragraph states that "it would not be possible to add [the proposed extension] without an application for planning permission", which is incorrect, because such an extension could be added subject to prior approval (i.e. via limitation A.1(g)).

On page 19 of the "Technical Guidance" document, in the section relating to limitation A.1(g), a new paragraph has been added about how limitation A.1(ja) relates to limitation A.1(g). In my opinion, this new paragraph doesn't directly provide any new information (albeit see the note below about the sentence "Where a new extension is joined to an existing extension ...").

On pages 21-22 of the "Technical Guidance" document, in the section relating to limitation A.1(h), several paragraphs have been amended to reflect how limitation A.1(ja) relates to limitation A.1(h). In particular, the amended paragraph on page 22 now states that the proposed extension shown within the second diagram on this page would fail because of "[the] total enlargement" (i.e. limitation A.1(ja)), rather than because of "the enlarged part of the dwellinghouse" (i.e. limitation A.1(h)). Note: In my opinion, there is the additional issue that, for this proposed extension, "the enlarged part of the dwellinghouse" would be contrary to limitation A.1(f)(ii) (note: for more information, please view this previous post).

On page 23 of the "Technical Guidance" document, in the section relating to limitation A.1(i), one of the paragraphs has been amended to reflect how limitation A.1(ja) relates to limitation A.1(i). In my opinion, this amended paragraph doesn't directly provide any new information (albeit see the note below about the sentence "if the proposed extension ... is being joined to a previous enlargement ...").

On page 24 of the "Technical Guidance" document, in the section relating to limitation A.1(j), a new paragraph has been added about how limitation A.1(ja) relates to limitation A.1(j). This new paragraph gives two examples of where a proposed side extension would fail because of because of "[the] total enlargement" (i.e. limitation A.1(ja)).

On pages 28-29 of the "Technical Guidance" document, in the section titled "Rear and side extensions", several paragraphs (and the annotation for the diagram on page 28) have been amended to reflect how limitation A.1(ja) relates to limitation A.1(j). In particular, the amended paragraph on page 28 (and the amended annotation) now state that the proposed extension shown within the diagram on this page would fail because of "[the] total enlargement" (i.e. limitation A.1(ja)), rather than because of "the enlarged part of the dwellinghouse" (i.e. limitation A.1(j)).

On page 29 of the "Technical Guidance" document, a new section relating to limitation A.1(ja) has been added. In my opinion, this new section doesn't directly provide any new information (albeit see the note below about the sentence "Where the proposed extension is to be joined to an existing extension to the original house ..."). Furthermore, this new section states that "[the] total enlargement" includes an attached existing extension "whether that was built following a planning application or under permitted development rights". In my opinion, the latter sentence might give the incorrect impression that "[the] total enlargement" does not include an attached existing extension that was erected unlawfully but has become lawful through the passage of time.

On page 31 of the "Technical Guidance" document, in the section relating to limitation A.2, a new paragraph has been added about how limitation A.2(d) relates to limitations A.2(b) and A.2(c). In my opinion, this new paragraph doesn't directly provide any new information (albeit see the note below about the sentence "Where an extension is to be joined to an existing enlargement to the original house ..."). Furthermore, on this page, the wording of the new limitation A.2(d) has been quoted, albeit that it has been written as limitation A.2(ca).

Note: The new advice on pages 16, 18, 19, and 22 includes the sentence "Where a new extension is joined to an existing extension ...", the new advice on pages 23 and 24 includes the sentence "if the proposed extension ... is being joined to a previous enlargement ...", the new advice on page 29 includes the sentence "Where the proposed extension is to be joined to an existing extension to the original house ...", and the new advice on page 31 includes the sentence "Where an extension is to be joined to an existing enlargement to the original house ...". In my opinion, these sentences make it clear that, for the purposes of the new limitations A.1(ja) and A.2(d), "[the] total enlargement" includes only those existing extensions that would be joined to the proposed extension (i.e. rather than all existing extensions). This means that, within these new limitations, the phrase "to which it will be joined" corresponds to the preceding phrase "any existing enlargement" (i.e. rather than the preceding phrase "the original dwellinghouse"). For more information about this (potential) ambiguity within the legislation, please view the "Note" in this previous post about the "Kensington" High Court judgment.

As a result of the above amendments, the following conclusions have been added to "The enlarged part of the dwellinghouse" topic and "[The] total enlargement" topic of the "GPDO Part 1 (All Classes) - LDC Appeal Decisions" document on this website:

• The "enlarged part of the house" [sic] is the enlargement which is proposed to be carried out under Class A.
  [Source: Permitted development rights for householders - Technical Guidance].
  [This advice is since April 2017].
• The "total enlargement" is the proposed enlargement together with any existing enlargement of the original dwelling house to which it will be joined.
  [Source: Permitted development rights for householders - Technical Guidance].
  [This advice is since April 2017].

In addition, the following conclusion has been added to ""More than one storey" / "More than a single storey"" topic of the "GPDO Part 1 (All Classes) - LDC Appeal Decisions" document on this website:

• Where a proposed first floor extension would be on top of an existing (non-original) ground floor extension, then “[the] total enlargement” has “more than a single storey” / “more than one storey” (i.e. rather than “a single storey”).
  [Source: Permitted development rights for householders - Technical Guidance].
  [This advice is since April 2017].
  [Note: The information on page 22 (“April 2017” version) of the above document states that "If a detached house has an existing, single storey, ground floor extension that was not part of the original house, and which extended beyond the rear wall by more than 3 metres, then it would not be possible to add an additional first floor extension above this without an application for planning permission - because the total enlargement of the house would then consist of more than one storey and would extend beyond a rear wall by more than 3 metres.".].

Other (insignificant) amendments:

• On page 4 ("Introduction"), the previous reference to Statutory Instrument (SI) 2016/332 has been removed (i.e. this page now simply refers to SI 2015/596 "as amended"). Furthermore, the previous footnote relating to Part 3 Class PA has been removed, and the dates set out by this footnote have been incorporated into the main text.
• On page 17 (relating to A.1(f)), the annotations "Front" and "Rear" have been added to the diagram.
• On page 23 (relating to A.1(j)), the annotation "This is the width of the original house ..." has been added to the diagram.
• On page 33 (relating to condition A.3(c)), the wording of the replacement condition A.3(c) has been quoted, albeit that no new advice about this condition has been added.
• On page 33 (relating to "Solid Wall Insulation"), the previous reference to "Solid Wall Installation" has been replaced with a reference to "Solid Wall Insulation".
• On page 44 (relating to E.1(e)), a reference to "... the whole development ..." has been replaced with a reference to "... the total development ...".

Additional notes:

• All links on the Planning Jungle website to the "Technical Guidance" document have been updated to ensure that they link to the current version of the document (i.e. the "April 2017" version).

Comments by the Planning Jungle website:

• In my opinion, this updated version of the "Technical Guidance" document is another missed opportunity by DCLG. Despite the fact that this is now the 8th version of the "Technical Guidance" document, it still doesn't resolve a number of significant ambiguities within the legislation that even government Inspectors are unable to interpret consistently. For example, 8 1/2 years after the legislation came into force (on 01/10/2008), it's still not possible to give a definite answer to the simple question "is it permitted development (on a typical house) to replace timber windows with UPVC windows?".
• DCLG could have identified most of these ambiguities by talking to Inspectors (or by referring to the documents on this website), and then could have taken the opportunity to resolve them via this updated version of the "Technical Guidance" document. Instead, most of these ambiguities still remain.