House extensions Q & A DCP Section 12.2

This section is primarily concerned with extensions to the living accommodation of houses within conventional urban or suburban areas. This will consist of developments to the rear or side of the dwellinghouse, and includes front porches.

Q & A    12.2/10

Neighbouring occupiers of a pair of semi-detached houses wish to carry out symmetrical forward extensions sharing a common party wall. The local authority concerned does not object in principle but is concerned that it may not be able to ensure that each half is built simultaneously. Is there way of overcoming the local authority's fears through a planning condition or obligation?

This local authority may be constrained by the advice in Circular 11/95 which states that conditions requiring that the whole of a development is to be completed are likely to be difficult to enforce and should not normally be imposed. However, this guidance was probably not conceived with regard to the specialised type of situation that we have here and one can envisage a form of condition that would ensure a simultaneous and symmetrical development, such as would require no occupation of either extension until both are completed. If there are still doubts as to the suitability of such a condition, a section 106 planning obligation could doubtless be devised.

A local planning authority grants a planning permission for an extension that is within their guidelines relating to rear amenity space. A condition removes permitted development rights for further outbuildings in order to protect the amenity area. If the applicant were to build a structure at the end of the garden prior to starting the permitted extension, would there be breach of the condition? My opinion is that there is no breach provided the planning permission has not been implemented.

It is accepted practice that a condition cannot be breached if the development authorised by the permission upon which it is imposed has not been commenced. The only exception to this rule is in the case of standard time limits to which the permission itself is subject. In terms of breach of condition notices the law makes it clear that a notice may only be served on a person who is carrying out or has carried out development to which the condition relates.  Your question would appear to indicate a loophole in planning control, but I am not sure that it is one that is widely exploited. Have any other local authorities had cause for concern?


Until recently I worked for a local authority where the regular practice was to impose a condition which removed permitted development rights "prior to or during the construction of the development hereby approved". A further condition took away the effect of the permission itself if any freestanding building were erected prior to commencement of that permission. These conditions were most often used in cases of green belt development where the LPA was seeking to minimise potential impact on openness.

My authority has recently been advised by the Environment Agency to refuse planning permission for a two-storey extension encroaching closer than 5 metres to a watercourse. The Agency wishes to retain access to the watercourse to carry out its functions and protect the river environment.  The proposed extension replaces existing hardstanding and would be permitted development if single-storey.  There are no other planning objections and my question is whether it is a legitimate reason to refuse planning permission based on the Agency’s recommendation?  Under the terms of the Water Resources Act 1991 and the Land Drainage Byelaws 1981 the prior written consent of the Agency is required to undertake the development. Should not the issue of access be dealt with as a civil matter between that body and the land owner?

There seems to be no planning reason why planning permission should be refused for this development unless contrary to a provision in a local plan that the access or amenity of watercourses should be safeguarded. As there is no power of direction and other effective legislation secures that the requirements of the Environment Agency are met, I can see no compelling reason why the application should be refused planning permission on this one ground. Have any readers had experience of this situation?


In the Agency’s experience there are often relevant local plan provisions. In any event, the Agency would be concerned if planning officers did not give due consideration to its objection as a statutory consultee. This is notwithstanding whether there is other legislation under which the Agency’s specific consent is required, and this should be clarified in any particular case and not assumed by planning officers. The agency’s concerns may in themselves be relevant material planning considerations. Should a local authority decide to grant planning permission in circumstances where a further Agency consent is necessary, it might be advisable to draw the developer’s attention to this in a note to the permission.   The obtaining of planning permission does not, of course, in any way affect the Agency’s separate determination of a subsequent Water Resources Act/Land Drainage Act/Land Drainage Byelaws application.

When granting permission for a two-storey extension to a dwellinghouse with full permitted development rights, is it reasonable to impose a condition to prevent further windows at first floor level in a wall of the original dwelling, as well as the extension? In addition, could the authority refuse the application if the submitted plans show a window in a wall of the original dwelling that would give rise to an undue loss of privacy?

If the new window in the original dwelling is a direct consequence of the proposed extension, in that is needed to compensate for the loss of an existing window, and would result in unacceptable overlooking of adjoining property from a habitable room, in my opinion it would be reasonable to refuse the application. I also think that a condition to remove permitted development rights to prevent the insertion of such a window in the existing or extended dwelling would be justified, but only where there would be alternative natural lighting. In my view, such a condition would satisfy the relevant tests of Circular 11/95 and in particular the requirement that it should be necessary, reasonable and relevant to the development to be permitted. However, the use of high level windows or those glazed with obscure glass will often be an acceptable alternative.

I have recently come across a decision where permission was refused for a two-storey rear extension to a single dwellinghouse because there would be a loss of outlook from and light to windows to the side of the proposed extension to the same dwellinghouse. Is this a legitimate reason for refusal?

PPG1 explains that the planning system exists to protect the amenities of land and buildings in the public interest rather than to safeguard individual interests. It could be held that it is in the public interest to protect internal residential amenity levels for the benefit of existing or future occupiers, but only if it is judged that some problem that would concern land-use planning would follow. This is the line normally taken by the Planning Inspectorate. However, it is a little difficult to envisage such circumstances here unless the resulting living conditions were so bad as to make the dwelling unusable as part of the housing stock. In the absence of clear Government advice, the extent to which the planning system should control basic living requirements continues to be a matter for debate and it is fair to say that planning authorities and inspectors will often countenance lower levels of amenity for future occupiers than for existing residents affected by a development proposal.

My client wishes to extend both halves of a pair of semi-detached houses, which he owns, as part of an overall harmonious design.  The dwellings would continue to be occupied as separate residences. The authority argues that applications are required for each extension, as they relate to separate planning units.  However, I cannot see why the authority should not accept a single application. Is the authority right?

It is not uncommon for occupiers of semi-detached dwellings to promote a joint development where to extend one property without the other would cause problems of asymmetrical visual impact or harm to adjoining living conditions. Although the extensions could be considered separately, where they are interdependent and their acceptability turns on the completion of the entire development, clearly there must be some mechanism to ensure that this happens, such as through a planning obligation or a condition. If such circumstances apply in this case, even though each dwelling forms a separate planning unit, since they are in the same ownership I think a single application for a joint development would be appropriate.


Your reply did not address the fundamental point that the planning authority has no basis in law to refuse to entertain such an application. As an agent, when confronted with a similar situation I submitted separate applications as it is not possible to foresee the future. Circumstances could change within the lifetime of the permission and the landowner might want to sell off the houses individually with separate permissions. Where permission would only be given if both halves of a matching pair in different ownership are extended, the planning authority I mostly deal with has not been able to come up with a way of ensuring that both are done at once, so will not accept such an application. I understand that the difficulty is that it would require a condition that is out of the control of each applicant and a planning obligation is too complicated. I therefore advise potential clients wanting to do a joint application with a neighbour that if they do get a permission that relies on both sides being done together, they must be certain that the neighbour won't die, sell on, change their mind and so forth, because the permission will become worthless. So in my view it is better to get a single permission for each if possible. But perhaps you could explain how an obligation would work?

I can see no compelling reason why a planning condition or obligation could not negatively worded so as to prevent completion of the permitted extension until the other is substantially completed. The effect of this would be to ensure that they are carried out as a joint operation. However, this will only be appropriate where the extensions physically adjoin each other.

Further response

My authority had received applications from each of a pair of semi- detached bungalows for rear dormers. Both applications were refused and appealed. In granting permission for both developments, the inspector attached the following condition:

"Construction of the rear dormer shall not commence until a contract has been let for the construction of the dormer at [adjacent property] which is the subject of appeal"

The authority has also used section 106 agreements to overcome the same problem: requiring that each owner enters into an agreement that provides that their development is completed either prior to or within a specified number of months of the adjoining owner commencing their development.

Permission was granted in 1973 for a house followed closely by permission for a single-storey rear extension. The house and extension were constructed together in a single building operation, as evidenced by their continuous foundations and uninterrupted external brickwork. Do you agree that the original dwellinghouse in this case includes the extension?

Article 1(2) of the General Permitted Development Order (GPDO) 1995 defines "original" as meaning a building as existing on 1 July 1948 and, in relation to a building built on or after that date, "as so built". The latter words clearly cover the type of circumstances you describe. Therefore the extension forms part of the original dwellinghouse.


While I agree with your advice, if the foundations and walls are continuous they must have been built at the same time. Therefore, although they are now immune from action, both the dwelling and the extension must be unauthorised. Permission cannot be granted for an extension to a building that does not exist. If the house were built at the same time as the extension, the resulting building is not the house that had been permitted. The obvious solution would have been to have applied to build a different house type - the one with the extension. The applicants could then choose which house they built. This would also be the cheaper option because no fee is payable for the resubmission. I often encourage major house builders to apply for an estate of houses with conservatories, which are then optional extras, depending on customer demand. While this makes no difference to the query, it does raise an issue that many practising in development control must come across. Your views would be helpful.

I agree that planning permission should not be granted to extend a dwelling that has not yet been built. However, where separate permissions have been granted for a new house and for its extension before it is completed, it seems perverse and of little relevance to regard the built structure as being unauthorised.

A householder built a single-storey rear extension in 2000 as permitted development. He has recently completed a dormer loft conversion that would be permitted development were it not for the ground floor extension and which he accepts is unlawful. However, would this become lawful if the householder were to remove the rear extension? Or is the lawfulness of a development determined at the time of its completion, once the four-year immunity period has passed or when permission is granted? I can find no authority that governs such a situation and have heard differing opinions. IT.

For the reasons given in my advice to AS (Planning, 24 August, p25), if the ground floor extension is removed in my view this would make the loft conversion lawful. Paragraph 8.3 to Circular 10/97 explains that by virtue of Section 191(2) of the Town and Country Planning Act 1990 uses and operations are "lawful" if no enforcement action may be taken against them and they are not in contravention of any enforcement notice which is in force. This would apply once the time-limit for taking enforcement action has passed or the development is authorised by a permission, including that granted by a development order. PM. 


In Watts v Secretary of State for Transport, Local Government and the Regions 19/4/02, the court held that inherent in the GPDO was a degree of artificiality in that its availability depended on which works were done first. So if between the start of works and their conclusion the building was otherwise enlarged, improved or altered so that the cubic content of the resulting building together with the GPDO works would be more than relevant allowance, the GPDO works would cease to be protected. The court went on to find that prospective cubic content, however imminent, was to be ignored because once prospective cubic content became relevant one would be driven to accept as relevant that which might never exist as cubic content. It follows that prospective demolition must be ignored for the same reasons. The GPDO grants permission for development in the making not for the retention of that which has already been done. A number of inspectors have taken the same view. NW.

Further Response

In his reasoning PM relies on a different case (Planning, 24 August, p25). The two are distinguishable. In IT’s case the rear extension was not demolished before the dormer was constructed. The Article 3(1) permission enables development to commence and, provided it remains within the terms of that permission from the outset and during construction, the development benefits from the permission upon substantial completion. If it exceeds the permitted development limits it cannot benefit from the GPDO permission, is unlawful and can be enforced against. Albeit in different circumstances that is to be found in R (oao Watts) v Secretary of State for Transport, Local Government and the Regions [2002]. So the issue is whether an Article 3 permission can be gained retrospectively. I find nothing in the 1990 Act or the GPDO to suggest that it can and it is now too late to rely on the order’s protection through demolition. Of course a permission under s73A may be sought, but the dormer would stand to be considered on its merits with or without the rear extension. AK.

My local authority has recently granted permission for a substantial replacement dwelling with permitted development rights removed for extensions and outbuildings. However, before commencing any work the developer has constructed a detached garage adjoining the existing dwelling, and also a large outbuilding in the rear garden. It is accepted that both would be permitted development in relation to the existing house. The new garage is sited and designed so that it could become attached to the new house when built. The developer has declined to stop work and enforcement is being considered. Is there any legal scope to stop this blatant attempt to subvert planning control and to achieve, by the back door, a larger development than the council is prepared to accept? DG.

In this case the important point to establish is whether, at the time of the construction of the new buildings, the original house remained a lawful ‘dwellinghouse’ to which permitted development rights would still apply. Definitions in planning law do not provide an answer, but the court led tests for abandonment  of use may be applicable. If the original residential use  remains capable of resumption, and no works have been commenced  to demolish the house and implement the planning permission for a replacement dwelling, my feeling is that the building is still lawfully a ‘dwellinghouse’. I agree that what has taken place seems to be a cynical manipulation of the planning system. Forum will be very interested to hear of any reader’s experience with this issue.GH.

Part of our two storey house was demolished a few years ago and was replaced with a single storey building which occupied the same footprint. The demolished part existed in 1948.  We wish to add a first floor to the extension which would result in a building of similar form and volume to the original. There have been no other extensions to the property. Is planning permission required? TY.

Forum advice on this subject has always been that the cubic content of a formerly attached but now demolished part of an ‘original dwellinghouse’ may be offset when calculating permitted development rights for future extensions. This interpretation has been upheld on appeal in several instances , such as in (DCS Number 038-065-695). Therefore it would appear that express permission may not be required for your extension if none of the other Class A permitted development conditions are breached. However, the authority will doubtless need to be persuaded by evidence showing the extent of the original dwellinghouse. GH

I am dealing with a case where a condition was placed on a green belt replacement house stating that "no replacement floorspace, including  mezzanine floors, additional to that approved shall be created." I understand that the reason for the imposition of such an onerous condition was because the dwelling had used up the maximum available replacement policy floorspace. My client now wishes to create a mezzanine floor within the existing building envelope. There would be   no material alteration to fenestration and it is not intended to increase occupancy resulting in any intensification of use. It seems to me that there is a complete absence of harm to the green belt arising from my client’s proposal. Could this amount to a very special circumstance which would offset any possible pure policy objection? I would be interested to have an opinion on this and any other observations you may have. EA.

My first comment stems from the peremptory nature of the wording of the condition. A sounder version would read something like "No additional habitable floorspace, including mezzanines and roof space conversions, shall be created within the envelope of the building hereby approved without the  approval of the local planning authority". This quibble aside, I think that the imposition of such a condition is reasonable, provided that the planning authority is able to demonstrate that there would be potential green belt harm without it. However, having allowed a building of this size and bulk the planning authority is impotent to assert that the proposed mezzanine would cause any further visual impact, only that there would be a technical transgression of replacement floorspace policy. A stronger authority case could be mounted on the basis of potential green belt harm because the additional floorspace would enable great occupation levels, and hence increased activity such as the more frequent coming and goings of vehicles. Although your client does not intend to use the property in a more intensive way, this will be very difficult for a planning authority to secure with an enforceable condition.

I have looked at how inspectors have approached the matter at appeal in similar situations, and found that a few take a more dogmatic approach than many others. In one case it was reasoned that increased floorspace breaching development plan policy for replacement dwellings rendered it inappropriate in terms of PPG2 policy. This states that inappropriate development is by definition harmful. Others have held that floorspace controls are a crude tool and have taken a more pragmatic stance based on the realities of particular situations.

While I have seen cases where lack of harm has been argued as a ‘very special circumstance’  it is normally benefits that are taken to fall appropriately under this heading. GH.

We have a joint householder planning application for a two-storey front extension crossing two semi-detached properties in different ownerships. Both landowners are referred to as applicant and both have signed Certificate A. Our normal approach with joint applications would be for one applicant to take the lead to sign Certificate B and serve notice on the adjoining landowner. Notwithstanding, is there any impediment to us dealing with the application in the manner submitted? EE.

Technically, both parties should serve Certificate B on each other but in the circumstances where two householders are the joint applicants, and both have signed Certificate A, I cannot see that there could be any prejudice to any party in so doing and thus no possibility of any future legal challenge. GH.

An appeal decision (DCS Number 100-054-060) was reported in Casebook on 11 April 2008. The case related to a conservatory extension to a green belt dwelling, and the issues appeared to revolve whether the house constituted the ‘original’ dwelling. It had been created from an extension to a house which in 1991 had been severed. An inspector felt that the 1991 permission had created a new dwelling which constituted the ‘original’  building for PPG2 purposes. However, last year I was involved in a replacement dwelling case where this dwelling similarly been formed from an extended and then subdivided house. Here the inspector averred that the ‘original building’  was the house prior to subdivision. Which inspector was right? DH.

PPG2 states that provided that it does not result in disproportionate additions over and above the size of the original building, the extension or alteration of dwellings is not inappropriate in green belts. It goes on to say that the replacement of existing dwellings need not be inappropriate, providing the new dwelling is not materially larger than the dwelling it replaces. PPG2 does not define the term ‘original building’ although over the years detailed green belt policies in development plans have sought to do so, and have also applied the concept to replacement policies. As a result the detailed application of green belt policy can vary from area to area, which might account for the apparent discrepancy you cite. It is more likely, due to the rarity of the situation you describe, that these two inspectors were obliged to make their own individual assessments. GH.

An application for a first-floor extension to a house in the countryside to be built over an existing flat roofed extension was refused as it would add more than 30% to the floor area of the house as it existed in 1948. Before submission, a council officer advised the house could have extensions under last year’s General Permitted Development Order amendment on the opposite side and to the rear without permission which would be much larger than the submitted proposal.  Why is this disparity not taken in account in determining the application?  The client wants a modest extension which integrates better with the existing house’s layout. GM

The issue of fallback rights in relation to permitted development is considered in section 4.346 of Development Control Practice. Provided there is a reasonable prospect of the applicant using such rights, they should be taken into consideration in determining applications. In your case it would seem appropriate to negotiate with the council and see if they would be willing to allow the scheme with either a condition or a planning obligation taking away the permitted development rights. Having said that, foregoing rights to enlarge the property further could affect its value and your client needs to be aware of the implications of this. JH

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