Domestic extensions and replacement dwellings guidance document

Planning information leaflet: Domestic Extensions and Replacement Dwellings

Introduction

This advice note has been produced to assist applicants and decision-makers in applying the relevant policies of the adopted New Forest National Park Local Plan. It relates to proposals for domestic extensions, outbuildings and to proposals for replacement dwellings. The note does not create new policy, but explains the purposes of the relevant Local Plan policies and how they are applied.

The Government’s National Planning Practice Guidance on ‘Determining a planning application’ confirms that a material planning consideration is one which is relevant to making the planning decision in question. Although this advice note does not form part of the statutory development plan for the New Forest National Park, it is a material planning consideration that can be taken into account by decision makers (including National Park Authority planning officers, members of the Authority’s Planning Committee, or the Planning Inspectorate for appeals or ‘called in’ applications) when determining relevant applications.

Permitted Development Rights

You can make certain types of minor changes to your home without needing to apply for planning permission. These are called “permitted development rights”. They derive from a general planning permission granted not by the local authority but by Parliament. Bear in mind that the permitted development rights which apply to many common projects for houses do not apply to flats, maisonettes or other buildings.

More restricted permitted development rights apply in ‘designated areas’ which include National Parks and Conservation Areas. Sometimes permitted development rights may have been withdrawn as a result of a condition imposed on an earlier planning permission or you may live in an area affected by an ‘Article 4 Direction’ removing certain permitted development rights.

Applying for Planning Permission

Like many local planning authorities, the National Park Authority has agreed planning policies against which it considers planning applications for domestic extensions (including attached outbuildings) and replacement dwellings – Policies DP35 and DP36 of the adopted New Forest National Park Local Plan 2016-2036 (the ‘local plan’).

Successive local plans in the New Forest, dating back to the 1990s, have sought to limit the size of extensions and replacement dwellings to minimise their impact on the landscape, to help protect the unspoilt character of the New Forest and to maintain a range of housing types, particularly the stock of smaller dwellings to meet the needs of the New Forest community. The Local Plan Inspectors’ Report (2019) supported the policies on replacement dwellings and extensions to dwellings, considering them to be justified on the basis of protecting the sensitive landscape of the National Park; and seeking to achieve a balanced housing stock. The planning policy approach is consistent with that taken in several other adopted National Park development plans and accords with national policy on protecting the landscape of National Parks (paragraph 176, NPPF, 2021) and planning for a mix of dwelling types.

Extensions to Dwellings

Policy DP36 allows householders to extend and improve their homes although there are certain limitations, depending on where you live and whether your home has been extended in the past.

As a general rule, you can extend the habitable floor space of your home by up to 30% providing that other standard planning considerations are met, such as scale, appearance and consideration of impacts on neighbours and the wider area.

But there are two exceptions to the “30% rule”:

1. If you live within one of the four main villages of Ashurst, Brockenhurst, Lyndhurst or Sway, you can extend your property beyond the 30% but again, normal planning considerations still apply.
2. If your property is classed as a ‘small dwelling’ – which is defined as a dwelling of 80 sq. metres or less – then that can normally only be extended up to a maximum of 100 sq. metres.

The baseline for calculating increases in floor space and defining a ‘small dwelling’ is 1 July 1982 – this is the baseline date that has been used in nearly all of the New Forest since the 1990s. It applies to all replacement dwellings built after 1 July 1982 as these would have replaced an earlier existing dwelling. There are circumstances when a larger extension may be permitted and these are explained in the policy.

Policy DP36: Extensions to Dwellings

Extensions to existing dwellings will be permitted provided that they are appropriate to the existing dwelling and its curtilage.

In the case of small dwellings and new dwellings permitted by Policies SP19 to DP31 of this Local Plan, the extension must not result in a total habitable floorspace exceeding 100 square metres.

In the case of other dwellings (not small dwellings) outside the defined villages the extension must not increase the floorspace of the existing dwelling by more than 30%.

In exceptional circumstances a larger extension may be permitted to meet the genuine family needs of an occupier who works in the immediate locality. In respect of these exceptional circumstances, the total internal habitable floorspace of an extended dwelling must not exceed 120 sq.metres.

Extensions will not be permitted where the existing dwelling is the result of a temporary or series of temporary permissions or the result of an unauthorised use.

Definitions and clarifications

• original dwelling means the dwelling as first built
• existing dwelling means the dwelling as it existed on 1 July 1982, or as the dwelling was originally built or legally established, if the residential use post-dates 1 July 1982
• small dwelling means a dwelling with a floor area of 80 sq. metres or less as it existed on 1 July 1982, or as the dwelling was originally built or legally established, if the residential use post-dates 1 July 1982
• floorspace of original, existing and small dwellings will be measured as the total internal habitable floorspace of the dwelling but will not include floorspace within conservatories (footnote 41), attached outbuildings and detached outbuildings (irrespective of whether the outbuilding’s current use is as habitable floorspace)
• floorspace of proposed extensions will include conservatories and attached outbuildings and any habitable floorspace provided within a detached outbuilding
• a conservatory is defined as having not less than three-quarters of the area of its roof and not less than one-half of the area of its external walls made of clear or translucent material
• a modest basement will not normally be regarded as habitable floorspace. However, some judgement will need to be applied in terms of whether it is genuinely a secondary space in association with the main dwelling. Key criteria to consider include availability of light; size (in relation to the main dwellings); access; use; layout and headroom. Basements to houses set into a hillside with any form of exposed elevation will usually be treated as habitable accommodation
• genuine family need is defined as an exceptional and unique family need that could not have been reasonably anticipated at the time of purchase of the property. For example, additional floorspace may be required to cater for specialist equipment and facilities required in connection with an unforeseen event, such as a severe disability arising from an accident whilst in occupation of the property; but, it normally would not cater for the needs of growing families or the need to care for elderly relatives, as these needs are not considered to be so ‘exceptional’ as to warrant a departure from the floorspace restrictions set out in this policy

Footnote 41 – This only applies to conservatories in New Forest District that have previously been permitted as an ‘exception’ to policy and which are the subject of a planning condition that limits their use as a conservatory.

Further guidance on measuring floorspace (existing and proposed)

Calculation of Habitable Floor Space

This is calculated as gross internal floor space including all floors and stairwells.

Accommodation within the Roof Space

This is included in the calculation of habitable floor space where there is natural light (e.g. via a dormer window or roof light), a permanent stair case and headroom of 1.5 metres or more.

Double Height Living Rooms

As planning permission is not required to extend or add a mezzanine floor within a dwelling, double height living rooms with glazing up to what would be first floor, will be regarded as having two floors. Where glazing is not proposed at first floor level, there may be scope to include only the ground floor subject to a restriction on any further windows at first floor level (if it is likely that any further accommodation will exceed floor space limits).

Attached Outbuildings

The policy excludes attached outbuildings when calculating the existing internal floor space. Outbuildings are normally defined as subsidiary buildings which have not been designed or built for habitable use as part of the main dwelling. Examples include log stores, sheds, carports, garages and greenhouses. Outbuildings will often be distinguishable from the main dwelling both in their visual appearance and physical construction. Attached garages may be excluded from calculations where there is no internal connection, they retain the appearance and all the characteristics of a garage and their future use as a garage can be suitably controlled through an appropriate condition.

Open-Sided Areas Covered by a Roof

Verandas

May be excluded from calculations if they are constructed of lightweight materials and are conditioned to remain open.

Porches

If the porch is more than the permitted development allowance, this is included in the floor space calculation. If the porch is open-sided, it would not be included in the floor space calculation. Open-sided areas more than the permitted development allowance will be conditioned to remain open.

Balconies

The covered space below a balcony/terrace will be included within the calculations (as it could be enclosed), but the floorspace of the balcony/terrace is not included.

Chimneys

External chimney breasts are excluded.

Basements

A modest basement with no external door or window openings will not normally be regarded as habitable floorspace. However, some judgement will need to be applied in terms of whether it is genuinely a secondary space in association with the main dwelling. Key criteria to consider include:

• Availability of light;
• Size (and relation to the main dwelling);
• Access;
• Use;
• Layout;
• Headroom

Basements should not contain habitable accommodation. Appropriate secondary spaces would include storage and plant equipment but would not include car parking areas.

Basements to houses set into a hillside with any form of exposed elevation will usually be treated as habitable accommodation.

Conservatories allowed under previous exemptions policy

Under previous policies in New Forest District, conservatories of up to 20 square metres were allowed as an “exception” to policies relating to floor space subject to a planning condition limiting their use as a conservatory.

This ‘exemption’ policy ceased to apply on adoption of the first Park wide Local Plan in 2010 although the Authority has subsequently allowed the replacement of such conservatories on a strict ‘like for like’ basis where the replacement structure continues to comply with the definition of a conservatory contained within the supporting text to Policy DP36.

However, in light of sustainability and tranquillity considerations, a revised approach of allowing their adaption or replacement with a more solid roof and/or external walls may be considered acceptable, subject to the footprint, scale and siting of the adapted/replaced ‘conservatory’ being the same as before with no increase in floor area. Any increase in height of the adapted/replaced ‘conservatory’ must be kept to the absolute minimum and limited to what is reasonably required to achieve the necessary thermal insulation to the roof.

In circumstances where adaptions to, or replacement of, a previously exempt conservatory are permitted, the floorspace of the former conservatory will continue to be excluded from the floorspace calculations in consideration of future proposals to extend and/or replace the dwelling. This will be made clear through an informative attached to any planning permission granted.

Replacement Dwellings

Policy DP35 relates to replacement dwellings and states that a replacement dwelling, located outside of the defined villages, should be of no greater floorspace than the existing dwelling. However, should there be further scope to extend the existing dwelling (before it is replaced), then as a pragmatic approach, an extension that would be compliant with Policy DP36 may be allowed at the same time as the replacement, providing it reads as an “extension” and the additional floorspace does not increase the overall bulk of the replacement dwelling.

When considering proposals to extend (or even replace) a replacement dwelling, the ‘base point’ for calculating the floorspace of the property remains the 1 July 1982. In the case of new dwellings built after 1 July 1982 (where no dwelling previously existed), including their subsequent replacements, then the baseline is the date on which that ‘new’ dwelling was first built. In other words, you only consider the dwelling as originally built, or when it was legally established to mean ‘existing dwelling’ if the first instance of residential use post-dates 1 July 1982.

A policy that sets a proportionate limit on enlargements to dwellings must have a base date and this must apply to all proposals, whether extensions or replacements. Paragraph 7.79 of the Local Plan expands upon the reasoning behind Policy DP36 and the limitations imposed upon extensions:

“Proposals to incrementally extend dwellings in a nationally designated landscape can affect the locally distinctive character of the built environment of the New Forest. In addition, extensions can over time cause an imbalance in the range and mix of housing stock available. For these reasons it is considered important that the Local Plan continues to include a clear policy to guide decisions for extensions to dwellings. Successive development plans for the New Forest have included such policies which strike an appropriate balance between meeting changes in householder requirements and maintaining a stock of smaller sized dwellings.”

This approach ensures that a replacement dwelling only gets a 30% allowance once. If the dwelling is subsequently replaced and enlarged at the same time, there is no additional 30%, which would be contrary to the aims of successive Local Plan policies which seek to maintain a stock of smaller sized dwellings.

Case Study

Planning permission was granted in 1992 for a replacement dwelling. The former dwelling it replaced was built in 1975 and at the time of the 1992 planning application, it had not been previously extended. The approved 1992 replacement dwelling therefore included an additional 30% of floorspace.

In 2021, a new owner wishes to extend the dwelling further. However, as a dwelling was already clearly established on this site prior to 1 July 1982 and was then replaced and enlarged post 1 July 1982 (using all of the floorspace allowance), no further increase in habitable floorspace would be allowed under Policy DP36.

The base point is not the date the replacement dwelling was built.

Other Relevant Local Plan Policies

There are a number of other local plan policies that you should have regard to when drawing up your plans, in particular:

• Policy DP2 General Development Principles
• Policy SP7 Landscape Character
• Policy SP15 Tranquillity
• Policy SP17 Local Distinctiveness
• Policy DP18 Design Principles

These policies focus on the need to ensure that all new buildings are sympathetic and in keeping with their surroundings. The New Forest is a very special place and one that has a rich and locally distinctive built heritage.

Design guidance

Design is therefore a very important consideration. All extensions should:

• Be compatible with the main buildings, avoiding significant impact on the scale of the core or original element
• Avoid impacts on neighbouring properties, such as building bulk and loss of light
• Use a sympathetic choice of materials
• Minimise bulk by setting back with reduced height and smaller roof spans

For more information about design please do take a look at the Authority’s Design Guide Supplementary Planning Document and the Village Design Statements prepared by local parish councils.

We positively encourage pre-application discussions with prospective applicants before an application is submitted and can provide further guidance and assistance as required.

Planning Designations

Contact us for help identifying any planning designations that may relate to the property such as areas of flood risk, nature designation or whether the property is in a conservation area. You can also check the property’s development history in the ‘planning history’ section.

Planning Application Forms

Planning application forms can be downloaded from the Authority’s website which includes a link to the Planning Portal.

Building Regulations

Whether your extension is permitted development or requires planning permission, you must also consider whether you need to submit a Building Regulation application. The Building Regulations control the way in which a building is constructed, for example, the type of foundations, walls, insulation required. You will need to check with your local district/borough/unitary authority whether you need to also apply for Building Regulations Approval.