What original dwellinghouse means for permitted development

The original dwellinghouse definition that runs through householder permitted development has nothing to do with when you bought the house. Article 2 of the General Permitted Development Order 2015 defines "original" as the building as it existed on 1 July 1948 if it was standing then, or as it was first built if it was built after that date. Every limit in Part 1 of Schedule 2 that refers to the original dwellinghouse is measured from that baseline, not from the house you moved into.

So a rear extension added by an owner in 1994 uses up part of your allowance. A conservatory added in 2008 uses up more. You inherit the arithmetic with the deeds.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. A Lawful Development Certificate is the only formal way to confirm that works are lawful.

The 1 July 1948 baseline

The date is not arbitrary. It is when the modern planning system came into force under the Town and Country Planning Act 1947, so it is the point from which development control has operated continuously.

For a Victorian terrace, a 1930s semi or a pre-war bungalow, the original dwellinghouse is the house as it stood on that day in 1948. Anything added since, whether under planning permission or as permitted development, counts as an enlargement of the original house.

That applies to several limits at once. The single-storey rear extension depth is measured from the original rear wall. The side extension width limit of half the width of the original dwellinghouse uses the 1948 width. And the rule that buildings within the curtilage must not cover more than half the curtilage excludes the footprint of the original dwellinghouse from the calculation, so a house that has grown since 1948 has a larger "buildings" figure and a smaller allowance than its current footprint suggests.

One consequence surprises people. Demolishing a 1970s extension and rebuilding it in the same place is still an enlargement of the original dwellinghouse. The clock does not reset because you took something down.

Why previous owners matter to your allowance

Permitted development rights attach to the land and the building, not to the person. There is no personal allowance that refreshes on sale, and conveyancing rarely tells you what has been used.

In practice this is the most common reason a householder discovers, halfway through a build, that they needed permission. The current single-storey rear extension limits under Class A are four metres for a detached house and three metres for any other house, with eight and six metres available through the prior approval procedure for larger extensions. If a previous owner added three metres at the back of a semi, the ordinary allowance is gone, and the larger extension route would only give you another three.

The same logic applies to outbuildings under Class E, to the curtilage coverage test, and to the restriction on extending beyond a side elevation. A garage built in 1985, a garden room in 2015 and a utility extension in 2002 are all counted.

Where rights have been removed altogether, the arithmetic is beside the point. Conditions on the original planning permission for a new estate commonly remove Class A rights, and an Article 4 direction can withdraw householder rights across a whole area. Our note on Article 4 directions and the move between C3 and C4 explains how those directions work, and the principle is the same for householder rights.

Finding evidence of what was there originally

You need to establish two things: the footprint and form of the house at the baseline date, and every enlargement since. Six sources do most of the work.

1. Historic Ordnance Survey maps at 1:1250 or 1:2500, which show building footprints and are usually available through the county records office or the local studies library.
2. Aerial photography from the 1940s onwards, held by national and local archives.
3. The council's own planning history for the address, searchable on its public register, which often goes back to the 1950s in some form.
4. Building control records, which sometimes survive where planning records do not, particularly for extensions built as permitted development.
5. Title deeds and Land Registry plans, which can show a footprint at the date of a past transfer.
6. Estate agents' particulars from previous sales, which frequently describe an extension and its date.

Where the evidence is thin, say so rather than assuming the most generous reading. An officer comparing your plan with a 1950s map will spot a discrepancy, and the consequence of getting it wrong is not a refusal but unauthorised development.

One caution on maps. A footprint on a 1:2500 map is a generalised outline, so it establishes that something existed rather than its exact dimensions. For a measurement dispute you need a dimensioned survey alongside it.

Rebuilt and substantially altered houses

The definition splits neatly. A house standing on 1 July 1948 has its original state fixed at that date, however much it has been altered since. A house built after that date has its original state fixed as built.

So if a pre-war house was demolished and a new house built on the plot in 1998, the original dwellinghouse is the 1998 house as built, and the allowance runs from there. That is why a replacement dwelling is one of the few things that resets the position, and why replacement schemes are often worth considering where a house has been extended to the limit.

Substantial alteration is different. Reroofing, rendering, internal reconfiguration, new windows and a loft conversion do not change what the original dwellinghouse was. Nor does a change of use into and back out of the dwelling. The baseline only moves if the building itself was replaced.

A partial rebuild is the hard case. Where a house has been progressively demolished and reconstructed around a retained element, whether a new building has come into existence is a question of fact and degree, and it is exactly the situation where a Lawful Development Certificate is worth the fee rather than a judgement call on site.

New houses and the as-built position

For anything built since 1948 the baseline is the house as first completed, which sounds simple and is not.

The complications are these. Where a house was built under a planning permission that was varied during construction, "as built" is what was actually built, so check the as-built drawings rather than the approved ones. Where a developer offered an extension as an option at the point of sale and it was built at the same time, it forms part of the original house. Where the same extension was added a year after completion, it does not.

New houses also carry the highest chance of having rights removed by condition, particularly on smaller plots and in schemes where the council wanted to control the pattern of extensions. Read the decision notice for your own house before you measure anything. The conditions are usually on the council's public register under the estate's original application, and they bind the plot even though the house changed hands years ago.

Solar panels, heat pumps and other equipment sit under different classes with their own limits rather than the Class A allowance, so they do not eat into your extension depth. Our note on the 200 millimetre projection limit for domestic solar panels sets out how one of those limits works.

When the allowance has already been used up

Running out of permitted development is not the end of a project. It changes the route and the evidence.

A householder planning application is the straightforward answer, determined against the council's own design guidance rather than against prescribed dimensions, which sometimes allows more than permitted development would. The practical work is demonstrating that the enlarged house still respects the neighbouring properties on light, outlook and overlooking, and that the design relates to the host dwelling.

A Planning Statement is not compulsory for a householder application and is often worth including where the cumulative extensions are part of the argument, because it lets you set out the planning history and explain why the further addition reads as proportionate. Expect eight weeks for determination on a householder application.

The other route, where you believe the works are permitted development but the position depends on contested facts, is a certificate of lawfulness of proposed use or development under section 192 of the Town and Country Planning Act 1990. It costs less than a full application, it produces a binding determination, and a mortgage lender or buyer will accept it. Section 191 covers works already carried out.

Proving the position to a council

Present the history rather than the conclusion. What a case officer wants is a short schedule with a drawing, not a paragraph of assertion.

Produce a plan showing the original footprint hatched and each subsequent addition shaded and dated. Alongside it, list each addition with its date, its source of evidence, and the relevant permission or prior approval reference where there is one. State the measurement you are relying on for each limit and where it was taken from. And attach the map extract or photograph you used, with its date and source.

That package answers the officer's first three questions before they are asked, and it is the difference between a smooth prior approval and a request for further information that costs a month.

Enter your postcode on PlanScope to see which documents a householder extension on your property is likely to need.

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