Discovering building work that does not appear to have the right approvals can turn what looked like a straightforward renovation into a much more complicated project.
Perhaps you have bought a house with an unauthorised extension. Maybe an old floor plan does not match the property you now own. Or you have started planning a renovation and discovered that a previous owner removed walls, altered the layout or added space without leaving a clear planning or Building Regulations record.
The first point to understand is that “the previous owner built without permission” does not describe one single problem.
Planning permission, Building Regulations approval and structural safety are separate matters. One may be missing while the others are in place. In some cases, planning permission may never have been required, but Building Regulations approval was. In others, the external development itself may need to be addressed through the planning system.
The safest starting point is therefore not to apply retrospectively straight away. It is to establish what was built, when it was built, what approvals should have applied and what evidence still exists.
That is the approach AC Design Solution had to take at its real Finchley Road, South Hampstead project, where earlier alterations by previous owners had been carried out without the necessary planning consent. The wider project then involved retrospective planning submissions, major structural changes and a new 38 sqm single-storey rear extension.
This guide covers properties in England and concentrates on the architectural, planning, Building Regulations and structural questions. Issues such as seller disclosure, contractual liability or indemnity insurance should be discussed separately with a solicitor or conveyancer.
First, Work Out What “Without Permission” Actually Means
A homeowner will often say there is “no permission” when what is actually missing is a completion certificate, a set of structural calculations or a planning decision notice.
Those are not interchangeable documents.
| What appears to be missing | What it relates to | What needs checking |
| Planning permission | Whether development was acceptable in planning terms | Was permission required, did permitted development apply, and is there an existing decision? |
| Building Regulations approval or completion certificate | Technical compliance of the construction | Was a Building Control application made, inspected and completed? |
| Structural calculations or drawings | Safety of altered load-bearing elements | What was removed or altered, and how is the structure currently supported? |
GOV.UK makes the distinction clear: Building Regulations approval is different from planning permission, and a project can require both. Building Regulations cover construction and many types of alteration, while planning permission is considered under a separate system.
This distinction matters particularly where a previous owner did building work without permission, because applying for the wrong type of approval will not resolve the underlying issue.
Check What Was Actually Approved Before Assuming the Work Is Unauthorised
Start with the paperwork, but do not stop there.
The planning history for the property should be compared with what physically exists today. Look for approved plans, decision notices, descriptions of development and any later amendments. If an extension is shown on the house but not on approved drawings, that is a reason to investigate further rather than immediate proof of the exact planning breach.
For a Camden property, homeowners can use Camden’s planning application search to search by address, application number or description. Other local authorities provide their own planning-history systems.
Building Control records should then be checked separately.
Camden, for example, allows property owners to request certain Building Control documents, including drawings and structural calculations. The council notes that record availability depends on the age and type of application, so an absent document should not automatically be treated as proof that no application ever existed.
This is where accurate existing drawings become valuable. A measured record of the house can be compared against the historic planning information so that differences are identified before a new renovation is designed.
For more complicated properties, AC Design Solution’s architectural services cover existing surveys, design development, planning applications and technical design, making this a more appropriate internal landing page than inventing a separate planning-service URL.
What If the Previous Owner Did Not Get Planning Permission?
If the work required planning permission but was carried out without it, one possible route is a retrospective planning application.
A retrospective application allows a local planning authority to consider development after it has already taken place. It is not an automatic approval simply because the work has been there for some time.
Current government enforcement guidance confirms that retrospective applications form part of the planning enforcement framework, and local authorities can take enforcement action where unauthorised development cannot be satisfactorily resolved.
The existing development still needs to be assessed on its planning merits.
That may involve its scale, design, effect on neighbours, conservation considerations, local planning policy and how closely the completed work matches what would ordinarily be acceptable.
This is important if a previous owner built an extension without planning permission. The sensible question is not simply, “Can we get retrospective permission?” It is, “Would the extension as it currently exists be acceptable, and if not, what needs to change?”
In some cases the design can be supported as built. In others, alterations may be required. There will also be cases where a different planning route is more appropriate.
The age of the work can affect the planning position, but enforcement rules have changed in recent years. Homeowners should not assume that old work is automatically lawful simply because no one has challenged it. The timing and circumstances should be checked against current guidance rather than relying on outdated references to old enforcement rules.
Planning Approval Does Not Resolve Missing Building Regulations
A second common situation is planning approval but no Building Regulations record. Planning permission does not certify that foundations, beams, insulation, drainage, fire precautions or other technical work were constructed correctly.
GOV.UK specifically states that Building Regulations approval is separate and may be needed for extensions and many alteration projects. A lack of approval can also leave the owner without compliance certificates that may later be required when selling the property.
If the previous owner did not obtain Building Regulations approval, the next step depends on what work was carried out and what records can be found.
For work that has already been completed without Building Control approval, Building Regulations regularisation may be relevant.
Camden describes regularisation specifically as a route for unauthorised building work, including work completed by a previous owner. For eligible work, Building Control may inspect the construction and can require parts of it to be opened up so that compliance can be assessed. Alterations may be necessary before a regularisation certificate can be issued.
In England, GOV.UK says regularisation is available through a local authority building control body for eligible work carried out after 11 November 1985.
The important point is that retrospective planning permission and Building Regulations regularisation solve different problems.
A planning approval does not remove the need to address a Building Control issue, and a regularisation certificate does not retrospectively provide planning permission.
Where technical documentation is needed for new works, AC Design Solution provides building regulation drawings covering the wider construction information required for Building Control.
Unauthorised Structural Alterations Need Their Own Investigation
Paperwork becomes even more important when the previous work changed the load path of the building.
A load-bearing wall removed without calculations is not something that should be assessed only by looking at whether a room appears stable today.
Removing or substantially altering a structural wall changes how loads from floors, walls and sometimes the roof are transferred through the building. There may already be a steel beam in place, but its size, bearings, connections or supporting structure may not be documented.
Where there is uncertainty about the existing structure, a structural survey can help establish the condition of visible and accessible structural elements before further renovation is planned. AC Design Solution specifically positions this service for buyers, renovators and properties undergoing significant alterations.
Further investigation may then be necessary before an engineer can confirm what the structure is doing. The appropriate response depends on the individual property; it should not be based on generic beam sizes or DIY assumptions.
Where engineering design is required, structural drawings and calculations provide the technical information for beams, supports, foundations and other structural components and can be coordinated with Building Control documentation.
This distinction also protects the homeowner from solving only the paperwork problem while leaving a physical structural problem unexamined.
Real Project: What Happened at Finchley Road, South Hampstead?
The Finchley Road project is useful because the team was not starting with a clean, untouched house. When AC Design Solution became involved, previous alterations had already been carried out without the necessary planning consent. The new owner therefore had to deal with the existing planning position while also preparing a much wider renovation.
The property was a Victorian home within a Camden conservation-area context. The eventual project added 38 sqm of floor area through a single-storey rear extension and substantially reorganised the internal accommodation.
Instead of treating the earlier unauthorised development as an isolated paperwork exercise, the team considered it alongside the new design.
Retrospective planning submissions were prepared to address the previous work. According to the project information supplied by AC Design Solution, those retrospective applications were approved by Camden Council and the issue was resolved without enforcement action.
At the same time, the new layout required major structural modifications.
Load-bearing walls were removed to create a more open living arrangement. The engineering team assessed how the building was supported, calculated where new structural support was required and introduced steel beams as part of the coordinated design.
The architectural and structural work then had to integrate with the new rear extension and the existing building fabric.
This is where the project provides a useful lesson for homeowners who have bought a house with unauthorised building work: the old problem and the new renovation should be assessed together.
If a previous alteration affects the location of a future opening, extension, beam, foundation or drainage route, resolving the old paperwork without understanding the proposed project can lead to duplicated design work later.
The Finchley Road outcome was not simply a retrospective approval. It was a coordinated renovation in which the existing planning position, new architecture, structural engineering, Building Regulations and construction information were brought into one project strategy.
Practical Steps if You Discover Previous Unauthorised Work
1. Identify what has actually changed. Compare the physical building with older plans, sales particulars, planning drawings and any records supplied during the purchase.
2. Search the planning history. Establish whether permission was granted for the extension or alteration and whether the completed work matches the approved proposal.
3. Check Building Control separately. Look for Full Plans, Building Notice or other Building Control records and determine whether a completion certificate exists.
4. Create an accurate record of the property as it stands. Existing floor plans, elevations and photographs make it easier to compare the house with historic approvals and identify undocumented work.
5. Investigate structural alterations. If walls, chimney breasts, floors, roofs or other load-bearing elements have been changed, establish what structural information exists and whether further professional assessment is needed.
6. Determine the correct route for each issue. Missing planning consent may require a different solution from missing Building Regulations approval. Do not assume one retrospective application resolves both.
7. Coordinate the problem with any new renovation. If you intend to extend, remodel or remove additional walls, resolve the existing condition as part of the new architectural and structural strategy rather than designing around uncertain information.
8. Keep the final approval record together. Drawings, planning decisions, structural calculations, Building Control documents and completion information should form one clear project record for future use.
Can You Still Renovate or Extend the Property?
In many situations, yes. Finding previous unauthorised building work does not automatically mean the house cannot be improved. What matters is establishing the present position before adding another layer of development.
The Finchley Road project is a good example. Earlier planning issues were dealt with while a new single-storey extension, structural alterations and full internal renovation were developed as part of the same project.
What should be avoided is designing a major renovation on the assumption that everything already in the house is approved and structurally understood.
A proposed kitchen extension may rely on an existing wall whose history is unclear. A loft conversion may add loads to walls that have previously been altered. New open-plan layouts may interact with undocumented steelwork.
Finding those issues while drawings are still being developed is considerably more manageable than discovering them once a builder has opened the structure.
When Is Professional Advice Worth Getting?
Professional input becomes particularly valuable when the council’s records do not match the building, when no Building Regulations information can be found, when previous structural alterations are visible, or when the property is about to undergo further major renovation.
An architectural review can help establish what was approved and how a new proposal should respond to the existing condition. Structural input can determine whether previous alterations require investigation or engineering work. Building Regulations documentation can then be coordinated with the final design.
The objective should not be to collect as many retrospective certificates as possible. It should be to establish a clear, technically sound and documented position for the property.
If you have discovered previous unauthorised work and are planning further alterations, you can contact AC Design Solution to discuss the property, the existing records and the proposed project.
