Class Q Structural Surveys: Supporting Agricultural Building Conversions
Class Q Structural Surveys: Supporting Agricultural Building Conversions
By Joseph Lawson MEng (Hons), Director / Structural Engineer, Lawson Cook Limited
Class Q permitted development rights can allow certain agricultural buildings and former agricultural buildings in England to be converted to residential use without a full planning application, subject to the relevant limitations, conditions and prior approval process.
For many Class Q proposals, one of the key practical questions is whether the existing building is genuinely capable of conversion or whether the works required would amount to substantial rebuilding.
A structural survey can therefore form an important part of the supporting information for a Class Q prior approval application.
What Is Class Q?
Class Q of Part 3, Schedule 2 of the General Permitted Development Order provides permitted development rights for the change of use of qualifying agricultural buildings to dwellinghouses, together with certain building operations reasonably necessary to enable the conversion.
The current Class Q provisions can, subject to all relevant criteria being satisfied, allow up to 10 dwellinghouses, with up to 1,000m² of cumulative residential floorspace and a maximum of 150m² per dwellinghouse. The amended right also permits certain single-storey rear extensions of up to 4m where the relevant conditions are met.
However, Class Q is fundamentally intended to facilitate the conversion of an existing building, rather than the construction of a substantially new building.
Why Is the Existing Structure Important?
Class Q permits specified building operations to the extent that they are reasonably necessary for the building to function as a dwellinghouse. These can include works to windows, doors, roofs, external walls and services, together with limited associated demolition.
The important distinction is between:
converting an existing agricultural building, and
effectively rebuilding or replacing that building.
Government planning guidance describes the Class Q right on the basis that the agricultural building is capable of functioning as a dwelling.
This is where a structural survey can provide useful technical evidence.
What Does a Class Q Structural Survey Assess?
At Lawson Cook Limited, a Class Q structural survey would normally assess the existing building from a structural engineering perspective and consider whether the principal structure appears suitable for retention and conversion.
Depending on the form of construction, this may include consideration of:
Foundations, where visible or where information is available
External masonry walls
Steel or timber frames
Columns and posts
Roof trusses, rafters and purlins
Primary beams
Existing floor structures
Bracing and overall stability
Corrosion, decay or deterioration
Cracking, distortion or movement
Localised structural defects
The likely extent of strengthening or repair works required
Whether the proposed conversion appears capable of retaining the principal existing structure
The purpose is not simply to state that a building is standing.
The survey should consider whether the existing structural form can reasonably accommodate the proposed residential conversion and identify any significant structural works that are likely to be necessary.
What Is Included in the Structural Report?
Following the site survey, we can prepare a structural report suitable for use alongside the wider Class Q submission.
The report would typically include:
Existing construction
A description of the principal structural form, including walls, frames, floors and roof structure.
Observed condition
A record of significant visible defects such as corrosion, cracking, deformation, decay or deterioration.
Structural assessment
Our engineering opinion on the general structural condition of the building and its suitability for the proposed conversion.
Conversion considerations
Commentary on structural works that are likely to be required, such as local strengthening, replacement of defective elements or formation of proposed openings.
Conclusion
A clear conclusion regarding whether, based on the visible evidence and information available, the building appears structurally capable of conversion while retaining its principal structural form.
The report can then be coordinated with the architect or planning consultant preparing the Class Q prior approval submission.
Can a Structural Survey Help a Class Q Application?
Yes.
Structural condition is not simply a question of whether a building has defects. The more important Class Q consideration is usually whether the proposed works remain a genuine conversion of the existing structure.
Some local planning authorities specifically encourage structural appraisals to demonstrate that an agricultural building is capable of conversion without extensive replacement of the principal structure.
Structural reports are also regularly submitted as supporting documents with Class Q prior approval applications.
A well-prepared structural report can therefore help provide the planning consultant and local planning authority with clear technical evidence regarding the existing building.
What If the Building Requires Repairs?
An agricultural building does not necessarily need to be in perfect condition to be considered for conversion.
Existing agricultural buildings commonly contain:
Localised corrosion to steelwork
Deteriorated timber
Cracked masonry
Damaged roof sheeting
Localised settlement
Defective cladding
Areas requiring strengthening
The significance depends on the scale of the repairs required.
Local replacement or strengthening may be very different from a scheme that requires wholesale replacement of the roof, external walls, structural frame and foundations.
The structural report should therefore distinguish between localised remedial works and fundamental reconstruction.
What If Parts of the Structure Cannot Be Seen?
Class Q structural surveys are normally visual and non-intrusive unless additional investigations are specifically agreed.
Agricultural buildings can often have concealed foundations, inaccessible roof areas or structural elements hidden behind cladding and finishes.
Where necessary, further investigation may be recommended, including:
Trial holes to foundations
Opening-up works
Timber inspections
Corrosion investigation
Material testing
Measured surveys
Additional structural calculations
Where the adequacy of an element cannot be confirmed visually, this should be clearly identified rather than assumed.
Should the Structural Engineer Be Involved Before the Class Q Design Is Finalised?
Where possible, yes.
An early structural assessment can identify issues that may influence the architectural proposal before significant time is spent developing the submission.
For example, the proposed arrangement may require:
Large new openings
Removal of existing columns
Significant modification to roof trusses
Replacement of extensive wall sections
Major foundation works
Identifying these issues early allows the architect and planning consultant to develop a proposal that better responds to the existing building.
This can be considerably more efficient than preparing the complete Class Q submission first and investigating the structure afterwards.
Structural Survey vs Planning Advice
Our role as structural engineers is to assess the building and provide engineering advice regarding its structural condition and suitability for conversion.
We would not normally determine whether the site satisfies every requirement of Class Q.
Matters such as agricultural use history, qualifying dates, planning designations, highways, ecology, flooding and the wider interpretation of permitted development rights should be confirmed by the appointed planning consultant or other appropriate adviser.
The current Class Q provisions also contain specific restrictions relating to matters including protected land, listed buildings, scheduled monuments, dwelling sizes and highway access.
The strongest submissions therefore normally involve coordination between the planning consultant, architect and structural engineer.
Class Q Structural Surveys
Lawson Cook Limited undertake structural surveys of barns, agricultural buildings and other existing structures in support of proposed conversion projects.
Our involvement can include:
Initial structural site survey
Structural condition appraisal
Class Q structural reporting
Review of proposed architectural layouts
Advice on likely structural alterations
Structural calculations and drawings following planning approval
Design of steelwork, timber, masonry and foundations required for the conversion
Where a Class Q prior approval application is being prepared, we recommend sending us the architectural drawings, site information and any planning consultant's brief before the survey so that our assessment can be targeted to the proposed conversion.
If you are considering the conversion of an agricultural building under Class Q, please contact us with the site address, photographs, existing/proposed drawings and any planning information available, and we can advise on the appropriate structural survey scope.
Lawson Cook Limited
Structural Engineers
Hertford, Hertfordshire
info@lawsoncook.co.uk