Getting planning permission for your house extension is a major milestone.
After weeks of developing the design and waiting for the planning decision, receiving approval can feel like you are finally ready to appoint a builder and start construction.
But there is an important next stage.
Planning permission does not mean your extension is ready to build.
Before construction begins, most house extensions need to progress through Building Regulations and technical design.
This is the stage where your approved architectural design is developed into much more detailed information showing how the extension will actually be constructed.
At Connor Ferris Architects, we work with homeowners across Chelmsford and Essex from initial design and planning through to Building Regulations, technical design and contractor quotations.
In this guide, we explain what typically happens after planning permission and what you should have in place before your builder starts on site.
Planning Permission and Building Regulations Are Different
One of the most common misconceptions we encounter is that planning approval means the drawings have been fully approved for construction.
Planning and Building Regulations are separate processes.
Planning permission is principally concerned with whether the proposed development is acceptable in planning terms. This can include its size, appearance, relationship with neighbouring properties and impact on the surrounding area.
Building Regulations deal with how the building is designed and constructed from a technical and safety perspective.
For a typical house extension, this can include:
- Structural stability
- Foundations
- Fire safety
- Insulation and energy efficiency
- Ventilation
- Drainage
- Roof construction
- Floor construction
- Windows and glazing
- Electrical safety
- Accessibility
- Moisture and weather protection
So although your planning drawings establish what you have permission to build, considerably more technical information may be required before construction.
What Happens After Planning Permission Is Granted?
For many residential projects, the next architectural stage is RIBA Stage 4 – Technical Design.
This is when the planning design is developed into a coordinated technical package.
The exact information required depends on the project, but for a typical extension this can involve architectural construction drawings, detailed sections, construction build-ups, structural information, energy calculations and drainage information.
Other consultants may also become involved.
The objective is to resolve as many technical decisions as reasonably possible before the builder is constructing them on site.
What Are Building Regulations Drawings?
Building Regulations drawings contain significantly more information than planning drawings.
A planning floor plan might show the size of your proposed extension, the position of the kitchen and the location of new windows and doors.
The technical drawings need to go much further.
Depending on the project, they may establish matters such as:
- Foundation construction
- Ground-floor build-ups
- External wall construction
- Roof construction
- Insulation thicknesses
- Damp-proofing
- Ventilation
- Structural openings
- Fire protection
- Drainage
- Threshold details
- Window and door requirements
- Internal wall construction
- Ceiling construction
- Relevant Building Regulations notes and specifications
Sections and construction details may also be developed to explain how different parts of the building come together.
This is important not only for Building Control, but also for the contractor who will eventually have to price and construct the project.
Will I Need a Structural Engineer?
Most house extensions involving structural alterations will require input from a structural engineer.
Your architect and structural engineer perform different but complementary roles.
The architect develops and coordinates the overall design and technical architectural information, while the structural engineer designs and calculates the structural elements required to support it.
For a residential extension, this could include:
- Steel beams
- Structural openings
- Padstones
- Posts
- Foundations
- Roof structure
- Floor structure
- Supporting existing walls
- Removing existing load-bearing walls
For example, creating a large open-plan kitchen may involve removing a substantial section of the original external wall.
Architecturally, that opening can completely transform the relationship between the existing house and the extension.
Structurally, however, the loads previously supported by that wall still need to be safely transferred.
The structural engineer will therefore determine the appropriate structural solution and provide the necessary calculations and details.
At the technical design stage, this information should then be coordinated with the architectural drawings.
What About Foundations?
Foundations are another important part of Building Regulations design.
There isn’t one foundation specification that is automatically suitable for every extension.
Ground conditions, nearby trees, drainage, existing structures and the loads imposed by the proposed building can all influence the appropriate solution.
In some circumstances, Building Control or the structural engineer may require additional information before the final foundation design is confirmed.
This is why simply writing “foundations to Building Regulations” on a basic drawing is not the same as properly developing the technical design.
Drainage Can Have a Major Impact on an Extension
Drainage is something we consider carefully because it can significantly influence what is possible.
An existing drain or sewer may run directly beneath or close to the proposed extension.
Depending on its status and location, this could mean considering:
- Existing foul and surface-water drainage routes
- New drainage connections
- Inspection chambers and manholes
- Relocating drainage
- Diverting a sewer
- Building near or over a public sewer
- Approval from the relevant water authority
- Rainwater disposal
This is particularly important where an existing inspection chamber sits within the footprint of a proposed extension.
Finding this out once foundations are already being excavated is very different from identifying and resolving it during technical design.
Will My Extension Need Energy Calculations?
Building Regulations place requirements on the thermal performance and energy efficiency of extensions.
Your technical design will therefore need to consider elements such as:
- Roof insulation
- Wall insulation
- Floor insulation
- Windows and doors
- Thermal bridging
- Heating
- Ventilation
- The amount of glazing proposed
A common issue arises where a homeowner wants substantial areas of glazing, such as large sliding doors, rooflights or a highly glazed rear elevation.
There are limits on the amount of glazing that can be introduced using the standard approach under Building Regulations.
Where the design exceeds those parameters, additional energy calculations may be required to demonstrate that the overall proposal still achieves an acceptable level of performance.
This does not necessarily mean that large areas of glazing cannot be achieved.
It means the design needs to be assessed properly rather than assumed to comply.
What Is Building Control?
Building Control is responsible for checking compliance with the Building Regulations.
For most domestic extension projects in England, homeowners can use either their local authority Building Control service or a registered building control approver, subject to the applicable building-control regime.
At Connor Ferris Architects, we generally recommend progressing a developed technical package through the appropriate Building Control process before construction.
For residential projects, a Full Plans application can provide an opportunity for the drawings, specifications and supporting calculations to be reviewed before work progresses too far on site.
Building Control may issue comments or request additional information during this process.
These comments can then be addressed by the relevant designer or consultant.
Does Building Control Approval Mean They Design the Extension?
No.
This distinction is important.
Building Control’s role is to assess compliance with the Building Regulations. It is not their role to act as the architect, structural engineer or designer of the project.
The project team remains responsible for producing and coordinating the necessary design information within their respective appointments.
This is another reason why technical design should not be viewed simply as an administrative exercise to “get Building Regs”.
It is a genuine design stage.
What Is the Principal Designer for Building Regulations?
Changes introduced under the Building Safety Act regime have also increased the focus on formal dutyholder responsibilities.
Domestic projects can involve dutyholders including the:
- Client
- Designer
- Principal Designer
- Contractor
- Principal Contractor
Where more than one designer is involved, a Principal Designer must be appointed for the Building Regulations duties.
The Principal Designer has specific responsibilities relating to planning, managing and monitoring the design, if constructed, it complies with the Building Regulations.
This role should therefore be understood and agreed as part of the professional appointments rather than assumed to sit automatically with a particular consultant.
Do I Need a Party Wall Agreement?
Possibly.
Building Regulations approval and the Party Wall etc. Act 1996 are separate matters.
Party Wall considerations can arise where work involves, amongst other things:
- Building close to a neighbouring structure
- Excavating near neighbouring foundations
- Work directly to a party wall
- Cutting into a party wall
- Constructing certain walls on or close to a boundary
Whether the Act applies depends on the proposed works and the relationship with neighbouring structures and boundaries.
Where it does apply, the necessary notices and procedures should be considered sufficiently early so they do not unexpectedly delay the construction programme.
When Should You Start Getting Builder Quotations?
This is where progressing the technical design before obtaining final quotations can make a significant difference.
Imagine sending the same basic planning drawings to three builders.
Builder A assumes one specification.
Builder B assumes another.
Builder C excludes several items entirely.
You receive three prices, but you aren’t necessarily comparing the same thing.
A more developed technical package gives contractors considerably more information about what they are actually being asked to construct.
That can make quotations more detailed and easier to compare.
At Connor Ferris Architects, once the appropriate technical information has been prepared, we can also assist our clients by issuing project information to suitable contractors to obtain competitive quotations.
The client remains free to choose their preferred contractor.
The aim is to make the quotation process clearer and give contractors a consistent package of information from which to price.
Should I Choose the Cheapest Builder?
Not automatically.
Price is obviously important, but it should be considered alongside:
- What has actually been included
- What has been excluded
- The contractor’s experience
- Quality of previous work
- References
- Availability
- Proposed construction programme
- Insurance
- Communication
- Understanding of the drawings
- How variations will be dealt with
- The proposed building contract
A quotation that initially appears cheaper can become considerably more expensive if important elements have been excluded or left as assumptions.
This is another reason why good technical information has value before a contractor is appointed.
Can I Start Building Before Everything Is Approved?
There are Building Control routes that can allow certain works to commence without formal Full Plans approval having first been issued.
However, being legally able to commence work and being properly prepared to commence work are not necessarily the same thing.
For most homeowners, we would rather see the important technical matters understood and coordinated before significant construction begins.
Changes are generally easier to make on a drawing than when foundations have been excavated, steelwork has been ordered or walls have already been constructed.
Good preparation at Stage 4 can therefore reduce uncertainty during construction.
How Long Does the Building Regulations Stage Take?
There is no single timescale because every project is different.
A straightforward extension will usually require less coordination than a substantial renovation involving major structural alterations, complex drainage, large areas of glazing or specialist consultants.
Time also needs to be allowed for:
- Developing the technical architectural drawings
- Obtaining structural engineering information
- Obtaining any required energy or specialist calculations
- Coordinating the different consultant information
- Submitting the Building Regulations application
- Responding to Building Control comments
- Finalising information for contractor pricing
For that reason, we recommend treating technical design as a proper stage of the project rather than something to begin a few days before you want your builder on site.
What Should Be in Place Before Your Builder Starts?
For a typical house extension, we would ideally want the project to have progressed through the relevant pre-construction matters before significant work begins.
Depending on the project, that may include:
- Planning permission or confirmation of the appropriate planning route
- Discharge of any relevant planning conditions
- Building Regulations technical drawings
- Structural engineering design and calculations
- Energy calculations where required
- Drainage strategy
- Building Control application
- Party Wall matters where applicable
- Any required sewer or water-authority approvals
- Contractor quotation and agreed scope
- Appropriate building contract
- Clear understanding of who is responsible for each element of the project
Not every extension requires every item on this list.
The important point is establishing which ones apply to your project before construction starts.
Planning Approved? This Is Where the Project Becomes Technical
Planning permission is an exciting milestone, but it is not the end of the architectural process.
In many ways, it is where the project begins moving from an architectural proposal into something that can actually be constructed.
A successful technical design stage brings together the architectural design, structure, energy performance, drainage and Building Regulations requirements into a coordinated package.
It also gives your contractor better information to price and build from.
That can mean fewer assumptions, fewer unanswered questions and a much clearer route towards construction.
Building Regulations Drawings in Chelmsford and Essex
Connor Ferris Architects is a RIBA Chartered architectural practice based in Chelmsford, providing residential architectural services throughout Essex and the surrounding areas.
We work on house extensions, loft conversions, renovations and new-build homes across areas including Chelmsford, Great Baddow, Writtle, Danbury, Maldon, Billericay, Brentwood, Ingatestone, Braintree, Witham and surrounding towns.
Our services can continue beyond planning permission into RIBA Stage 4 Technical Design and Building Regulations, including coordination with structural engineers and other consultants where required.
Once the technical package is sufficiently developed, we can also assist clients with obtaining competitive contractor quotations.
If you already have planning permission for an extension and are wondering what happens next, we can review the approved design and discuss the technical information required to move your project towards construction.
