When planning a house extension in London or a loft conversion, it’s important to understand that there are costs beyond architectural design and planning. These additional expenses typically include council submission fees, building control charges, structural engineering costs, and various specialist surveys such as drainage CCTV surveys, tree surveys, or ecology assessments.
Below we’ve set out examples of the professional fees and third-party costs that have applied to past projects we’ve worked on — ranging from chimney removals to full loft conversions. These are provided as guidance only, since every property and project is unique. For example, your own loft conversion may require different approvals or fewer consultants depending on the design and local authority requirements.
It’s also worth noting that Party Wall Agreements can apply across almost all project types, whether you’re extending, converting your loft, or removing a chimney breast. The exact scenario will depend on your property’s relationship with neighbouring walls. If neighbour relations are positive, costs are often lower as they are less likely to appoint their own surveyor.
For more detail on our core service fees, see our guides on house extensions in London, loft conversions, planning permission, and building regulations.
Chimney Removal & Creation of WC
Design and Planning Phase:
- Measure and Design Fees: Contact Detailed Planning for a quote
Technical Phase:
- Building Regulation Drawings: Contact Detailed Planning for a quote
- Structural Engineer Fee: £840
- Building Control Inspection Fees: £890 inc VAT
- Party Wall Agreements: A notice was served to one neighbour as the chimney was being removed, the fee for the notice was £150 inc vat. The neighbour opted for a schedule of condition rather than a full party wall agreement costing the owner £900 inc vat rather than the typical £1500 inc VAT for a full party wall agreement.
Simple Single Storey Ground Floor Rear Extension
Design and Planning Phase:
- Design and Planning Phase Fees: Contact Detailed Planning for A quote
- Lawful Development Council Fee: £349
Technical Phase:
- Building Regulation Drawings: Contact Detailed Planning for a quote
- Structural Engineer Fee: £900-£1,300
- Building Control Inspection Fees: £1,000-£1,300
- Thames Water Build Over Agreement: £105
- Party Wall Agreements: A notice was served to two neighbours as the excavation were within 3m of the neighbours, the fee for each notice was £150 inc vat. One neighbour signed the notice and the other opted for party wall agreement and agreed to using the suggested surveyor costing the owner £1500
Wrap Around Single Storey Ground Floor Rear Extension With Chimney and WC
Design and Planning Phase:
- Design and Planning Phase Fees: Contact Detailed Planning for A quote
- Householder Planning Application Council Fee: £613
Technical Phase:
- Drainage Investivations: As drainage was unknown the seweres were mapped by a drainage surveyor for £400
- Building Regulation Drawings: Contact Detailed Planning for a quote
- Structural Engineer Fee: £1,300-£1,800
- Building Control Inspection Fees: £1200-£1,800
- Thames Water Build Over Agreement: £105
- Party Wall Agreements: A notice was served to two neighbours as the excavation were within 3m of the neighbours and shared walls were proposed, the fee for each notice was £150 inc vat. One neighbour agreed to use the suggested surveyor costing the owner £950 inc VAT. The other owner opted for their own surveyor, therefore the owner had to pay two surveyors fee for one neighbour, the suggest surveyor cost £950 inc VAT, the neighbours surveyor cost and additional £1500 inc VAT.
Permitted Development Loft Conversion (semi detached)
Design and Planning Phase:
- Design and Planning Phase Fees: Contact Detailed Planning for A quote
- Lawful Development Application Fee: £349
Technical Phase:
- Building Regulation Drawings: Contact Detailed Planning for a quote
- Structural Engineer Fee: £800-£1,300
- Building Control Inspection Fees: £1,000-£1,300
- Party Wall Agreements: A notice was served to one neighbour as beams were installed within the party wall, the fee for each notice was £240 inc vat. The neighbour agreed to use the suggested surveyor costing the owner £1500 inc VAT.
Large Double Storey Extension, Loft Conversion and Roof Extension (detached house)
Design and Planning Phase:
- Design and Planning Phase Fees: Contact Detailed Planning for A quote
- Householder Planning Council Fee: £613
Technical Phase:
- SAP Calculations: Due to large amounts of glazing a SAP (Energy calculation) was required at a fee of £500
- Building Regulation Drawings: Contact Detailed Planning for a quote
- Structural Engineer Fee: £2,000-£3,500
- Building Control Inspection Fees: £2,000-£3,000
- Drainage Investivations: As drainage was unknown the seweres were mapped by a drainage surveyor for £400
- Party Wall Agreements: Excavations were within 3m of one neighbour, a notice was served costing the owner £240 inc VAT, the neighbour signed the notice allowing the works to proceed.
Other less typical requirements:
- Arboriculturist (if near trees) – £1,000 – £2,000
- CIL payments (if building over 100sqm)
- Biodiversity Reports
- Traffic/highway consultants
