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City of London, London

Structural calculations in the City of London

The Square Mile has few houses and a great many listed buildings, so structural work here is a retrofit exercise. Our calculations start at £295 including VAT. The City's retrofit guidance makes a request that fits our approach: structural audit early; retrofit = 50% superstructure by mass retained.

From £295 (VAT included)

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    Architectural model of a four-storey London stucco townhouse in its terrace, with a portico, area railings, sash windows, a cornice and chimney stacks
    The house as it stands: four storeys over a lower ground floor.Existing Proposed worksAn illustrative model, built for this page.

    How we work on structural calculations

    Four steps from first call to approval.

    The same model cut through the middle: every floor, the stair, the chimney breasts, the new mansard, rear extension and basement in section
    Section through the model: every floor on one datum.

    1. Enquiry and constraints check

      We check the property against conservation areas, listed status, Article 4 directions, tree preservation orders, flood zone and planning history. We choose the right route and send a fixed quote.

    2. Measured survey

      We survey the house on one datum: rooms, levels, boundaries, drains, trees and the neighbours' windows that the 45° and 25° tests depend on.

    3. Building regulations

      Technical drawings are coordinated with the structural engineer's calculations, the drainage and the planning conditions.

    4. Approval and hand-over

      Building control approval, then a next-steps pack covering the commencement notice, party wall timing and CIL.

    Free redraws until approval. Every drawing set is checked independently, and the checker is never the person who drew it.

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    Steel beams supporting exposed timber floor joists on temporary props during a house renovation

    Structural calculations and the City retrofit approach

    The City of London Corporation guides alterations through its retrofit advice. It asks for a structural audit, with testing where relevant, early in the design, and it defines retrofit by how much existing structure is kept: structural audit early; retrofit = 50% superstructure by mass retained. For a flat in a post-war block or a converted warehouse, that audit is the starting point for every structural calculation.

    A calculation for an old building begins with what is there, not with what a new building would need. We record floor construction, wall thickness and the presence of steel or concrete frames, then check the proposed opening or loading against that measured capacity.

    Where the council wants reuse to be demonstrated, the same document tells the planning team why the original structure is being retained.

    We also record the age of any steel or concrete frame. The guidance asks for existing structural capacity to be understood and put to use, and a tested capacity can sometimes avoid strengthening that a cautious assumption would demand.

    Brick house being extended, with a wide new opening supported over the ground floor

    Local figures for City of London

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Small residential alterations, Full Plans (excl. VAT, GBP): 10,000 works plan 978 inspection included; 20,000 1,342; 40,000 plan 755.20 + inspection 1,132.80; 100,000 plan 1,046.40 + inspection 1,569.60. Building notice 978 / 1,342 / 1,888 / 2,434 / 2,616 for the same cost bands.GBP 978 for 10,000 of small residential alteration works (building notice)—cityoflondon.gov.uk, Building Control charges - City of London, Small residential alterations table
    City SFRA 2023: London Clay about 35 m thick over the Lambeth Group and Chalk; groundwater risk centres on River Terrace Deposits; two areas of increased groundwater potential where new basements and basement extensions are advised against.avoid new basements in two elevated-groundwater areas—cityoflondon.gov.uk, City of London Strategic Flood Risk Assessment 2023, groundwater flooding section; Appendix A map
    Retrofit guidance: undertake a structural audit (including relevant testing) early to understand the condition and capacity of the existing structure, and optimise existing structural capacity for alterations and extensions. The City defines retrofit as retaining and reusing at least 50% of the existing superstructure by mass.structural audit early; retrofit = 50% superstructure by mass retained—cityoflondon.gov.uk, City of London Planning for Sustainability SPD (February 2025), Chapter 3 Retrofit and Reuse, PDF p.18 ('Undertake a structural audit'); definition PDF p.16
    Pre-deconstruction audit (reuse schedule) should be supported by salvage/demolition drawings from the architects and deconstruction drawings from structural engineers; where not practical at application stage, the information can be triggered by conditions.deconstruction drawings from structural engineers—cityoflondon.gov.uk, City of London Planning for Sustainability SPD (February 2025), Chapter 3 Retrofit and Reuse, PDF p.15
    Households4,914Census 2021 (21 March 2021)nomisweb.co.uk
    Households living in a house2 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Conservation areas28 named conservation areas published by the council—planning.data.gov.uk
    Listed building entries637 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Grade I listed entries86 list entries—planning.data.gov.uk
    Building Regulations 2010 reg 11FDesign work must be done by a competent person—legislation.gov.uk

    A blank value means the figure has not been published, not that there are none. Check your own address with the council.

    Councils bordering City of London
    Building regulations, layer by layerPart A: structure: Approved Document A: Structure, 2004 edition incorporating 2004, 2010 and 2013 amendments. Part B: fire safety: All dwellings: fire detection and alarm system minimum Grade D2 Category LD3 (BS 5839-6), mains-operated smoke alarms to BS EN 14604. Part L: insulation: New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4. Part K: stairs: 2.0 m clear headroom over stairs. Full plans application: Building control body must decide a full plans application within 5 weeks, or longer if agreed in writingPart A: structurePart B: fire safetyPart L: insulationPart K: stairsFull plans applicationABCDE

    Building regulations, layer by layer

    The Approved Documents that shape most house projects, from structure to the application itself.

    A · Part A: structure
    Approved Document A: Structure, 2004 edition incorporating 2004, 2010 and 2013 amendments
    B · Part B: fire safety
    All dwellings: fire detection and alarm system minimum Grade D2 Category LD3 (BS 5839-6), mains-operated smoke alarms to BS EN 14604
    C · Part L: insulation
    New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4
    D · Part K: stairs
    2.0 m clear headroom over stairs
    E · Full plans application
    Building control body must decide a full plans application within 5 weeks, or longer if agreed in writing

    Deconstruction drawings and conditions

    Larger schemes are asked for more: deconstruction drawings from structural engineers. A small residential project does not usually reach that scale, but the principle carries across, since taking something apart in an orderly sequence is also what a safe alteration needs.

    If the information cannot be ready at application stage, the council may attach a condition. We write method notes on temporary supports and sequencing so that a condition can be discharged without a second round of design.

    Groundwater and clay beneath the Square Mile

    The City's flood assessment describes the ground in layers: London Clay of considerable thickness sits over the Lambeth Group and Chalk, and groundwater risk centres on river terrace deposits. It adds a firm view on basements: avoid new basements in two elevated-groundwater areas.

    A residential owner thinking of a lower floor should treat that as a serious warning. We would test the idea with a desk study before any drawings are produced.

    What it costs to have the building control file checked

    The City's published charges for small residential alterations are tiered by the cost of work, shown as plan and inspection fees. The first band reads: GBP 978 for 10,000 of small residential alteration works (building notice). Those fees go to the council and sit outside our price.

    Higher bands rise with the value of the work. Having the structural package complete at submission helps avoid queries that stretch the inspection period.

    A small residential area inside a large commercial one

    The City has only 4,914 households and 2 per cent of them live in a house, so almost every project is a flat. 36.5 per cent are owner-occupied, and a flat averages £709,939.

    Planning decisions are few: 1 householder decision in the latest return, so there is little local pattern to read from statistics. What the council does publish is guidance, which is why we follow it so closely.

    Working inside managed buildings

    Many City flats sit in blocks with a managing agent and strict rules on noise, deliveries and lifts. A structural change usually needs the agent's approval as well as the council's, and the agent will want the calculation and a temporary works note. We prepare both together so one pack serves every party.

    Because there are so few houses in the Square Mile, a calculation here usually concerns a floor slab, a column or a partition with some structural role, not a masonry wall, and the checks differ accordingly.

    Heritage everywhere

    There are 28 conservation areas and 637 listed building entries, with 86 at Grade I and 82 at Grade II star. Even a simple opening can need listed building consent, so the calculation is prepared as part of that application, not afterwards.

    The Barbican alone has its own Barbican Estate Listed Building Management Guidelines: Volume I Introduction and Volume II Residential (SPD), which governs what can be changed in a listed estate. Structure inside such a building is usually concrete, and the sizing approach differs from brick.

    Fee and next steps

    Calculations start at £295 including VAT. For frames and heritage schemes the fee is fixed after we have seen the building. Related pages: structural engineering in the City of London, building regulations drawings in the City of London and the City overview.

    Nearby, see Hackney and Camden. Competence is a legal point: Design work must be done by a competent person.

    What you receive

    Structural calculation sheet for a steel beam
    Sample drawing. Structural calculation for a steel beam, coordinated with the engineer.
    House extension under construction with scaffolding, new glazed doors and building materials
    Load take-down
    Brush across the bars.

    Other services in City of London

    Structural calculations nearby

    Questions

    What does the City ask for on structural audits?

    An early audit, in this form: structural audit early; retrofit = 50% superstructure by mass retained.

    Can I add a basement in the City of London?

    The flood assessment says: avoid new basements in two elevated-groundwater areas.

    What is the council fee for a small alteration?

    The first band is GBP 978 for 10,000 of small residential alteration works (building notice).

    What are your fees for calculations?

    From £295 including VAT, fixed once we have seen the building.

    Sources and dates

    City of London skyline glowing at dusk across the Thames under a dramatic orange sky

    Tell us about your property.

    We check the constraints, then send a fixed fee. Messages before 3pm get a reply the same working day.

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