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Single-storey rear extension in grey blockwork under construction with a steel beam spanning the new opening in the old rear wall

Blog: building regulations

How much do structural calculations cost in London?

By Property Architecture drawing team, chartered architectural technologists (MCIAT). Published . 3 minute read.

Structural calculations for a London house cost £385, with no VAT to add, and that fee is for the calculations on their own. They prove that a new beam, opening or floor carries its load, which is what building control asks to see before it will let the work start. The fee is the same whether the house is a terrace in Hackney or a semi in Barnet.

From £385 total

  • MCIAT chartered
  • £2m PI insured
  • LABC Partnered
  • Fixed fees, no VAT to add

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    Key takeaways

    What the fee buys

    Our fee is £385 for the calculations. They set out the loads each new member must carry, the size and grade of each steel or timber beam, the padstones or columns that carry them, and the points where the load reaches the foundations. A builder can order steel from them, and building control can check them.

    That is a deliberately narrow job. The calculations do not include the survey or the architectural drawings, which are priced separately, because many owners already have a drawing set and just need the beam sized. If you do not, our building regulations drawings are from £729, and the two work together.

    What the fee includesLoads and sizes for each new beam or support; Padstone and column checks; A calculation pack for building control; A plain summary your builder can order from; Bearing points shown for each supportWhat the fee includesLoads and sizes for each new beam orsupportPadstone and column checksA calculation pack for building controlA plain summary your builder can orderfromBearing points shown for each supportFixed fee from £385, no VAT to add
    What a structural calculation pack includes.

    Why building control asks for them

    The Building Regulations put the requirement in one sentence. Under requirement A1: loads must be sustained and transmitted to the ground safely, without impairing the stability of another buildingBuilding Regulations 2010, Schedule 1, requirement A1. A beam over a wide opening is the clearest case, because removing a wall transfers its load somewhere else, and only a calculation shows that the new support can take it.

    It is also a matter of who may do the design. The regulations say: anyone doing design work must have the skills, knowledge, experience and behaviours neededBuilding Regulations 2010, regulation 11F. That is why an experienced owner-builder still needs the figures signed off by someone who can prove competence.

    New timber roof rafters set out over a masonry wall during a house renovation
    Roof and floor timbers are sized in the calculation, just like steel. Photo: Bryn Pinzgauer, CC BY 2.0

    Jobs that usually need calculations

    The usual triggers are a rear wall opened for bi-fold doors, a chimney breast removed, a kitchen-diner knocked through, a loft floor strengthened, and a new first-floor extension on old foundations. Each is a case of a load changing path.

    Your project may need one calculation or several, and we say which at the start. The set is normally prepared alongside the drawings, because the calculation depends on the layout and the drawing depends on the beam depth. For a loft, see our loft conversion drawings; for an extension, our rear extension drawings.

    When to order them, and what it saves

    Order the calculations before you submit to building control, not after. A full plans application is answered within five weeks, or longer if agreed in writingBuilding Regulations 2010, regulation 14A, and one that arrives with the structure already shown is less likely to be sent back with a question.

    Getting them early also helps the builder. Remember that building regulations approval is different from planning permission, and you might need bothGOV.UK, Building regulations approval, so planning permission does not cover this step. A quote that names the steel sizes is a firmer quote, and a beam that turns out deeper than assumed can change the ceiling height after the plasterer has been booked.

    How the job runs, step by stepSend your drawings, or order them from us Then: We check the layout and where each load goes Then: Beams, columns and bearings sized in a calculation pack Then: Pack checked by a second person Then: Sent to you for building control and your builder Then: Issued as a calculation pack for building controlSend your drawings, or order them fromusWe check the layout and where eachload goesBeams, columns and bearings sized in acalculation packPack checked by a second personSent to you for building control andyour builderIssued as a calculation pack forbuilding control
    From your drawings to a signed-off calculation pack.

    What if the work is already done?

    Sometimes a wall has already been opened without any figures. The answer is not to leave it. Contravening the regulations is an offence: on conviction on indictment, imprisonment for up to two years or a fine, or bothBuilding Act 1984, section 35. The practical route is regularisation, where the council accepts the work after an inspection, and the calculations are done retrospectively. Our regularisation drawings cover that, and the retrospective calculation is what shows whether the existing steel is adequate.

    The figures, with sources

    Building regulations requirement A1
    loads must be sustained and transmitted to the ground safely, without impairing the stability of another buildingBuilding Regulations 2010, Schedule 1, requirement A1Checked 25 October 2026
    Competence of designers
    anyone doing design work must have the skills, knowledge, experience and behaviours neededBuilding Regulations 2010, regulation 11FChecked 25 October 2026
    Time for the council to decide a full plans application
    five weeks, or longer if agreed in writingBuilding Regulations 2010, regulation 14AChecked 25 October 2026
    Penalty for contravening building regulations
    on conviction on indictment, imprisonment for up to two years or a fine, or bothBuilding Act 1984, section 35Checked 25 October 2026
    Notice for work to a party structure
    a party structure notice must be served at least two months before the work beginsParty Wall etc. Act 1996, section 3Checked 25 October 2026
    Building regulations and planning
    building regulations approval is different from planning permission, and you might need bothGOV.UK, Building regulations approvalChecked 25 October 2026

    Questions

    Does the fee include a site visit?

    The fee covers the calculations. If we cannot size the steel from your drawings or photographs, we say so and price a survey, rather than guess.

    Do I need calculations for a Velux or small dormer?

    Usually the roof timbers still need checking. Tell us what you are changing and we will say whether a calculation is needed, so you pay only for what building control will ask for.

    Is a party wall notice part of this?

    No. If a beam bears on a party wall, the neighbour must be told at least two months before work starts. Our party wall notices are priced separately, from £45.

    Can my builder just pick a steel size?

    A builder's rule of thumb is not accepted by building control for anything unusual, and the regulations require design to be done by someone competent. A calculation protects you if the sizes are ever questioned.

    Header photo: A single-storey rear extension in grey blockwork under construction, with a steel beam spanning the new opening into the house by Brett Jordan, Pexels License.

    The fixed fee for structural calculations

    Fixed fee
    from £385
    Total you pay
    from £385
    Council fee
    paid to the council separately

    No VAT to add. The fee is fixed in writing after a free constraints check of your address.

    What you get

    • Loads and sizes for each new beam or support
    • Padstone and column checks
    • A calculation pack for building control
    • A plain summary your builder can order from
    • Bearing points shown for each support
    • More about our structural calculations
    Request your fixed quoteCall 020 7131 9703
    Brick house under construction with a large new opening in the rear wall spanned by a steel beam

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    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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