Structural Drawings Explained: Plans, Calculations and Sign-Off
Structural drawings are technical drawings that show how a building — or an alteration to one — is physically supported: the size and position of beams, joists, columns, foundations and structural openings, backed by structural calculations that prove the structure can safely carry the loads placed on it. They are distinct from architectural plans, which show layout and appearance; a structural drawing answers "will this stand up and stay up", not "what does this look like".
For most London home improvement projects — loft conversions, extensions, removing a load-bearing wall, underpinning a basement — structural drawings are a legal requirement, not an optional extra, because building control will not issue a completion certificate under the Building Regulations 2010 without them where the work affects the structure of the building. This page explains what structural drawings actually contain, when building control demands them, how a steel beam schedule works, who is qualified to sign them off, and how they fit into a wider building regulations submission alongside architectural plans.
What do structural drawings actually contain?
A typical structural drawing set for a domestic project includes:
- A structural layout plan showing beam and joist positions, spans and sizes, overlaid on the architectural floor plan
- A beam schedule listing each steel beam (often referred to as an RSJ, or Rolled Steel Joist) by reference number, size (for example a 203x133 Universal Beam), and the load it carries
- Foundation drawings showing depth, width and type — strip, trench-fill or pad foundations — particularly important where a new foundation is close to an existing one, a tree, or a drain
- Connection details showing how beams bear onto walls or padstones, and how new structure ties into existing structure
- The structural calculations themselves — the engineer's numerical justification for every beam size and foundation, checked against the loads imposed by the building above
These drawings are prepared alongside, and cross-referenced to, the architectural floor plans and elevations, so that a builder on site can read both sets together without ambiguity about where a wall is structural, where an opening needs support, and what size of beam goes in.
When does building control actually demand structural drawings?
Under the Building Regulations 2010, any work that affects the structure of a building needs Building Regulations approval, assessed primarily against Approved Document A (structure), and structural drawings are the evidence building control uses to check the work is safe. In practice, this covers: removing or altering a load-bearing wall, forming a new opening for a door, window or bi-fold doors, converting a loft (which adds new floor loads the original roof structure was never designed for), building any extension with a new roof or floor structure, and underpinning or excavating for a basement.
Some minor works fall under the exemptions listed in Schedule 2 of the Building Regulations 2010 — for example certain small detached buildings — but any structural alteration to an occupied dwelling almost always requires full plans or building notice submission with structural calculations attached. Building control surveyors, whether from the local authority or an approved inspector, will not sign off completion, and in some cases will not even approve the building notice, without seeing calculations for any new structural element.
What is a steel beam schedule and why does it matter?
A steel beam schedule is a table, usually included on the structural drawing itself, listing every steel beam in the project by a reference mark, its size and steel grade, its span, the load it carries, and the padstone or connection detail at each end. For a loft conversion this might list beams supporting the new floor and the staircase opening; for an extension it might list a beam over new bi-fold doors and, for a two-storey scheme, a beam supporting the first floor above.
The schedule matters for three practical reasons: it lets the steel fabricator order the right sections without ambiguity, it gives building control a clear, checkable record that beam sizes match the calculations, and it protects the homeowner, because if a beam is under-specified and a defect appears later, the schedule and calculations are the record of what was designed, by whom, and against what loading assumptions.
Who actually signs off structural drawings — an engineer or a technologist?
Structural calculations are prepared and signed by a qualified structural engineer, typically chartered through the Institution of Structural Engineers (IStructE) or the Institution of Civil Engineers (ICE), because they carry professional indemnity insurance specifically for structural design and are the professionally recognised authority for calculating loads, beam sizes and foundation design. An MCIAT-chartered architectural technologist, by contrast, is qualified to prepare the architectural drawings, coordinate the overall building regulations submission, and liaise with the structural engineer to make sure structural and architectural drawings match — but does not typically produce the calculations themselves.
How do structural drawings fit into the wider building regulations submission?
A full building regulations submission bundles several drawing types together: architectural floor plans and sections showing the proposed layout, structural drawings and calculations showing how it's supported, and specification notes covering insulation values (checked against Approved Document L), fire safety and escape routes (Approved Document B), drainage (Approved Document H) and ventilation (Approved Document F). Building control — whether the local authority's own building control team, used by most London boroughs including Southwark, Ealing and Croydon, or a private approved inspector — reviews the full package together, because a beam that's correctly sized on paper is only compliant if it also sits within a wall build-up that meets the insulation and fire requirements around it.
This is also why structural drawings shouldn't be commissioned as an afterthought once building work has already started: the beam size and position affects headroom, ceiling depth and sometimes the layout itself, so structural input at the drawing stage — before a planning or building notice application goes in — avoids costly redesign once a contractor is already on site.
Do I need structural drawings for a loft conversion specifically?
Yes, in almost every case. A loft conversion adds an entirely new floor load onto a roof structure that was originally designed only to carry roof loads, not a habitable room's worth of furniture, people and finishes. Structural drawings for a loft conversion typically size new floor joists (frequently steel beams given the spans involved in a typical London terrace), the opening for the new staircase, and confirm whether the existing walls below can carry the additional load down to the foundations without strengthening. Because loft conversions in terraced and semi-detached houses usually also involve a beam bearing onto a shared party wall, the structural drawings often become part of the Party Wall etc. Act 1996 notice served on the neighbour, so getting this element right early avoids delays on two fronts — building control and the party wall process — at once.
What's the difference between architectural plans and structural plans?
Architectural plans (floor plans, elevations, sections) describe the design intent: room layout, external appearance, dimensions and how spaces relate to each other. Structural plans describe how that design intent is physically achieved: which walls carry load, where beams and columns go, how deep the foundations need to be, and what the calculations behind each of those decisions are. The two sets of drawings must agree with each other — an architectural plan showing an open-plan kitchen extension is only buildable if the structural plan shows a beam sized to span that opening — which is exactly the coordination role an architectural technologist plays between the client's design brief and the structural engineer's calculations.
How does building control actually check structural calculations?
In London, structural drawings and calculations can be checked by two different routes: the local authority's own building control team (LABC), used by most boroughs including Southwark, Croydon, Ealing and Hackney, or a private approved inspector working under the Building (Approved Inspectors etc) Regulations. Both routes have the same legal effect once a completion certificate or final certificate is issued, but the process differs slightly. LABC teams check drawings against the borough's own building control register and often carry out site inspections at set stages — foundation, damp-proof course, drainage and completion — cross-checking what's built against the approved structural drawings each time. Approved inspectors work independently of the council, issuing their own initial notice and final certificate, and are often used where a project needs a faster turnaround or where the design team already has an established relationship with a particular inspector.
Either way, the reviewing body checks three things against the structural drawings: that every beam and foundation has calculations behind it, that the calculations use recognised design standards (such as the Eurocodes, which replaced British Standards for structural design), and that what's actually built on site matches what was approved on paper — which is why site inspections at key stages, not just a paper review, are a standard part of the process for any structural work.
What loading assumptions go into a set of structural calculations?
Structural calculations are only as good as the loading assumptions behind them, and a structural engineer working on a London property has to account for several categories of load. Dead loads cover the weight of the structure itself — the beam, the floor joists, the finishes such as screed or tiling. Imposed loads (sometimes called live loads) cover the weight of people, furniture and stored items, with residential floors typically designed to a standard imposed load allowance regardless of how the room is actually furnished, so the structure has margin for a heavily loaded room such as a home gym or a library. Wind and, where relevant, snow loads are also factored into roof and beam design, particularly for loft conversions and roof extensions where the existing roof structure is being altered.
For older London housing stock — Victorian and Edwardian terraces are common across boroughs such as Lambeth, Wandsworth and Hackney — the engineer also has to assess the condition and likely composition of existing walls and foundations, since these properties predate modern construction standards and often have shallower foundations or solid (rather than cavity) walls, which affects how new loads can be safely transferred down through the building. This is one of the reasons a site visit by the structural engineer, not just a desk-based calculation from architectural drawings alone, is standard practice before calculations are finalised on an older property.
What standards and limits do the calculations actually check against?
Steel beams in UK domestic structural work are designed to BS EN 1993 (Eurocode 3), which superseded the older BS 5950, and timber elements to BS EN 1995 (Eurocode 5). A common check within the calculations is deflection: a domestic floor beam is typically limited to a deflection of span/360 under imposed load, meaning a beam spanning 4,000mm should deflect no more than roughly 11mm — enough stiffness that plaster and floor finishes don't crack. Domestic floors are usually designed to an imposed loading of 1.5 kN/m² under BS EN 1991 (Eurocode 1), covering people, furniture and normal domestic use, on top of the dead load of the floor construction itself.
Bearing detail matters as much as the beam size: a steel beam typically needs a minimum of 100mm end bearing onto a padstone or wall plate, spreading the point load from the beam into the masonry below without local crushing — a detail building control checks on site as much as on paper. These are the kind of numerical checks that separate a structural calculation from a rule of thumb, and why an undersized bearing or an under-checked deflection limit, not just an undersized beam, is one of the more common site queries on London loft conversions and extensions.
What does building control approval actually cost and how long does it take?
Building control fees are separate from design fees and are paid to whichever route is used — the local authority's building control team or a private approved inspector. For a typical loft conversion or single-storey extension in London, local authority building control charges (covering plan checking and site inspections) commonly fall in the £500–£1,000 range depending on the borough and project size, quoted on request by the specific council's building control team, for example the London Borough of Camden, the London Borough of Islington or the Royal Borough of Kensington and Chelsea. Approved inspectors quote separately and can sometimes turn plan checking around faster than a full-plans local authority submission, which typically takes around 5 weeks for the initial check once a complete application, including structural calculations, is deposited.
On top of building control fees, a structural engineer's fee for calculations and a beam schedule on a typical loft conversion or single-storey extension often sits in a similar range, while this practice's own drawing packages, which include structural liaison, roughly 30% below typical London architect rates for the same scope.
Do structural requirements change in a conservation area or listed building?
Conservation area status doesn't usually change the structural engineering itself — a beam still has to satisfy the same Eurocode checks whether the property sits in the Hampstead Conservation Area in Camden or a plain suburban street in Bromley. What does change is the surrounding process: works in a conservation area, or to a listed building, often need Local Planning Authority consent alongside Building Regulations approval, and the local plan or a Supplementary Planning Document (SPD) covering that conservation area may restrict visible alterations even where the structural change itself is straightforward. For listed buildings specifically, any structural intervention — a new beam, an underpinned foundation — typically needs Listed Building Consent in addition to Building Regulations approval, and the structural engineer's drawings often need to show a more sympathetic, minimal-intervention approach than would be used on an unlisted property, to satisfy the conservation officer as well as building control.
Frequently asked questions
Do I need structural drawings for a small extension?
If the extension involves any new opening, beam, or altered roof or floor structure — which is true of almost every extension, even a modest single-storey one — building control will require structural calculations under Approved Document A before issuing approval.
What is the difference between structural drawings and structural calculations?
Structural drawings show the physical layout — beam positions, sizes and connection details. Structural calculations are the underlying engineering maths that prove those beam sizes and foundations are adequate for the loads involved; building control typically requires both together.
Who is qualified to produce structural calculations?
A structural engineer, usually chartered through the Institution of Structural Engineers or the Institution of Civil Engineers, carrying professional indemnity insurance specific to structural design work.
Can an architectural technologist do structural calculations?
Generally no — an MCIAT-chartered architectural technologist prepares and coordinates the architectural drawings and manages the wider building regulations submission, but the structural calculations themselves are produced by a qualified structural engineer, often brought in as part of the same project.
How much do structural drawings cost?
Cost depends on the scope of structural work — a single beam over a doorway is far cheaper to calculate than a full loft conversion floor or a two-storey extension.
Does every wall removal need structural drawings?
If the wall is load-bearing, yes — a structural engineer needs to calculate a suitable beam and building control will require the calculations before signing off the work. If the wall is confirmed as genuinely non-load-bearing, the requirement is reduced, but this should always be verified by a professional rather than assumed.
What's the difference between LABC and an approved inspector?
LABC is the local council's own building control service; an approved inspector is a private, independently regulated alternative that performs the same statutory checks and issues its own final certificate. Both are equally valid routes to Building Regulations compliance in London.
Do older London properties need different structural calculations?
Often yes — Victorian and Edwardian terraces common across boroughs like Lambeth, Hackney and Wandsworth typically have solid walls and shallower foundations than modern construction, so a structural engineer usually needs a site assessment of the existing structure's condition before finalising calculations for new loads.
Do I need a structural engineer for a basement conversion?
Yes — basement work involves underpinning existing foundations and retaining walls, among the most structurally complex domestic work, and needs detailed calculations from a structural engineer alongside geotechnical input on ground conditions before building control will approve the scheme.
What standards do UK structural engineers design to?
Modern structural calculations in the UK are produced to the Eurocodes, the harmonised European structural design standards that replaced the older British Standards, covering everything from steel beam design to foundation and timber design.
What deflection limit do domestic floor beams need to meet?
A common limit is span/360 under imposed load — for a beam spanning 4,000mm, that's a maximum deflection of around 11mm, keeping plaster and floor finishes from cracking under normal use.
How much do building control fees cost for a loft conversion or extension?
Local authority building control fees for a typical London loft conversion or single-storey extension commonly fall in the £500-£1,000 range, quoted by the specific borough's building control team, separate from design and structural engineering fees.
How long does building control take to check a full-plans submission?
A full-plans submission to local authority building control, including structural calculations, typically takes around 5 weeks for the initial check once the application is complete, though site inspections continue at key stages through to completion.
