Structural Calculations for Loft Conversions
Structural proof · section and beam detailTurning a loft into a room means putting new loads on your house. Structural calculations prove the new floor, steel beams and altered roof can carry them safely, and structural drawings show your builder exactly what to install. They are prepared with our building regulations drawings for homes across Essex, Hertfordshire and North and East London.
Not included
Supply and installation of steels, site inspections by the engineer, and building control fees are not included. If opening up reveals something unexpected on site, additional design may be needed.
What you receive
- Structural calculation pack
- Structural drawings and connection details
- Steel beam, padstone and joist specifications
- Coordination with building regulations drawings
- Responses to building control structural queries
How the coordinated package is paid
Planning drawings & submission
£950The initial planning/design stage.
Building Regulations drawings + structural calculations
£550Payable after full-planning approval and finalised within a further few working days.
How it works
- 01
Survey information
Measurements and structural observations from our survey are passed to the engineer.
- 02
Design
The engineer designs beams, joists and connections for the agreed layout.
- 03
Drawings
Structural drawings and calculations are coordinated with the building regulations set.
- 04
Building control
The pack is submitted and any inspector queries are answered.
What gets designed
Every loft is different, but calculations for a typical conversion cover: • New floor joists, spanning between steel beams or load-bearing walls • Steel beams supporting the new floor and any cut roof timbers • Padstones and bearings where beams sit on existing masonry • Ridge beams and supports for dormers or hip-to-gable alterations • Trimming around the new stair opening • Checks on existing walls and foundations taking the new loads
When you need them
Structural calculations are needed for building regulations approval on almost every loft conversion that creates a habitable room. They are usually prepared once the planning design is settled, so beam positions and sizes suit the final layout. They are especially important for dormer, L-shape and hip-to-gable conversions, where large parts of the roof are removed or rebuilt.
Not sure which conversion suits your loft?
We’ll assess the roof and explain what the space can realistically deliver.
Calculations and structural drawings
The calculation pack is what building control review. The structural drawings translate it into plans and details — beam locations, bearing details, joist layouts and connections — so your builder can order materials and install them correctly. Both are coordinated with our building regulations drawings, so the structure, stair and fire protection all match.
Frequently asked questions
01Why does a loft conversion need structural calculations?
Existing ceiling joists aren't designed to carry a habitable floor, and most conversions alter the roof structure. Calculations show building control that new joists, steel beams, padstones and connections can safely carry the loads down to the existing walls.
02What's the difference between structural calculations and structural drawings?
The calculations are the engineer's design document: loads, member sizes and checks. The structural drawings show where each beam and joist goes and how it connects, so your builder can install it correctly.
03Who prepares the calculations?
They are prepared by a structural engineer we work with, based on our survey and the agreed design, and coordinated with our building regulations drawings.
04Can I get structural calculations on their own?
Structural calculations form part of the £550 technical stage with Building Regulations drawings. On a full-planning case this is payable after approval, following the £950 planning/design stage; the coordinated package totals £1,500. If you already have drawings from elsewhere, get in touch and we'll confirm what is possible.
05Will building control accept the calculations?
They are prepared for submission to building control alongside the building regulations drawings. If the inspector raises questions, we coordinate the response with the engineer.
06Do steel beams always need to be craned in?
Not always. Beam sizes and splice positions can often be designed so steels can be brought in through the roof or house. This is discussed during design so your builder can plan the installation.
See examples
Sample structural documents from a loft conversion. Each opens as a PDF in a new tab.
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