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UK Structural Engineering · Loft Conversions

Loft Conversion Structural Calculations & Drawings

Building Control-ready structural calculations and drawings for loft conversion companies across London and the UK. Fixed fee. Fast turnaround. Done properly.

Practical structural plans and calculations designed to make the construction details clear for builders, loft conversion companies and Building Control.

Send Your Loft Plans Request a Fixed Fee Quote
30 Years' Experience
250+ Packages Delivered
Fixed Fee
Insured
Building Control Ready
5–10 Day Turnaround
Sound Familiar?
✕
Waiting 2–3 weeks for structural calculations

Long turnarounds from busy general engineers disrupt your programme and delay Building Control submissions.

✕
Building Control keeps querying the calculations

Incomplete or generic structural calculations attract queries — and the delays that follow stall the whole job.

✕
Structural drawings the builder can't follow on site

Vague layouts that miss beam positions, padstone sizes and joist centres make life harder for everyone on site.

Design Axis solves all three. Specialist loft conversion structural packages — fixed fee, 5–10 day turnaround, Building Control-ready.
30+
Years of structural engineering experience across residential and loft conversion projects
250+
Loft conversion structural calculation packages completed and accepted by Building Control
5–10 days
Standard turnaround — priority service available for urgent submissions
Fixed Fee
Confirmed in writing before work starts. No hourly rates. No additions.
What's Included

A complete structural package for your loft conversion

Calculations, structural layout plans, section details and member schedules — so builders can price, Building Control can check, and the project can move forward.

  • Structural Layout & Section Plan Dimensioned plans showing beam positions, joist layout, padstone locations, key section details and all structural member references.
    Structural Layout — Extract
    B1 — 254×146×37 UB S275 47×195 C24 @ 400 c/c P1 P1 6.700 m
  • Structural Member Schedule Every steel and timber member listed with section size, grade, span and drawing reference — ready for the builder, estimator and Building Control.
    Member Schedule Extract
    RefSectionGradeSpan
    B1254×146×37 UBS2754.80 m
    B2203×133×25 UBS2753.20 m
    J147×195 C24C243.60 m @400
    R12/47×225 C24C245.20 m
    P1215×215×140 pad.C25 conc.—
  • Beam Loading Summary A clear breakdown of the floor, roof, partition and dormer loads applied to each beam, with the final design loads set out so Building Control can check the calculation route easily.
    Loading Summary Extract
    LOFT FLOOR LOADING — ULS DESIGN
    ElementGk kN/m²Qk kN/m²Fd kN/m²
    New loft floor0.851.503.22
    Ceiling below0.35—0.47
    Partitions0.50—0.68
    Self weight0.20—0.27
    Total ULS load to B128.4 kN/m
  • Steel Beam Calculations EC3 bending, shear, deflection and web bearing checks for every UB, UC and RSJ included in the package.
    Calculation Package — Example
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  • Timber Flitch Beam Calculations Combined steel plate and timber flitch beam design where composite sections are used instead of solid steel.
    Flitch Beam Calculation Extract
    FLITCH BEAM CHECK — 2/47×225 C24 + 10mm S275 plate
    Span3.800 m (s.s.)
    UDL (ULS)12.6 kN/m
    Steel plate contribution61% of moment capacity
    Design moment Msd22.7 kNm
    Moment capacity Mc,Rd27.4 kNm ✓
    Deflection (total)L/412 ✓
    ✓ PASS — flitch beam adequate
  • Floor Joist Calculations EC5 design for new loft floor joists at the specified centres, including bending, shear, deflection, trimming and support checks.
    EC5 Calculation Extract
    FLOOR JOIST CHECK — 47×195 C24 @ 400 c/c
    Span3.600 m (s.s.)
    Bending stress σm,d5.64 N/mm²
    Bending capacity fm,d9.47 N/mm² ✓
    Utilisation0.60
    Shear τd / fv,d0.41 / 1.54 N/mm² ✓
    Deflection (total)L/358 ✓
    ✓ PASS — all checks satisfied
  • Rafter Calculations EC5 rafter design for altered roof structures, including ridge beams, purlins, collar ties and new roof members where required.
    EC5 Calculation Extract
    RIDGE BEAM CHECK — 2/47×225 C24
    Span5.200 m (s.s.)
    Rafter load (UDL)8.4 kN/m
    Design moment Msd28.5 kNm
    Moment capacity Mc,Rd34.2 kNm ✓
    Utilisation0.83
    DeflectionL/384 ✓
    ✓ PASS — all checks satisfied
  • Stair Opening & Trimmer Calculations Trimmer joist and trimming joist checks around the stair opening, with hanger, bearing or steel support details as required.
    EC5 Calculation Extract
    TRIMMER JOIST CHECK — Stair Opening
    Trimmer section2/47×195 C24 (doubled)
    Trimming span1.200 m (opening width)
    Reaction to trimmer14.2 kN (point load)
    Bending utilisation0.71 ✓
    Shear utilisation0.58 ✓
    Hanger spec.Joist hanger — LUS46 or equal
    ✓ PASS — doubled joist adequate
  • Steel Connections & Splices Fin plate, end plate, splice plate and beam-to-beam connection design where required, including practical installation notes.
    EC3 Calculation Extract
    BOLTED FIN PLATE — B1 to supporting UC
    Plate100×200×8 S275
    Bolts3No. M20 Gr 8.8
    Design shear Vsd59.2 kN
    Bolt shear cap. (3 off)188.5 kN ✓
    Plate bearingOK ✓
    Weld to UC (6mm FW)OK ✓
    ✓ PASS — connection adequate
  • Padstone, Bearing & Restraint Details Padstone sizes, bearing requirements, restraint straps, hangers and key support notes clearly specified so the steelwork and joists can be installed correctly on site.
    EC6 Calculation Extract
    PADSTONE CHECK — B1 onto 215mm brick wall
    Beam reaction R94.5 kN
    Wall thickness215 mm
    Padstone size215×215×140 mm
    Padstone gradeDense concrete C25
    Bearing stress fi2.04 N/mm²
    Capacity fi,Rd2.10 N/mm² ✓
    Restraint strap30×5 galv. @ 2.0m c/c
    ✓ PASS — 215×215 padstone adequate
Delivered as one clear PDF package, including structural calculations, layout plans, member schedule, loading summary, padstone details and key construction notes. Prepared using Tekla Tedds and suitable for Local Authority Building Control and Approved Inspectors.
Send us your architectural drawings and we'll confirm the fixed fee, scope and turnaround.
Loft Conversion Types

Every standard loft conversion type. Covered

The structural scope varies by conversion type — we confirm exactly what's required as part of your fixed fee quote.

1

Velux / Rooflight

Trimmer joists, rafter checks, stair opening.

2

Rear Dormer

Steel beam, flat roof framing, floor joists, bearing checks.

3

Hip-to-Gable

Hip removal, new gable framing, ridge extension.

4

Mansard

Steelwork, mansard wall structure, full load redistribution.

5

L-Shaped Dormer

Valley beam, compound joists, dual dormer framing.

6

Front Dormer

Steel beam, front elevation framing, bearing checks.

7

Side Dormer

Flank wall steelwork, side framing, floor joists.

8

Bungalow

Full load path redesign, new floor structure, steelwork.

Not sure which type applies? Send your architect's drawings and we'll confirm the structural scope with your fixed fee quote.
How It Works

Simple to Instruct
Fast to Receive

We work from your architect's drawings. No site visit required.

1

Send Your Drawings

Email floor plans, roof plans and elevations as PDF or DWG. Include any existing structural information you have.

2

We Confirm the Fee

We review the scope and confirm a fixed fee in writing, usually within 24 hours. No obligation to proceed.

3

We Produce the Package

Load path assessment, member sizing and a complete Tekla Tedds calculation and structural drawing package.

4

Submit to Building Control

You receive the complete PDF pack by email. We respond to any Building Control queries on our package directly.

Turnaround & Fees

Fixed fee. Confirmed before we start

No hourly rates. No additions once the scope is agreed. Fee confirmed after drawing review — typically within 24 hours.

Standard Service
5–10
Working days
Standard Turnaround
Full structural calculation and drawing package within 5–10 working days of instruction. Available for all conversion types.
Priority Service
2–3
Working days
Priority Turnaround
For urgent Building Control submissions or tight programmes. Subject to availability — contact us before sending plans.
Trade Clients
Trade Rates
Regular instructions
Standing Arrangement
Loft conversion companies placing regular instructions can discuss a standing pricing arrangement to suit their pipeline.
Enquire

Send your architect's drawings and we'll confirm a fixed fee and scope. No commitment required.

Request a Fixed Fee Quote
Get Started

Ready to get started?

Email your architect's drawings — we'll confirm a fixed fee and scope within 24 hours. No commitment required.

Send Your Loft Plans Request a Fixed Fee Quote
tjwilkinson@proton.me
Structural Calculations — Example Package
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