Structural Engineer for Loft Conversion Floor Strengthening • Roof Beams • Dormer Design • Building Control
Converting your loft? We provide fixed-fee structural calculations for Velux, dormer and hip-to-gable loft conversions across the UK. A complete Building Control-ready pack, delivered to your architect and builder without a site visit in most cases.
5.0/5 from 150+ reviews • Loft conversions across the UK
Get Your Loft Conversion Quote
Tell us about your project and we'll confirm a fixed fee within one working day.
Which Loft Conversion Do You Need a Structural Engineer For?
All loft conversions require Building Control approval and structural calculations, regardless of type. Here is what each one involves structurally.
Velux / Roof Light Conversion
The simplest loft conversion — Velux windows are cut into the existing roof slope with no change to the roof shape. The main structural work is strengthening the existing floor.
- Existing floor joist assessment
- New floor strengthening or sister joists
- Stairwell opening calculations
- Structural support for Velux frames
Rear Dormer Conversion
A dormer projects from the rear roof slope, adding a box structure with a flat or low-pitch roof. More structural work is involved as the existing roof structure is significantly altered.
- Dormer frame and flat roof design
- Trimmer and trimming joist calculations
- Ridge or purlin support assessment
- Floor strengthening and stairwell
Hip-to-Gable Conversion
A hip-to-gable changes the sloping hip end of a roof to a vertical gable wall, extending the ridge. Usually combined with a rear dormer. The most structurally complex residential loft conversion.
- New gable wall and extended ridge beam
- Hip rafter removal and replacement structure
- Full dormer calculations if combined
- Foundation check for new gable wall load
What Our Loft Conversion Structural Calculation Pack Includes
Everything your builder needs to build it and Building Control needs to approve it — in one fixed-fee pack.
Floor Strengthening Design
Existing loft floors are almost never strong enough to use as habitable space. We assess the existing joists and design the strengthening required.
- Existing joist capacity check
- Sister joist or new joist design
- Deflection and vibration checks to BS EN 1995
Roof Beam and Ridge Design
Where the ridge or roof structure needs a new steel beam or a support column removed, we design the steel and the connections.
- Ridge beam sizing for open-plan loft spaces
- Purlin and rafter support design
- Steel beam and column calculations
Dormer Structural Framing
The dormer structure, its flat roof, and its connection to the existing roof and external walls all need structural design.
- Dormer flat roof joist or SIP design
- Trimmer and trimming joist calculations
- Dormer cheek wall framing design
Stairwell Opening Calculations
Cutting a stairwell opening through the existing ceiling structure requires trimmer beams to carry the loads from the interrupted joists.
- Trimmer beam sizing for stairwell opening
- Connection and bearing details
- Coordinated with staircase position
Structural Drawings
Clear, dimensioned drawings showing everything your builder needs to construct the loft conversion accurately and safely.
- Floor plan with new joist layout
- Roof structure arrangement drawing
- Steel beam and connection details
Building Control Support
We respond directly to any Building Control technical queries on the structural calculations and provide revisions until formal approval is granted.
- Direct response to Building Control queries
- Reasonable revisions included in the fee
- Support through to completion certificate
From First Enquiry to Building Control Approval
We work from your architect's drawings and photographs of the existing roof and floor structure. A site visit is rarely needed.
Send Your Drawings
Share your architect's drawings and photographs of the existing loft, roof timbers and floor joists. We confirm what we need and send a fixed fee within one working day.
Fixed Fee Agreed
You receive a clear scope, fixed price and programme. No hourly rates and no surprises. Your architect and builder know when to expect the calculation pack.
Calculations and Drawings
We design the floor strengthening, roof structure, dormer framing and stairwell — and produce clear drawings your builder can follow from day one.
Building Control Support
Once submitted, we deal with any technical queries from Building Control directly and revise the pack as needed until formal approval is in place.
Information We Need to Start Your Loft Conversion Calculations
Clear information at the start means a faster turnaround and fewer revisions.
Architect's Drawings
- Proposed floor plans and sections in PDF
- Roof structure layout if drawn
- Dormer elevations and dimensions
Existing Roof and Floor
- Photographs of existing roof timbers from inside the loft
- Photographs of existing ceiling joists from below
- Joist sizes and spacings where visible
Property Details
- Property type: detached, semi-detached or terrace
- Approximate age of the property
- Full address or postcode
Programme and Requirements
- Intended start on site
- Whether Building Control has been notified
- Any specific requirements from your architect or builder
Loft Conversions We Have Designed
Comments from homeowners and architects on loft conversion structural calculation projects across the UK.
"Our architect said SECalcs were the best structural engineers they'd worked with for loft conversions. The calculations were thorough, the drawings were clear and Building Control approved everything first time."
Rear Dormer Loft Conversion — Bristol
"Hip-to-gable conversions can be tricky structurally, but SECalcs handled ours without fuss. Fixed price, quick turnaround, and the pack was exactly what Building Control needed. We'd use them again without hesitation."
Hip-to-Gable with Rear Dormer — Manchester
"I just wanted a straightforward Velux conversion and was worried it would be expensive to get structural calculations done. SECalcs were very competitive on price and the calculations came back quickly. Highly recommend."
Velux Loft Conversion — Leeds
Loft Conversion Structural Engineer Questions Answered
Common questions from homeowners and architects planning a loft conversion.
Yes. Building Control requires structural calculations for all loft conversions. The existing floor almost always needs strengthening, the roof structure is altered, and any new steel beams must be properly designed and signed off by a chartered engineer. Without structural calculations, Building Control cannot issue a completion certificate.
A typical loft conversion requires: existing floor joist assessment and strengthening design; ridge beam or steel support calculations if the roof is being restructured; dormer structural framing calculations where applicable; stairwell trimmer beam design; and connection details throughout. We provide all of this as a single fixed-fee pack.
Structural engineer fees for a loft conversion start from £450 for a straightforward Velux conversion with floor strengthening only. Dormer loft conversions typically start from £600, and hip-to-gable conversions from £700. All fees are fixed and agreed before any work begins — no hourly rates.
A Velux or roof light conversion keeps the existing roof shape and adds windows into the slope — the simplest structural option. A dormer adds a box-shaped structure projecting from the rear roof slope, creating a vertical wall and a flat or low-pitch roof. A hip-to-gable conversion changes the sloping hip end of a roof into a vertical gable wall, often combined with a rear dormer — the most structurally complex of the three.
Yes, always. All loft conversions require Building Control approval regardless of their size or type. This covers structural calculations, fire safety, insulation, means of escape and staircase design. Unlike some other home improvements, there is no permitted development route that exempts a loft conversion from Building Control.
In most cases, yes. We work from your architect's drawings and photographs of the existing roof timbers and floor joists. Where the existing structure is unclear from photographs alone, your builder or architect can take measurements on site and send them through — which is usually quicker and cheaper than arranging a formal site visit.
Ready to Get Your Loft Conversion Calculations Started?
Send us your architect's drawings and photographs of the existing roof and floor. We'll confirm a fixed fee — most enquiries answered within one working day.
- Head Office: Corwell Lane, Uxbridge, England, UB8 3DE.
- 07359 267907
- info@structuralengineercalcs.com
- Company No: 12653163