Structural Engineer for Home Extension Calculations • Steel Beams • Foundations • Building Control
Planning a home extension? We provide fixed-fee structural calculations for single and double storey extensions across the UK. Everything your builder and Building Control need, delivered in a clear, jargon-free pack.
Get Your Extension Calculation Quote
Tell us about your project and we'll confirm a fixed fee within one working day.
Structural Calculations for Home Extensions — What We Cover
A complete Building Control-ready structural calculation pack for your extension project, from foundation design to roof connections.
Foundation Design
We size your strip or pad foundations based on the soil type, loads from above, and Building Control requirements.
- Foundation depth and width calculations
- Bearing pressure checks to BS EN 1997
- Reinforcement details where required
Steel Beams and Lintels
Every opening in your extension needs a properly sized steel beam or lintel. We calculate each one and specify the padstone bearings.
- RSJ or universal beam sizing to BS EN 1993
- Padstone design for masonry bearings
- Lintel sizing for window and door openings
Roof and Floor Calculations
New floor joists and roof rafters or structural roof timbers sized to carry the loads safely and meet deflection limits.
- Floor joist sizing and span checks
- Roof rafter and purlin design
- Flat roof structural options
Connection to Existing Structure
How the new extension ties into your existing house matters structurally. We design the junction and confirm load paths are continuous.
- Wall plate and joist hanger details
- Load path through existing and new walls
- Any strengthening required to existing structure
Building Control Drawings
Clear structural drawings your builder can use on site and your Building Control officer can approve without further queries.
- Foundation plan and section
- Structural arrangement drawing
- Steel beam and padstone details
Building Control Support
If Building Control raises technical queries on our calculations or drawings, we respond directly and provide revisions until approval is granted.
- Direct response to Building Control
- Reasonable revisions included
- Support until formal sign-off
From First Enquiry to Building Control Sign-Off
Most extension projects do not need a site visit. We work from your architect's drawings, photos and builder notes.
Send Your Drawings
Share your architect's drawings or a sketch of the proposed extension. Photos of the existing house help too. We confirm what we need and send a fixed fee within one working day.
Fixed Fee Agreed
You receive a clear scope of work, a fixed price with no hourly rates, and a programme so your architect and builder know when to expect the pack.
Calculations and Drawings
We produce the full structural calculation pack — foundations, beams, floor and roof — with drawings your builder can follow and Building Control can approve.
Building Control Support
Once submitted, we handle any queries from Building Control directly and provide revisions as needed until the structure is formally approved.
Information We Need to Start Your Extension Calculations
The more detail you can share, the quicker we can confirm your fee and get started.
Drawings and Plans
- Architect's drawings or planning drawings in PDF
- Site plan showing extension position
- Sections and elevations if available
Existing House Details
- House type: detached, semi, terrace
- Approximate age of the property
- Photos of existing walls, floors and roof
Ground Conditions
- Site address or postcode
- Any known ground issues or previous works
- Soil type if a ground investigation has been done
Scope and Programme
- Intended start on site
- Whether Building Control has been notified
- Any specific builder or architect requirements
Home Extension Structural Calculation Packages
Fixed prices agreed before any work begins. No hourly rates. No hidden extras.
Single Storey Extension
Structural calculations for a straightforward single storey rear or side extension to a residential property.
- Foundation design and depth calculations
- Steel beam and lintel sizing
- Floor joist and roof rafter design
- Building Control drawings and calculation pack
Double Storey Extension
Full structural design for double storey extensions including additional load paths, floor structures and more complex steelwork.
- First and ground floor structure design
- Increased foundation loading calculations
- Steelwork for both storeys
- Full Building Control submission pack
Wraparound Extension
Structural calculations for side-return and L-shaped wraparound extensions with multiple steel frames and complex junction details.
- Multiple beam and frame design
- Complex junction and connection details
- Foundation design across two elevations
- Coordinated with architect's layout
Extension with Wall Removal
Combined calculation pack for extensions that also involve removing an internal load-bearing wall to open up the ground floor plan.
- Extension structural calculations
- Internal load-bearing wall RSJ design
- Combined load path analysis
- Single Building Control submission
Extension Projects We Have Designed
Comments from homeowners and architects on extension structural calculation projects across the UK.
"We needed structural calculations quickly to keep our build on programme. SECalcs came back with a fixed fee the same day, and the full calc pack was with us inside a week. Building Control passed it without a single query."
Single Storey Rear Extension — Leeds
"Our architect recommended SECalcs and we can see why. The drawings were exactly what Building Control needed, and the engineer explained everything clearly when we had questions. Highly recommend for any extension project."
Double Storey Side Extension — Birmingham
"I was worried the wraparound extension would be complicated, but SECalcs handled it efficiently. Clear pricing, quick turnaround, and the builder said the drawings were the best he'd seen. Nothing was left to guesswork."
Wraparound Extension — Manchester
Home Extension Structural Engineer Questions Answered
Common questions from homeowners and architects planning a home extension.
Yes, in almost all cases. Building Control requires structural calculations for any extension that affects the existing structure — which includes virtually every single and double storey extension. Without a structural engineer's calculations, Building Control will not issue a completion certificate. Your builder cannot sign off the work without it.
A typical home extension requires: foundation design and depth calculations; steel beam or lintel sizing for all structural openings; floor joist and roof rafter design; padstone specifications where beams bear onto masonry; and connection details between the new and existing structure. We provide all of this as a single fixed-fee pack ready for Building Control submission.
Structural engineer fees for a home extension start from £550 for a straightforward single storey rear or side extension. Double storey extensions typically start from £800, and wraparound or more complex projects from £950. All fees are fixed and agreed before any work begins — no hourly rates and no surprises.
Most single storey extension calculation packs are completed within five to ten working days of receiving all project information. Double storey and complex extensions may take slightly longer. We confirm a programme at the outset so your architect, builder and Building Control can plan around it.
Yes. The large majority of residential extension projects do not require a site visit. We work from your architect's drawings, photographs of the existing structure, and information from your builder about the existing foundations and floor construction. Where a site visit is genuinely needed, we will tell you upfront.
Planning permission covers the external appearance and impact on neighbours — it is granted by the local planning authority. Building Control covers the structural safety, fire safety and energy performance of the building — it is handled separately by Building Control officers. Structural calculations are a Building Control requirement. Many extensions built under permitted development still require full Building Control approval including structural calculations.
Ready to Get Your Extension Calculations Started?
Send us your architect's drawings or a sketch of the extension. We'll review the project and 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