Timber floor joists and beams
- ✓Joist sizes, spacing and grades for domestic and light commercial floors.
- ✓Trimmers around stair openings, fireplaces and double height spaces.
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Floors • Roofs • Timber frame structural design
Structural engineer timber frame for floors, roofs and full frame design
★★★★★ 5.0 rating
Timber is light, fast to build and cost effective, but only when the spans, depths and connections are checked properly. We design timber floors, roofs and walls with clear drawings and Building Control ready calculations.
As your structural engineer for timber projects we look at strength, stiffness, vibration and fire resistance, not just the joist size on the plan.
- ✓Timber floors, roofs, beams and full timber frame structural calculations for new build and extensions.
- ✓Checks for bending, shear, vibration, deflection and fire resistance in line with Eurocode 5.
- ✓Fixed fee timber design packs with schedules your carpenter can follow on site.
We support loft conversions, extensions, timber frame houses and garden rooms across the UK, working from your architect drawings or simple sketches and measurements.
Timber design snapshot
Domestic timber floor over lounge
timber floor joist snapshot
Timber joist strip between supports
- ✓Joists spanning between steel or timber beams at regular centres.
- ✓Allowances for notches, holes and service runs checked against the code.
- ✓Span: 4.2 m | Grade: C24
- ✓Depth: 220 mm | Deflection limit: span/360
- ✓Design scope: Joists, trimmers, trimmer joists and hangers
- ✓Checks carried out: Bending, shear, vibration and deflection
- ✓Fire resistance: 30 or 60 minutes to suit Building Control
- ✓Pack includes: Calcs, joist layout plans and schedules
★ Timber frame structural calculations
Structural engineer timber frame – what we design for your project
We cover the main timber elements your project needs, from single flitch beams through to full timber frame packages.
Timber roof design
- ✓Cut roofs, purlins, rafters and ridges for loft conversions and new roofs.
- ✓Check of ceiling ties, collars and spread to keep walls stable.
Timber frame walls and panels
- ✓Stud sizes, sheathing and hold down requirements for timber frame walls.
- ✓Wind loads, racking resistance and tie down to foundations.
Glulam and flitch beams
- ✓Design of glulam beams for long spans and exposed feature members.
- ✓Flitch beams sized where steel plates are combined with timber for lofts.
Timber connections and fixings
- ✓Specification of hangers, bolts and screws with simple schedules.
- ✓Checks on bearing, fastener capacity and splitting of members.
Fire resistance and service holes
- ✓Fire resistance calculations and charring allowances where needed.
- ✓Rules for notches and drilled holes so plumbers and electricians know what is safe.
When you must involve a timber structural engineer
Some timber work is simple, some is not. These are the situations where proper timber frame calculations are essential.
Long spans or heavy loads
- ✓Floors over open plan rooms, bifold doors or large feature spaces.
- ✓Pool tables, kitchens with stone worktops or storage loads on floors.
Loft conversions using timber or flitch beams
- ✓New beams to support existing rafters and floor joists.
- ✓Checking if a flitch beam or full steel beam is more suitable.
Timber frame new builds and garden rooms
- ✓Full timber frame packages where walls, floors and roofs work together.
- ✓Racking checks, tie downs and bracing to resist wind.
Fire rated floors and separating walls
- ✓Conversion to flats or HMOs where higher fire resistance is required.
- ✓Upgrading existing timber to meet Building Regulations for change of use.
Key points we check in timber design
These are the simple ideas we explain to clients so they understand why we choose certain timber sizes and layouts.
Span, depth and spacing
Longer spans or higher loads need deeper or closer spaced joists. We use span rules of thumb first, then confirm with full calculations so floors feel solid underfoot.
Vibration and deflection
A floor can be strong enough but still feel bouncy. We check vibration and deflection limits so rooms do not feel springy, especially under tiles or brittle finishes.
Fire and durability
Timber chars in a fire which reduces the effective size. Where needed we allow for charring or specify protection so the floor or beam meets the required fire period.
Timber design video lessons
A few short videos from our YouTube channel that explain how we size timber elements in simple terms.
Effortlessly calculate timber floor span
How to pick sensible starting sizes for timber floors before detailed design.
How to design timber joists
Worked example covering bending, shear and deflection checks for joists.
Timber beam or flitch beam?
Simple comparison of timber and flitch options for typical loft projects.
Information we need to design your timber structure
A few clear details at the start help us give you an accurate fixed fee and avoid changes later.
Drawings or sketches
- ✓Plans and sections showing spans, supports and room uses.
- ✓Any known beam positions, openings or roof layouts from your architect.
Loading and finishes
- ✓Whether floors will have tiles, stone, screed or heavy storage.
- ✓Any known plant loads such as baths, tanks or air handling units.
Existing structure
- ✓Construction of existing walls and supports where new timber will bear.
- ✓Photos of lofts, floors or garden rooms are very helpful.
Fire and regulations
- ✓Whether the project involves change of use, flats or escape routes.
- ✓Any specific Building Control comments you already have.
Timber design – frequently asked questions
Short answers to the questions we hear most often about timber floors, roofs and frames.
Do I always need a structural engineer for timber joists?
Simple like for like replacements can sometimes be done by a competent contractor using standard tables. Where spans, loads or layouts change, Building Control normally ask for structural calculations from an engineer.
Can I drill holes through timber joists for services?
Yes, but only within strict limits. We tell you where holes can go and what sizes are allowed so plumbers and electricians do not weaken the structure by accident.
What timber grade should I use?
Most domestic work uses C24 or C16 softwood. We state the required grade on our drawings and schedules so your supplier and carpenter know what to order.
How do you allow for fire resistance in timber?
We either rely on plasterboard and tested systems or allow for charring of the timber itself. The approach depends on the required fire period and project type. Our calcs make this clear for Building Control.
Can timber replace steel in my project?
Sometimes yes, especially for shorter spans or where headroom allows a deeper member. We can compare timber, flitch and full steel options so you, your builder and your architect can pick the best solution.
Clients who used us for timber design
A few short comments from projects where timber floors, roofs or frames were a key part of the design.
★★★★★
“They explained the pros and cons of timber verses flitch clearly and gave a layout my builder was happy with. Building Control accepted the calcs straight away.”
Loft conversion – Manchester
Timber floor and flitch beam
★★★★★
“The stud and racking design made the frame feel solid even in strong winds. The drawings were simple and easy for our timber frame contractor to follow.”
Garden room – Birmingham
Timber frame and roof
★★★★★
“SECalcs upgraded the existing joists with extra layers and clear fire notes. This helped keep costs under control while meeting Building Regulations.”
Flat conversion – London
Fire rated timber floors
Request a timber design structural engineer quote
Use this form to outline your timber floor, roof or frame project. Your enquiry goes straight to an engineer.
Email
Phone
Typical Response
Within one working day for timber design enquiries.
Areas we commonly cover
London and the South East, Manchester and Greater Manchester, Birmingham and the West Midlands, Bristol, Nottingham, Leeds, Sheffield, Liverpool and surrounding towns.
Most timber design work can be completed from drawings, photos and simple measurements. If a visit is needed, we will say so and include it in the quote.
Ready to move your timber project forward?
If you are planning a timber floor, roof or full timber frame and want clear structural calculations, send us a few details and we will confirm the next steps and a fixed fee.