Roof Truss Types: Fink, Attic, Mono, Hip and Scissor — Specification and Load Guidance

Quick Answer: Eight in ten UK pitched roofs use a Fink truss — the W-shaped softwood truss spanning 5–11m at 600mm centres, designed to BS EN 14250 with TRA-certified manufacture. Attic, mono-pitch, hip and scissor trusses are specified where the Fink can't deliver clear span, asymmetric pitch, or usable loft volume; each carries different deadload allowances and bracing requirements that the truss designer issues with the production drawings.

Summary

A trussed rafter is an engineered timber structure made under factory conditions from C24 stress-graded softwood with metal nail-plate connectors at every joint. It replaces traditional cut-roof carpentry on the vast majority of new UK housing because it ships flat-pack, lands on a ring beam in one crane lift, and lets a roofer dry the building in two days rather than two weeks. The trade-off is that a trussed roof is a designed structure — every truss in the package is specific to that roof, the bracing pattern is non-negotiable, and you cannot cut, drill, notch or splice a trussed rafter without re-engineering.

This article covers the eight truss types that account for almost every UK pitched roof: Fink, fan, king post, queen post, attic, mono-pitch, hip and scissor. Each section gives typical span ranges, depth/height proportions, the live and dead loads they're designed for, and the situations where they're specified. Loadings are referenced to BS EN 1995-1-1 (Eurocode 5) with the UK National Annex.

The price-impact item to know early in any quoting conversation: the design and manufacture of a truss package is a fixed lead-time cost. Two weeks for a standard Fink package, four to six weeks for attic trusses, and eight to twelve weeks for hip/scissor combinations. Builders who order trusses too late hold up the entire programme; pricing must include realistic lead-time so the brick-up and truss-erection week align.

Key Facts

Quick Reference Table

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Truss Type Span Range Pitch Range Typical Use Depth/Height
Fink 5–11m 15°–45° Standard duo-pitch dwelling Span × tan(pitch)/2
Fan 8–12m 17.5°–35° Bungalow with longer span Span × tan(pitch)/2
King Post up to 8m 30°–45° Small span, traditional aesthetic Span × tan(pitch)/2
Queen Post 8–14m 30°–45° Larger span with central clear zone Span × tan(pitch)/2
Attic 6–10m 35°–55° Habitable loft (rooms-in-roof) Min 2.4m head height
Mono-pitch up to 10m 5°–25° Lean-to extensions, garages Single slope
Hip End varies matches main roof Hipped corner; needs girder + jacks Reduces to apex
Scissor 6–12m duo-pitch Vaulted internal ceiling Internal pitch ½–⅔ external

Detailed Guidance

Fink — the workhorse

The Fink is what comes off the lorry on three-quarters of UK new builds. Two top chords meeting at the apex, two bottom chords (the ceiling tie), and four diagonal webs forming a "W" between them. Excellent strength-to-weight ratio for spans 5–11m, economic at 600mm centres, and the geometry leaves clear triangles for routing services and hatches.

Standard limitations: the W-pattern means there is no clear central zone in the loft. Anyone planning a future loft conversion onto a Fink-trussed roof faces a complete re-roof or a sister-built independent floor structure — a £40,000+ job. If the client even mentions "we might convert the loft one day", price an attic truss instead.

Attic truss — the rooms-in-roof option

The attic truss carries a clear central rectangular zone designed for habitable use. Two top chords, a thick floor beam (the bottom chord doubled or upgraded to a deeper section), and a vertical post at each side framing the room volume. Designed to a 1.5 kN/m² imposed floor load (the BS EN 1991-1-1 domestic floor live load), so the attic space is engineered for sleeping accommodation, not just storage.

Pitch typically 40°–55° to give 2.4m clear head height in the centre. The span/pitch geometry is the constraint — narrow spans don't generate enough roof volume to make an attic worthwhile, hence the 6m minimum. Above 10m, the floor beam becomes uneconomic and a hybrid attic + secondary floor joist solution wins.

Premium over Fink: roughly 2.5×–3× the per-truss cost. But the alternative — building a Fink roof and converting later — costs 5–10× the attic truss premium.

Mono-pitch — single-slope structure

Mono-pitch trusses have one top chord, one bottom chord, and a vertical post or angled web giving the depth. Used on:

Mono trusses are cheaper than duo-pitch per metre of span but suffer at lower pitches (below 12.5°), where wind uplift dominates and tile choice becomes restricted. Below 12.5°, switch the conversation to flat roof construction — see the flat-roof selection and fire requirements.

Hip-end roofs — girder + jack assembly

A hipped corner is constructed from a girder truss (multi-ply, often three or four trusses bolted together) supporting an array of hip jack trusses that reduce in length toward the apex. The girder carries the entire load of the hip section into the wall plate.

Pricing implications:

Scissor truss — vaulted ceiling

The scissor truss has bottom chords angled upward (rather than horizontal), creating a vaulted ceiling internally. Internal pitch is typically half to two-thirds the external pitch. Used in churches, conversions, and aspirational open-plan kitchen-diners with timber ceiling.

Loadings are significantly more onerous than a Fink at the same span — the angled bottom chord generates outward thrust at the wall plate, which requires either a steel ring beam, a heavy timber tie, or a buttressed wall design. The structural engineer is involved, not just the truss designer. Expect 3–4× the per-truss cost of a Fink and a programme that adds two weeks for the design coordination.

Bracing — the part roofers skip and shouldn't

Every truss package ships with a bracing diagram from the truss designer. Three types of bracing:

The bracing pattern is non-negotiable. Skip a longitudinal brace at the ridge and a 35mph gust can rack the entire roof. Tilers must not load the roof until all bracing is in place — TRA technical guidance gives a clear sequence.

For the homeowner — what does a truss package cost?

A typical 3-bed detached new-build needs 28–36 Fink trusses + bracing + accessories. Expect £2,200–£3,800 for the truss package alone, design and delivery included. An attic-truss equivalent on the same footprint runs £6,500–£10,500. A hip-and-valley with girder runs £4,800–£8,000.

Truss erection labour is a 1-day, 2-carpenter, 1-crane job for most domestic roofs — £900–£1,400 typical. Beyond that, all costs are tile/slate, underlay, scaffolding and roofline finishes — see the roofline replacement pricing breakdown.

Frequently Asked Questions

Can I cut or notch a trussed rafter to fit pipework?

No. Cutting or notching any chord or web voids the truss designer's certificate and the manufacturer's warranty. If a service has to pass through the truss zone, route it through the triangle voids between webs, or notify the truss designer before manufacture so a service truss can be supplied with pre-engineered openings. Field modifications require a structural engineer's calculation and remedial work — typically £500+ per truss.

What's the difference between a trussed rafter roof and a cut roof?

A trussed roof is engineered, factory-made flat-pack assembly using nail-plate connections, designed for a specific building. A cut roof is built on site by a carpenter from individual rafters, ridge boards, ceiling joists, struts and purlins, mostly using traditional birds-mouth joints and skew-nails. Cut roofs are slower (1–2 weeks vs 1–2 days), more expensive in labour, but easier to modify and convert later. Cut roofs persist on conservation work, complex geometry roofs, and self-builds where speed isn't the priority.

Do trussed rafters need to be tied down?

Yes. Holding-down straps (typically 30×5mm pre-galvanised steel) connect the wall plate to the masonry below at maximum 2m centres, and rafter-to-wall-plate strapping prevents wind uplift. BS 5268-3 (now Eurocode 5) and Approved Document A both require this. In high wind zones (Scotland, exposed coastal sites), additional truss-to-truss strapping is specified by the designer.

How are trusses delivered and stored on site?

Bundled and craned off the lorry, then either erected the same day or stored vertically on bearers off the ground. Storing trusses flat causes permanent bow. They must be kept dry — wet trusses with wet connector plates are a long-term corrosion risk. Cover with breathable sheeting if storage exceeds 48 hours.

When does a roof need a structural engineer rather than just a truss designer?

The truss designer is competent for the trusses themselves under their TRA scheme. A structural engineer is needed when:

Regulations & Standards