How the two differ in kind
The two roofs differ before anyone has priced either. A truss is triangulated: the bottom chord ties the feet of the top chords, so the frame delivers its load straight down onto the two outer bearings and pushes outward on nothing. Cut rafters are two leaning beams, and leaning beams spread. Something has to stop that — ceiling joists acting as ties, fixed to the rafter feet rather than merely present in the room below, or a structural ridge beam carried on posts down to a footing. Most of what follows is that one fact working its way outward.
The second difference arrives years later. A truss fills the roof void with webs, arranged to make the frame work rather than to leave you room; the volume is still there and still unusable. Attic trusses solve that, but they are a different product — tighter span limits, a heavier frame, ordered as such from the start. A cut roof leaves the volume open by default: vault it, board it for storage, or leave the decision to whoever owns the house next. If 'might anyone want to be up there?' is not a confident no, that has already narrowed this page.
The third is about when the decisions close. Trusses move the roof off site — designed, fabricated, delivered, set in a day or two, usually by crane — so the geometry freezes at the order and the roof's price is knowable exactly before a nail goes in. Cutting keeps the roof on site: stock timber, decisions made at the saw, a structure that can absorb whatever the building turns out to be once it is open. One route front-loads the thinking and buys certainty with it; the other defers the thinking and pays for that freedom in days.
The factors that actually differ
| Engineered roof trusses | Stick-framed common rafters | |
|---|---|---|
| What stops the roof spreading | The bottom chord ties the feet — load arrives vertical at the two outer bearings. | Nothing until you provide it: ceiling joists tying rafter feet, or a structural ridge on posts. |
| The roof void | Webbed and unusable as standard; a room up there means attic trusses, committed at order. | Open by default — vault it, board it, or leave the decision to the next owner. |
| Where the money goes | Material, fabrication, delivery, a lifting day — mostly fixed by span and count, quotable before work starts. | Carpentry hours, scaling with how many different rafters the roof holds; the price discovers itself. |
| Lead time and the design freeze | Weeks to fabricate, and the geometry closes at order — a change after that is a re-fabrication. | Stock timber from the yard; the roof can start this week and change while it rises. |
| Days on the walls | A repetitive run lands and decks fast — the building is weathertight sooner. | Setting out, cutting and hanging one member at a time, open to the sky throughout. |
| Getting it up there | Needs a wagon to the plot and standing room for a crane; frames lifted in their own plane, stored upright or flat on level bearers. | Ordinary lengths up a scaffold, fixed one at a time — no access constraint but the timber's length. |
| Erection discipline | Temporary and permanent bracing is specified, not judged; an unbraced run is genuinely dangerous. | Stability accumulates in the order any carpenter knows — ridge, ties, then sheathing. |
| Cutting into it later | No notching, drilling or removing without the truss designer; rooflights and flues are designed in up front. | Trimmed like joists — a rooflight added later is trimmers, headers and an afternoon. |
| Clear span and the walls below | Long spans in shallow timber, so internal walls can be partitions rather than structure. | A bending member that deepens fast; long spans want purlins and struts onto a bearing line. |
Which one, and when
Choose engineered roof trusses when…
- A long, repetitive run of identical frames — trusses at their cheapest.
- The plan below wants no internal load-bearing walls.
- The roof must be weathertight fast, and the site takes a wagon and a crane.
- The design is settled enough to freeze and price exactly before work starts.
Choose stick-framed common rafters when…
- Anyone might want the space up there — a vault, storage, a conversion later.
- Access rules out the crane: a back garden, a terrace, nowhere to stand a lift.
- A small or awkward area where designing and delivering a set is out of proportion.
- The roof meets an old building whose real geometry appears only once it is open.
- There is a carpenter who can set out a hip, and days in the programme.
Now run your own numbers
This page holds no prices on purpose — a national average is wrong for almost every real project. Quantify both options with your dimensions and your local quotes.
Frequently asked questions
- Which is cheaper — trusses or cutting rafters on site?
- It depends on the shape of the roof, and the two costs are made of different things — which is why no figure appears here. Trusses are material and logistics: mostly fixed once span, count and loading are known, quotable exactly before work starts, and carrying a delivery and a lifting day that barely shrink for a small roof. Cutting costs hours, which scale with how many different rafters there are and who holds the saw. A long simple run favours trusses; a small awkward one is where fixed logistics swallow the saving. A real truss quote is exact and easy to get — set it against a day rate and an honest count of days.
- Can I convert a trussed loft later?
- Only by building a new roof structure inside the old one. The webs are not clutter in the way of a room — they are what makes a truss a truss, and removing them means new floor members, new support for the roof plane and an engineer's design. It is a common job and never a cheap one. If the attic is a maybe rather than a no, the inexpensive moment to decide is before the order: attic trusses cost more and span less than standard frames, but far less than buying the space back afterwards.
- Can I drill or notch a truss to run services?
- Not without the truss designer's approval. Chords and webs are sized with nothing spare, and the punched plates at the joints rely on full tooth contact, so a hole in the wrong place removes strength that was doing a job. Service routes go through the triangles the design already allows, or they are designed in at the start. Cut rafters and ceiling joists follow the ordinary notching and drilling rules for solid timber, which is why a duct added a year later is a much smaller conversation.
- Can I use both on the same roof?
- Yes, and it is normal practice rather than a compromise: trusses over the long repetitive run, cut infill for dormer cheeks, a valley, the return over a bay, the piece meeting the old house at an angle nobody drew. The rule is that the truss designer must know about anything landing on a truss — an infill valley, or load from a stick-framed section, needs the frame beneath it designed as a girder. That is settled on the enquiry sheet, not on the day.
- Do trusses really need no internal load-bearing walls?
- Clear span is the point of them, and the load does go to the two bearings named on the design. Two caveats travel with it. The bottom chord is designed to span clear and it moves, so partitions built tight underneath want a fixing that lets it deflect and lift seasonally rather than one that fights it. And the clear span covers the trusses as designed — a boarded storage deck later hung from that chord is load nobody allowed for. A cut roof at the same span usually needs a bearing line or engineered members instead: a real cost, but one visible on the plan from the start.
- Is one stronger — in snow, or in wind?
- Neither, inherently. Both are designed for the same loads on the same building; what differs is who does the designing and whether the result is written down. A truss arrives with a design drawing per type, stating the load cases it was sized for — something building control reads and a future owner can find. A cut roof is justified by span tables or an engineer's calculation, and what ends up on the walls depends on the cuts made that week. The truss's advantage is documentary; the cut roof's is that a carpenter can adapt it to what the building turned out to be.