TryBuildCalcFraming Resources
Rafter vs. Truss: Which Should You Use?
Rafters and trusses solve the same problem — holding up a roof — with almost opposite trade-offs: one is built on-site board by board with full design flexibility, the other arrives pre-engineered and gets set in place in hours. Picking between them earlier rather than later matters, because attic usability in particular is a decision that's very hard to change once the roof is up.
Last updated: September 7, 2026
There's no universally "better" choice between rafters and trusses — the right one depends on what the roof actually needs to do: span a wide space without interior support, leave room for a future attic conversion, follow a complex custom roofline, or go up as fast and cheaply as possible.
This guide covers cost, span, attic space, installation speed, and design flexibility side by side, plus the mistakes that come from deciding too late or modifying a truss in the field.
Rafters vs. Trusses at a Glance
| Factor | Rafters | Trusses | Why It Matters |
|---|---|---|---|
| Typical installed cost | $5-14 per sq ft | $7-30 per sq ft | Trusses are generally cheaper due to lower field labor |
| Typical achievable span | Up to ~80 ft (most homes need 30-40 ft) | ~12-24 ft without a ridge beam or interior bearing wall | Trusses clear-span far more easily without interior support |
| Usable attic space | Generally yes — open volume, no internal webbing | Only with "attic trusses" specified at design stage | Standard trusses can't be converted to usable attic space after installation |
| Installation speed | Slower — built member by member on site | Fast — factory-built, craned into place | Trusses need far less skilled on-site labor time |
| Design flexibility | High — easy to accommodate custom rooflines | Fixed at design/fabrication — limited field changes | A truss can't be safely modified on site without engineering re-approval |
Attic usability is the hardest factor to change after the fact — decide on this before the roof design is finalized, not after.
When Each One Makes More Sense
A few situations tend to point clearly toward one system over the other:
- Choose trusses when the roof needs to clear-span a wide open floor plan without interior bearing walls, when installation speed/budget is the top priority, or when the roofline is a standard, straightforward shape.
- Choose rafters when a future (or immediate) usable attic space matters, when the roofline is complex or custom (multiple intersecting planes, dormers, irregular pitches), or when on-site design flexibility during construction is genuinely needed.
- If attic space matters but truss economics are still preferred, specify attic trusses (room-in-attic trusses) at the design stage — they cost more than standard trusses but solve the usable-space limitation.
Worked Example — 32 ft Wide Home, Two Approaches
Same Building Width, Truss vs. Rafter-with-Ridge-Beam
Illustrative example
| Approach | Interior Support Needed? | Attic Usable? |
|---|---|---|
| Standard prefabricated truss (32 ft clear span) | No — clear-spans the full width | No, unless attic trusses specified upfront |
| Stick-built rafters with structural ridge beam | Ridge beam needs its own end support (post or wall) | Yes — open attic volume |
Both approaches can clear a 32 ft span without an interior bearing wall mid-floor — the truss does it inherently, while the rafter approach needs a properly engineered ridge beam sized for that span, carried down to its own end supports.
Common Mistakes
Deciding on Rafters vs. Trusses After the Roof Design Is Locked
Attic usability in particular is very hard to change after the fact — a standard truss roof generally can't be retrofitted into a usable attic, so this decision (and, if attic space matters, specifying attic trusses specifically) needs to happen at the design stage, not after fabrication has started.
Field-Modifying an Installed Truss
Cutting or altering any member of an installed truss — even something that looks minor, like notching a web for a duct run — compromises the engineered load path the whole truss depends on; any needed change has to go back through the manufacturer's engineer for a proper repair design.
Building a Ridge-Board Rafter Roof Without Adequate Ties
A simple ridge board (as opposed to a structural ridge beam) doesn't carry roof load to its own supports — it relies on rafter ties, correctly-positioned collar ties, or ceiling joists to resist the outward thrust at the wall plates; skipping or under-sizing this detail lets the roof slowly spread the walls apart.
Assuming Rafters Are Always Cheaper Because the Lumber Costs Less
Raw material cost for stick-built rafters can look comparable to or even less than a truss package, but the INSTALLED cost comparison (which is what actually matters for a project budget) is usually decided by labor time, not material — trusses generally win on total installed cost specifically because of faster, lower-skill-requirement installation.
Assuming Every Truss Spans as Far as the Roof Needs Without Checking
Truss span capability depends on the specific engineered design, lumber, and load conditions for that truss — not every truss automatically spans 80 ft; the actual span capacity for a given roof needs to come from the truss manufacturer's engineered design for that specific job, not a general "trusses span far" assumption.
Relevant Standards and References
Rafter framing and truss design are governed by different reference documents even within the same code — trusses in particular are always project-specific engineered products.
| Region | Relevant Codes / Guidance |
|---|---|
| United States | IRC Chapter 8 (Roof-Ceiling Construction) covers rafter framing; truss design is governed by ANSI/TPI 1 (National Design Standard for Metal Plate Connected Wood Truss Construction) |
| Europe / UK | Eurocode 5 (BS EN 1995) covers structural timber design for both rafter and truss roof systems, alongside national building regulations |
| India | IS 883 covers structural timber design; engineered truss systems typically follow manufacturer-specific engineering rather than a single national truss standard |
| Australia / New Zealand | AS 1684 (Residential Timber-Framed Construction) and AS 4440 (Installation of nail-plated timber roof trusses) cover both systems |
| General guidance | Truss design is always project-specific engineering from the manufacturer — treat any span/load figures here as illustrative, not a substitute for the manufacturer's actual engineered truss design. |
Final Verdict
Trusses generally win on cost, span, and installation speed; rafters generally win on attic usability and design flexibility. Neither is universally correct — the decision should follow from what the specific roof actually needs, decided before the design is finalized.
- Decide on attic usability BEFORE finalizing the roof design — it's very difficult to change after a standard truss roof is built.
- If attic space matters and trusses are still preferred on cost/speed, specify attic (room-in-attic) trusses at the design stage.
- Never field-modify an installed truss without going back through the manufacturer's engineer for a repair design.
- If using a rafter roof without a structural ridge beam, confirm adequate rafter ties/collar ties/ceiling joists to resist outward wall thrust.
- Compare INSTALLED cost, not just raw lumber cost — labor time is usually the larger factor between the two systems.
- Get an actual engineered truss design (not a general span assumption) from the manufacturer for the specific span and loads involved.
Related calculators
Use these calculators when you need to turn this reference information into project quantities:
- Rafter Calculator
Find rafter length, count, and spacing for a stick-built roof.
- Roof Truss Calculator
Find truss count and spacing for a prefabricated roof system.
- Hip Roof Calculator
Size common, hip, and jack rafters for a hip roof framed with stick-built rafters.
Related resources
- Rafter Span & Sizing Guide
How rafter span, spacing, roof pitch, and ground snow load relate to each other — reading a rafter span table correctly, why snow load can cut allowable span dramatically, and how pitch changes the load a rafter actually sees.