The cost of a roof rafter — that's one of the first questions that comes up when an investor gets a truss quote from a carpenter or a sawmill. Rafters often account for more than half of the timber volume in the whole roof structure, so a mistake in choosing the cross-section or spacing costs the most — and it only becomes visible once the roof starts to "work" under snow load. At JB Tartak we've been supplying C24 timber for rafters for 35 years, so I know exactly which dimensions hold up at which span, and how much you realistically need to pay in 2026.

In this guide I break the topic into three parts: how to match rafter dimensions to the roof span, what spacing is safe for different roof coverings, and finally — how much a rafter actually costs, starting from the price of the timber itself. If you want the wider picture of the whole roof structure, take a look at our article on roof trusses , where rafters are covered as just one part of the whole. Here, I go into the details.

What a rafter is and what it does

A rafter is the sloped timber member that runs from the wall plate (the beam resting on the wall) up to the ridge or the purlin, forming the skeleton of the roof slope. Rafters carry the entire roof covering — tiles, metal sheeting, battens, counter-battens, membrane — and transfer that load down to the wall plates and the load-bearing walls. Without a correctly sized rafter, nothing else in the truss really matters, because this is the member under the greatest bending stress.

Rafters versus the other truss members

A rafter doesn't work alone. A collar tie stiffens a pair of rafters across the span, a purlin supports them somewhere in the middle of their length, and a wall plate spreads the load onto the wall. For the full picture of how these elements work together and how a roof structure comes together, see our article on roof trusses — what they are and what they're made of. Here I focus purely on the rafter, because that's where most pricing mistakes happen.

Rafter sizes — how to choose the right cross-section

Rafter dimensions depend mainly on the span between supports (wall plate–purlin or wall plate–ridge), the snow and wind load, and the spacing at which the rafters are laid out. The European standard PN-EN 1995-1-1 (Eurocode 5) gives a designer the tools to calculate the exact cross-section — but the rough ranges used in practice look like this.

Rafter thickness should never go below 5 cm — a thinner section simply can't carry the bending loads over a typical span. There's also a rule carpenters have applied for generations: the depth of the section is usually about twice the width. That's not arbitrary — a rafter works mainly in vertical bending, so a tall, narrow section carries more than a square one of the same area.

I've seen plenty of projects where the investor wanted to "round down" — take 6×10 instead of 7×14, because the price difference seemed negligible. On a typical house, the difference in the cost of the timber alone is a few hundred zloty. Rafter deflection after the first harsh winter, cracked plasterboard in the attic, and having to reinforce the structure after the roof is already closed up — that's an expense counted in the thousands.

Timber class and rafter sizing

The cross-section alone is one variable — the other is the timber's strength class. A 7×14 cm rafter made from C24 timber can carry more than the same cross-section in C18, because the difference concerns bending strength, not just geometry. At JB Tartak we supply rafters exclusively in C24, kiln-dried to below 18% moisture — that's the standard structural designers assume in calculations under Eurocode 5. Ungraded or wet timber, even in the "right" cross-section, doesn't deliver the same load-bearing capacity — and that's not somewhere to cut corners on rafters.

Rafter spacing — what it depends on

Rafter spacing is the centre-to-centre distance between neighbouring rafters, measured along the slope. It typically falls between 60–120 cm, but the final figure depends on three things: the type of roof covering, the snow load in the region, and the span of the rafter itself.

Spacing and the type of roof covering

Heavy ceramic or concrete tiles (40–50 kg/m²) call for tighter rafter spacing — usually 70–90 cm — because the rafters and battens have to carry the extra dead weight of the covering before any snow load is even added. Lightweight metal roofing or profiled steel sheet (5–8 kg/m²) lets you safely increase the spacing to 90–100 cm, sometimes more — provided the rafter and batten sizes are matched accordingly. The roofing manufacturer always states the maximum allowed batten spacing in the technical data sheet, and that in turn determines the rafter spacing.

Spacing and snow zones — a note from Silesia

In Silesia, where some counties (especially those closer to the Beskid mountains) fall into a higher snow zone than central Poland, the design snow load on a roof can be noticeably higher. That means a spacing that works fine on a roof near Poznań might be too generous for an identical house built closer to Bielsko-Biała. I always ask about the project's location before recommending a specific spacing, because snow zone 2 and snow zone 3 mean very different requirements for the same rafter cross-section.

How do I know? Because I've seen projects where the general contractor copied a design "one to one" from a different location, and in our region it turned out the rafters had to be spaced closer together or made thicker already during construction — after the structural engineer checked the design against the local load zone.

How much does a rafter cost — 2026 prices

This is the question we get asked most often — and here the numbers are concrete. Rafter cost depends on three things: the cross-section (i.e. the timber volume per running metre), the length, and the price of the C24 raw material itself.

Price per running metre and per cubic metre

The going market rate for C24 structural timber (kiln-dried, planed on four sides, with a certificate) in Poland in 2026 is roughly 1,100–1,900 PLN per m³ net, depending on cross-section, length and region. Taking an example price of around 1,350 PLN/m³ (a value within that range, used here purely for illustration), the approximate cost of a rafter in common cross-sections looks like this:

For example: an 8×16 cm rafter, 5 metres long, costs roughly 85–90 PLN in raw material at the example price of 1,350 PLN/m³. Multiply that by the number of rafters on the roof (see below) and you get a realistic material budget — before labour, fasteners, or preservative treatment.

How many rafters, and how much timber, a typical roof needs

The number of rafters per slope is calculated with a simple formula: the length of the slope in metres divided by the spacing (in metres), plus one extra rafter at the end. For a 10 m long roof with 80 cm spacing, that's 10 / 0.8 + 1 ≈ 13–14 rafters per slope, or 26–28 rafters for a whole gable roof.

Rafters typically account for the single largest share of the total timber volume used in a rafter-type roof truss — there are simply more of them, so together they use more material than the purlins, wall plates, collar ties and struts combined. The exact percentage depends on the specific design, span and number of additional elements, so there's no single universal figure to quote. If you're looking for a full cost breakdown of the entire roof structure, not just the rafters, we have a dedicated, detailed article: how much does a roof truss cost — material and labour prices 2026. It breaks down the whole budget there, including carpentry labour.

Don't want to work it out by hand? Send us your roof plan — a material quote for the rafters and the whole truss, ready in 15 minutes. Get in touch.

How to estimate the number and cost of rafters yourself — step by step

1. Measure the slope length — the distance from the eaves to the ridge along the slope (not the horizontal footprint of the house).
2. Determine the spacing according to the roofing manufacturer's technical data sheet (see the section above).
3. Calculate the number of rafters per slope: roof length (along the ridge) / spacing + 1.
4. Multiply by 2 (both slopes of a gable roof) — for more complex roof shapes, add hips and valleys separately.
5. Multiply the number of rafters by the volume of a single piece (from the table above) and by the price per m³ to get the cost of the raw material.

This is an approximate method. A precise structural design, sized for the actual snow zone and wind load, should always be prepared by a qualified structural engineer. But for early-stage budgeting, this approach works well and helps you avoid surprises when the first quote lands in your inbox.

The most common mistakes when choosing rafters

Undersizing the cross-section "to save money." This is mistake number one. The difference in material cost between a 6×10 and a 7×14 cm rafter is a few hundred zloty across the whole roof — but the consequences of undersizing the cross-section are deflection, cracked finishes, and sometimes having to reinforce the structure from scratch.

Copying the spacing from a ready-made design without checking the local snow zone. A design pulled "from the internet," or repeated from a different building site, doesn't account for local conditions. Snow and wind zones can change even within a single region.

Timber with no C24 certificate. It looks exactly like certified timber but has no documented strength. Without a certificate, a structural engineer has no basis for treating the structure as compliant with the design — and that becomes a real problem at building acceptance.

Ignoring the timber's moisture content. A rafter made from wet timber (above 20–25% moisture) will keep drying out after it's already installed — it warps, cracks, and loses its original shape at the joints. Always ask about moisture content at the time of delivery, not just about the strength class.

Have a roof plan and want to know exactly how much rafter timber you need? Write to us or call — quote ready in 15 minutes.

FAQ — rafters: sizes, spacing and price

What is the standard spacing for roof rafters?
Usually 60–100 cm, depending on the roof covering and the load. Heavy tiles call for spacing closer to 70–90 cm, while lightweight metal roofing allows spacing up to 100 cm or more — always within the limits set by the roofing manufacturer and the structural design.

What is the minimum thickness of a roof rafter?
The theoretical minimum is 5 cm, but in practice, for the typical spans found on single-family homes, cross-sections from 6×8 up to 10×18 cm are used, depending on the span and the load.

How much does a single rafter cost?
At the going market rate for C24 timber (1,100–1,900 PLN/m³), an 8×16 cm rafter 5 metres long costs roughly 70–120 PLN for the raw material alone — the exact price depends on the current offer, region and order size. The price rises with length and cross-section, and falls with bulk orders placed directly with a sawmill.

Does a rafter have to be made from C24 timber?
The European standard PN-EN 1995-1-1 (Eurocode 5) and most structural designs assume C24 for load-bearing truss members, including rafters. Lower grades (C14–C18) don't guarantee the same load-bearing capacity and shouldn't be used for structural roof elements.

What's the difference between a rafter, a purlin and a wall plate?
A rafter is the sloped member carrying the roof covering, a purlin is a horizontal beam supporting the rafters partway along their span, and a wall plate is the beam resting on the masonry wall that the rafters are fixed to at the bottom. You'll find the full breakdown of the whole truss structure in our article on roof trusses.

Choosing rafter dimensions and spacing isn't a place to guess — too much rides on this one decision to make it without solid numbers. At JB Tartak we've supplied certified C24 structural timber for roof trusses for 35 years, and we advise builders and carpenters alike on the right cross-section and spacing for a given span and location. Check out our range of roof trusses — or simply send us your roof plan and get a quote in 15 minutes.