Traditional roof frame or trusses? How to decide for your family home

The deciding factor is primarily how much you want to use the space under the roof. If you don't need the attic, trusses are the fastest and most economical route. If you want an attic, you have two options: a truss with living space or a traditional roof frame. For standard layouts, a habitable truss is often a better solution than you might expect.

The difference between the two structures is often described as a contrast between mass production and traditional carpentry. That is not how it works today. Both roof frames and trusses are created in our facility on the same machines, and on-site, both become a simple assembly job.

What both solutions have in common

Both are processed on CNC machines. The components arrive at the construction site with finished joints, carpentry notches, and holes, so assembly is just a matter of putting them together according to the drawings. On-site improvisation, which used to be common with roof frames, is eliminated, along with most inaccuracies.

This also dictates the timeframe. For a family home, both cases take days, not weeks. The deciding factor is not the type of construction, but whether the shell of the building is ready and whether there is space to position a crane.

Both structures are also created based on structural calculations using kiln-dried timber. The differences worth discussing lie elsewhere.

How roof frames and trusses differ

Traditional roof frame

A system of rafters, purlins, wall plates, and collar beams. The space between the rafters remains completely open, so the attic layout is not restricted in any way. A traditional frame can also be designed for exposed construction, where the structure becomes part of the interior.

The span of a traditional frame is determined by the position of load-bearing walls and internal supports. Creating an open space across the entire house is more difficult with this method.

Roof truss

A planar beam composed of elements connected by metal nail plates. Trusses are installed in a grid from 900 to 1200 mm; the exact spacing is based on the roof composition and load requirements.

A truss transfers the load across the entire span. It can handle up to 30 meters on two supports; for family homes, we typically work with spans between 12 and 15 meters. This means you don't need a load-bearing wall inside the house where it might get in your way.

Trusses are made in several types, which determines how the attic can be used. A standard truss is crisscrossed with diagonals, leaving the space suitable only for technical use. Truss with living space has an open central area that can accommodate a full-sized room. Scissor truss provides a vaulted ceiling that makes the space feel more open and airy.

Comparison in five points

Five points where the two solutions truly differ. In all other respects, they perform practically the same.

Span. This is where the difference is greatest and what makes a truss a truss. It can span up to 30 m with two supports, and typically 12 to 15 m for family homes, meaning there is no need for a load-bearing wall in the middle of the house. A traditional roof frame is tied to the position of load-bearing walls and internal supports, and struggles with open spaces spanning the entire house.

Attic. A traditional roof frame leaves it completely open, with the layout unconstrained. With trusses, the type is the deciding factor: a standard one provides a utility attic, while a habitable truss provides a full-fledged room, though its shape is defined by the structure.

Hipped roofs and complex shapes. Both can handle this. However, trusses usually work out better for hipped roofs because they are mass-produced. A traditional roof frame can do them too, just without the cost savings.

Exposed structure. The only point where trusses fail completely. An exposed structure in the interior is the domain of the traditional roof frame.

Renovations. The standard solution is a traditional roof frame. With trusses, the geometry of the building and whether there is space for a crane are the deciding factors, so each specific structure needs to be assessed.

This comparison applies to a standard family home. For halls, sports facilities, or buildings with large spans, the solution shifts elsewhere, toward glued laminated timber.

When you won't use the attic

Bungalows, single-story houses, houses with a flat ceiling over the entire floor. Here the choice is clear: a standard truss. It is the most cost-effective, the fastest to install, and leaves technical space above the ceiling for utilities and insulation.

Likewise, when you need a large open space without columns. A truss transfers the load across the entire span, so you won't be left with a load-bearing wall in the middle of your living room on the ground floor.

When you want an attic

This is where you decide between a habitable truss and a traditional roof frame.

Habitable truss is often a better choice for standard layouts than is usually assumed. It comes with the structural engineering already solved, is mass-produced, and can be installed on-site in a single day. The limitation is the shape and size of the room, which the truss defines.

Traditional roof frame offers complete freedom. The attic layout is not restricted in any way; you can add dormers as needed, and the structure can be left exposed.

The decision must be made during the design phase, not later. The diagonals of a standard truss are load-bearing and cannot be removed later, so you cannot turn a technical attic into a room without structural intervention.

If you are unsure, first ask yourself what will be above the ground floor ceiling in ten years. The answer to this question will decide for you.

When to choose a roof truss anyway

     
• The structure is meant to be seen. A truss with metal connector plates is not something you want above your head in the living room. An exposed roof truss made of larch or glued laminated timber, however, is.
     
• You are renovating. With older buildings, the geometry may not accommodate a truss grid, and there is often no space to position a crane. We will evaluate this based on the specific building.
     
• You have a highly individual roof shape. Trusses handle hip roofs and complex floor plans well, but for completely atypical designs where every piece would be different, the advantage of mass production is lost.
     

And then there is the common combination where the main part of the house stands on trusses and the garage or extension has a roof truss. Or vice versa.

How we handle it

At KASPER CZ, we do both, so we won't push you toward one solution just because we don't know how to do the other.

We start with a structural design and preliminary statics. This results in a price quote where you can see how much each option costs for your specific house. Only then do you decide. Production runs on Hundegger K2i and SpeedCut SC3-160 CNC machines, so the parts arrive at the construction site machined to the millimeter. We provide both transport and assembly.

We process 16,580 m³ of timber annually and have been in the industry for over thirty years. Most of our work consists of exactly these situations, where someone is unsure whether to choose a truss or a roof truss.

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Frequently Asked Questions

Can you have an attic with a truss roof?

Yes, but it must be designed that way from the start. There are attic trusses that leave an open space in the middle for a room, and for standard layouts, they are often a better choice than a traditional roof frame. You cannot retroactively build an attic into a standard truss, as its diagonals are load-bearing.

What span can a truss handle?

Up to 30 meters on two supports. For family homes, we typically work within the 12 to 15-meter range, as more is rarely needed. For larger spans, it is often more cost-effective to switch to glued laminated timber.

Can trusses be used for a hip roof?

Yes, and they are usually better for hip roofs than a traditional frame. Trusses can also handle more complex shapes; the advantage of mass production only diminishes with completely atypical designs where every piece would be different.

How long does installation take?

For a standard family home, it takes a matter of days, whether using trusses or a traditional frame. All processing is done in our factory, so on-site work is just assembly according to the drawings. The deciding factor is having the structure ready and ensuring access for a crane.

Are trusses cheaper than a traditional roof frame?

For a simple gable roof over an unused attic, generally yes, as they are mass-produced. With attic trusses, the price increases, and whether it remains cheaper than a traditional frame depends on the specific layout. A reliable answer can only be provided once we price your project.

What is the spacing between trusses?

Between 900 and 1200 mm. The exact value depends on the roof structure and load requirements; it is not a fixed number.

Do I need a finished project to request a quote?

No. A floor plan, a cross-section, and an idea of the roof shape are enough. We will work out the rest together, and the sooner you get in touch, the more we can influence the design.

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