Timber Roof Structures

And Their Static Systems

Hi friends, 👋👋

Today we are starting a new series about the structural design of timber roofs.

We’ll start off by giving an overview about the different types that can be used. And more importantly for us engineers, how their static systems look like.

In the next couple of weeks, we’ll then dive deeper, showing how to dimension each roof type.

For each roof type, we’ll leave a link to a step-by-step guide on how to design it.

Alright, let’s get into it. 🚀🚀

#1 Rafter roof

The rafter roof is one of the most common timber roofs.

It consists of 2 inclined timber beams (=rafters) which are connected to each other at the top with a hinge and at the bottom to the ceiling with 2 pin supports.

The reaction forces of the pin supports are then applied to the ceiling.

3D visualization of a timber rafter roof.

2D static system: 👇👇

Static system of rafter roof.

#2 Truss roof

A timber truss roof is beneficial for longer roof spans.

There are a lot of different types of trusses. You can check them all out in our article about trusses.

Roof trusses consist of horizontal and diagonal members. To be able to calculate the internal forces by hand, all connections need to be hinges. This is however not 100% accurate as some members are continuous. To be able to calculate the internal forces of trusses with continuous members, advanced software programs need to be used.

3D visualization of timber truss roof.

2D static system: 👇👇

Static system of timber truss roof.

#3 Timber purlin roof

A timber purlin roof consists of 2 static systems:

• The rafters and

• the purlins

2D static system of the rafters (rafters are supported by the purlins): 👇👇

2D static system of the rafters of the purlin roof.

#4 Collar beam roof

The collar beam roof is like a rafter roof with an additional horizontal element, allowing for a longer span.

Check it out. 👇👇

2D static system: 👇👇

#5 Flat roof

The flat roof can also have many different variations. Instead of beams, CLT could be used, the secondary beams could be supported by steel beams or walls, etc.

2D static system: 👇👇

The secondary beams are simply supported beams.

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This was it for this week. And the beginning of a new series about timber roof design.

See you next week with the first roof design. 🚀🤘

Cheers,

Laurin.