A roof structure (roof frame) is the complete load-bearing framework of a roof, consisting of trusses, purlins, rafters and all the connections between them. It is the construction that gives the roof its shape and transfers the weight of the roofing material, wind and snow loads to the walls or columns.
Roof structure vs. truss — what is the difference?
These terms are often used interchangeably, but there is a difference:
- Truss — A single triangular or A-shaped frame
- Roof structure — The entire system of all trusses plus the purlins, rafters and connections that together form the roof
A roof structure therefore consists of multiple trusses, connected by purlins.
Components of a roof structure
| Component | Function |
|---|---|
| Trusses | The A-shaped frames that bear the load |
| Ridge purlin | The horizontal beam at the highest point |
| Wall plate | The beam on the wall on which the rafters rest |
| Purlins | Horizontal beams between ridge and wall plate |
| Rafters | Sloping beams from ridge to wall plate (carry the roofing) |
| Collar tie | Horizontal beam connecting two rafters (prevents sagging) |
| Braces | Diagonal supports for extra stability |
Types of roof structure
The shape of the roof structure determines the roof type:
Gable roof
Two sloping surfaces meeting at the ridge. The most common roof structure for houses, sheds and garages. Simple to construct and drains water well.
Mono-pitch roof (lean-to)
A single sloping surface. The roof structure is simpler: rafters from high to low, without a ridge. Widely used for extensions and modern garden rooms.
Hip roof
A gable roof with sloping surfaces on the short sides as well. More complex roof structure with additional hip rafters.
Flat roof
Technically not a roof structure but a flat-roof construction with joists carrying the roof deck. Always with a slight fall for water drainage.
Roof structure for self-build projects
When building a shed, garden room or garage, the roof structure is one of the most important components. The most common choices:
- Shed — Usually a gable roof with simple trusses. For small sheds (up to 4 m wide) you can work without trusses, using only rafters on the purlins.
- Garden room — Gable or mono-pitch roof. For an insulated garden room, you need to allow for a vapour barrier and ventilation in the roof structure.
- Garage — Often a gable roof with a steeper pitch (30-45 degrees) if you want to use roof tiles. Truss spacing is typically 60-100 cm on centre.
Building a roof structure yourself
For a simple construction (shed, garden room) you can build the roof structure yourself:
1. Calculate the roof pitch — Depending on the roofing material (30-45 degrees for tiles, 3-5 degrees for EPDM)
2. Determine truss spacing — Typically 60 cm on centre for lightweight roofing, 100 cm for heavier
3. Build the trusses — Cut the rafters to size and connect them with a collar tie
4. Install the wall plate — Fix it to the top of the wall
5. Mount the trusses — Place them on the wall plate and connect them with the ridge purlin
6. Check — Verify everything is level and square before installing the roofing
Related terms
- Truss
- Purlins
- Ridge purlin
- Wall plate
- Rafter
- Gable roof
- Mono-pitch roof