When people talk about roofs, they usually focus on the covering. Tiles or sheeting. Colour and profile. But the real performance of a roof depends on what holds it up. Timber truss designs determine how your roof carries load, how straight it stays over time, and whether the space below feels open, quiet, and comfortable.
In South Africa, timber trusses remain a favourite because they are efficient, fast to install, and flexible enough to suit everything from modern skillions to classic gables. This guide explains what timber trusses are, the most common timber truss designs, and the pros and cons of each so you can make a smarter decision before you build.
What are timber trusses?
A timber truss is a structural framework made from straight timber members connected in a triangulated pattern. The top chords follow the roof slope, the bottom chord forms the ceiling line, and the internal webs create triangles that resist bending and deflection.
Most modern trusses are prefabricated in a controlled factory environment and delivered to site labelled, ready to install. Joints are typically made using pressed steel nail plates, while feature or exposed trusses can use bolts, steel gussets, or traditional joinery depending on the design intent.
Common timber truss designs used for roofs
1) King post truss
What it is: A simple triangular truss with a single central vertical member.
Advantages:
- Cost-effective for short spans
- Simple geometry and easy installation
- Works well for basic gable roofs
Disadvantages:
- Limited span range
- Less flexible for complex roof shapes
- Not ideal where ceilings need to be very flat with minimal deflection
Best for: Smaller houses, cottages, verandas, and uncomplicated roof lines.
2) Queen post truss
What it is: Similar to the king post but with two vertical members and a horizontal straining beam between them.
Advantages:
- Spans longer distances than king post with moderate material increase
- Offers more headroom in the centre zone
- Good balance between cost and performance
Disadvantages:
- Still not the best option for very long spans
- Can require careful detailing to control deflection if loads increase
Best for: Medium spans in traditional homes where simplicity and economy matter.
3) Fink truss
What it is: The well-known “W” web configuration. It is one of the most common timber truss designs in residential construction.
Advantages:
- Excellent efficiency for typical housing spans
- Good deflection control when correctly sized
- Easy to manufacture and fast to install
- Works well with tiles, metal sheeting, and many roof pitches
Disadvantages:
- Web pattern can limit open attic space
- Needs careful trimming and reinforcement around skylights or large openings
- Complex roof intersections may require girder trusses and additional detailing
Best for: Standard gable and hip roofs in suburban housing developments.
4) Howe and Pratt trusses
What they are: Both are classic triangular web patterns. The key difference is the diagonal orientation, which changes how tension and compression are shared.
Advantages:
- Efficient for longer spans or heavier roof coverings
- More flexible web layouts to accommodate openings and load concentrations
- Often a good choice where roof geometry is complex
Disadvantages:
- Typically requires more design input than a basic Fink
- Can use slightly more material if not optimised properly
Best for: Larger residential roofs, mixed-use buildings, and areas with heavier coverings or wide open spaces.
5) Warren truss
What it is: A repeating pattern of alternating triangles, often without vertical members.
Advantages:
- Clean load distribution and strong material efficiency
- Works well where panel lengths are regular
- A tidy option for certain long-span roofs
Disadvantages:
- Not always the most convenient for openings or services
- Can require careful detailing at supports and intersections
Best for: Modern roofs, long and regular spans, and projects where a simple repeating pattern is preferred.
6) Scissor truss
What it is: A truss where the bottom chord slopes upward, creating a vaulted ceiling inside.
Advantages:
- Creates attractive interior volume without stick framing
- Adds architectural appeal to living rooms and entrance halls
- Works well with open-plan designs
Disadvantages:
- Often deeper and heavier than standard trusses
- Requires more careful deflection control
- Can complicate insulation and ventilation if not planned correctly
Best for: Homes that want vaulted ceilings with the efficiency of prefabrication.
7) Mono-pitch (skillion) truss
What it is: An asymmetrical truss that forms a single sloping roof plane.
Advantages:
- Clean, contemporary roof profile
- Simple drainage direction
- Often pairs well with metal sheeting and solar-ready layouts
Disadvantages:
- Wind uplift can be higher on certain elevations, requiring strong tie-downs
- Interior ceiling lines and insulation zones must be planned carefully
Best for: Modern houses, additions, and mixed roofscapes.
8) Attic (room-in-roof) truss
What it is: A deeper truss designed to create usable space within the roof.
Advantages:
- Adds storage or even a habitable loft area without extending the footprint
- Can be more cost-effective than adding a new storey
- Creates clear structural zones for flooring and ceiling lines
Disadvantages:
- More complex design and higher material cost
- Requires careful load planning for floors, stairs, and openings
- Insulation and ventilation detailing is more involved
Best for: Homes needing extra space, storage, or compact loft rooms.
9) Girder truss
What it is: One of the stronger timber truss designs, it is a built-up truss that carries other trusses framing into it at hips, valleys, and big openings.
Advantages:
- Essential for complex roof shapes and intersecting roof lines
- Concentrates strength where loads collect
- Enables large openings like double garages or wide living areas
Disadvantages:
- Heavier and requires careful lifting and installation
- Needs precise hanger and connection detailing
- Often drives the complexity of the entire roof layout
Best for: Hipped roofs, valley intersections, and large openings.
Choosing the right timber truss design
When comparing timber truss designs, consider:
- Span and pitch: Longer spans and steeper pitches often benefit from Howe, Pratt, or deeper trusses.
- Covering weight: Tiles and slate typically demand more stiffness than lightweight metal sheeting.
- Interior goals: Want a flat ceiling, a vault, or attic storage? That alone narrows the options.
- Wind zone: Edges and corners need stronger fixings and bracing, especially with mono-pitch roofs.
- Future upgrades: Plan for PV, skylights, and service routes before fabrication.
A good truss supplier will model options side-by-side so you can balance cost, stiffness, and build speed.
Conclusion
The best roofs start with the right structure. By choosing the correct timber truss designs for your span, roof covering, and interior goals, you get straighter lines, quieter rooms, and fewer maintenance issues down the line. If you want help selecting the most efficient option for your plans, Dezzo Roofing can compare designs, optimise the layout, and deliver a complete truss package with the fixing schedules and documentation needed for a smooth, compliant build.
FAQs
What is the rule of thumb for truss design?
A useful rule of thumb is that depth drives stiffness. Deeper trusses generally deflect less over the same span. But rules of thumb are only a starting point. Final truss sizing, spacing, and connection design should be engineered for your loads, covering, and wind zone.
How far apart should roof trusses be in South Africa?
Many residential roofs are designed between 600 mm and 900 mm centres, adjusted for span, covering weight, wind zone, and deflection limits. Your final spacing should come from the truss designer and the covering manufacturer’s requirements.
How thick should a timber truss be?
Truss members in housing often use 38 mm thick timber, with depth selected by engineering. Longer spans, heavier coverings, or special trusses like girders may require thicker or deeper members or engineered timber.
What are five types of roof trusses?
Five common trusses are King post, Queen post, Fink, Howe, and Scissor. Depending on the roof, you may also use Pratt, Warren, Mono-pitch, Attic, and Girder trusses.