Oak Roofs and Trusses - Technical


The below summary details the components that can be used and some basic designs.

Liaising with your builder, architect or engineer is all part of the process!  Call 01423 593794


Component List

1. Purlin – 2. Ridge – 3. Principle Rafter – 4. King Post – 5. Diagonal or Strut

6. Tie Beam or Chord – 7. Cleat – 8. Base Purlin – 9. Common Rafter – 10. Laths

Type of Oak Trusses


King Post Truss

The most common truss; It is represented by a triangular structure and a central vertical post (the king post). Sometimes additional diagonal struts are placed between the base of the king post and principle rafter.

Queen Post Truss

As pictured right (top), a similar construction except the centre post has been replaced with 2 small posts either side.

Mono Truss

This is basically half of a king post truss.  Normally used for pitch roofs being built perpendicular to the gable end of a house.

Raised Tie Truss

Pictured right (bottom), Similar to the king post truss except the tie beam is situated higher up the principal rafter giving additional headroom.  A rule of thumb is that the tie beam should not be more than one-third distance up from the base of the principal rafter.

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oak king post roof trusses

Structural Calculations & Grades

Grading oak is a visual task.  Compared to softwood, hardwood has a different grading system.

Softwood Grades tend to be C16 or C24 – these are fine when using softwood for stud walls, common rafter and timbers not seen after installation.

Hardwood Grades tend to be D30, D35 or D40.  D40 is the better grade although most oak framework and roof trusses would use a minimum of D30 unless otherwise specified.

Structural calculations should be performed by a structural engineer.  This service can be offered if required.  For smaller projects, for example, an open porch, an engineer is not required as the weight-bearing elements are not large enough.

When a roof or supporting beam carries weight, oak can deflect and therefore other considerations need to be taken in to account.  In a roof, this may mean the roofing material, insulation used and pitch of the roof.

For expert advice, further prices and general help, call 01423 593794