Graphical Construction Glossary >> Roofs and roofing. >> Roof Trusses >> queen post truss

Queen post truss
A roof truss mostly wooden with two principal rafters and two vertical Queen posts with a restraining tie beam at the bottom and a straining beam at the top.

a simple queen post roof truss

Above is a simple truss that is a modern restoration of what would have been in the original early 19Th century building. This type of truss, that stops at the top straining beam was the most economical with no joints in the principal rafters and possibly joints in the. The common rafters continue up to the ridge.

A detail of this sketch of this truss is below.

Above, queen post roof trusses to the roof of the Romanesque church of Santa Chiara d'Assisi in Ravenna, Northern Italy. From memory these trusses which span the nave are something like 35 feet span.
I doubt that these are the original trusses but they would be replacements built very similar to what was originally used some few hundred years ago. Note the extra stiffening members at the wall seats and under the queen posts. These joints are reinforced with bolted wrought iron straps.

At a guess these trusses are spanning 40 feet or so. The extra span is gained by heavier jointed timbers.

a variation of a queen post truss

Original trusses spanning about 30 feet. Built around 1820 at the Chatham Royal Dockyard,UK. These queen post trusses have a king post type layout on top of the straining beam.

Note that all old trusses like this that survive, use wrought purpose made straps and brackets to hold the joints.

queen post roof truss

A queen post truss is a step up from the king post truss in that it can span a greater distance. Variations of these trusses are used to provide room space or at least storage space. A mansard type roof is of course a better choice if room space is required. Nail plate truss manufacturers make them for this purpose with the bottom chords being deeper to provide for the floor loads.

They can of course be made out of steel, but in general modern truss design has left the Queen Post behind.

traditional queen post

In a traditionally framed wooden truss of this type, as an example say spanning 35ft the member sizes would be in inches:-

  • Tie beam - 5"X11", with two pieces spliced.
  • Principal Rafter- 5"X7"
  • Queen Post - 5"X5"
  • Strut 5"X5"
  • Straining Beam 5"X8"
  • Straining Sill 5"X3"
  • Purlin 4"X7"
  • Common Rafter 2"X4"
  • Ridge Board 1 1/2"X9"

These sizes are of course generalisations as the pitch, strength grade of the timber all come into the equation.

lapped rafters

As the size of the roof gets larger so the rafters get longer until they have to be used in two lengths. They are normally lapped side by side on a purlin. They are shown here lapped on the same purlin, but a good practice is to alternate the joints if possible from one purlin to another.

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