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Roof trusses

Frame truss (A-truss)

A frame truss (A-truss) is a roof truss built as an open frame of rafters, tie, collar beam and side struts, leaving the roof space free for a room.

Also known as frame truss, A-truss, A-frame truss, collar truss, room-in-roof frame truss

In Scandinavian practice roof trusses are divided into two main families. Triangulated trusses (such as the W or fink truss) are fully braced by webs and span from wall to wall. Frame trusses are built as an open frame: top chords, a bottom chord, a collar beam higher up and short struts at the sides, so the space inside the roof stays open.

Because the frame is not fully triangulated, it usually needs an intermediate load-bearing wall under the floor. Frame trusses suit storey-and-a-half houses and steeper roofs, typically around 27–50° in Sweden, where the loft is used as living space or storage.

Related terms
Attic trussAn attic truss leaves an open rectangular space in the middle of the roof, so the loft can be used as a room. Collar beamA collar beam is a horizontal member that ties a pair of rafters or top chords together part-way up the roof. Storey-and-a-half houseA storey-and-a-half house has a full ground floor and a second floor built into the roof, with sloping ceilings and knee walls. Centre bearing wallA centre bearing wall is a load-bearing interior wall, usually along the middle of a house, that supports floors or roof between the external walls.
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