What is a Raised Tie Beam Truss?
A raised tie beam truss is a roof truss in which the horizontal tie beam is positioned above the level of the wall plate, rather than at the base of the rafters. This design raises the ceiling height within the roof space, creating more usable interior volume while still providing structural restraint against rafter spread.
How it differs from a standard truss
In a standard roof truss, the tie beam sits at the very bottom, connecting the feet of the rafters at wall plate level. This creates a flat ceiling at the top of the wall, but it limits the height of any space within the roof.
In a raised tie beam truss, the tie beam is moved upward along the rafters to a higher position. The rafters extend below the tie beam down to the wall plates, and the space between the wall plate and the tie beam becomes usable interior volume with sloping walls. The result is a taller, more open room within the roof.
Structural considerations
Raising the tie beam introduces additional structural challenges. Because the tie beam no longer acts at the base of the rafters, the outward thrust at wall plate level is not fully restrained by the beam alone. The walls must be strong enough to resist the remaining horizontal forces, or additional measures must be taken.
Common solutions include:
- Reinforced walls or buttresses — Thicker walls or external supports to handle the lateral thrust.
- Steel or timber knee braces — Angled members connecting the rafters to the walls below the tie beam to redirect forces.
- Ring beams — A continuous reinforced concrete or timber beam at wall plate level that distributes thrust around the perimeter of the building.
- Wall anchors — Metal ties that connect the roof structure to the walls, preventing outward movement.
Where raised tie beam trusses are used
This truss type is common in buildings where the attic or loft space needs to be habitable. Residential buildings, particularly renovations that convert attic space into living areas, frequently use raised tie beam trusses. They are also found in churches, barns, and historic buildings where a tall, open interior was desired.
Design and building regulations
When designing a raised tie beam truss, a structural engineer must calculate the remaining thrust forces and ensure the walls and connections can handle them. Building regulations typically specify minimum ceiling heights for habitable rooms, which influences how high the tie beam must be raised.
Related terms
- Tie beam
- Collar beam
- Roof truss
- Attic conversion
- Rafter
- Knee wall
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