Recommended test
Compare a solid-bottom attic truss with a lattice variant using the same building envelope.
- In Build, choose Truss and Lattice attic truss, then keep Manual while inspecting the layout.
- Change Floor girder total depth and check the upper floor level and remaining clear room height.
- For an enabled calculation service, review Automatic loads and restraints and calculate without changing CC.
- Generate and inspect both floor chords, diagonals, knee posts and the deck position; save and reopen.
Choose the lattice variant
Select Lattice attic truss in Build’s truss dialog, or Lattice loft in Truss Builder. The floor structure has an upper chord, a continuous lower chord and diagonals between them. Knee posts and the attic deck sit on the upper chord.
This is a separate geometry and calculation model. It is not an I-beam replacement or a promise that a span shown in an illustration will work for the project’s loads.
Set girder depth and room dimensions
Floor girder total depth starts at 800 mm in Build and accepts 400–1600 mm. Truss Builder chooses an initial 400–800 mm depth for its current span. A deeper floor girder takes space from the attic; check both the floor level and clear height beneath the collar before applying.
Manual mode keeps explicit member dimensions. Automatic retains the chosen girder depth, room dimensions, CC, common 36/48 mm thickness and declared bearings. It sizes both floor chords to the same section; posts and lattice diagonals share the web section. New designs use C30, with C24 also available.
Calculate and review
With the calculation service enabled, use the Automatic workflow. Roof loads act on the rafters; attic floor loads act on the upper floor chord inside the room; ceiling loads are separate. Floor loads remain active when the deck is hidden. An internal wall counts only when explicitly declared as an eligible bearing.
The tool accepts Manual geometry and bounded preliminary calculations up to 20 m, but this is an input limit, not a 20 m capacity rating. A failed search applies no Automatic result. Review the governing member, restraints and support reactions instead of assuming that a deeper floor alone solves every check.
Connections, chord splices, bracing capacity, floor vibration, wind and complete Norwegian compliance still require design. Dormers, porches and edited-roof contexts are outside this variant’s supported automatic building workflow.
Apply to the model
Apply the reviewed draft and regenerate the building. Inspect the upper deck level, lattice depth, knee-post contact and usable room. Existing A/W models keep their saved geometry; changing a definition or calculation does not reshape placed trusses until they are replaced or regenerated.