Adding 2 Additional Storeys to the existing timber frame residential house

[Supun93]

I'm working in a project where i need to strengthen a building to add 2 more additional storeys. Now it is just a single story timber frame building consist with timber 2x4 studs in 18" spacing. Exterior walls are load bearing shear walls and interior walls are non load bearing.
The problem is when i design the building for 3 storeys the ground floor walls require high resistance to lateral loads. I can have power trusses to increase the resistance but seems it is not economical. Is there a way to strengthen the walls without actually reconstructing the walls or do i need to demolish everything and work on it again. Please help

 

[jayrod12]

If I'm understanding your question correctly, your existing walls are adequate for the gravity loads, but inadequate for the lateral loads in-plane (i.e. shear walls).

If it is just failing as a shear wall, you could add sheathing to the inside face of the walls. All hold-downs between floors would need to be installed prior to sheathing them.

Adding two storeys to a wall only designed as a single storey is a tall ask. The owner should be expecting that some potentially significant upgrades are required. I'm honestly surprised that the foundation elements are adequate for essentially tripling of the load.