| The wall between the diningroom and kitchen is a partition, non-load bearing. Can be torn down. The other wall is "load bearing" technically. Your correct w/ a truss bearing on the exterior walls. That is why there are 2x4's zig zagging on the truss (webbing). Dead and live load is transfered through the webbing to bear down on the exterior walls. So basically the "load bearing" wall can be torn down w/o any header being installed. Make sure none of the trusses have been altered in any way before doing so.
As far as the ceiling caving in, it wont, but if you live in an area with snow, you may see drywall cracks in the ceiling with snow load on the roof.
The support beam in the basement is to support the floor system.
Note: when in doubt contact a structural engineer.
Also, before tearing down any walls make sure you know where your relocating any electrical, plumbing and/or heating pipes/ducts. |