Please help, I am in the process of finishing a basement. 2x4 walls are 5" from concrete foundation due to plumbing issues. Everything will be drywalled. Soffits are framed w/ 2x2 and osb exterior then drywalled. Where do I need fireblocking and how do I do it? If the exterior walls run perp to the ceiling joist do I need to file the joist space above the top plate. Meaning I need to fill 8"x16" between the joists. Is this right? What about soffits, when they say the ends must be capped, What does that mean? Any help would be great. Thanks

In modern platform framing,ie. floor system, wall system, ceiling/roof system, etc... Each component is an encapsulated unit. Think sandwiches! Walls are framed(normaly) single bottom plate, stud, double top plate, exterior shell and interior shell. The lower plate always seals the bottom of the floor system, while the plywood sub deck seals the top.
But in the world of remodeling, especially basements, things are never normal. Top and bottom plates are(normaly) steel track and ceilings and soffits are never resting on an enclosed top plate.
The product you need to locate is "rock wool". It is a fireproof insulation sometimes known by the trade name therma fibre. If you ask around you should be able to locate. Google the phrase "rock wool insulation" and I'm sure you will find a supplier.
Wherever the wall meets a horizontial intersection, whatever the angle(45,90), stuff the cavity with rock wool as if you were trying to prevent cold air from entering. Do this at every bay junction, wall to soffit, soffit to ceiling, or wall to ceiling. Think of it as insulating a roof wall junction or a floor wall junction and stuff it with rock wool. Also dont forget to fire caulk(which is available at big box stores)all small drill hole penetrating the floor above, may it be in framing lumber or the plywood sub deck.
Rock wool and fire caulk are always needed in any remdodeling project where new penetrations are made, so if you dont use the whole bundle mabye it will get used in the future where it should be used.
Just to make a statement from the previous post, only materials that have a burn rating specified by you state and local agencies should be used as fire blocking..

The purpose of fireblocking is to restrict the movement of flame and gases through concealed spaces in the building via the horizontal and vertical connection of the floor and wall cavities. In typical platform frame construction this connection is blocked by the top and bottom plates of the stud wall. Where construction occurs that allows communication between the floor and wall spaces, fireblocking is required. A good example of this is the building of soffit at the junction of a wall and floor. The soffit now communicates the wall and floor spaces and allows the free passage of fire. Another example would be a drop ceiling. Just think, you are trying to stop the movement of fire up the stud space through the soffit and on through the space between the floor joists.
The building code used in most jurisdictions allows a number of methods for fireblocking. More commonly, is the installation of 2x4 wood blocking in the 2x4 stud space at the point where a soffit connects to the wall. Not only does the wood blocking restrict the passage of fire through the concealed space, it provides a solid nailing point for the connection of the soffit. Another material allowed for fire blocking is 1/2" drywall. You could simply apply drywall to the stud wall from the bottom plate to the top plate of the wall and then construct your soffit. The top plate of the wall blocks communication between the wall and the floor spaces, and the drywall blocks the opening between the wall space and the soffit. Mineral wool insulation, or "therma-fiber", is also permitted as a fireblocking material. However, the building code requires that the integrity of all fireblocks be maitained. The typical installation of mineral wool is to friction-fit the material between the framing members. I would not recommend this as a fireblocking memthod at the point where a soffit connects to a stud wall.
The other concern in the construction of a soffit is the ends of the soffit. If one end of the soffit is at the corner junction of two walls then the blocking methods above would apply. If the end or ends of the soffit occur in the room space then the application of drywall on the ends, as the finish material, would suffice.

Thanks for all of your help. I have a free standing wall, top plate and bottom plate attached. The top plate runs to the floor joists, it forms a 90* angle. If I drywall the ceiling I assume I need to fireblock the joists space above the top plate. So it will be as if the wall runs into the floor of 2nd floor forming a barrier. My soffit will run the length of the basement and finish directly into yhe new walls. It sounds like if I drywall the walls then build the soffit it will close off the soffit at both ends. Does this sound close? Thanks again to all.