This place was built in 1915. Sorry, no truss. There is no direct access into the attic space. When I was stripping wallpaper and skim coating the back bedroom I decided to cut a hole in the ceiling with a recip to get a peek. You would not belieive what I found.
I cut through some drywall and found a grid of 2x4, but no attic. There was another ceiling above (the original 9ft plaster ceiling). So I cut through that (slats and plaster only).
So here I was staring at the attic space. I managed to wiggle my way up there and noticed that the original ceiling was being held up by 2x4's running freely about 15 feet. There was quite a bit of deflection so I clinged to the rafters and used the make shift plank running the length of the house. Luckily the middle of the house us supported all the way to the attic by the stair well and it's interior walls.
It is an open space, no truss, no waste vents or wires, etc. Just cross vents, insulation and an old wasp nest. I patched the hole in the ceiling and that was that. There is no support up there for boxes or anything. Especially with that second ceiling hanging there. Two ceilings, original plaster at 9ft, hung drywall ceiling at almost 8ft. I guess the original plaster started to deflect and crack. So, instead of laminating they dropped it. Don't ask me why they did that, but the dropped ceiling seems to be reinforced on the side walls a bit.
Over the last two weekends I did some more work on the second floor. You may notice from the first diagram there is an open triangular space on the left and right. Well, in the back room there are two full length walk in closets hung with plaster (even under the rafters). In the front room, there was one partial length closet and an empty cavity on the other side of the room.
I cut out a vanity wall in the partial closet, removed the plaster hanging from the wall "roof actually", extended the floor, innsulated, framed for drywall and hung it. I knew the other side of the room had to be identical in specs for another 12x4 walk in closet. So, I cut a hole in between studs and found a nice open cavity. I put in a plywood floor, slap studded, insulated with 2" foam board, r-13 and hung drywall. I also framed a door to match the closet door on the other side of the room. But I still have not cut out the bottom plate, where the door will go. Although the new studs for the door sit right on top on the (bottom plate) directly over the floor joists.
The second closet gave me a great insight into how the roof is setup. I was able to take a good look at the bones of the house. And I see that the rafters are tied in maybe 3 places. The rafters have a 2ft runout for a sofft. I can't see what they are attached to at the runout. There is a knee wall 21" high that matches the ext wall. The rafter has a bird's mouth notch on top of 2 2x4's (knee wall top plate), which is also tied to the floor joists (2x10). Then the rafter contues up 86" to the interior wall of the second floor to another bird's mouth notch on top of one 2x4 top plate (about 80" above the 2nd floor, but lower than the original or dropped ceiling). Then the rafter contines along about 2 more feet (9ft above 2nd floor) and passes by the 2x4 that hold the original plaster ceiling, but there is no bird's mouth here. The 2x4's are just tapped into the side of the 2x6 rafters. After that, the rafter continues along about 8-9 more feet (7ft high from original ceiling to ridge) to meet the ridge board (2x6).
I beleive the 2x4's that are holding the original plaster ceiling are more closely related to a collar tie than a rafter tie. Even though they are located 1/2 the way up, which puts them in rafter tie territory (2/3 bottom).
After finishing the side closets, which would be like a mini part of a cathedral ceiling I have learned my lesson of pain. This is not an easy project, ceilings are a mess to deal with and old growth wood is very hard to cut compared to that ripe fresh stuff you get these days. There is not much room for insulation with the 2x6's and foam board is expensive. Old houses have coal dust, plaster and all kinds of crap in them. I would like to raise the ceiling back the original 9ft height. I would love to strip all of the plaster from those 2x4's and hang drywall, but I am afraid it would deflect just like the original ceiling probably did.
Did I mention the interior walls of the second floor go straigh up until 7ft, then taper in with the roof line. It is a neat effect since they did this on all 4 walls, but when you have to drywall, it's a pain to deal with all those angles. There is a word for this type of ceiling, mandr(???)