I realize that I’m too late to help the original poster, but I think lots of stuff in the thread about reinforcing the attic “floor” was misleading (some of it was good!)
If what I’m posting here seems way off base to some of you framers out there, please post your take on it. If I’ve got it wrong, I’d like to learn. So here goes:
There are no floor joists in an old attic. Those 2x4s are CEILING JOISTS and are not meant to carry any weight except that of the ceiling itself.
As for sistering in more 2x next to the existing rafters. That works fine unless there is still existing plaster and lath. If plaster and lath is still the ceiling below you will damage the ceiling if you knock off the lumps of plaster that stick up between the pieces of lath. It’s that bit of plaster sticking through that primarily holds the plaster on the ceiling and banging around on it, adding weight to it, etc. is likely to start or worsen the plaster cracking.
Strongbacks were not originally used to increase the load bearing capacity of ceiling joists. The original purpose was to straighten wavy rough sawn lumber and to spread out the weight over all the ceiling joists. Remember, that lumber was not graded and while some of it was great, some of it had too many and too big knots and other flaws.
In the instance cited by the original poster the strongback idea was NOT a good one. Did anyone notice that he said the lenght of the strongbacks was 22′? A 2×6, or even a few 2x6s, laid out in the strongback method, is not going to do much to increase weight bearing capacity. He also said that he added more framing plus ply to the new surface to hold his storage items. Thus, he added even more weight to the already inadequate frame.
Since his roof was 12/12 or so (allowing better access to the top of the top plate), I’d suggest sistering 2×6 minimum (assuming nothing heavy was going to go up there) or preferrably 2×8. I’d suggest setting the ends of the new 2x on 1/2″ ply scraps (or similar) to hold the new ceiling joist bottoms off the plaster (again if it was plaster) and then glueing and side nailing the new to the old. I wouldn’t have used screws unless they were going to be quality screws of a heavy guage. (Piffin would suggest drywall screws, right? ; ) )
Some of you may note that I didn’t look at the posted pictures in the thread I’m referring to.
OK, guys, what about this don’t I get?
You’re unique! Just like everyone else! Scott Adams
Replies
While I agree that strongbacks would not be the ideal "fix" for the instance as you`re describing it, my impression of the original thread was that the poster was attempting to improve an existing situation which included light storage. He also spoke of a desire to increase insulation capacity which strongbacks do not adress.
Had I taken the intent of the original thread as I`m taking your query....create a storage....I would have to agree with you....strongbacks are not the answer.
Being a carpenter as opposed to an engineer, it is my opinion that strongbacks placed properly would in fact increase the strength of the attic floor (ceiling to floor below) considerably. To the degree necessary to meet homeowners intentions? Without a rereading or original post and possibly more info, I`m not sure.
J. D. Reynolds
Home Improvements
"DO IT RIGHT, DO IT ONCE"
Hadbeen,
I think your "fix" is very safe and very well thought out one. Only thing I would possibly do differently is to not join the new floor joists to the existing ceiling joists. The 1/2" ply standoff is a great idea and works double duty in 1) not disturbing the existing plaster, and 2) further working to isolate the ceiling framing from the floor framing. I'm just thinking better safe than sorry in not allowing the new "floor" and it's deflection to interfere with the plaster/lathe. Like two independant systems, one for the floor, and one for the ceiling......
I'm really just thinking out loud here and running with your idea.
I also think that some of the other options presented in the original post would probably work equally as well, and possibly be less labor intensive.
How's that for wishy-washy?
I see your point.but as to the original post he was just looking to reinforce the ceiling joists. and strong backs at mid span of the rafters would do that.another thing is that any space beyond the strong backs would be un useable with head room and all. so he can do what ever he wishes in between the strong backs for useable storage and insulation and beyond the strong backs he can just blow in more insulation. he is just going to have to live with what space he can attain. as far as the span goes I'm sure there must be some bearing points along the way
Since his roof was 12/12 or so (allowing better access to the top of the top plate), I'd suggest sistering 2x6 minimum (assuming nothing heavy was going to go up there) or preferrably 2x8. I'd suggest setting the ends of the new 2x on 1/2" ply scraps (or similar) to hold the new ceiling joist bottoms off the plaster (again if it was plaster) and then glueing and side nailing the new to the old. I wouldn't have used screws unless they were going to be quality screws of a heavy guage. (Piffin would suggest drywall screws, right? ; ) )
Your absolutely right except you shouldn't attach or even put the new against the old. I did a renovation a few years ago and did exactly as you say but I did not want the floor activity to wiggle or flex the old plaster below. The local code enforcement was impressed.
The client is still a current customer and after 5 years there is no cracking.
Ya just gotta think of that old house as a flexing, breathing swaying creature.
but I did not want the floor activity to wiggle or flex the old plaster below
I'm curious, how did you keep the new work from rolling? Was there enough depth change to allow "x" bridging, of did you notch solid blocking?Occupational hazard of my occupation not being around (sorry Bubba)
The orig. ceiling joist were 2x4's and the new floor joist were 2x8's. I did a reverse stiff back as it were. 2x4's between joist and a 2x4 on the flat let in flush to the surface. This was done at either end, in about 1/4th of the span. I then glued and screwed the floor t&g sheathing to death.
I did it differently.
I started by shop vacing all the dust and broken plaster keys out. Then I used the pole and screw jack to push some loose plaster up into place. I went over the whole ceiling from above injecting yellow water based woodworking glue in between the shrunken lath and the plaster.
With the plaster stabilized, I raked out the keys along the old 2x4 joists where the sisters would go. I spent some time at HD picking Sel Str and 1 & Btr for the sisters. I put them in crown upward, pushing the ceiling up with the screw jack to match, and glued and nailed them in place. Then I ran two rows of solid 2x6 blocking, notched around the old 2x4's. I cut those to fit snug, and gently opened the gaps with a small bottle jack to drop them in. Stabilizing the 2x6 sisters against edge deflection like that makes them a lot stiffer.
So, did I do it all wrong?
-- J.S.
Sounds like an excellent solution to me.You're unique! Just like everyone else! Scott Adams
Good point. Just drop some Tji's (resting on 2x4 shims) between the existing ceiling joists. Now, the next comment on bracing them would make things a bit interesting.
>> Ya just gotta think of that old house as a flexing, breathing swaying creature.
Excellent point. Where we live there are mostly older homes - very few built after 1950. We are often faced with the question: Has it moved or is it moving?
When you are looking at a foundation of sandstone rocks that were laid into poor quality mortar 80 years ago.... How do you answer that question?!?!
: )You're unique! Just like everyone else! Scott Adams
When you are looking at a foundation of sandstone rocks that were laid into poor quality mortar 80 years ago.... How do you answer that question?!?!
I saw a fieldstone foundation fail. The mortar was little more than crumbling sand.
We got cracks in plaster walls, doors out of jambs, plumbing leaks, everything you could imagine. Ended up with jacks all over the basement. And the hasty reconstruction of one corner of the foundation that just crumbled. Perhaps the compression had been holding it in place?
I'm not a mason. I just watched the work proceed with great interest.