Surprise in the attic - Please advise

[Patrick McCarthy]

Absent a clear understanding of the cause, you are only addressing the symptoms. . . . and even then, perhaps for the first of several timeS??? Where I live, along the coast, we have Adobe clay soil, which is highly expansive, so things move with the change in soil moisture. I have no idea re soil issues in your area, but the comment about getting a structural engineer to look at it is, IMHO, excellent advice. I would caution against being "penny wise and pound foolish".

Something caused significant stress to cause the damage. Fixing the damage does not address the cause. The cause is your real problem. I will get off my soapbox now. I wish you well with this, and will be curious to learn what you find.

[Karl Andersson]

Raymond,
Those 2x4s are not part of a "normal" structural assembly - it appears that the installer hung the floor below off the rafters by using the 2x4s -like hanging a catwalk from cables. I've done numerous heavy residential carpentry builds/ repairs and I have never seen anything like that offered as a solution to achieve a joist span support - there is probably a bearing beam or similar structural component missing. It may meet some code loophole, but what you're seeing is a result of the someone trying to span too great a distance with too small joists. The deflection must have been several inches and there may be some damage to the floor joists as well, or they may have taken the bow permanently. As some have said, you must have had some heavy load on the floor; if not, then the floor is extremely under-built to deflect that much with just sheetrock on them - I would make sure it's strong enough to support your weight (or add more jacks before going up). T

he 2x4s look like they are lighter than the rafters, so they may have been added after the fact by a homeowner who removed a wall or support beam with columns so they could have more open space in the garage. If you look at the garage floor, you may even see anchor holes or other remnants of a missing wall. I seriously doubt a qualified carpenter installed those 2x4s originally. You could do the repairs yourself if you're confident in your ability to understand span tables and basic carpentry; the difficult repair is the floor sagging - the rafters can be addressed more easily AFTER you fix the floor. There are ways to fix failed rafters/ joists with plywood faces glued and bolted to them (the plywood can be in 8' sections, with joints staggered 2' on each side) - there are online sources for ideas like that if you google "sistered joist", so don't tear up the sheetrock until you have looked at all the possibilities.

Of course, this is a lot of assumption, based on two pictures
good luck,
Karl

[Mike Cutler]

There are some serious issues going on. You should be talking with an eyes-on structural engineer.

I couldn't agree more.

Raymond
You really need to find the reason that the rafters are splitting. It could be as a simple as the truss design is incorrect, maybe more.
A "mending plate" can be used ,as with all things, there are rules and codes that apply to their installation. They will be much longer than the area that is split,and being as close to the end as it is, I don't know if it would work. The same goes for a sistered rafter, beam, or joist. They can be used, but there are code requirements. Basically they have to go full length, equal width and thickness, and be supported, if they are carrying the load.
You need a civil guy, as Bruce suggested.

[Brian Tymchak]

Agreed here. Looks like sister boards are the solution. I always just research alternatives.

To get around my problem getting a 14' max 2 x 6 through the space I have available, I had this idea and would like your opinions on this. Could I make a rafter that was joined in the middle with a 1' long half lap joint and assemble it in the attic? Surely that would be strong enough? Do you think?

Without more pictures it's impossible to tell, but can you tear out the soffit (if it exists) and slide boards up into place from below?