You seem to have posts at the face of the existing wall. If that's the case, you don't really need to attach the beams other than to hold them in place in a superficial manner.
Otherwise, joist hangers or full bearing on framing in the wall. In either case you need suitable backing structure on which to mount the hangers or bear the beams. If you don't have studs in the right locations, look into top-bearing hangers that you can fasten to the top of your wall plates.
The fact that one beam appears to connect at an outside corner may complicate things a bit. You won't have room for a standard hanger. You might be able to attach around the corner by flattening out one leg of the hanger. That also may be a good location to cut into the corner stud cluster and bear directly.
We worry about verticals loading AND horizontal loading. Resting the joists on the double top plate works great for vertical loading and using hangers to keep them aligned until the loft floor sheathing is installed is a great idea, because you can’t end nail them through the rim joist. (A cheaper clip, like Simpson’s A34 or A35 on one side of each joist would work too.)
However, I’d worry about 1) spacing of the joists, 2) securing that overhead load to the vertical supports (stud wall), 3) keeping the loft from rotating or moving away from the main building.
1) You said, “above you office”, so it’s not residential storage. The Code requires a minimum of 125 lbs. per square foot for light loads and 250 lbs. per square foot for heavy loads. (See ICC Table 1607.1.) That means those 2x6’s need to be 12” oc to span you 8’ loft.
2) You don’t have to design against wind loading, because you’re inside another building. However, depending where you’re located, seismic loading could be severe and you can’t rely on toe-nailing to secure the loft framing to the studs.
I’d use either a clip from the joist to the top plate or studs at about 24” oc or I’d use plywood sheathing to hold the joists to the top plate (and keep the loft framing rigid...but more about that in item 3) below. )
When you have a lot of weight up in the air, an earthquake can get (and keep) it moving. Gypsum board (wallboard) can resist this movement, but it’s fairly weak. OSB board or plywood is much better. If you told me you were going to store your Christmas decorations up there I’d thing gypsum board would work. But if you are putting books, dead files, or that old transmission you were going to fix someday, up there, I’d worry....then you’re well into the 250 lbs. per square foot.
3) The whole loft needs to be rigid enough to keep everything in the loft off your head while you’re preparing your will. I like 1/2” plywood nailed at 6” oc to all WALLS and all supports, including the loft rim joists. That way you solve item 2) above, and item 3).
Fastening the office and loft to the main building is a good idea, but I’d need more info on type of building, height, material, etc.
Best Answer
Nah - most of the strength is in shear, and joist hanger nails are nice and fat so they have good shear strength.
also, yanking them is likely to be harder than you think.
The actual nailing schedule seems to be here:
http://www.strongtie.com/products/connectors/H.asp
That suggests that 10d are one size larger than you should use in a model H1Z hanger (since that's the one you pictured and you did not give a model, I have to assume that's the model you have.) The specs call for 8dx1-1/2 (joist hanger) and 8d (standard 2-1/2") - if you are forcing 10d in there they might end up weaker due to surface damage.
The table appears to include a column for "uplift with 8dx1-1/2" implying that installing them with joist hanger nails everywhere is not unheard of. It changes the uplift from 585 to 455 pounds (per hanger) on the H1 size hanger (Z is a coating suffix) (those values are for "DF/SP" presuambly douglas fir and similar quality spruce - for "SPF/HF" the difference is only 400 lbs .vs. 370 lbs.