Installing a ledger board

I'm getting ready to install a 2x8x16' ledger board for a patio roof (see related thread "new patio roof"). The ledger will be installed on a stucco wall along the family room which is open beam construction. The ledger will be below the 2x4 double top plate so I can't secure to that. I will use 5 1/2" lag bolts with washer to secure. My challange is to hit the vertical 2x4 studs in the wall. The ledger is above a 6' sliding glass door so I should hit the header above the door.

Any tips on installing the ledger? Such as how to find the vertical 2x4 studs. Will a stud finder work through stucco? I find these stud finders not so accurate in the first place. I know the studs should be laid out 16" o.c. But finding out how they were laid out is difficult at best.

I could use the old method of sinking a nail every 1/2" to find a stud but there has to be a better way. Sometimes the horizontal fire breaks between studs can also be misleading.

Suggestions?

go inside and using a method of your choice find a stud or three under the drywall then refrencing off a known point such as a door jamb transfer your locations.

Try measuring from the end of the exterior wall. Try one way, then drive a nail. If it hits nothing, then try measuring from the other wall. You still have to drive nails, but two should hit a stud. The carpenters had to put their tape on one end or the other when they laid out the wall. The way I look at it, you got a 50% chance.

One more thing, you mentioned using 5½ long lag bolts, but not the diameter. If they are 3/8 or ½ you probably should drill holes for them first. Wedging a bolt that big into a 2x4 stud that is 1½ inches wide may split the stud. If that happens you could not only lose precious grip on the lag bolt, but seperate drywall sheets inside and risk popping screws or nails in the drywall as well. Drilling holes would be great insurance. It would:

Make sure you are hitting something very solid
Prevent studs from splitting

I am just stating my opinion and trying to help you reduce some work for yourself...I am in no way trying to be a know it all.