Anchoring a Sail Shade to the house

I'd like to put up a sail shade, or two, out over my patio. It will need metal anchors, attached to the house.
Is there a good way to find the near-center of the outer joist?
I wonder if I can find the center by simply measuring: I know the distance to the ceiling inside, and so I should be able to find that spot, or very close, on the outside. Then add the thickness[?] of the ceiling wallboard. And add 3" to that [1/2 the 6" joist], and I might be close. Unless I'm missing something important...?
I wonder if a stud finder would be accurate enough.
thanks marc
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On Thu, 6 Feb 2014 14:55:49 -0800 (PST), snipped-for-privacy@gmail.com wrote:

I have found *electronic* stud finders to be very accurate and precise when working thorugh sheet rock.
Magnetic stud finders only looked for nails and I was never satisifed.
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On Thursday, February 6, 2014 4:09:43 PM UTC-8, micky wrote:

will a Studfinder work [reasonably well] on the Outside of the house?
you have all that stucco to go through
marc
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On Fri, 7 Feb 2014 07:20:06 -0800 (PST), snipped-for-privacy@gmail.com wrote:

Stucco too! Does that have a wire mesh backing. I don't know.
I'd look for studs inside the house and then look for studs outside the house and see if they match.
Another way I could tell the electronic stud finder was working is that the light or buzzer went on at one point and off 1 1/2 inches later, the width of a stud.
The other way people look for studs is to drill a small, tiny if possible, hole through the sheetrock, or the lath and plaster, and see if it brings out sawdust at a certain depth. Or if it just gets easier to drill. Once you get sawdust in one place, you can mark the depth by wrapping some vinyl electrical tape around the drill bit, maybe exactly 1/2 up from the boundary of what you can't see because the bit is in the wall. Normally I'd wrap the tape at the depth I want to make the hole, but here the goal is not to make a hole of a certain depth, but to see what his beyond that depth. I think I'd want to push the bit in a little farther to make sure sawdust doesn't show up an eighth or a quarter inch later.
OTOH, if you make the gap too big, an inch, well that would probably be okay too. It's not like the exrtra half inch will leave a hole on the insdie wall.
You can get long but quite thin drill bits somewhere.
OTOH, I have no experience with stucco but I think you'll have to patch every hole you don't use so water doesn't get in and under the stucco. I don't know how hard that is to patch or to make the patches match the wall. Maybe you can just repaint that whole section after patching.
And finally, you should learn more about framing and know where studs are normally put. There is usually a box built around doors, I think, inclduign sliding glass doors, but I never really paid attention. And then there is the end of a wall. If it's a corner, does it matter which wall extends to the corner and which wall only extends to the other wall that was erected first. Maybe not. Go look at some housees under construction, or look at drawings in books, or exhibits if any at the hardware store. Unless your house is so old things are done differently now. How old would that be? Older than 1945? 1900?

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wrote:

That's why I said they were precise. It was right on the money, less than 1/10, 1/20 of an inch possible difference from the right width, whether I went left to right or right to let. It's really amazing, when there's only one layer for sheetrock at least, how well they work.
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