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Re: electronic stud finder to detect roof joists?

> > Electronic stud finders detect a change in dielectric constant when you
> > move the stud finder to an area that has a wooden stud behind the wall. 
> > I'm curious if anybody on this list has successfully used an electronic
> > stud finder to locate the joists under a roof.  I think the change in
> > dielectric constant would be much more subtle when you have to sense
> > through the thickness of the shingles and a layer of 1/2 inch plywood
> > (composition shingles, not wood shingles).
> As an owner of an 80-year-old house with lath-and-plaster walls, I can
> tell you that electronic stud-finders *do not* work at my house. I think
> they are rather finely tuned to the material of the wall...

I have one of those stud finders, and have used them many times, although never on a 
roof.  For the most part, they work very well, even through fairly thick 1" walls.  The 
problem I had most recently, was that the walls I was sensing through were not 
mounted directly on the studs, but instead on furring strips, and the sensor ended up 
detecting where the furring strips were rather than the studs.  But as long as the 
material you are sensing through is homogeneous, there is a good deal of adjustment 
possible, to vary the sensitivity, and there is a good chance that it would work.  Of 
course, I can see where lath/plaster would give it problems, but roofing material might 
be easier.  It's a nice tool to have even if it fails in this project.

 *Bill Jones  N3JLQ  Sweden Maine                                *
 * wejones@megalink.net                                          *
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