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Re: electronic stud finder to detect roof joists?

As Maggie mentioned, they don't work too well with plaster walls.  I
have had fairly good results with drywall.  I doubt that you would get
a very good reading with shingles, since there are possibly small air
gaps between the shingles and the sheathing.  Perhaps you could make
some measurements while the sheathing was stripped of shingles (or even
note the location of the nails fastening the sheathing to the joists. 
The roofers might be willing to do this for you.

Bob, N7XY

On Wed, Jan 24, 2001 at 11:04:20AM -0600, Estes Wayne-W10191 wrote:
> This spring I will take down all my roof antennas in order to get a
> new roof installed.  When I put the roof tripods back up, I want to
> ensure that the lag bolts engage the roof joists whenever possible,
> not just the plywood roof sheathing.  One tripod will be in an area
> where there is no attic underneath because of a cathedral ceiling. 
> Consequently, I don't have the option to add any reinforcement from
> underneath the roof.
> 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).
> I suppose I could just buy an electronic stud finder and return it if
> it doesn't work.  But it would be nice to know in advance if it's
> likely to work.

Bob Nielsen, N7XY                          nielsen@oz.net
Bainbridge Island, WA                      http://www.oz.net/~nielsen
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